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In deuterium-filled inertial confinement fusion implosions, the secondary fusion processes D(³He,p)4He and D(T,n)4He occur, as the primary fusion products ³He and T react in flight with thermal deuterons. In implosions with moderate fuel areal density (~5-100 mg/cm²), the secondary D-³He reaction saturates, while the D-T reaction does not, and the combined information from these secondary products is used to constrain both the areal density and either the plasma electron temperature or changes in the composition due to mix of shell material into the fuel. The underlying theory of this technique is developed and applied to three classes of implosions on the National Ignition Facility: direct-drive exploding pushers, indirect-drive 1-shock and 2-shock implosions, and polar direct-drive implosions. In the 1- and 2-shock implosions, the electron temperature is inferred to be 0.65 times and 0.33 times the burn-averaged ion temperature, respectively. The inferred mixed mass in the polar direct-drive implosions is in agreement with measurements using alternative techniques. [ABSTRACT FROM AUTHOR]

Pinhole imaging of large (mm scale) carbon-deuterium (CD) plasmas by proton self-emission has been used for the first time to study the microphysics of shock formation, which is of astrophysical relevance. The 3 MeV deuterium-deuterium (DD) fusion proton self-emission from these plasmas is imaged using a novel pinhole imaging system, with up to five different 1 mm diameter pinholes positioned 25 cm from target-chamber center. CR39 is used as the detector medium, positioned at 100 cm distance from the pinhole for a magnification of 4×. A Wiener deconvolution algorithm is numerically demonstrated and used to interpret the images. When the spatial morphology is known, this algorithm accurately reproduces the size of features larger than about half the pinhole diameter. For these astrophysical plasma experiments on the National Ignition Facility, this provides a strong constraint on simulation modeling of the experiment. [ABSTRACT FROM AUTHOR]

A compact spectrometer for measurements of the primary deuterium-tritium neutron spectrum has been designed and implemented on the OMEGA laser facility [T. Boehly et al., Opt. Commun. 133, 495 (1997)]. This instrument uses the recoil spectrometry technique, where neutrons produced in an implosion elastically scatter protons in a plastic foil, which are subsequently detected by a proton spectrometer. This diagnostic is currently capable of measuring the yield to ~±10% accuracy, and mean neutron energy to ~±50 keV precision. As these compact spectrometers can be readily placed at several locations around an implosion, effects of residual fuel bulk flows during burn can be measured. Future improvements to reduce the neutron energy uncertainty to ±15-20 keV are discussed, which will enable measurements of fuel velocities to an accuracy of ~±25-40 km/s. [ABSTRACT FROM AUTHOR]

Shock-driven implosions of thin-shell capsules, or "exploding pushers," generate low-density, high-temperature plasmas in which hydrodynamic instability growth is negligible and kinetic effects can play an important role. Data from implosions of thin deuterated-plastic shells with hydroequivalent D3He gas fills ranging from pure deuterium to pure 3He [H. G. Rinderknecht et al., Phys. Rev. Lett. 112, 135001 (2014)] were obtained to evaluate non-hydrodynamic fuel-shell mix mechanisms. Simulations of the experiments including reduced ion kinetic models support ion diffusion as an explanation for these data. Several additional kinetic mechanisms are investigated and compared to the data to determine which are important in the experiments. Shock acceleration of shell deuterons is estimated to introduce mix less than or comparable to the amount required to explain the data. Beam-target mechanisms are found to produce yields at most an order of magnitude less than the observations. [ABSTRACT FROM AUTHOR]

A magnetic recoil spectrometer (MRS) has been built and successfully used at OMEGA for measurements of down-scattered neutrons (DS-n), from which an areal density in both warm-capsule and cryogenic-DT implosions have been inferred. Another MRS is currently being commissioned on the National Ignition Facility (NIF) for diagnosing low-yield tritium-hydrogen-deuterium implosions and high-yield DT implosions. As CR-39 detectors are used in the MRS, the principal sources of background are neutron-induced tracks and intrinsic tracks (defects in the CR-39). The coincidence counting technique was developed to reduce these types of background tracks to the required level for the DS-n measurements at OMEGA and the NIF. Using this technique, it has been demonstrated that the number of background tracks is reduced by a couple of orders of magnitude, which exceeds the requirement for the DS-n measurements at both facilities. [ABSTRACT FROM AUTHOR]

