Alpha Particle Physics Experiments in the Tokamak Fusion Test Reactor

Abstract

Alpha particle physics experiments were done on the TokamakFusion 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 singleparticle 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. † åe (s) ≈ 0.4 (T e /10 keV) 3/2 / (n e /10 20 m -3 ) [3]This e-folding time on electrons is typically † åe ≈ 0.4 s at the plasma center of high performance TFTR shots in which T e (0) ≈ 10 keV and n e (0) ≈ 10 20 m -3 , corresponding to a few hundred thousand toroidal transits of the machine. The time required for alphas to reach thermal energy, including ion drag, is [1]:where E åo is the alpha birth energy and E crit is the alpha energy below which ion drag dominates the thermalization process (typically E crit ≈ 35 T e for alphas). For an idealized plasma small gyroradius without alpha loss, these collisions produce the well-known slowing-down distribution [1]: * J. Cordey, private communication (1998)

H-mode power threshold and confinement in JET H, D, D-T and T plasmas

“…The fit to the τ χ core data gives τ fit ∝ (M/2) −0.36 τ EPS97(y) ∝ M −0.16 which is in agreement with a gyroBohm type scaling but without any other explicit M dependence. In addition, it has emerged from extensive local transport analyses [49] that the thermal ion diffusivity χ i in the core region of the plasma is larger in T than in D whereas towards the edge the results indicate the opposite dependence. Fits to the isotope data of effective thermal diffusivity χ eff at the half radius of the plasma also show that the core transport is gyroBohm-like.…”

Density limits in toroidal plasmas

“…Radiated power increased but remained below 50% of the input power. The change in confinement has also been correlated to a change in the relative magnitudes of the ExB shearing rate and the linear growth rate for ITG modes in the region just inboard of the pedestal [104]. At high densities, n/n G ~ 0.85, the balance shifts to the instability growth, implying less stabilization and higher transport.…”

Simulation and Analysis of the Hybrid Operating Mode in ITER

“…It can be seen that the hybrid operating mode has physics features somewhat between the ELMy H-mode and steady state regimes, and can provide very long pulse lengths, giving it the potential of providing high neutron fluence (neutron wall load $ flattop time) for nuclear testing. Systems Analysis, 1.5D Discharge simulations with the Tokamak Simulation Code (TSC) [4] and TRANSP [5], and MHD stability with JSOLVER/BALMSC/PEST2 [6][7][8] of the hybrid operating mode in ITER will be discussed in the following.…”