Transport simulation on L-mode and improved confinement associated with current profile modification

Abstract

A unified model of the L-mode confinement i n t o k o d s and the improved modes associated with current profile modification is investigated by means of a onedimensional m s p o n simulation. The thermal transport coefficient employed is based on the theory of selfsustined turbulence due to the current-diffusivity-driven modes. In the case of low pp (& being the ratio of the plasma pressure to the pressure of the poloidal magnetic field), the simulation results show fairly good agreement with empirical L-modc scaling laws of the thermal energy confinement time rE. indicating favourable dependence on the plasma current. When Bp exceeds about unity. however, the t r m ~p ~r t in the core region is strongly reduced. This confinement improvement is attributed to the weak or negative magnetic shear due to the bootstrap current and the Shafranov shift of the magnetic surface. The enhancement factor of Q scales BT and is consistent with experimental observation. The effect of current profile modification due to the current ramp down and the lower hybrid current drive is also studied.

Current Profile Control for High Bootstrap Current Operation in ITER

“…In order to get high bootstrap current, the internal transport barrier (ITB) is required, and here we used current-diffusive ballooning mode (CDBM) model [4,5] as a heat transport model. Thermal diffusion coefficient χ is…”

Formation and Sustainment of ITPs in ITER with the Baseline Heating Mix

“…The thermal diffusivity profile is computed using either a modified Coppi-Tang model 6 or the CDBM model 12 , which has been recently implemented in TSC.…”

“…represents the reduction in the thermal diffusivity due to weak or negative magnetic shear and large Shafranov shift 12 . It is a function of the magnetic shear s ≡ rq −1 (dq/dr) and of the normalized MHD pressure gradientα, which includes the fast ion contribution.…”

Integrated Modeling of Whole Tokamak Plasma

“…The mode growth rate γ nm is evaluated on the basis of analytical theory [14]. Since a particle is resonated with the modes at the velocity v // = v A (v A Alfven velocity) and the population of resonant particle decreases with decreasing in v from the birth velocity v α , a part of distribution function resonated with the modes f res is assumed as f Figure 3 shows (a) the time evolution of fusion gain Q and a growth rate of (n, m) = (3,3) mode, and (b) profile of pressure gradient of alpha particles at t = 30 s for three cases of transport model used in simulations with parameters similar to the ITER standard scenario, i.e., B t = 5.2 T, I p = 15 MA, R = 6.3 m, a = 2 m. In TOPICS-IB, the bulk plasma transport is calculated by a model of current diffusive ballooning mode [15]. A TAE mode with (n, m) = (3,3) is excited from t = 10 s in Fig.…”