For the first time high areal-density (ρR) cryogenic deuterium-tritium (DT) implosions have been probed using downscattered neutron spectra measured with the magnetic recoil spectrometer (MRS) [J. A. Frenje et al., Rev. Sci. Instrum. 79, 10E502 (2008)], recently installed and commissioned on OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. The ρR data obtained with the MRS have been essential for understanding how the fuel is assembled and for guiding the cryogenic program at the Laboratory for Laser Energetics (LLE) to ρR values up to ∼300 mg/cm2. The ρR data obtained from well-established charged particle spectrometry techniques [C. K. Li et al., Phys. Plasmas 8, 4902 (2001)] were used to authenticate the MRS data for low-ρR plastic capsule implosions, and the ρR values inferred from these techniques are in excellent agreement, indicating that the MRS technique provides high-fidelity data. Recent OMEGA-MRS data and Monte Carlo simulations have shown that the MRS on the NIF [G. H. Miller et al., Nucl. Fusion 44, S228 (2004)] will meet most of the absolute and relative requirements for determining ρR, ion temperature (Ti) and neutron yield (Yn) in both low-yield, tritium-rich, deuterium-lean, hydrogen-doped implosions and high-yield DT implosions. [ABSTRACT FROM AUTHOR]

Laser-driven magnetic-field compression producing a magnetic field of tens of megaGauss is reported for the first time. A shock wave formed during the implosion of a cylindrical target traps an initial (seed) magnetic field that is amplified via conservation of magnetic flux. Such large fields are expected to magnetize the electrons in the hot, central plasma, leading to a cyclotron frequency exceeding the collision frequency. The Omega Laser Facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] was used to implode cylindrical CH targets filled with deuterium gas and seeded with an external field (>50 kG) from a magnetic pulse generator. This seed field is trapped and rapidly compressed by the imploding shell, minimizing the effect of resistive flux diffusion. The compressed field was probed via proton deflectrometry using 14.7 MeV protons from the D+3He fusion reaction emitted by an imploding glass microballoon. Line-averaged magnetic fields of the imploded core were measured to between 30 and 40 MG. Experimental data were analyzed with both a magnetohydrodynamic version of the one-dimensional hydrocode LILAC [J. Delettrez et al., Phys. Rev. A 36, 3926 (1987); N. W. Jang et al., Bull. Am. Phys. Soc. 51, 144 (2006)] and the particle propagation code GEANT4 [S. Agostinelli et al., Nucl. Instrum. Methods Phys. Res. A 506, 250 (2003)]. [ABSTRACT FROM AUTHOR]

Determining fuel areal density (ρR) in moderate-ρR (100–200 mg/cm2) cryogenic deuterium-tritium (DT) implosions is challenging as it requires new spectrometry techniques and analysis methods to be developed. In this paper, we describe a new method for analyzing the spectrum of knock-on deuterons (KO-Ds), elastically scattered by primary DT neutrons, from which a fuel ρR can be inferred for values up to ∼200 mg/cm2. This new analysis method, which uses Monte Carlo modeling of a cryogenic DT implosion, improves significantly the previous analysis method in two fundamental ways. First, it is not affected by significant spatial-yield variations, which degrade the diagnosis of the fuel ρR (spatial yield variations of about ±20% are typically observed), and second, it does not break down when the fuel ρR exceeds ∼70 mg/cm2. [ABSTRACT FROM AUTHOR]

By fielding several compact proton spectrometers at various locations around an ignition-capsule implosion at the National Ignition Facility [G. H. Miller, E. I. Moses, and C. R. Wuest, Nucl. Fusion 44, S228 (2004)], ρR and ρR asymmetries of the ablator for a failed implosion can be obtained through absolute measurements of knock-on proton (KO-P) spectra. For ignition capsules with a Cu-doped beryllium (Be) ablator, 50:50 mixture of deuterium-tritium (DT) fuel and ∼1% residual hydrogen (H) by atom, failed implosions can be diagnosed for neutron yields ranging from ∼1011 to ∼6×1015 and local ρRs up to ∼240 mg/cm2. For capsules with an ablator of Ge-doped CH, which contains a large amounts of H, failed implosions can be diagnosed for neutron yields ranging from ∼1010 to ∼6×1015 and local ρRs up to ∼200 mg/cm2. Prior to the first ignition experiments, capsules with a Cu-doped Be ablator (or Ge-doped CH ablator), more deuterium-lean fuel mixture and H-dopant levels up to 25% in the fuel will be imploded to primarily reduce the neutron yield. The HDT-filled Be-capsule implosion, which can be diagnosed for neutron yields ranging from ∼5×109 to ∼6×1015 and local ρRs up to ∼240 mg/cm2, is more suitable to diagnose using KO-Ps as the signal-to-background ratio is significantly higher than for an ignition-capsule implosion. In addition, analysis of CH-ablator data obtained from analogous OMEGA [T. R. Boehly, D. L. Brown, R. S. Craxton et al., Opt. Commun. 133, 495 (1997)] experiments indicate that the shape of the KO-P spectrum is affected mainly by the ablator ρR. Other effects such as ablator-density-profile variations, time evolution of the ablator ρR, fuel-ablator mix and electron temperature variations typically predicted for the ablator play minor roles. [ABSTRACT FROM AUTHOR]

