The time-dependent simulation of CFETR baseline steady-state scenarios

One of the key issues to achieve the phase I mission of China fusion engineering test reactor (CFETR) is steady-state operation with a modest fusion power up to 200 MW. To study this feasibility, time-dependent modeling of CFETR baseline scenario is performed. The time-dependent scenario design examines actual discharge features, including auxiliary heating and current drive scheme, equilibrium, transport, PF coil systems and plasma control system during the plasma evolution. During plasma current ramp-up, 10 MW of EC or LH heating is used to effectively save volt-second consumption to a reasonable level within magnet coil capability and to reduce li for better plasma control. Three reference scenarios are designed to target full non-inductive operation with different external heating and current drive (H&CD), which are NB + EC, NB + LH, and LH + EC, respectively. Two scenarios with neutral beams reach the required fusion power of CFETR phase I target, while for LH + EC scenario the fusion power and confinement is somewhat lower. A reversed magnetic shear with q(min) > 2 is sustained with off-axis current drive and bootstrap current for all cases examined. Ideal MHD analysis shows that both large toroidal mode number n ballooning mode and low n kink mode are stable in the three reference cases independent of whether the current is totally relaxed or not. The L mode and H-L back transition ramp-down are designed to successfully reduce the plasma current to 2 MA and keep li below 2 with ramp-down rate of 80 kA s(-1). The H-L back transition ramp-down yields improvements in the power transfer and coil current evolution as well as the li evolution. The heating and current drive characteristics of three auxiliary heating sources are indicated by scanning studies. A 2D scan of NB energy and tangency radius indicates the features of NB power deposition, current drive, torque and shine through issue. Both ramp-up and flattop are considered in the scanning of radio frequency parameters. For EC waves, the ramp-up phase constrains the parameter space more. The 2D scan of EC launch angle shows that EC waves launched above the midplane yield a better CD efficiency than using a midplane launcher. Specifically, 10 MW of EC waves launched from LFS above the midplane yield a maximum on axis driven current of about 0.55 MA, while waves launched from top yield a maximum near edge driven current of about 0.45 MA in the region of rho > 0.5. Scanning of n(vertical bar vertical bar) in LH spectrum shows that n(vertical bar vertical bar) should be set around 1.7 to get enough penetration (inside rho = 0.7) for current drive and avoid strong accessibility problem. It is found that LH waves launched from HFS drives more current than that launched from LFS when n(vertical bar vertical bar) is small. 'the maximum LH driven current reaches 1.1 MA with 10 MW of LH power launched from HFS.