Showing papers by "R. K. Fisher published in 1997"
TL;DR: A summary of recent alpha-particle experiments on the tokamak fusion test reactor is given in this paper, where the theoretically predicted toroidicity-induced Alfv?n eigenmode has been seen in discharges of of alpha power, but only in plasmas with weak magnetic shear.
Abstract: A summary is presented of recent alpha-particle experiments on the tokamak fusion test reactor. Alpha particles are generally well confined in MHD-quiescent discharges, and alpha heating of electrons has been observed. The theoretically predicted toroidicity-induced Alfv?n eigenmode has been seen in discharges of of alpha power, but only in plasmas with weak magnetic shear.
20 citations
TL;DR: In this paper, it was shown that the measured PCX alpha signal exhibits a depletion region near the outboard region and that stochastic ripple diffusion is the cause of the depletion.
Abstract: The pellet charge exchange (PCX) diagnostic on the Tokamak Fusion Test Reactor (TFTR) presently measures trapped alpha distribution functions with very small pitch angles ( nu ||/ nu ~0.05) at the midplane. The measured PCX alpha signal exhibits a depletion region near the outboard region. Results of the alpha energy spectra and radial profile suggest that stochastic ripple diffusion is the cause of the depletion. Comparison of the ripple stochastization boundary with Goldston-White-Boozer theory also shows the correct functional dependence on alpha energy and q profile
19 citations
TL;DR: In this article, the authors considered the effects of the alpha particles' helical Larmor orbits, which causes the alphas to make multiple passes through the cloud, and reformulated the signal level calculation, and used a Monte-Carlo approach to calculate the neutralization fractions.
Abstract: The energy spectra of energetic confined alpha particles are being measured using the pellet charge exchange method [R. K. Fisher, J. S. Leffler, A. M. Howald, and P. B. Parks, Fusion Technol. 13, 536 (1988)]. The technique uses the dense ablation cloud surrounding an injected impurity pellet to neutralize a fraction of the incident alpha particles, allowing them to escape from the plasma where their energy spectrum can be measured using a neutral particle analyzer. The signal calculations given in the above-mentioned reference disregarded the effects of the alpha particles’ helical Larmor orbits, which causes the alphas to make multiple passes through the cloud. Other effects such as electron ionization by plasma and ablation cloud electrons and the effect of the charge state composition of the cloud, were also neglected. This report considers these issues, reformulates the signal level calculation, and uses a Monte-Carlo approach to calculate the neutralization fractions. The possible effects of energy loss and pitch angle scattering of the alphas are also considered.
12 citations
TL;DR: In this paper, the authors describe the diagnostic capabilities of PCX demonstrated on TFTR and discuss the prospects for applying this technique to ITER, where the pellet perturbation to the plasma and obtaining satisfactory penetration into the plasma are discussed.
Abstract: Confinement of alpha particles is essential for fusion ignition and alpha physics studies are a major goal of the TFTR, JET, and ITER DT experiments, but alpha measurements remain one of the most challenging plasma diagnostic tasks. The pellet charge exchange (PCX) diagnostic has successfully measured the radial density profile and energy distribution of fast (0.5–3.5 MeV) confined alpha particles in TFTR. This article describes the diagnostic capabilities of PCX demonstrated on TFTR and discusses the prospects for applying this technique to ITER. Major issues on ITER include the pellet’s perturbation to the plasma and obtaining satisfactory pellet penetration into the plasma.
7 citations
TL;DR: In this article, the first two years of the Tokamak test fusion reactor (TFTR) D-T operation is summarized and a brief summary of the concept, instrumentation, and analysis techniques for each diagnostic is given, followed by examples of alpha physics results.
Abstract: Experience with the α charge exchange recombination spectroscopy and pellet charge exchange confined, nonthermal alpha particle diagnostics over the first two years of Tokamak test fusion reactor (TFTR) D–T operation is summarized. A brief summary of the concept, instrumentation, and analysis techniques for each diagnostic is given, followed by examples of alpha physics results. Issues important to further development of these diagnostic techniques for TFTR and ITER are discussed.
6 citations
TL;DR: In this article, the authors describe the status of the pellet charge exchange (PCX) diagnostic including a brief description of the measurement technique and discussion of operational experience, as well as measurements of the energy spectrum, radial density distribution, and heating deposition profile of rf-driven tritium ions during 2ΩT heating of L-mode plasmas are presented.
Abstract: Charge exchange interactions of ions with the ablation cloud of an injected low-Z impurity pellet can be used to measure the energy spectrum and radial profile of confined fast ions in a fusion plasma. On the Tokamak Fusion Test Reactor we use this technique to directly measure energetic alphas from D–T reactions, tritons from D–D reactions, and radio frequency (rf)-driven minority tail ions (e.g., H, 3He, T). We describe the status of the pellet charge exchange (PCX) diagnostic including a brief description of the measurement technique and discussion of operational experience. PCX measurements of the energy spectrum, radial density distribution, and heating deposition profile of rf-driven tritium ions during 2ΩT heating of L-mode plasmas are presented.
5 citations