ITER alpha particle diagnostics using knock-on ion tails
- and others
Alpha particles will play a critical role in the physics and successful operation of ITER. Achieving fusion ignition requires that the {alpha} particles created by deuterium-tritium (D-T) reactions deposit a large fraction of their energy in the reacting plasma before they are lost. Toroidal field ripple can localize any alpha particle losses and cause first wall damage. We have proposed a new method of measuring the fast confined {alpha}-particle distribution in a reacting plasma. The same elastic collisions that transfer the alpha energy to the D-T plasma ions and allow fusion ignition will also create a high energy tail on the deuterium and tritium ion energy distributions. Some of these energetic tail ions will undergo fusion reactions with the background plasma producing neutrons whose energy is increased significantly above 14 MeV due to the kinetic energy of the reacting ions. Measurement of this high energy tail on the D-T neutron distribution as a function of plasma minor radius would provide information on the alpha density profile with a time response equal to the ion slowing-down time. Although this technique may provide only limited information on the {alpha}-particle energy distribution, experimental studies of fast ions on existing tokamaks have shown that the observed slowing-down is essentially classical. Hence the {alpha}-energy distribution is expected to be classical except in situations where the {alpha}-confinement is poor. The confinement of {alpha}`s can be affected by ripple losses and a number of instabilities. Toroidal field ripple can cause both prompt orbit losses and stochastic ripple diffusion losses. Magnetohydrodynamic activity, including fishbone instabilities, toroidal Alfven eigenmodes, and sawtooth oscillations, may also affect alpha confinement. The diagnostic proposed here, by monitoring the confined alpha population, can provide valuable information on the confinement of fast alphas in a reacting plasma.
- Research Organization:
- General Atomics, San Diego, CA (US); Princeton Univ., NJ (US). Plasma Physics Lab. (US)
- Sponsoring Organization:
- USDOE, Washington, DC (US)
- DOE Contract Number:
- FG03-92ER54150; AC03-94SF20282; AC02-76CH03073; W-7405-ENG-36
- OSTI ID:
- 120919
- Report Number(s):
- GA-A-22140; LA-UR-95-4153; CONF-950848-3; ON: DE96001855; ON: DE96001855; TRN: US200202%%139
- Resource Relation:
- Conference: International workshop on diagnostics for ITER, Varenna (IT), 08/28/1995--09/01/1995; Other Information: Supercedes report DE96001855; PBD: Sep 1995; PBD: 1 Sep 1995
- Country of Publication:
- United States
- Language:
- English
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