Welcome to the inaugural installment in a series detailing the wonderful devices and contraptions of my upcoming novel No Frills. I have a bad habit of drifting between the real and fictitious worlds, but to a first approximation, everything here is in-universe (circa 1976) unless otherwise noted.
Asterius is best described as a cross between a dynamic experiment (in the sense of a hydrodynamic or subcritical test) and a laser-driven inertial-confinement “hybrid fission-fusion” experiment, operated by the Energy Research and Development Administration’s Office of Defense Programs. It is very much dual-use — in addition to defense applications experiments, it performs a wide variety of non-defense nuclear physics, astrophysics, and high-energy-density physics experiments, including non-nuclear experiments that require copious quantities of laser energy or laser-produced plasma. In particular, it is coveted as a source of ultra-intense neutron pulses. Because large quantities of conventional high explosives are required to drive the final laser power amplifier, it is (like the U1a complex) located at the Nevada Test Site, rather than a national laboratory. The very first shot in 1969 delivered a “gigajoule fusion yield and target gain of several hundred.”
Asterius is the perfect gift for the nuclear weapon physicist and designer who has it all. The energy output of the explosively-pumped argon-ion laser may pale in comparison to that of a nuclear weapon in an underground test, but the energy output of a permanent laser system with solid-state optics pales in comparison to that of the explosively-pumped argon-ion laser! This step-change in the energy budget, by orders of magnitude, relaxes the constraints on the design of experiments that can be performed in the laboratory, rather than in the field. It accelerates the design process by reducing the need for underground tests with longer lead times. You can do some back-of-the-envelope calculations (quite possibly with a slide rule), fabricate a quick and dirty target, and get on a short waitlist. You can cheaply test unconventional, exploratory and exotic targets. It is a veritable inertial-confinement “hybrid fission-fusion” playground. In my wildest dreams, there would be elaborate targets with many stages, networks of “coupled hohlraums,” and even targets with capsules “on the corners of a polyhedron” surrounding a central capsule with exotic fusion fuels that burn only at preposterously high temperatures — high even by the standards of D-T fusion — and could be used in order to study stellar and supernova nucleosynthesis.
Asterius enhances the credibility of the United States’ nuclear deterrent in a number of ways. First, like any ICF experiment, it is another tool in the nuclear weapons design toolbox, mostly orthogonal and complementary to numerical simulation and full-scale underground testing. Second, the explosively-pumped argon-ion laser will have to be fabricated and assembled with dimensional accuracy similar to or perhaps even higher than that required by nuclear weapons. Third and most importantly, Asterius solves a difficult multi-physics problem consisting of many smaller but tightly-coupled problems with widely varying degrees of relevance or irrelevance to the design of nuclear weapons. This is a powerful signal that American know-how is not only deep, but also broad, and inspires confidence in the non-nuclear workings of American nuclear weapon systems.
I’m not married to any one layout of the facility, but as I currently imagine it, the laser system is on top of the target chamber, for two reasons. First, I’m hoping that radionuclides will tend to flow down and away from the “laser beam port” (the largest penetration through the chamber wall) under the influence of gravity, simplifying decontamination and turnaround. Second, positioning over 1000kg in the center of the target chamber without making a large contribution to the generation of radioactive waste during the shot implies suspension from the ceiling by a lightweight tensile structure, quite possibly stiff and low-Z graphite fiber-reinforced epoxy. This obviously restricts targets to single-sided, indirect-drive configurations, but these have outstanding weapons relevance and diagnostic access. The Teller-Ulam design is, of course, a single-sided indirect-drive design, with a radiation case and interstage that allow a single primary to illuminate the secondary with such a high uniformity that the spherical symmetry of the implosion is, for all practical purposes, unbroken. In Asterius, the copious energy delivered by the EPAIL can easily overcome the “inefficiency of coupling X-rays to the opposite end of the hohlraum from the laser entrance hole” in a labyrinth hohlraum, and “generate very smooth drive.” It’s hard to imagine a more weapons-relevant ICF target than a single-sided indirect-drive ⁶LiD target with a miniature, boosted spark plug (the original fast ignition scheme). This might lead to a highly unusual situation in which the target is at a higher temperature than the chamber walls. If decay heat from the D-T boosting gas is inadequate, the dry fusion fuel may have to be kept warm by laser light in order to accurately represent that in a weapon.
I haven’t really considered what all diagnostics there might be, because I’m much more interested in the experimental platform than the experiments themselves. My first thought is that there will be at least one X-ray backlighter. This will be a betatron light source comprising a plasma cathode, a space-charge-neutralized dielectric wall accelerator, a magnetic chicane for longitudinal bunch compression, and a metallic nanostructure similar to that in a solid-state tube wakefield accelerator. The betatron light will be exceptionally hard and forward-directed, but what’s really interesting is the possibility that it will be coherent, like that from an ion-channel laser. In my wildest dreams, mid-shot X-ray holograms of the target could be recorded in a photorefractive crystal, and read out after the fact by a visible laser, no computed tomography required. These metallic nanostructures (which may be as simple and unsexy as very-high-aspect-ratio, 200nm-diameter holes in suitably oriented beryllium single crystals) are at the heart of Excalibur, the 1PeV muon collider at Fermilab that I will detail later in the series.
The name “Asterius” has a double meaning. It, of course, means “starry” in Greek, suggestive of applications to astrophysics. It is also the name of an Argonaut, the idea being that the machine assists JASON in its quest for a sort of Golden Fleece (American national security and world leadership). It makes perfect sense that EG&G would be the prime contractor, because Asterius is not unlike a stadium-sized high-speed camera, with flashes, shutters, and film of sorts. The EPAIL is a glorified argon bomb. Say cheese! You could also think of Asterius as the HO scale model railroad equivalent of the Nevada Test Site, where you might perform weapons effects tests on the Neighborhood of Make-Believe. I am curious to see how well it could toast slices of bread. It must also be said that Asterius is quite Soviet. Nikolay Basov might have gotten a kick out of the laser system, and Vyacheslav Danilenko might dig the blast chamber.
