Fusion Science and Technology / Volume 50 / Number 1 / July 2006 / Pages 76-83
Burning plasma simulation experiments were performed for burn control study on ELMy H-/L-mode plasmas and reversed shear (RS) plasmas with an internal transport barrier in JT-60U. In a burning plasma simulation scheme, two neutral beam (NB) groups were used: one that simulates alpha-particle heating and another that simulates external heating. For the alpha-particle heating simulation, the heating power proportional to the deuterium-deuterium (D-D) neutron yield rate was injected. The behavior of the part of the NB heating simulating alpha-particle heating was varied by increasing the proportional gain relating the applied power to the measured neutron yield rate in both ELMy H-mode and RS plasmas, while the part of the NB power in the role of external heating was held constant i.e., no-burn-control case. Above a certain value of the proportional gain, a runaway effect was triggered where excursive increases in the neutron yield rate and stored energy were observed. With burn control, where the stored energy was controlled at a constant value by a feedback control system using the external heating, the runaway was not triggered, and the neutron yield rate was kept at a constant value in the L-mode plasmas. Zero-dimensional calculation indicated that the runaway triggered by increasing the proportional gain well simulates the runaway triggered by improved confinement. The limitations came from differences between deuterium-tritium and D-D plasmas, such as the dominant reaction for the neutron yield and the temperature dependence of the fusion reaction rate, which were discussed together with improvement on the burning plasma simulation scheme.