A monoenergetic, isotropic proton source suitable for proton radiography applications has been demonstrated at the National Ignition Facility (NIF). A deuterium and helium-3 gas-rilled glass capsule was imploded with 39 kJ of laser energy from 24 of NIF's 192 beams. Spectral, spatial, and temporal measurements of the 15-MeV proton product of the ³He(d,p)4He nuclear reaction reveal a bright (1010 protons/sphere), monoenergetic (ΔE/E = 4%) spectrum with a compact size (80 µm) and isotropic emission (~13% proton fluence variation and <0.4% mean energy variation). Simultaneous measurements of products produced by the D(d,n)³ and D(d,n)³He reactions also show 2 x 1010 isotropically distributed 3-MeV protons. C 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License. [ABSTRACT FROM AUTHOR]

A fusion-product source, utilizing a 150 kV Cockraft–Walton linear accelerator, has been refurbished to provide a reliable nuclear diagnostic development tool to the national inertial confinement fusion (ICF) research program. The accelerator is capable of routinely generating DD reaction rates at ∼107/s when using a 150 kV, 150 μA deuterium (D) beam onto an erbium (Er) or titanium (Ti) target doped with D, and D3He reaction rates at ∼5×105/s when using a using a 120 kV, ∼100 μA D beam onto a Er or Ti target doped with 3He. The new accelerator is currently being used in a number of projects related to the national ICF program at the OMEGA Laser Fusion Facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)], which includes the wedge range filter charged-particle spectrometry program [F. H. Seguin et al., Rev. Sci Instrum. 75, 3520 (2004)] and the magnetic recoil neutron spectrometer [J. A. Frenje et al., Rev. Sci. Instrum. 72, 854 (2001)]. [ABSTRACT FROM AUTHOR]

Radial profiles of nuclear burn in directly driven, inertial-confinement-fusion implosions have been systematically studied for the first time using a proton emission imaging system sensitive to energetic 14.7 MeV protons from the fusion of deuterium (D) and 3-helium (3He) at the OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Experimental parameters that were varied include capsule size, shell composition and thickness, gas fill pressure, and laser energy. Clear relationships have been identified between changes in a number of these parameters and changes in the size of the burn region, which we characterize here by the median “burn radius” Rburn containing half of the total D3He reactions. Different laser and capsule parameters resulted in burn radii varying from 20 to 80 μm. For example, reducing the D3He fill pressure from 18 to 3.6 atm in capsules with 20 μm thick CH shells resulted in Rburn changing from 31 to 25 μm; this reduction is attributed to increased fuel-shell mix for the more unstable 3.6 atm implosions rather than to increased convergence, because total areal density did not change very much. Fuel-shell-interface radii estimated from hard (4–5 keV) x-ray images of some of the same implosions were observed to closely track the burn radii. Burn radii from one-dimensional (1D) simulations agree fairly well with measurements for glass-shell capsules, but are systematically smaller than measurements for CH-shell capsules. A search for possible sources of systematic measurement error that could account for this discrepancy has been unsuccessful. Possible physical sources of discrepancies are mix, hydrodynamic instabilities, and/or preheat not included in the 1D code. Since measured burn-region sizes indicate where fusion actually occurs as a consequence of all the complicated processes that affect capsule implosion dynamics, it provides exacting tests of simulations. [ABSTRACT FROM AUTHOR]

Capsule-areal-density (ρR) asymmetries are studied for direct-drive, spherical implosions on the OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Measurements of copious 14.7-MeV protons generated from D[SUP3] He fusion reactions in the imploded capsules are used to determine ρR. As they pass through the plasma, these protons lose energy, and this energy loss reflects the areal density of the transited plasma. Up to 11 proton spectrometers simultaneously view D[SUP3] He implosions on OMEGA from different directions. While the burn-averaged and spatially averaged ρR for each implosion is typically between 50 and 75 mg/cm[SUP2] for 20-μm plastic shells filled with 18 atm of D[SUP3] He gas, significant differences often exist between the individual spectra, and inferred ρR on a given shot (as large as ∼ ±640% about the mean). A number of sources inherent in the direct-drive approach to capsule implosions can lead to these measured ρR asymmetries. For example, in some circumstances these asymmetries can be attributed to beam-to-beam energy imbalance when this imbalance is relatively large (∼ 25% rms). However, for more uniform illumination the source of the asymmetries is still under investigation. [ABSTRACT FROM AUTHOR]

