Predictions of Alpha Heating in ITER L-mode and H-mode Plasmas
Authors: R.V. Budny
Abstract: Predictions of alpha heating in L-mode and H-mode DT plasmas in ITER are generated using the PTRANSP code. The baseline toroidal field of 5.3 T, plasma current ramped to 15 MA and a flat electron density profile ramped to Greenwald fraction 0.85 are assumed. Various combinations
of external heating by negative ion neutral beam injection, ion cyclotron resonance, and electron cyclotron resonance are assumed to start half-way up the density ramp with the full power planned
of Pext=73 MW. After 50 s the applied power is reduced to 48 MW to increase QDT. The time evolution of plasma temperatures and, for some cases, toroidal rotation are predicted assuming
GLF23 and boundary parameters. Conservatively low temperatures (≈0.6 keV) at the boundary (r/a = 0.85) are assumed. Two alternative options are used to predict the toroidal rotation and
flow shearing rate induced by the neutral beam torques in order to get a range of predictions and assess uncertainty. One option assumes the momentum transport coefficient χφ is half the energy
transport coefficient χi predicted consistently with the GLF23-predicted temperatures. In this case flow shearing does not have significant effects on the energy transport, and the alpha heating powers
for the various heating mixes are predicted to be 8-20 MW (with Pext=73 MW). The second option uses GLF23 to also predict toroidal rotation. Significantly higher flow-shearing rates are predicted
and the alpha heating power is predicted to be 8-70 MW (with Pext=73 MW). External heating mixes with higher beam injection power have higher alpha heating power. If the L → H power
threshold is twice the ITPA fit then the heating mixes with the highest neutral power (and the most alpha heating) transition to H-mode during the density ramp. Other heating mixes remain
in L-mode. Predictions of H-mode temperatures and alpha heating depending sensitively on the assumed pedestal temperatures. A scan in pedestal temperatures is presented using the more
pessimistic option assuming χφ/χ¡ = 0.5. Cases with Pext=48 MW and fusion gain greater than 10 are predicted to have alpha heating greater than 80 MW.
__________________________________________________
Submitted to: Nuclear Fusion
__________________________________________________
Download PPPL-4590 (pdf 757 KB 26 pp)
__________________________________________________