In the world of the novel, there are no major open problems with regards to energy. When I finally get around to the alternate-history EIA Annual Energy Review Sankey diagram, you’ll see that a mix of nuclear fission energy and fish-friendly run-of-the-river hydropower meet the United States’ needs. But even if there were such problems, nuclear fusion would not be taken seriously as a solution to any of them, because fusion reactors are, and always will be, science experiments. As such, there is almost no public funding for magnetic-confinement fusion research outside of astrophysics. Another important piece of context is that there are actually two nuclear weapon test sites in the continental United States: lower-yield devices are tested above the water table at the Nevada Test Site, and higher-yield devices are tested under the water table at the Alternate Test Site, inside the salt domes (and possibly beds) of the Paradox Basin. There, bomb debris is kept out of communication with nearby groundwater by the exceptionally ductile halite, impermeable crestal and lateral caprocks, and extensive groundwater engineering that recirculates upward-flowing briny groundwater, both to keep salt out of the Dolores River (as part of the Colorado River Basin Salinity Control Program) and inhibit dissolution of the salt structures. And of course, as a freakish hybrid of a dynamic experiment and a laser-driven inertial-confinement fusion experiment, Asterius can perform shots that actually obviate some full-scale underground nuclear tests, thereby reducing the generation of nuclear waste and exposure to the risk of radionuclide breakout.
What is my authorial intent here? Is this just hard science fiction, or am I actually advocating for something like Asterius as a missing link between underground testing and ICF as we know it? The answer is the former, because the combination explosively-pumped argon-ion laser and colliding shock lens is all questions and no answers, and the use of conventional high explosives may severely limit what diagnostics and associated structures can be placed near the target without generating fragments that become embedded in or even penetrate the blast chamber wall (hence the emphasis on remotely diagnosing the target using X-ray holography). Lasers have been pumped by shock waves (as well as light from argon bombs), but I am not in any way qualified to rule out showstopping problems in the fine details of the laser action, such as “blocking of the laser transition by population of the lower levels,” radiation trapping, “blackbody conditions,” superradiance, amplified spontaneous emission, optical nonlinearities in the solid-density plasma, or perhaps even laser-plasma instabilities not unlike those in the target. The astronomical costs are another matter entirely, and such a monstrously large facility could easily cannibalize public funding from other projects with greater scientific and technical merit. As far as I can tell, the next logical step for stockpile stewardship in the current, real-world context of anemic drivers and exquisite targets is to build a Z-pinch-driven ICF experiment with impedance-matched Marx generators. While Z-pinch drivers may generate more low-level radioactive waste (namely, the MITL debris) than laser drivers, all else equal, they have much higher wall-plug efficiencies, because they minimize the transduction of energy (with its unavoidable losses).
It is interesting to note that, while “it appears that a Z-pinch could only be used for a portable pure-fusion weapon if the microsecond pulses produced by the explosive flux-compression generators could be shortened by more than an order of magnitude while preserving adequate efficiency,” the EPAIL might provide inherent, built-in energy storage and pulse compression, in that it is gas-dynamically pumped on a microsecond timescale, and then optically discharged on a nanosecond timescale. But don’t worry — the “tons of explosives” would render the EPAIL “too large in size to be of any interest for military applications where they would have to compete with fission triggers in the kilogram range.” This all raises the question: if the EPAIL concept was taken seriously enough to be “classified in 1970,” why exactly was it then “declassified in 2007?” Was it simulated or even tested, found to be unworkable, and disclosed as a means to send foreign nuclear weapons programs on wild goose chases? Was it, after exhaustive study, found to have no military utility whatsoever? Is it even harder for non-traditional actors to build and use than existing nuclear weapons, or just common knowledge among nuclear weapons states? I have no idea.
EG&G Asterius (inertial confinement fusion experiment) [“hollow-cathode” Q-switched argon-ion laser oscillator] [hypocycloidal pinch flashlamps] [optically-pumped Q-switched XeF(C→A) exciplex laser “power preamplifier”] [plasma-electrode Pockels cells] [explosively-pumped argon-ion laser power amplifier] [colliding shock lens] [light-initiated detonation system] [fast-acting closures] [“frost wall”] [“automatic washdown cleaning system”]
It is installed at the Nevada Test Site, and can be used as a very intense “pulsed neutron source for scattering experiments.” The hypocycloidal pinches are “open discharges” with “no containing transparent tubes.” The target chamber is a blast chamber, and has “an oil-free vacuum system.” The combination “target positioner boom” and “beam tube” is a “vertical tube extending into the chamber… located directly in line with the chamber center.” The outer surface of the axisymmetric “thick… shell of high explosive” is coated in Pb(N₃)₂ “that can be detonated with a flash of light.” The “closed-loop process water system” includes some combination of “ion exchange, solvent extraction, precipitation, distillation, electrolysis, and membrane separation.” The target chamber has a diameter of at least 26.7m, and can contain shots with yields of at least 2500kgᴛɴᴛ. The ideas are that 1.) the “convergence of the toroidal shock wave” forms a “cigar-shaped” “plasma laser rod” that doubles as a colliding shock lens, 2.) the power amplifier is located inside a “glass fiber-reinforced cycloolefin polymer” “boom section of the target positioner” transparent to ultraviolet “laser beam illumination” of the “entire lateral surface of the explosive charge,” 3.) the explosively-pumped power amplifier delivers a “megajoule-petawatt” pulse, such that “ignition is easy,” “the target configuration is of secondary importance,” and “gigajoule fusion yields and target gains of several hundreds” are readily achieved despite the relatively low performance of targets that are “overbuilt and far from optimized,” “severely constrained… to minimize calculations,” “use parts that could be rapidly fabricated,” and “avoid or overpower failure modes,” 4.) it can perform “defense applications experiments” with “micro-fission explosions” and or “single-sided indirect-drive,” “non-cryogenic targets,” 5.) it can easily overcome the “inefficiency of coupling X-rays to the opposite end of the hohlraum from the laser entrance hole,” and “generate very smooth drive” inside labyrinth hohlraums, 6.) the hypocycloidal pinch flashlamps have a “pumping spectrum” matched to the “absorption spectrum of XeF₂ vapor,” and a low impedance suitable for discharge over the “few hundred nanoseconds” required for the “multipass optical scheme… to obtain… the desired high total gain factor,” 7.) the “power preamplifier” delivers a “several nanoseconds FWHM duration pulse” with energy sufficient to “launch the avalanche in the argon plasma rod with a high population inversion,” without any “serial amplification,” “angular multiplexing,” or “pulse stacking,” because the “saturation energy density” of the XeF(C→A) lasing medium is very high, 8.) the power amplifier debris shields “the expensive… optics up-beam” from “large X-ray and… ion fluences,” 9.) the “time… between removal of the cryostat and… firing of the driver” is sufficient for “laser alignment,” because the frost wall imposes a low “heat load” on the power amplifier, 10.) it can be decontaminated in less than eight hours and fired “a few times per day,” with low “machine downtime” and high “shot productivity,” because the power amplifier “debris is not radioactive,” and “any activated target materials or fissionable materials from defense applications experiments” condense on the frost wall rather than the cold wall, such that “post-shot warmup of the wall followed by a water spray and pumping” removes “all condensates and vapors, thereby leaving the target chamber in the same condition after a shot as it was before a shot,” and 11.) it obviates some “full-scale underground nuclear testing,” such that there is a “net reduction in radioactive waste volume generated” by the “United States’ nuclear weapons program.”
