Fast-ion effects during test blanket module simulation experiments in DIII-D

Abstract

Fast beam-ion losses were studied in DIII-D in the presence of a scaled mockup of two Test Blanket Modules (TBM) for ITER. Heating of the protective tiles on the front of the TBM surface was found when neutral beams were injected and the TBM fields were engaged. The fast-ion core confinement was not significantly affected. Different orbit-following codes predict the formation of a hot spot on the TBM surface arising from beam-ions deposited near the edge of the plasma. The codes are in good agreement with each other on the total power deposited at the hot spot predicting an increase in power with decreasing separation between the plasma edge and the TBM surface. A thermal analysis of the heat flow through the tiles shows that the simulated power can account for the measured tile temperature rise. The thermal analysis, however, is very sensitive to the details of the localization of the hot spot which is predicted to be different among the various codes.

A description of the full-particle-orbit-following SPIRAL code for simulating fast-ion experiments in tokamaks

“…In order to calculate accurately the location where the particle impacts the wall, it is important to take into account the full-particle orbit because the Larmor radius, in this case up to about 4 cm at the point of impact, is comparable or larger than the characteristic TBM field gradient scale lengths near the tile surfaces. The heat loads from the SPIRAL simulations reproduce the measured temperature increase at the back of the 2.5 cm thick protective carbon tiles in the TBM experiments as was reported in [29].…”

“…Two examples of toroidal ripple fields are shown in figure 10 where a conventional ripple induced by a finite number of toroidal field coils is shown for NSTX while a localized ripple in DIII-D that was deliberately induced by a set of coils to create the expected (scaled) fields in ITER induced by one pair of TBMs. The fields in DIII-D were used to study the impact of such localized perturbed fields on the plasma performance [28] and first wall heat loads [29].…”

“…In the first example heat loads on the TBM surface are calculated and compared with measured temperatures. Full-orbit effects in this case only become apparent near the wall at the point where they are lost [29]. In the second example simulated triton losses are compared with neutron signals that were measured during the TBM mock-up experiments in DIII-D [28].…”

“…Tile temperature rises were then calculated from the simulated heat loads and compared favorably with measured tile temperature rises. Details of this experiment are given in [28,29]. The heat load was caused by 60-80 keV beam ions that are lost shortly after injection before the ions have time to slow down significantly.…”

Synergy between fast-ion transport by core MHD and test blanket module fields in DIII-D experiments

“…To mimic the ITER fields, the DIII-D installation contains two racetrack coils and a vertical solenoid that are both energized in the present experiment. The amplitude of the perturbed field exceeds the amplitude of a single ITER TBM by a factor of ∼3. Previous experiments found that the mock-up TBM fields degrade both fusion product [4] and beam-ion [5] confinement. During beam injection, localized heating on the graphite tiles that surround the TBM port is observed [5].…”