Charged-particle spectroscopy: A new window on inertial confinement fusion

A new charged-particle diagnostic for inertial confinement fusion experiments has been designed, constructed and fielded on the OMEGA laser system. The spectrometer consists of a 7.6 kilogauss permanent magnet and CR-39 nuclear track detectors which can probe energies between 0.1 30 MeV and particle yields between 108 101". A rapid track scanning system that has been developed is used to analyze between 103 106 particles per shot. Highly resolved spectra have been obtained for a wide range of primary fusion products, such as D-D protons and tritons, D-3He protons and alphas, D-T alphas, as well as neutron-scattered fuel ions, or "knock-ons". Benchmark comparisons of the data with available neutron measurements show reasonable agreement: fusion yields are similar, on the average, as are fuel ion temperatures measured by Doppler broadening and line ratio techniques in certain regimes. The spectrum of triton and deuteron knock-ons have enabled fuel pR's to be determined, while the energy downshift of the fusion products has been used to determine ablator pR. In addition, copious fluxes of ablator protons have been detected with energies up to 1.4 MeV when laser intensities exceed a threshold of 1x 1014 W/cm 2 , while fusion products are sometimes measured with accelerations of several hundred keV. The symmetry of all measurements is assessed by using two nearly identical spectrometers mounted with orthogonal views of the target. Thesis Supervisor: Richard D. Petrasso Senior Research Scientist, Plasma Science and Fusion Center, Massachusetts Institute of Technology