Q: Can conventional high explosives directly ignite fusion fuel?
A: No.
“The Russian weapons labs… attempted to generate pure fusion explosions with implosions driven directly by chemical explosives… In theory, it should be possible to create a shock pressure high enough to achieve ignition… in a spherical system consisting of alternating layers of dense and light materials. In practice, however, deviations from perfect symmetry and mixing between the D-T fuel and the liner compressing it… limited the temperatures achieved to an order of magnitude below the ignition threshold and neutron yields to less than 10¹⁴ neutrons.”
Q: Can conventional high explosives directly pump a laser, along the lines of how they pump flux-compression generators?
A: If real-life mad scientist Friedwardt Winterberg is to be believed (one of these documents actually seems to be an FOIA disclosure), then converging shock waves in a tailored argon bomb may be able to produce a highly population-inverted, solid-density argon ion rod capable of laser power amplification.
“If [an intense laser pulse heats a very small pellet of fusionable material to ignition], thermonuclear reactions will occur releasing substantial energy… this energy release would be much lower [0.1–100tᴛɴᴛ] than the minimum practical yields… from fission-implosion systems… In attempting to minimize the energy required to trigger the fusion reaction, pulse shaping is critical… For an expendable system, the problems of focusing the laser beam onto the fuel pellet would be essentially eliminated because [they] could be constructed as one unit.” “The advantage of lasers for inertial confinement fusion power plants is their good standoff… from the thermonuclear microexplosion. A disadvantage is the enormous size and high cost, primarily because of the laser’s inefficiency. Electric pulse power ICF drivers depend on transmission lines connecting the pulse power source with the thermonuclear target. Following each microexplosion, the transmission lines have to be replaced. This [generates large volumes of low-level] radioactive waste. In addition, the neutron [moderation] and absorption in the transmission lines leads to blast waves inside the microexplosion chamber… The large density of chemically stored energy (on the order of 10¹¹erg/cm³) and the speed [with which] it can be released in the detonation of a high explosive raises the question, could this energy be used to pump a laser… Glass lasers can be efficiently pumped with argon flash lamps, because at a temperature of a few electronvolts, argon is a brilliant light source. In the argon flash lamp, argon has a low density. A much more powerful light source is an argon bomb, where a detonation wave from a high explosive goes into solid argon… Because of the high energy density of chemical explosives, lasers driven by them would be much more compact than conventional lasers… The price paid for this advantage is that the laser must be replaced following each thermonuclear microexplosion, but unlike the replacement of the debris from a disposable transmission line in electric pulse power driven thermonuclear micro-explosions this debris is not radioactive… A scheme of this sort will therefore resemble a thermonuclear bomb with a fissionless trigger… In order to get a large population of upper laser levels per unit volume, the laser material has to be… in the liquid or solid state… Because the argon ion has fewer low-lying energy levels than would normally exist in molecules, the blocking of the laser transition by population of the lower levels is less likely to occur… The entrapment of radiation will make a photon be emitted and resonance-reabsorbed many times inside the laser material. This… will result in an increased effective lifetime for the upper laser level which is of importance for a large population inversion. There is… the possibility of approaching black body conditions. In this case, no laser action is possible. Black body conditions are more likely to occur in systems with a high density of energy levels such as molecules… After the laser material has been energized, the laser can be triggered according to the principle of the laser amplifier… the light pulse of a Q-switched gas laser, consisting of the same laser material as the dense rod, is [launched into] the high-energy high-density laser rod. If the Q-switched gas laser releases a pulse of sufficient intensity, the activated material in the high-density laser will be depopulated in one run by a light wave going [down-beam] and increasing exponentially. The resulting laser beam is then focused onto the thermonuclear material by an optical lens… energy inputs in excess of [10GJ] seem to be required, which correspond to an explosive charge in excess of one ton.” “A laser… powerful enough to ignite a D-T microexplosion [comprises] a cylinder of solid argon, [inside] a thick cylindrical shell of high explosive. If simultaneously detonated from outside, a convergent cylindrical shockwave is launched into the argon… If the shock is launched from a distance of 1m onto an argon rod with a radius equal to 10cm, the temperature reaches 90,000K, just right to excite the upper laser level of argon. Following its heating… the argon cylinder radially expands and cools, with the upper laser level frozen into the argon. This is similar to a gas dynamic laser, where the upper laser level is frozen in the gas during its isentropic expansion in a [de] Laval nozzle. To reduce depopulation of the upper laser level during the expansion by superradiance, one may dope to the argon with a saturable absorber, acting as an ‘antiknock’ additive. In this way, megajoule laser pulses can be released within 10ns… because of what Freeman Dyson described as the ‘tyranny of the critical mass,’ small fission bombs or fission-triggered fusion bombs become extravagant, with only a fraction of the nuclear material consumed.” “Below a certain explosive yield on the order of a kiloton, nuclear weapons are grossly inefficient and extravagant.” “The minimum energy for ignition (several megajoules) is really not that large, but it has to be delivered in less than 10⁻⁸s, onto an area less than 1cm², with a power in excess of 10¹⁴W/cm². This is the principal problem of non-fission thermonuclear microexplosion ignition… One can conceivably avoid the problem of laser beam damage for glass lasers, if the high gain medium is a dense optically transparent plasma. For thermonuclear applications short wavelength lasers are… preferred… the most promising candidates are the noble gas ion lasers… The shortest reported laser line for the argon ion laser is in the visible blue at 4,879Å… An expansion immediately following the heating is likely to result in a lower temperature highly inverted argon plasma… in complete thermodynamic equilibrium there is no population inversion. However, the situation is quite different in the material just behind a strong shock wave. Immediately behind the shock wave one has a uniform isotropic velocity distribution rather than a Maxwellian. If the population inversion is achieved by a resonant cross-section of atomic particle collisions at a certain energy, and if the particles behind the shock front possess just this energy, by making a proper choice of [geometry], then a large population inversion is conceivable… ignition is easy with sufficiently large driver energies, but which are difficult to duplicate with lasers or electric pulse power. The problem therefore is not the configuration of the thermonuclear explosive… because for sufficiently large driver energies, the target configuration is of secondary importance.” “Shock-heated argon is often used as an extremely bright light source for high-speed photography of fast-acting experiments, such as explosive devices… Detonation of the explosive sends a shock wave into the argon. The temperatures and pressures behind the shock front are sufficient to excite the argon gas to the point that it emits electromagnetic radiation in the visible and ultraviolet parts of the spectrum… These sources have had many forms and have also been referred to as argon bombs, argon candles, and argon light sources… The noble gases argon, krypton, and xenon have very small specific heats and thus are shocked to high temperatures… At convergence, the waves reflect off of each other, further increasing the post-shock temperature and irradiance.”
