Fusion neutron energies and spectra

Brysk, Henry

doi:10.1088/0032-1028/15/7/001

Cited by 384 publications

(240 citation statements)

References 6 publications

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“…On NIF, six NTOF detectors measure the neutron spectrum as a function of neutron energy, integrated over the hot spot, which contains a distribution of temperature and burn rates. The thermal distribution results in a dispersion of the neutron arrival times at distant detectors [75] and allows extracting the relative ratio of down-scattered neutrons to the primary neutron signal [76].…”

Section: Entropymentioning

confidence: 99%

Cryogenic thermonuclear fuel implosions on the National Ignition Facility

et al. 2012

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The first inertial confinement fusion implosion experiments with equimolar deuterium-tritium thermonuclear fuel have been performed on the National Ignition Facility. These experiments use 0.17 mg of fuel with the potential for ignition and significant fusion yield conditions. The thermonuclear fuel has been fielded as a cryogenic layer on the inside of a spherical plastic capsule that is mounted in the center of a cylindrical gold hohlraum. Heating the hohlraum with 192 laser beams for a total laser energy of 1.6 mega joules produces a soft x-ray field with 300 eV temperature. The ablation pressure produced by the radiation field compresses the initially 2.2-mm diameter capsule by a factor of 30 to a spherical dense fuel shell that surrounds a central hot-spot plasma of 50 µm diameter. While an extensive set of x-ray and neutron diagnostics has been applied to characterize hot spot formation from the x-ray emission and 14.1 MeV deuterium-tritium primary fusion neutrons, thermonuclear fuel assembly is studied by measuring the down-scattered neutrons with energies in the range of 10 to 12 MeV. X-ray and neutron imaging of the compressed core and fuel indicate a fuel thickness of (14 ± 3) µm, which combined with magnetic recoil spectrometer measurements of the fuel areal density of (1 ± 0.09) g cm −2 result in fuel densities approaching 600 g cm −3 . The fuel surrounds a hot-spot plasma with average ion temperatures of (3.5 ± 0.1) keV that is measured with neutron time of flight spectra. Absolute neutron yields of (7.5 ± 0.1) × 10 14 have been recorded from the magnetic recoil spectrometer and nuclear activation diagnostics while gamma ray measurements provide the duration of nuclear activity of (170 ± 30) ps. These indirect-drive implosions result in the highest areal densities and neutron yields achieved on laser facilities to date. This achievement is the result of the first hohlraum and capsule tuning experiments where the stagnation pressures have been systematically increased by more than a factor of 10 by fielding low-entropy implosions through the control of radiation symmetry, small hot electron production, and proper shock timing. The stagnation pressure is above 100 Gbar resulting in high Lawson confinement parameters of P τ 10 atm s. Comparisons with radiation-hydrodynamic simulations indicate that the pressure is within a factor of three required for reaching ignition and high yield. This will be the focus of future higher-velocity implosions that will employ additional optimizations of hohlraum, capsule and laser pulse shape conditions.

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Section: Entropymentioning

confidence: 99%

Cryogenic thermonuclear fuel implosions on the National Ignition Facility

et al. 2012

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“…26,41,42 These spectra are isotropic with a maximum intensity at an energy that is close to the nominal neutron energy for the reaction (2.45 MeV for DD and 14.05 MeV for DT neutrons, respectively). As shown in the results of Sec.…”

Section: A Thermonuclear Spectramentioning

confidence: 93%

Neutron spectra from beam-target reactions in dense Z-pinches

Appelbe

Chittenden

2015

Physics of Plasmas

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The energy spectrum of neutrons emitted by a range of deuterium and deuterium-tritium Z-pinch devices is investigated computationally using a hybrid kinetic-MHD model. 3D MHD simulations are used to model the implosion, stagnation, and break-up of dense plasma focus devices at currents of 70 kA, 500 kA, and 2 MA and also a 15 MA gas puff. Instabilities in the MHD simulations generate large electric and magnetic fields, which accelerate ions during the stagnation and break-up phases. A kinetic model is used to calculate the trajectories of these ions and the neutron spectra produced due to the interaction of these ions with the background plasma. It is found that these beam-target neutron spectra are sensitive to the electric and magnetic fields at stagnation resulting in significant differences in the spectra emitted by each device. Most notably, magnetization of the accelerated ions causes the beam-target spectra to be isotropic for the gas puff simulations. It is also shown that beam-target spectra can have a peak intensity located at a lower energy than the peak intensity of a thermonuclear spectrum. A number of other differences in the shapes of beam-target and thermonuclear spectra are also observed for each device. Finally, significant differences between the shapes of beam-target DD and DT neutron spectra, due to differences in the reaction cross-sections, are illustrated.

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“…The neutron emission energy spectra of thermal DT plasmas can with good approximation be taken of Gaussian shape, where the width of the distribution is proportional to the square root of the temperature of the plasma, T i [46].…”

Section: Thermal Plasmasmentioning

confidence: 99%

Evaluation of neutron spectrometer techniques for ITER using synthetic data

Sundén

Ballabio

Cecconello

et al. 2013

Nuclear Instruments and Methods in Physics Research Section A:

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A neutron spectrometer at ITER is expected to provide estimates of plasma parameters such as ion temperature, T i , fuel ion ratio, n t /n d , and Q thermal /Q tot , with 10-20% precision at a time resolution, Δt, of at least 100 ms. The present paper describes a method for evaluating different neutron spectroscopy techniques based on their instrumental response functions and synthetic measurement data. We include five different neutron spectrometric techniques with realistic response functions, based on simulations and measurements where available. The techniques are magnetic proton recoil, thin-foil proton recoil, gamma discriminating organic scintillator, diamond and time-of-flight. The reference position and line of sight of a high resolution neutron spectrometer on ITER are used in the study. ITER plasma conditions are simulated for realistic operating scenarios. The ITER conditions evaluated are beam and radio frequency heated and thermal deuterium-tritium plasmas. Results are given for each technique in terms of the estimated time resolution at which the parameter determination can be made within the required precision (here 10% for T i and the relative intensities of NB and RF emission components). It is shown that under the assumptions made, the thin-foil techniques out-perform the other spectroscopy techniques in practically all measurement situations. For thermal conditions, the range of achieved Δt in the determination of T i varies in time scales from ms (for the magnetic and thin-foil proton recoil) to s (for gamma discriminating organic scintillator).

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Fusion neutron energies and spectra

Cited by 384 publications

References 6 publications

Cryogenic thermonuclear fuel implosions on the National Ignition Facility

Cryogenic thermonuclear fuel implosions on the National Ignition Facility

Neutron spectra from beam-target reactions in dense Z-pinches

Evaluation of neutron spectrometer techniques for ITER using synthetic data

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