Effects ofq(r) on the alpha particle ripple loss in TFTR

Abstract

An experiment was done with TFTR DT plasmas to determine the effect of the q(r) profile on the alpha particle ripple loss to the outer midplane. The alpha particle loss measurements were made using a radially movable scintillator detector 20º below the outer midplane. The experimental results were compared with TF ripple loss calculations done using a Monte Carlo guiding center orbit following code, ORBIT. Although some of the experimental results are consistent with the ORBIT code modeling, the variation of the alpha loss with the q(r) profiles is not well explained by this code. Quantitative interpretation of these measurements requires a careful analysis of the limiter shadowing effect, which strongly determines the diffusion of alphas into the detector aperture.

Distributions of Alpha Particles Escaping to the Wall because of Sawtooth Oscillations in TFTR

“…The instantaneous alpha loss can increase by up to a factor of 10 during the crash, but the time-integrated sawtooth-induced alpha loss is negligible with respect to the normal loss processes without the sawtooth, i.e., rst-orbit loss at the 90 detector 9 and toroidal eld ripple loss in the 20 detector. 10 The behavior of alpha loss during these DT sawteeth is very similar to that measured earlier for DD fusion products loss during DD sawteeth in TFTR. 12 The sawtooth-induced loss in the 90 detector occurs mainly near the passing-trapped boundary and near the birth energy.…”

“…The rst three of these apertures were located just behind the geometrical shadow of the outer limiter, 9 while the 20 detector was on a radially movable probe which could bepositioned within 2 c m of the outer limiter shadow. 10 The total scintillator light emission vs. time for each of these detectors was measured with a bandwidth of up to 150 kHz and digitized at a rate of up to 500 kHz.…”

Alpha particle physics experiments in the Tokamak Fusion Test Reactor

“…10. These results were highly reproducible, indicating that they were not due to the variable MHD activity, and the alpha loss rates were far larger than the expected first-orbit loss [62], suggesting that these signals were due to TF ripple loss.…”

“…This makes the calculation of the local alpha loss through the detector aperture prohibitively difficult, except for the simple first-orbit loss which is unshadowed by the limiters. An attempt to calculate the collisional TF ripple loss to the midplane detector was unsuccessful due to this problem [62], as illustrated in Fig. 11.…”

Fokker-Planck modelling of delayed loss of charged fusion products in TFTR

“…This effect becomes stronger with decreasing both major plasma radius and particle energy (see Figs.4,3) and, obviously, with increasing plasma current, as all of them result in a banana width reduction and in the enhancement the influence of vacuum field. In the following we will refer to this as the poloidal shadowing effect, in contrast to the toroidal shadowing effect due to the toroidally nonsmooth nature of the limiters in TFTR [19].…”