Divertor Power Deposition Control and ELM Mitigation with Supersonic Molecular Beam Injection in the EAST Tokamak

ELM mitigation with multi-pulses of SMBI has been demonstrated in EAST tokamak in quasi-steady state over 3 seconds. The ELM frequenc y increasing factor with SMBI is about 5-10. The energy confinement is slightly degraded during the ELM mitigation. Intermittent small scale turbulence, generated by SMBI inside the pedestal r egion, prevents the formation of ELMs, or reduces the amplitude of the ELM, while large scale turbule nc is triggered by the mitigated ELM. The power deposition width ( λq ) is increased by a factor of 2 with SMBI. The peak heat load is reversed from the outer strike point to the striated heat flux ar e with multi-pulses of SMBI, while the total heat on the outer divertor plates remains nearly constant. The heat transferred from the OSP to the SHF increases with SMBI pulse length. A combination of SMBI and LHCD can offer a large possibility for the control of the power deposition on the divertor plates by changing I p, the LHCD power, and the parameters of SMBI including the gas pressure, the pulse length, and the frequency. I) Introduction One of the major challenges for the magnetic fusio n c mmunity is how to extract energy from the core plasma of the fusion reactor w ithout endangering the plasma facing components, in particular the divertor plates. For ITER, in order to not damage the divertor plates, the peak power load on the target plates is limited to 10MW/m in steady condition and 20MW/m in transient condition during Type-I Edge Localize d Modes (ELMs) [1, 2]. How to reduce the power flux density on the divertor plate s is a critical issue. Techniques could be used to reduce the power flux density on the struct u e such as: inclining of the target plate for increasing the effective area; expanding of the fie ld line flux into divertor; power radiation from particles through ionizing collisions and elec tron relaxation. The existing ELM control techniques are the following: Pellet pacing [3], Re sonance Magnetic Perturbation (RMP) [4] and other external perturbation fields [5]. The Sup ersonic Molecular Beam Injection (SMBI) is a new technique for the ELM mitigation. The ELM mitigation with single pulse of SMBI has been firstly achieved in HL-2A [6], then confir med in KSTAR [7]. We report here the experimental results in EAST tokamak showing a very promising and effective technique with SMBI and Lower Hybrid Current Drive (LHCD) for the control of heat deposition on the divertor plates, and the mitigation of large ELMs i n quasi-steady state.