Implosions of capsules filled with small quantities of deuterium–tritium (DT) were studied using up to seven proton spectrometers on the OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Simultaneous measurements of elastically scattered protons, i.e., “knock-on” protons generated from DT neutrons were obtained in several directions. The capsules, nominally 945 μm in diameter and with CD shells of ∼20 μm thickness, were filled to about 15 atm and irradiated with 23 kJ of UV light. The high-energy protons from these implosions were used to infer fuel areal density (6.8±0.5 mg/cm[sup 2]), an average shell areal density (71±3 mg/cm[sup 2]), and shell asymmetries of up to about 25 mg/cm2. In addition to presenting new results, these measurements verify and significantly improve upon the accuracy of the fuel areal density results obtained utilizing knock-on deuterons from hydrodynamically equivalent, pure DT implosions [C. K. Li et al., Phys. Plasmas 8, 4902 (2001)]. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

If x-radiation penetrates the ablator of an ignition capsule too deeply or too little, ignition can fail. Typically an ablator areal density of ∼0.2 g/cm2 remains at ignition time. 20% more or less flux in the final pulse of radiation driving the capsule can change that areal density by ∼0.1 g/cm2 and halve the capsule yield. We propose a technique to measure ablator areal density in a surrogate capsule that would complement Cu activation [D. C. Wilson et al., Phys. Plasmas 5, 1953 (1998)]. Replace the DT ice layer by deuterium and 3He gas. Diagnose the number and spectra of D–3He protons escaping the surrogate capsule with wedge range filters. For a 0.02 g/cm3 gas fill and the optimal radiation drive, 1.2e+11 protons escape with energies above 3 MeV and a peak at 5 MeV. If ignition would fail due to ablator burn through, 1.7e+11 protons would escape but the peak moves to 11 MeV. If ignition would fail from too much ablator remaining, 3.2e+9 protons escape the surrogate and the peak moves near 3 MeV. The D+D neutron yield remains roughly constant over this range. Wedge range filters would be able to diagnose these proton yields and peaks above ∼4 MeV with a resolution of ∼0.3 MeV. [ABSTRACT FROM AUTHOR]

The neutron spectrum produced by deuterium-tritium (DT) inertial confinement fusion implosions contains a wealth of information about implosion performance including the DT yield, ion-temperature, and areal-density. The Magnetic Recoil Spectrometer (MRS) has been used at both the OMEGA laser facility and the National Ignition Facility (NIF) to measure the absolute neutron spectrum from 3 to 30 MeV at OMEGA and 3 to 36 MeV at the NIF. These measurements have been used to diagnose the performance of cryogenic target implosions to unprecedented accuracy. Interpretation of MRS data requires a detailed understanding of the MRS response and background. This paper describes ab initio characterization of the system involving Monte Carlo simulations of the MRS response in addition to the commission experiments for in situ calibration of the systems on OMEGA and the NIF. [ABSTRACT FROM AUTHOR]

A magnetic recoil spectrometer (MRS) has been installed and extensively used on OMEGA and the National Ignition Facility (NIF) for measurements of the absolute neutron spectrum from inertial confinement fusion implosions. From the neutron spectrum measured with the MRS, many critical implosion parameters are determined including the primary DT neutron yield, the ion temperature, and the down-scattered neutron yield. As the MRS detection efficiency is determined from first principles, the absolute DT neutron yield is obtained without cross-calibration to other techniques. The MRS primary DT neutron measurements at OMEGA and the NIF are shown to be in excellent agreement with previously established yield diagnostics on OMEGA, and with the newly commissioned nuclear activation diagnostics on the NIF. [ABSTRACT FROM AUTHOR]

Measurements of the D(d, p)T (dd) and T(t, 2n)4He (tt) reaction yields have been compared with those of the D(t, n)4He (dt) reaction yield, using deuterium-tritium gas-filled inertial confinement fusion capsule implosions. In these experiments, carried out on the OMEGA laser, absolute spectral measure-ments of dd protons and tt neutrons were obtained. From these measurements, it was concluded that the dd yield is anomalously low and the tt yield is anomalously high relative to the dt yield, an observation that we conjecture to be caused by a stratification of the fuel in the implosion core. This effect may be present in ignition experiments planned on the National Ignition Facility. [ABSTRACT FROM AUTHOR]