Q: The schematic of the explosively-pumped argon-ion laser seems to show the amplified beam being focused onto the target by a solid-state lens, but wouldn’t any optics down-beam of the “plasma laser rod” have to also be transient plasma structures with exceptionally high optical damage thresholds?
A: That seems reasonable enough, and as it happens, “colliding shock lenses” strikingly similar to that laser were proposed as damage-resistant final optics for ICF experiments. This might be taken to suggest that, if a “cigar-shaped” argon-ion rod was at once a laser rod and a colliding shock lens, it could act as both the final laser power amplifier and the final optic. This double duty would be similar to that of a solid-state “laser rod with curved end faces,” “which in addition to supplying optical gain, serves also as an image forming element — a lens.”
“Colliding shock lenses are… real optical elements, sometimes with a very good quality, and… dynamic lenses, which last for a few microseconds and are always evolving. Because these lenses are intended to be used with pulsed lasers, this is not a problem… These lenses have a very long focal length, in comparison with their small diameter… This means that the cone of light hitting the target… can be very sharp. In case of laser drilling, this allows a better quality hole.” “In the [plasma lens/isolator] four converging… plasmas were used either to focus or to interrupt a laser beam… By adjusting the time delay between convergence and the arrival of the pulsed laser beam, the aperture and focal length of the lens can be varied… A decimetric pulsed gas lens could serve as the final focusing element for a laser fusion reactor… The [converging] shock waves collide at the center of the CSL and a high pressure, temperature, and density region is created… A short time (of the order of microseconds) after collision, the expansion of this high density region results in the axisymmetric cigar-shaped density distribution which forms the graded-index lens… The focal spot size was near-diffraction-limited.” “Focusing is due to the radially symmetric density gradients within the expanding region. As the lens diameter increases, the density diminishes and the focal length increases… Converging shocks have been extensively studied from the early 1940s primarily because of their ability to produce extremely high pressures and temperatures on convergence. This property also made them very attractive for use in laser fusion schemes.” “…gas lenses… were invented at Bell Labs in the early 1960s with electrical power and information transmission in mind… gas lenses could play a part in laser fusion reactors… The CSL is the only lens capable of operating very close to the target…” “Before the development of fiber optics and before the realization that power conversion into laser light and back was very inefficient, high hopes were raised for information and power transmission by gas lenses and laser beams… Laser fusion is the one high power application where non-solid non-rigid optics have been routinely employed, namely in the… Nova plasma isolator… a gas lens would… reduce the radioactive waste.” “Pulsed gas lenses are… a solution to the problems of high laser fluence and radiation damage in post-breakeven fusion experiments.” “The… solution to the problem of scaling up the aperture and increasing the power of the lens is [to] put several CSLs in series and in close proximity. Not only does this increase the optical power by combining several lenses but it also affects the gas dynamic behavior. Shock waves that were expanding in three dimensions at least along part of their trajectory… now find themselves confined to two.” “…traditional solid-state optical components must be enlarged to avoid laser-induced thermal damage, which can be extremely costly and technically challenging for large-scale petawatt laser systems…” “The damage threshold of a plasma is orders of magnitude higher than that of a solid-state optic. Plasma optics use this to manipulate light at extreme intensities.”
Q: How would the convergent toroidal shock front be formed?
A: The outer surface of the high explosive shell would be coated in lead azide (or some other photosensitive explosive), and then illuminated by pulses of ultraviolet excimer laser light, from a number of directions and with high uniformity (not at all unlike direct-drive ICF). The “glass fiber-reinforced cycloolefin polymer” “boom section of the target positioner” has the strength, stiffness, and toughness to help suspend the 1000kg or more of high explosive, while also transmitting most of the incident ultraviolet laser light to the “lateral surface of the explosive charge” nested inside. The refractive indices of the glass fibers and organic matrix are closely matched (and the boom section may also have anti-reflection coatings) to minimize scattering. The use of lasers (with their “good standoff”) to not only drive the ICF target but also detonate the high explosive minimizes the content of dense and high-Z materials in the structure supporting the target, and with it, the generation of activated waste. The laser allows true area (rather than point or line) detonation of photosensitive explosive surfaces with “complex shapes,” and in turn, allows the single-stage explosive device to radiate a ‘designer’ shock front, without resort to a more complex multi-stage system of explosive lenses and or flying plates, or any “additional mass of explosives” that must be contained by the blast chamber, but does not pump the argon-ion laser.
“To simulate radiation-induced impulse on test structures having complex shapes, it is convenient to employ an explosive that can be detonated with a flash of light. The distribution of impulse, which is applied almost simultaneously, can be controlled by appropriate variation of the depth of the explosive on the surface of the test structure… The peak of the spectrum from xenon flashlamps operated at relatively high current densities approaches [the] absorption window of [Pb(N₃)₂].” “The main disadvantage of devices initiating a converging cylindrical… detonation wave is [that] an additional mass of explosives is used… the disadvantage [of multi-point initiation is] the impossibility of precision initiation of detonation simultaneously on the entire lateral surface of the cylindrical explosive charge… A thin layer (several millimeters) of a photosensitive explosive [with] high sensitivity to [pulsed laser] radiation, is applied to the surface of the explosive charge. Radiation, acting on a cylindrical explosive charge from four sides at [angles] of 90°, simultaneously excites detonation of the entire surface of the [photosensitive explosive]. As a result… a cylindrical converging detonation front is formed… The laser beam illumination of the entire lateral surface is carried out using mirrors… scattering lenses… and dividing plates… with a certain radiation transmittance… The alignment of the device elements and the laser beam path is carried out using a laser diode… The reflection and transmission coefficients of plates… are calculated so that the illumination of the lateral surface of the cylindrical charge is relatively uniform… The choice of explosive… wall thickness, shell and external radius of the explosive charge is made on the basis of the specified final shock-wave parameters… The device is intended for solving various scientific and practical problems in the fields of physics and chemistry [at] megabar pressures. To ensure high efficiency of a device that forms converging detonation (and shock) waves by laser initiation, an initial high accuracy of symmetry of the device elements is required.”
