high-energy-density physics

An Introduction to Charged Particle Spectroscopy on Omega

The MIT High-Energy-Density Physics group, in collaboration with the Laboratory for Laser Energetics at the University of Rochester, the Lawrence Livermore National Laboratory, and with the SUNY Geneseo Nuclear Structure Laboratory, State University of New York .

Abstract

This document provides an overview of our Charged-Particle Spectroscopy program, which is designed to provide diagnostic information about ICF plasmas by measuring energy spectra of charged fusion products and ablator ions. While the program is designed with the National Ignition Facility (NIF) in mind, it currently involves experiments on the OMEGA facility at the University of Rochester Laboratory for Laser Energetics. Two magnet-based spectrometers and several small range-filter-based spectrometers are used used for spectroscopic measurements of energetic charged particles on OMEGA. Measured spectra include lines of D3He protons (14.7 MeV) and alphas (3.6 MeV), DT alphas (3.5 MeV), and DD protons (3.0 MeV), tritons (1.0 MeV), and 3He (0.8 MeV), T-3He deuterons (9.5 MeV), and continuous "knock-on" spectra of deuterons, tritons, and protons ejected in elastic collisions with 14-MeV fusion neutrons. These and other measurements provide fusion yields, ion temperatures, <rR> of fuel and shell, stopping power in hot plasmas and quantification of anomalous acceleration effects. In addition, copious fluxes of energetic ablator protons have been observed from 100 keV to 1.4 MeV, sometimes including sharply-defined "lines". The maximum energy of the ablator protons strongly suggests that the capsule can be charged up to more than 1 MV while the laser is on.

High resolution neutron spectrometry for diagnosing capsule implosions at the NIF and OMEGA

Abstract

A neutron spectrometer, called a Magnetic Recoil Spectrometer (MRS), has been built and implemented at the OMEGA laser facility [T. R. Boehly. D. L. Brown, R. S. Craxton et al., Opt. Commun. 133, 495 (1997)] for absolute measurements of the neutron spectrum in the range 6 to 30 MeV, from which
fuel areal density (rhoR), ion temperature (Ti) and yield (Yn) can be determined. The results from the first MRS measurements of the absolute neutron spectrum are presented. In addition, measuring rhoR at the National Ignition Facility (NIF) [G.H. Miller, E.I. Moses and C.R. Wuest, Nucl. Fusion 44, S228 (2004)] will be essential for assessing implosion performance during all stages of development from surrogate implosions to cryogenic fizzles to ignited implosions. To accomplish this, we are also developing an MRS for the NIF. As much of the R&D and instrument optimization of the MRS at OMEGA is directly applicable to the MRS at the NIF, a description of the design and characterization of the MRS on the
NIF is discussed as well.

The MIT charged particle accelerator

Abstract

The MIT fusion product source (initially a Cockcroft-Walton accelerator) has been significantly upgraded through experimental and computational work, furthering the usefulness of this tool for many ICF applications. Additional hardware and software upgrades and testing of various components have improved and allowed greater control over yields and energies of several types of emergent fusion products. ICF diagnostics development is currently being done, including testing of different kinds of CR-39 detectors, calibration of charged particle spectrometers††. This effort also supports the development of the Magnetic Recoil Spectrometer (MRS)** in addition to the current ICF diagnostics.

This work was supported in part by the Laboratory of Laser Energetics, Lawrence Livermore National Laboratory, the U.S. Department of Energy, the University of Rochester, and the N.Y.State Energy Research and Development Authority.