Tokamak Diagnostics Using Fusion Products.
Measurements of neutrons and protons produced by the d(d,n)('3)He, d(t,n)(alpha), d(d,p)t, and d(('3)He,p)(alpha) fusion reactions are used to diagnose plasmas in the PLT and PDX tokamaks. An expression for the efficiency of proton detection is derived and confirmed experimentally. The time evolution of the ('3)He density indicates that a scoop limiter may pump ('3)He from the plasma faster than conventional limiters. The confinement of 1.0 MeV tritons and of 0.8 MeV ('3)He ions is studied by measuring the fraction of these fusion-produced ions that burn up in subsequent fusion reactions. In discharges with sawtooth activity and with B(,(phi)) > 2 T, the triton and ('3)He 'burnup' is consistent (within a factor of three) with predictions based on classical theories of ion confinement and slowing down. In discharges with large m = 2 or fishbone instabilities, the ('3)He burnup is less than classically predicted and, in PLT discharges at B(,(phi)) = 1.8 T, the triton burnup is over an order of magnitude smaller than predicted. Expressions for the energy spectrum of ions produced in beam-target fusion reactions are derived. Collimated measurements of the spectrum of 15 MeV protons produced by reactions between energetic ('3)He ions and relatively cold deuterons during fast wave minority heating indicate that the velocity distribution of fast ('3)He ions is peaked perpendicular to the tokamak magnetic field. The ion temperature profile and density of fast deuterons are measured with an array of collimated 3 MeV proton detectors. The fast ions produced by neutral beam injection and by launching lower hybrid waves are concentrated near the magnetic axis. Poloidal field measurements using 3 MeV protons also appear possible. In discharges in which the line radiation from central impurities does not decay, the plasma current profile is broader than in more typical discharges.
- Pub Date:
- Physics: Fluid and Plasma