Q: How would the cryogenic solid argon cigar be fabricated?
A: This is a tough one, because I imagine that it could be cast in Mylar-lined aerogel mold, but the inert aerogel might cause excessive attenuation of the shock wave. I wonder if an RDX or PETN aerogel or xerogel would stand the rod off from the fully-dense high explosive as necessary, but also be effectively transparent to the shock wave.
“The shield could be made by pouring liquid nitrogen into a cryostat suspended at the center of the target chamber. The cryostat would contain the fuel pellet, carbon spheres (used for alignment), carbon filaments (used to support the fuel pellet and alignment spheres), and the shield. Radial holes in the shield that provide lines of sight for driver beams, diagnostics, and alignment are made by positioning removable plugs in the cryostat. A thin Mylar balloon around the fuel pellet is inflated with gas to form the inner surface of the shield, the nitrogen is then frozen around the balloon, and the removable plugs are extracted… The cryostat is removed a few minutes before a shot, leaving the pellet, the alignment spheres, and the shield suspended from the target chamber by the carbon filaments. If the Mylar balloon is too thick to be penetrated by the driver beams, it will be destroyed a few seconds before a shot by mechanical means or by a driver energy prepulse… The shield also adds thermal inertia that maintains the fuel pellet’s cryogenic temperature after the cryostat is removed. Therefore, the time permitted between removal of the cryostat and the firing of the driver is increased from a few seconds to about 15 minutes. This makes positioning and aligning the fuel pellet easier.”
Q: How would you pull out all the stops to ensure that the conventional, permanent laser system delivers a pulse energy sufficient to efficiently depopulate the plasma laser rod in just one run? What if the real challenge is that the mere foot pulse of a Nuckolls pulse must be sufficiently energetic to induce lasing?
A: In a miraculous coincidence, the 488nm wavelength of this particular argon-ion laser light is very close to the 480nm center wavelength of XeF(C→A) excimer lasers that uniquely combine the high gain coefficients of “dimeric excimer molecules” with the exceptionally wide gain bandwidths of “trimeric molecules.” The wide gain bandwidth greatly simplifies the amplification of short pulses, and undesirable optical nonlinearities in the gaseous lasing medium are weak even at ultra-high intensities. A particularly heavy-duty, industrial-grade way to provide the necessary optical pumping is to thread tubes of lasing medium through coaxial stacks of hypocycloidal plasma pinches.
“A challenge to using KrF lasers for ICF is the mismatch between the high-energy amplifier operation and the several nanoseconds FWHM duration pulses needed for ICF… The amplifier needs a long-duration optical pulse to extract the energy while the target needs a much shorter pulse… The temporal pulse shape is produced using combinations of polarizers and Pockels cells… fogging from chemical attack can be resolved by using CaF₂ or MgF₂ for the windows.” “With its gaseous active medium, the XeF(C→A) excimer laser is readily scalable… XeCl and KrF excimer amplifiers… have a limited bandwidth (<5nm) and large cross-sections for stimulated emission that result in low saturation thresholds (1–2mJ/cm²) and high ASE levels. Other… amplifier media such as dyes or solid-state materials are limited in performance by induced nonlinear effects at high intensities.” “The blue-green XeF(C→A) transition is unique among laser transitions offered by diatomic excimer molecules owing to its very broad bandwidth (70nm) centered near 480nm, which is determined by the strongly-repulsive lower A-state… Furthermore, this transition possesses relatively long radiative lifetime (100ns) of the upper laser level and rather small stimulated emission cross section of 9×10⁻¹⁸cm² resulting in a much higher value of the transition saturation fluence, 50mJ/cm²… high-power photodissociation lasers… pumped by… such unconventional sources as a high-temperature electrical discharge or a strong shock wave in gas… have no shell separating the pumping source and the active medium [which] makes it possible to utilize… radiation in any spectral range, including the VUV… In contrast to ohmic heated emitting discharges, magnetoplasma compressors are based on shock-wave thermalization of the directional kinetic energy of high-velocity plasma streams formed by the electromagnetic forces which appear when specially configured discharge currents interact with their own magnetic fields… in ionic states of molecules, the equilibrium internuclear distance is, as a rule, far larger than that in covalent states. As a result, upon direct optical excitation of molecules into ionic states, transitions take place from lower vibrational levels of the ground covalent state to high-lying vibrational levels of the upper state, where the repulsive branch of the potential energy curve becomes very steep. In this case, according to the Franck-Condon principle, the absorption spectrum should display a large number of vibrational bands, thereby determining a wide pumping spectrum… the more than an order of magnitude longer lifetime of their upper laser levels results in lower small signal gain values and, thereby, [alleviates ASE]. As a result, contrast ratios can be made much higher and the laser energy storage mechanism more efficient… Unlike the case of electron pumping, the competition from the B→X transition is rather weak in the optically driven XeF(C→A) laser since the thermodynamic equilibrium between populations of the B and C states is determined by the buffer gas temperature, which is close to room temperature… during electron pumping… electrons at a temperature of ~1eV… mix these states to a high degree and may prevent an efficient laser action on the C→A transition because of the competition from the B→X transition. Under optical pumping, the electron concentration is negligibly low, thereby facilitating lasing in the visible spectrum… a high damage threshold and low nonlinear refractive index… makes possible the amplification of laser pulses at radiation intensities much higher than those for condensed matter… Contrary to the electron beam pumped XeF(C→A) gain medium… the photolytic XeF(C→A) gain medium does not require buffer gas pressures exceeding a few hundreds of millibars for efficient operation. This [alleviates] beam self-focusing induced by the cubic nonlinear susceptibility of the medium… The achievement of high energy levels… in the photolytically driven XeF(C→A) gain medium requires… optical pump sources producing high-intensity VUV radiation… a relatively low gain [<0.01cm⁻¹], inherent to the… XeF(C→A) laser medium, [requires] a multipass optical scheme in order to obtain long amplification path lengths and the desired high total gain factors… Consequently, an optimum pump pulse duration [is on] the order of a few hundred nanoseconds.” “…photodissociation XeF(C→A)… active media are very sensitive to the internal losses because they have much lower small‐signal gain as compared with excimers emitting… on the B→X transition due to the large width of their luminescence spectra and long radiative lifetime of the excited states… electron beam or fast discharge pumping of these active media [is] ineffective since electron excitation technique is based on plasmochemical reactions involving ionized and highly excited atoms and molecules that are characterized