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Title: Alpha Particle Physics Experiments in the Tokamak Fusion Test Reactor

Abstract

Alpha particle physics experiments were done on the Tokamak Fusion Test Reactor (TFTR) during its deuterium-tritium (DT) run from 1993-1997. These experiments utilized several new alpha particle diagnostics and hundreds of DT discharges to characterize the alpha particle confinement and wave-particle interactions. In general, the results from the alpha particle diagnostics agreed with the classical single-particle confinement model in magnetohydrodynamic (MHD) quiescent discharges. Also, the observed alpha particle interactions with sawteeth, toroidal Alfvén eigenmodes (TAE), and ion cyclotron resonant frequency (ICRF) waves were roughly consistent with theoretical modeling. This paper reviews what was learned and identifies what remains to be understood.

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
2545
Report Number(s):
PPPL-3333
ON: DE00002545
DOE Contract Number:
AC02-76CH03073
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION; TFTR Tokamak; D-T Operation; Plasma Diagnostics; Alpha Particles; Helium Ions; Magnetic Confinement; Sawtooth Oscillations; Ion Cyclotron-Resonance; Alfven Waves; Experimental Data

Citation Formats

Budny, R.V., Darrow, D.S., Medley, S.S., Nazikian, R., Zweben, S.J., and et al. Alpha Particle Physics Experiments in the Tokamak Fusion Test Reactor. United States: N. p., 1998. Web. doi:10.2172/2545.
Budny, R.V., Darrow, D.S., Medley, S.S., Nazikian, R., Zweben, S.J., & et al. Alpha Particle Physics Experiments in the Tokamak Fusion Test Reactor. United States. doi:10.2172/2545.
Budny, R.V., Darrow, D.S., Medley, S.S., Nazikian, R., Zweben, S.J., and et al. Mon . "Alpha Particle Physics Experiments in the Tokamak Fusion Test Reactor". United States. doi:10.2172/2545. https://www.osti.gov/servlets/purl/2545.
@article{osti_2545,
title = {Alpha Particle Physics Experiments in the Tokamak Fusion Test Reactor},
author = {Budny, R.V. and Darrow, D.S. and Medley, S.S. and Nazikian, R. and Zweben, S.J. and et al.},
abstractNote = {Alpha particle physics experiments were done on the Tokamak Fusion Test Reactor (TFTR) during its deuterium-tritium (DT) run from 1993-1997. These experiments utilized several new alpha particle diagnostics and hundreds of DT discharges to characterize the alpha particle confinement and wave-particle interactions. In general, the results from the alpha particle diagnostics agreed with the classical single-particle confinement model in magnetohydrodynamic (MHD) quiescent discharges. Also, the observed alpha particle interactions with sawteeth, toroidal Alfvén eigenmodes (TAE), and ion cyclotron resonant frequency (ICRF) waves were roughly consistent with theoretical modeling. This paper reviews what was learned and identifies what remains to be understood.},
doi = {10.2172/2545},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Dec 14 00:00:00 EST 1998},
month = {Mon Dec 14 00:00:00 EST 1998}
}

Technical Report:

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  • The toroidal Alfvén eigenmodes (TAE) in the Tokamak Fusion Test Reactor [K. Young, et al., Plasma Phys. Controlled Fusion 26, 11 (1984)]deuterium-tritium plasmas are analyzed using the NOVA-K code [C.Z. Cheng, Phys. Reports 211, 1 (1992)]. The theoretical results are compared with the experimental measurements in detail. In most cases, the theory agrees with the observations in terms of mode frequency, mode structure, and mode stability. However, one mode with toroidal mode number n = 2 is observed to be poloidally localized on the high field side of the magnetic axis with a mode frequency substantially below the TAE frequency.
  • The original description of alpha-particle-driven instabilities in the Tokamak Fusion Test Reactor (TFTR) in terms of Toroidal Alfvin Eigenmodes (TAEs) remained inconsistent with three fundamental characteristics of the observations: (i) the variation of the mode frequency with toroidal mode number, (ii) the chirping of the mode frequency for a given toroidal mode number, and (iii) the anti-ballooning density perturbation of the modes. It is now shown that these characteristics can be explained by observing that cylindrical-like modes can exist in the weak magnetic shear region of the plasma that then make a transition to TAEs as the central safety factormore » decreases in time.« less
  • Neoclassical simulations of alpha particle density profiles in high fusion power plasmas on the Tokamak Fusion Test Reactor (TFTR) [Phys. Plasmas 5 (1998) 1577] are found to be in good agreement with measurements of the alpha distribution function made with a sensitive active neutral particle diagnostic. The calculations are carried out in Hamiltonian magnetic coordinates with a fast, particle-following Monte Carlo code which includes the neoclassical transport processes, a recent first-principles model for stochastic ripple loss and collisional effects. New global loss and confinement domain calculations allow an estimate of the actual alpha particle densities measured with the pellet chargemore » exchange diagnostic.« less
  • Because alpha particle losses can have a significant influence on tokamak reactor viability, the loss of deuterium-tritium alpha particles from the Tokamak Fusion Test Reactor (TFTR) has been measured under a wide range of conditions. In TFTR, first orbit loss and stochastic toroidal field ripple diffusion are always present. Other losses can arise due to magnetohydrodynamic instabilities or due to waves in the ion cyclotron range of frequencies. No alpha particle losses have yet been seen due to collective instabilities driven by alphas. Ion Bernstein waves can drive large losses of fast ions from TFTR, and details of those lossesmore » support one element of the alpha energy channeling scenario.« less
  • Hamiltonian coordinate, guiding center code calculations of the toroidal field ripple loss of alpha particles from a reversed shear plasma predict both total alpha losses and ripple diffusion losses to be greater than those from a comparable non-reversed magnetic shear plasma in the Tokamak Fusion Test Reactor (TFTR) [Fusion Technol. 21, 1324 (1992)]. High central q is found to increase alpha ripple losses as well as first orbit losses of alphas in the reversed shear simulations. A simple ripple loss model, benchmarked against the guiding center code, is found to work satisfactorily in transport analysis modelling of reversed and monotonicmore » shear scenarios. Alpha ripple transport on TFTR affects ions within r/a=0.5, not at the plasma edge. The entire plasma is above threshold for stochastic ripple loss of alpha particles at birth energy in the reversed shear case simulated, so that all trapped 3.5 MeV alphas are lost stochastically or through prompt losses. The 40% alpha particle loss predictions for TFTR suggest that reduction of toroidal field ripple will be a critical issue in the design of a reversed shear fusion reactor.« less