Pellet charge exchange measurements of confined alphas in deuterium{endash}tritium plasmas (invited) (abstract)

Journal Article · Fri Jan 01 04:00:00 EST 1999 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/1.1149453· OSTI ID:295669

Fisher, R K ^[1]

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1. General Atomics, San Diego, California 92186 (United States)

Alpha particle confinement is essential to achieving ignition in deuterium{endash}tritium plasmas, and measuring the energy and spatial distributions of fusion alphas is one of the most challenging tasks in plasma diagnostics research. Confined trapped-alpha energy spectra and radial density profiles in the Tokamak Fusion Test Reactor (TFTR) have been obtained using the pellet charge exchange (PCX) diagnostic, which measures high energy (E{sub {alpha}}=0.5{endash}3.5 MeV), trapped alphas ({vert_bar}v{sub {parallel}}/v{vert_bar}=0.048) at a single time slice ({Delta}{ital t}{approximately}1 ms) with a spatial resolution of {Delta}{ital r}{approximately}5 cm. PCX measures the energy spectrum of energetic helium neutrals resulting from charge exchange interactions of alphas incident on the ablation cloud surrounding small boron and lithium pellets injected radially into TFTR. The success of PCX has led to a number of important results on the behavior of alphas in TFTR. The measured alpha energy spectrum in the plasma core of sawtooth-free discharges is consistent with the alphas being well confined and slowing down classically. Outside the plasma core, the trapped alphas show the effects of stochastic diffusion due to the toroidal magnetic field ripple, with the PCX measured profiles consistent with the functional dependence of the stochastic ripple diffusion on the alpha energy and the {ital q} profile. Large sawtooth instabilities result in radial redistribution of the trapped alphas to well outside the q=1 radius and beyond the stochastic ripple loss boundary. Broadening of the radial profiles of trapped alphas is also observed in reversed and reduced shear discharges on TFTR, with potential implications for reactor designs based on optimized shear configurations. Finally, radial redistribution of trapped alpha particles in the presence of core localized Toroidal Alf{acute v}en Eigenmode activity is also observed. Application of PCX measurements to future experiments, including the International Thermonuclear Experimental Reactor will also be discussed. {copyright} {ital 1999 American Institute of Physics.}

• OSTI ID: 295669
• Report Number(s): CONF-980605--
• Journal Information: Review of Scientific Instruments, Journal Name: Review of Scientific Instruments Journal Issue: 1 Vol. 70; ISSN 0034-6748; ISSN RSINAK
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ALPHA PARTICLES
CHARGE EXCHANGE
DEUTERIUM
FUEL PELLETS
IGNITION
PLASMA DENSITY
PLASMA DIAGNOSTICS
TFTR TOKAMAK
TOKAMAK DEVICES
TRITIUM