by strong absorption in the visible… Compared with the B→X transition, the broadband photochemical media are characterized by more than an order of magnitude larger gain bandwidth and saturation fluence allowing for several TW/cm² to be obtained… Behind the optical pumping… is the photolysis of XeF₂ vapor in the spectral range <204nm to produce XeF excimers mainly in the B state. The C state, lying lower than the B state, is populated due to collisional relaxation of the latter in the presence of a buffer gas.” “Photolytic pumping of XeF(C→A) by pulsed discharge or shock wave radiation allows one to amplify light beams with the cross-section at least up to ~1m².” “The C→A transition between bound and repulsive states is characterized by a continuous fluorescence spectrum… the absorption spectrum of XeF₂ vapor is… a wide structureless band in the region of 145–220nm with a maximum at 158nm… In proximity to the… pump source, a region is formed where the total dissociation of XeF₂… takes place. The products of photolysis practically do not absorb the pump radiation… photolysis by radiation of an open discharge is accompanied by disturbance of the optical homogeneity of the active medium… The stepwise change in refractive index observed in the bleaching wave in XeF₂ [results from] an increase in gas mixture pressure during XeF₂ dissociation because of heat release… To obtain lasing on the C→A transition, one must suppress competitive generation on the B→X transition characterized by approximately an order of magnitude higher gain… In the plane-conic resonator, a partial compensation of inhomogeneities caused by XeF₂ photolysis in the bleaching wave takes place.” “To improve the output power… it will be necessary to suppress the strong XeF(B→X) transition. This can be achieved by going to higher argon buffer gas pressures.” “…special optics with a high reflectivity at the broadband transition and a very low reflectivity at the B→X transition is needed.” “Although a variety of plasma compression devices have been designed… for thermonuclear fusion, some have… useful characteristics as a pumping source for lasers, particularly in the UV region of the spectrum… the principal element of the HCP device is a set of three parallel disk electrodes, each having a circular hole at the center. The disk electrode in the middle is an anode common to the two outer electrodes, which are cathodes. The insulators placed between the electrodes are also in the form of a disk and provide an inverse pinch geometry for the initial breakdown currents. The lower and upper current sheets launched from the insulators advance radially, by the [Lorentz] force, toward the center hole where they collapse and interact with each other… the HCP device… produces a hollow cylindrical column of pinched plasma, which allows insertion of a laser tube along the axis of the plasma cylinder for an efficient optical pumping… The bremsstrahlung spectrum of the plasma is [about 80%] narrower than that of the Planckian distribution due to the plasma compression… Since the plasma stream is self-focusing, the achievable photon flux density at the active medium in the absorption band is… an order of magnitude greater than [conventional] gas discharge tubes… The physical length of the pump light can be extended as long as necessary by stacking up additional electrodes to form an array… the all-metal construction of the plasma device allows for the input energies and thereby the resulting plasma light intensities to be much higher than that of the conventional flashlamps… a good spectral match between the pump light and the lasing medium can be achieved by the choice of the fill gas species for the line spectrum and of its fill pressure for the controlled continuum spectrum.” “When the current sheets arrive near the center hole, the plasma density and temperature are increased enormously by the Joule heating of the current and shock compression of the plasma… the HCP source can be operated to match the most efficient spectrum for blue-green… lasers at very high input levels.” “Very high input power levels to the array are possible without significantly shortening its useful life, in strong contrast with conventional xenon flash lamps… the rise time and the pulse width of the HCP are determined primarily by the external circuit. Therefore, the adoption of an ultrafast capacitor bank or a Blumlein power source for generation of submicrosecond light pulses is possible.” “For the purpose of generating temporally shaped laser pulses in the nanosecond domain a cavity-dumped Q-switched oscillator [is suitable]… There are many applications that require laser pulses with temporal profiles other than the Gaussian pulses which are naturally produced by Q-switched or mode-locked oscillators… the most important application of a non-Gaussian laser pulse is found in [ICF] experiments where ‘Nuckolls type’ pulses are… essential for efficient neutron production… The cavity dump acted as an electrically controlled light valve that regulated the release of energy from an otherwise closed laser cavity.” “In any low-gain, short-pulse laser system, rapid build-up of the optical field within the resonator is critical to good laser performance and extraction efficiency. Simultaneous injection of a ‘seed’ signal into a laser cavity with laser pump excitation can create a much faster increase in the intensity of the optical fields, compared to one that results from a build-up of spontaneous emission.”
Q: On the off chance that the permanent laser system would benefit from a more powerful argon-ion laser master oscillator, what might it look like?
A: There are a number of possibilities here, such as an RF-pumped laser with strong focusing by quadrupole magnets, or even a Z-pinch laser, but one particularly complexity-effective device resembles a pasotron, with argon ions back-streaming from the anode to a plasma cathode.
“Trapping of resonance radiation from the lower laser level to the ion ground state (reabsorption of radiation by ground state ions to bring the ion back to an excited lower level of the lasering transition) which occurs at extremely high current density (on the order of 10³A/cm²) can destroy the population inversion necessary for laser operation and thus reduce the output power to zero… In order to achieve a high output optical power per unit volume as well as a high inverted-state population necessary for gain, a high density of electrons is required. Associated with the high density of electrons is a… requirement for neutralization of the negative space-charge… in ion laser devices, the presence of ions is necessary to its fundamental operation and not merely for negative space-charge neutralization… Since the active discharge column is contained in a kind of ‘electrostatic tubing,’ it is therefore physically removed from any solid boundary. Thus the energy loss to the wall is reduced giving a higher efficiency. The damage to the wall is also reduced… anode power loss can be reduced to a minimum by a scheme involving a depressed anode bias technique sometimes used in microwave [tubes]… The plasma inside the cathode may be considered as a virtual cathode… With the device operating at relatively low beam power to keep the plasma alive, a high energy pulse can be applied to take advantage of a large momentary inversion during a short duration pulse (e.g. less than 10µs) before radiation trapping and beam instability (i.e. divergence) occur.”
Q: What about inertial-confinement fission driven by a laser, or a Z-pinch for that matter?
