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Bremsstrahlung x-ray generation for high optical depth radiography applications on the National Ignition Facility
摘要： We have tested a set of x-ray sources for use as probes of highly attenuating, laser-driven experiments on the National Ignition Facility (NIF). Unlike traditional x-ray sources that optimize for a characteristic atomic transition (often the n = 2 → n = 1 transition in ionized, He-like atoms), the design presented here maximizes the total photon ?ux by optimizing for intense, broadband Bremsstrahlung radiation. Three experiments were performed with identical targets, including a uranium x-ray source foil and a tungsten substrate with a narrow (25 μm wide) collimating slit to produce a quasi-1D x-ray source. Two experiments were performed using 12 beams from the NIF laser, each delivering approximately 46 kJ of laser energy but with different laser spatial pro?les. This pair yielded similar temporal x-ray emission pro?les, spatial resolution, and inferred hot electron temperature. A third experiment with only 6 beams delivering approximately 25 kJ produced a lower hot electron temperature and signi?cantly lower x-ray ?ux, as well as poorer spatial resolution. The data suggest that laser pointing jitter may have affected the location and intensity of the emitting plasma, producing an emission volume that was not well centered behind the collimating slit and lower intensity than designed. However, the 12-beam design permits x-ray radiography through highly attenuating samples, where lower energy line-emission x-ray sources would be nearly completely attenuated.
关键词： high optical depth radiography,laser-driven experiments,Bremsstrahlung radiation,x-ray sources,National Ignition Facility
更新于2025-09-23 15:21:01
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Debris and shrapnel assessments for National Ignition Facility targets and diagnostics
摘要： High-energy laser experiments at the National Ignition Facility (NIF) can create debris and shrapnel capable of damaging laser optics and diagnostic instruments. The size, composition and location of target components and sacrificial shielding (e.g., disposable debris shields, or diagnostic filters) and the protection they provide is constrained by many factors, including: chamber and diagnostic geometries, experimental goals and material considerations. An assessment of the generation, nature and velocity of shrapnel and debris and their potential threats is necessary prior to fielding targets or diagnostics. These assessments may influence target and shielding design, filter configurations and diagnostic selection. This paper will outline the approach used to manage the debris and shrapnel risk associated with NIF targets and diagnostics and present some aspects of two such cases: the Material Strength Rayleigh-Taylor campaign and the Mono Angle Crystal Spectrometer (MACS).
关键词： diagnostics,shrapnel,debris,National Ignition Facility,targets
更新于2025-09-23 15:19:57
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Progress on next generation gamma-ray Cherenkov detectors for the National Ignition Facility
摘要： Fusion reaction history and ablator areal density measurements for Inertial Con?nement Fusion experiments at the National Ignition Facility are currently conducted using the Gamma Reaction History diagnostic (GRH 6m). Future Gas Cherenkov Detectors (GCDs) will ultimately provide ～100x more sensitivity, reduce the effective temporal response from ～100 to ～10 ps, and lower the energy threshold from 2.9 to 1.8 MeV, relative to GRH 6m. The ?rst phase toward next generation GCDs consisted of inserting the existing coaxial GCD-3 detector into a reentrant well which puts it within 4 m of the implosion. Reaction history and ablator gamma measurement results from this Phase I are discussed here. These results demonstrate viability for the follow-on Phases of (II) the use of a revolutionary new pulse-dilation photomultiplier tube to improve the effective measurement bandwidth by >10x relative to current PMT technology; and (III) the design of a NIF-speci?c “Super” GCD which will be informed by the assessment of the radiation background environment within the well described here.
关键词： pulse-dilation photomultiplier tube,Gas Cherenkov Detectors,Gamma-ray Cherenkov detectors,Inertial Con?nement Fusion,National Ignition Facility
更新于2025-09-10 09:29:36
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Development of an ultra-fast photomultiplier tube for gamma-ray Cherenkov detectors at the National Ignition Facility (PD-PMT)
摘要： A new ultra-fast photomultiplier tube and associated drivers have been developed for use in the next generation of gamma-ray high pressure gas Cherenkov detectors for inertial con?nement fusion experiments at the National Ignition Facility. Pulse-dilation technology has been applied to a standard micro-channel-plate-based photomultiplier tube to improve the temporal response by about 10×. The tube has been packaged suitably for deployment on the National Ignition Facility, and remote electronics have been designed to deliver the required non-linear waveforms to the pulse dilation electrode. This is achieved with an avalanche pulse generator system capable of generating fast arbitrary waveforms over the useful parameter space. The pulse is delivered via fast impedance-matching transformers and isolators, allowing the cathode to be ramped on a sub-nanosecond time scale between two high voltages in a controlled non-linear manner. This results in near linear pulse dilation over several ns. The device has a built-in ?ducial system that allows easy calibration and testing with ?ber optic laser sources. Results are presented demonstrating the greatly improved response time and other parameters of the device.
关键词： inertial con?nement fusion,gamma-ray Cherenkov detectors,National Ignition Facility,ultra-fast photomultiplier tube,pulse-dilation technology
更新于2025-09-09 09:28:46
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Pulse dilation gas Cherenkov detector for ultra-fast gamma reaction history at the NIF (invited)
摘要： The Cherenkov mechanism used in Gas Cherenkov Detectors (GCDs) is exceptionally fast. However, the temporal resolution of GCDs, such as the Gamma Reaction History diagnostic at the National Ignition Facility (NIF), has been limited by the current state-of-the-art photomultiplier tube technology to ～100 ps. The soon-to-be deployed Pulse Dilation Photomultiplier Tube (PD-PMT) at NIF will allow for temporal resolution comparable to that of the gas cell or ～10 ps. Enhanced resolution will contribute to the quest for ignition in a crucial way through precision measurements of reaction history and ablator areal density (ρR) history, leading to better constrained models. Features such as onset of alpha heating, shock reverberations, and burn truncation due to dynamically evolving failure modes may become visible for the ?rst time. Test measurements of the PD-PMT at Atomic Weapons Establishment con?rmed that design goals have been met. The PD-PMT provides dilation factors of 2 to 40× in 6 increments. The GCD-3 recently deployed at the NIF has been modi?ed for coupling to a PD-PMT and will soon be making ultrafast measurements.
关键词： Gas Cherenkov Detectors,Pulse Dilation Photomultiplier Tube,National Ignition Facility,temporal resolution,Cherenkov mechanism
更新于2025-09-09 09:28:46
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Note: Radiochemical measurement of fuel and ablator areal densities in cryogenic implosions at the National Ignition Facility
摘要： A new radiochemical method for determining deuterium-tritium (DT) fuel and plastic ablator (CH) areal densities (ρR) in high-convergence, cryogenic inertial confinement fusion implosions at the National Ignition Facility is described. It is based on measuring the 198Au/196Au activation ratio using the collected post-shot debris of the Au hohlraum. The Au ratio combined with the independently measured neutron down scatter ratio uniquely determines the areal densities ρR(DT) and ρR(CH) during burn in the context of a simple 1-dimensional capsule model. The results show larger than expected ρR(CH) values, hinting at the presence of cold fuel-ablator mix.
关键词： cryogenic inertial confinement fusion,neutron down scatter ratio,National Ignition Facility,areal densities,fuel-ablator mix,plastic ablator,deuterium-tritium fuel,radiochemical method,Au hohlraum
更新于2025-09-04 15:30:14