A: It seems that this is possible, and that tight coupling of fission and fusion reactions would open up a world of possibility for target design.
“…a small (fractional gram) fissionable-material pellet, when compressed sufficiently by the ablation-driven implosion caused by symmetric laser… irradiation, will become supercritical and thus produce a fission microexplosion… The pellet must be made highly supercritical, and this condition significantly increases the necessary input energy… Because energy is carried off by ablated material, the necessary incident energy is probably at least ten times greater than the work. Any substantial deviation from adiabatic compression would further increase the required incident energy… of all the common fissionable materials… ²³⁹Pu has the smallest critical mass and the greatest average number of neutrons produced per fission. The latter is important because achievement of explosion conditions requires an extremely rapid growth of the neutron population with time… the pellet must be driven sufficiently supercritical for a significant fraction of the mass to undergo fission during the inertial confinement time… although a neutron reflector can greatly reduce the work necessary to attain criticality (by as much as a factor of ten for the optimum thickness of D-T), it has little effect on the work necessary to achieve a fission yield… For a highly supercritical configuration, the loss of neutrons through the surface (‘leakage’) is relatively small. If a low-Z reflector is used to return these lost neutrons to the core, the average neutron must undergo several scatterings — with substantial loss of velocity — before it returns. It must then travel a fission mean free path before it can affect the growth of the neutron population, which, at its reduced velocity, takes more than the e-folding time of the population as a whole. In short, the reflected neutron arrives too late to have much effect… it would almost certainly be necessary to use a low-Z ablating layer around the fissionable core to produce the necessary compression… such a layer can be used without increasing the total compression work requirement… The fission yield, [about 1500kgᴛɴᴛ], is large enough to make containment difficult… demonstration of the concept will be a significant physics experiment… the microfission explosion may provide a unique high-intensity short-duration source of nuclear radiations.” “A small critical mass could be created by imploding the fissionable material until it was 200–300 times its normal density. This could be achieved using a high energy, properly shaped laser pulse (of about 1ns duration). For a chain reaction to begin in the assembled critical mass, however, neutrons must be present to initiate the fission process… a small amount of D-T mixture could be embedded in the core of the sphere of fissionable material. Compression of the D-T core would induce thermonuclear fusion and produce 14MeV neutrons… Neutrons from this reaction have been produced by the compression of a D-T pellet with a laser pulse… A D-T mixture occupying 10⁻⁶ of the volume of the sphere of fissionable material gives 10¹² neutrons in 10⁻¹¹s (the approximate neutron doubling time in the fission reaction). So the D-T fusion reaction will produce copious quantities of neutrons in the necessary time interval, and will initiate the fusion reaction… having the D-T mixture in the core of the spherical critical mass makes the initial neutron density highest at the center of the sphere. It decreases radially outward, leading to an efficient chain reaction which develops from the middle toward the edges. Second, at the center of the sphere there would be a pressure spike from the implosion of the sphere to critical mass; this higher pressure (and density) would make the production of neutrons by D-T fusion more efficient. Finally, since the core would be the last part of the sphere to be compressed, no neutrons would be produced until a critical (or supercritical) mass was achieved. That would lead to high efficiency and would avoid the problems of a fizzle yield.” “The D-T mixture is compressed until a limited number of fusion reactions take place (well below ‘breakeven’ energy). The resulting fast thermonuclear neutrons… induce fission which in turn increases the fusion yield of the D-T core… the neutron release from fusion will result in more complete consumption of the fissile fuel, sustaining energy release. The sustained release extends the compression of the fusion reactants, yielding more fusion reactions. And of course more fusion release means more neutrons for more fissile consumption. This fortuitous cycle means that the fission event is not simply used to ignite fusion, but also helps achieve a more complete burnup of the fission and fusion fuels… Using fission-fusion synergy means that ignition may be achieved with lower energy input… The idea of combining fission and fusion, so that the former process assists the latter, is well established… in the field of nuclear weapons…” “…the fission and fusion reaction becomes important even at temperatures less than the D-T ignition temperature, and at densities less than solid state densities, because… fusion neutrons are… released at a sufficiently high rate…” “If… the fissionable pellet is surrounded by a layer of dense thermonuclear D-T material, to be compressed together with the fissionable pellet to high densities… thermonuclear reactions in the D-T [mantle] will be greatly enhanced by the fission chain reaction in the pellet making possible the fission-supported… release of thermonuclear energy. The system resembles a miniaturized conventional hydrogen bomb… the fissionable pellet will greatly reduce the laser energy input which would be normally required to ignite a D-T pellet without fission support… a [low-Z] material with a higher ablation product velocity will give rise to a larger pressure than for [high-Z] material… a high ablation product velocity can still be achieved by simply surrounding the [high-Z] pellet material with a concentric layer of solid hydrogen of proper thickness. During the irradiation by the laser light only the hydrogen layer will be ablated…” “…the pellet consists of a fissionable core surrounded by a [D-T] envelope. Almost the same [gain] would be achieved if the [D-T] is simply mixed with the fissionable material… Heating to thermonuclear temperatures is not necessary since, after achievement of high densities, the fission chain reaction will start by itself and result in subsequent heating of the thermonuclear material… Instead of D-T one could… use ⁶LiD as the thermonuclear material since the fission neutrons would transform a large portion of the ⁶Li nuclei into tritium. The transformation time for this process is [about 10⁻¹¹s] and, therefore, short compared to the hydrodynamic disassembly time.” “Secondary reactions such as the [breeding] of tritium can contribute a significant amount of energy to the system.”
Q: Could room-temperature ⁶LiD (rather than D-T ice) be reliably ignited, to physically simulate certain processes that occur in exploding thermonuclear weapons?
A: With a very large laser input and fast ignition by a miniaturized spark plug, perhaps.
“A hollow single-layer shell made of thermonuclear fuel is the simplest target for laser fusion… The thermonuclear fuel layer… also serves as an ablator… To minimize the energy losses on the intrinsic radiation of the plasma… the ablator… should consist of a [low-Z] material… D-T ice and light metal hydrides are the best such materials.” “…the use of a non-cryogenic fuel considerably simplifies the technology of manufacturing ICF targets, facilitates their delivery to the [target] chamber, and substantially reduces their cost… Due to a decrease in the fuel caloricity and an increase in self-radiation energy losses, the ignition of BeDT plasma is, naturally, more energy-consuming in comparison with the ignition of equimolar D-T plasma.” “The requirements for low-mode spherical symmetry and for high-mode uniformity of the target and drive are stringent in [central hot-spot ignition]; the former because a large spherical convergence ratio is needed to produce the ignition spark and the latter because the required high drive pressure leads to large Rayleigh-Taylor instability growth of high-mode number perturbations of the imploding shell… With [fast ignition] the compression and ignition steps are separated… The density and pressure are less than in central hot-spot ignition and therefore… easier to achieve, allowing some relaxation of hydrodynamic stability constraints… The bulk of the fuel does not have strict requirements for composition (it could be tritium-lean, for instance), or for shape (it should be in a roughly spherical form but irregularities are tolerable). Since a central spark is not needed, there is no problem with central mixing caused by a rough interior ice surface (in fact one might encourage mixing to keep any central gas cool).” “Fast ignition… reduces driver energy (by ten times or more) by reducing the implosion velocity and energy for a given fuel compression ratio… The fast ignition energy… has to be supplied before the heated region of compressed fuel can disassemble, in a time less than 20–100ps, hence the name… fast ignition… lengthens the pulse allowed for the compressor beams.”
Q: How would the blast be contained? How would the permanent diagnostics and other instrumentation be protected? How would the radioactive waste be collected and sequestered, and the target chamber turned around more generally?
A: The exceptionally large and highly unconventional target chamber would incorporate elements of the blast chambers used in “hydrodynamic tests and dynamic experiments,” as well as detonation diamond synthesis and explosive ordnance disposal.
“The… temperature of the product is never greater than 500–800K because water effectively absorbs the energy… The process of industrial detonation synthesis is carried out… with a manual loading of the blasting charge equipped with an electric detonator capsule. This is done through the upper porthole of the detonation chamber which is then sealed… a cylinder explosive charge placed in a plastic bag filled with water or ice is suspended [from] the chamber top.” “…the finished product is removed from the explosion chamber by washing the walls down with water… Synthesis involving ice cooling takes place… with [high explosive] charges encased in thick shells of ice.” “As a general rule of thumb, for every one kilogram of explosive material there needs to be [1–4m³] of volume… techniques used by Soviet and Russian developers to reduce the blast pressure and ensure the survival of the chamber… include… surrounding the explosive with sand, water, or foam shells, spraying the chamber with water, and placing the chamber under vacuum.” “Minimizing the scrap hardware removed from the chamber would be accomplished by… utilizing activation-resistant materials, minimizing weight and volume of structures, and discouraging the use of temporary experimental setups.” “A possible method to quickly insert [an] aluminum plate into the beam tube aperture is to accelerate two plates toward each other with pressurized gas. This ‘guillotine’ type valve would be placed just outside the chamber wall… the large impulsive forces from the acceleration and deceleration of the two plates will be equal and opposite. This reduces the concern that vibration from the valve will disrupt the laser alignment prior to the shot… crushable material will be placed at the center of the aperture to provide a stopping cushion for the plates.” “Material will… be vaporized from… the target, target mounts, cryogenic equipment, diagnostics, experimental apparatus, [and so on]. The vaporized material condenses after tens of milliseconds on any surfaces exposed to the inside of the target chamber, including optics and diagnostics. If any condensates are naturally radioactive (e.g. absorbed unburned tritium) or have been activated by fusion neutrons, then all chamber surfaces become radioactive. Such radioactivity might be embedded to depths of tens to hundreds of micrometers or more in the wall… Cleaning and deactivating a permanent first wall can thereby be a tedious and expensive process… The [idea is] to grow 2cm of frost within several hours at the appropriate water vapor pressure, then to cool it to roughly 130K, at which the vapor pressure from the frost would be 10⁻¹⁰ Torr. The cold wall would aid in achieving the desired chamber vacuum (10⁻⁵ Torr is thought to be adequate for diagnostics) through condensation (cryopumping) of all substances that vaporize above 130K. In addition, the heat load on a cryogenic target from a 130K wall with 300K laser beam ports would be lower by a factor of about ten than that from a room temperature wall… condensates will form directly on this frost/water, and not on the substrate. These condensates will include any activated target materials or fissionable materials from defense-applications experiments… post-shot warm up of the wall followed by a water spray and pumping will remove essentially all condensates and vapors, leaving the chamber in the same condition as it was before the shot. Exterior radioactive waste-handling and tritium scrubbing systems will be required… a replaceable frost layer will protect the substrate against permanent damage due to ablation by target X-rays and debris, and from shock-induced spallation. In addition, the frost need not permanently deposit on any surfaces, so the wall operation should have minimal impact on the other target-chamber systems (e.g. optics)… Although chamber entry may not be required for most shots, entry would be possible for repairs or equipment setup without waiting for more than one week for the dose rates to drop to acceptable levels.” “Contact maintenance of target chamber internal components following a laser-fusion shot, or series of shots, will require that residual radioactivity be reduced to an acceptable level… Automatic washdown… utilizes a high-velocity spray of water or detergent solution to remove radioactive particles. Systems designed for decontaminating large areas generally have several multi-nozzle manifolds… Carbide nozzle inserts are usually necessary to prevent excessive erosion of the nozzle by the liquid… If a detergent is used, a subsequent rinse is necessary… The [water] life can be extended and secondary waste volume minimized by removing dissolved metals and contaminants from the [wash] and rinse solutions… purification methods include ion exchange, solvent extraction, precipitation, distillation, electrolysis, and membrane separation… access to the chamber interior for decontamination and maintenance activities would be via… removable domes… Diagnostic penetrations, seams, and mechanical interfaces within the chamber would require special attention to ensure the complete removal of contaminated waste liquid. In fact, if flushing with quantities of liquid is not totally effective, it will only serve to accumulate radioactive particles in those areas that are most difficult to decontaminate… it would be highly desirable to accomplish the washdown operation with an eight-hour shift… Care must be taken to keep water and debris out of the instrumentation ports… the unit [would] be inserted and removed through an opening in the chamber rather than remaining in place during operations.” “Following the detonation of a maximum charge, gases and aerosols would fill the blast chamber, increasing the pressure to about 20psi… This pressure would bleed off through blast valves into the treatment area where the gases would be mixed with sufficient ambient air to allow filtration through HEPA filters… venting and purging gases would take about two hours. Following purging, an automated wash system using three ceiling-mounted, retractable water cannons would spray the walls and ceiling with water or other solutions. Washdown water or solutions would be collected in floor drains connected to a collection tank, filtered, and stored for reprocessing… Polymer extractant solutions would be used for decontaminating chamber surfaces.”
