2024 – Development of RMP SVR Scenario?

Development of RMP SVR Scenario?

2024 Research Campaign, Thrust: Shape Rise Divertor

Purpose of Experiment

This experiment aims to (1) mitigate the first giant ELM to help accessing stationary super-H-mode (SH) plasma in the strongly shaped SVR (shape and volume rise) configuration by using resonant magnetic perturbations (RMPs); (2) explore RMP ELM control (strongly mitigated or suppress) during high performance SH plasma via appropriate approaches and shape adjustment; (3) explore compatibility of RMP ELM control and radiative divertor in high performance plasma by utilizing impurity seeding; (4) document plasma response from low to high collisionality plasmas with different shapes and validate MHD model on.

Experimental Approach

This experiment will be conducted in the highly shaped SVR configuration, and the target plasma will be selected from the commissioning experiment. The basic strategy is to use RMP to access and sustain SH pedestal, mitigate/suppress ELMs during stationary SH plasma, and then explore radiative divertor with ELM control. The following elements/approaches will be deployed to realize the goals: Mitigate the first giant ELM to access and sustain SH pedestal: n = 2 and 3 RMP will be turned on after LH transition to (1) avoid the density overshoot and (2) mitigate/avoid the first giant ELM. This step is essential to explore the SH plasma in the normal Ip direction. RMP coil current and dRsep may be adjusted to ensure the effectiveness of the mitigation of the first ELM. This step can be combined in the SVR commissioning experiment.
Explore RMP ELM mitigation/suppression during stationary SH pedestal: after stationary SH plasma restored, we will take the following approaches/steps:
  • Turn on RMP with maximum current to mitigate/suppress ELMs. Performing RMP phasing for n = 2 or phase flip for n = 3 to measure the plasma response.
  • Increase dRsep from 0 to 2 cm to amplify the HFS plasma response and achieve stronger ELM mitigation/suppression. ML based 3D feedback controller will work in real-time to determine the optimal phase for RMP configuration.
  • Activate 1.5-3 MW edge localized ECCD to enhance RMP ELM suppression. At the same time, it is possible to bifurcate the ELM suppressed pedestal to the SH channel.

Explore compatible RMP ELM control with divertor detachment: To achieve stationary detachment, impurity injection will be utilized in addition to D2 puffing. Nitrogen is our higher priority impurity gas, Neon will be injected in high power plasma since Neon radiates at higher temperature. Divertor detachment will be achieved by using the detachment controller to ramp up and control the D2 and N2 puffing rate. Reversed Bt will be used to have ion B×∇B drift towards divertor to facilitate the achievement of partial detachment, and the upper outer cryo-pump is on to allow density control. After restored detachment, n = 3 RMP will be turned on to explore as strong as possible ELM mitigation. In addition, RMP phase slip with even and odd parity will be turned on in separate shots to document plasma response from low to high collisionality and compare the different response in even and odd parity. Upstream separatrix density will be determined by applying the power-balance technique to the profiles with good spatial and temporal resolution. Upstream impurity concentration will be determined from CER. Divertor diagnostics including Langmuir probe, IRTV, pressure gauge, tangential TV will be used to identify the detachment process. Filterscope and tangential TV will be used to diagnose divertor impurity distribution. Newly installed bolometer will be used to study the power balance. The obtained experimental data will be input to SOLPS-ITER, UEDGE, GPEC, TM1, EMC3-Eirene to better understand the underlying physics.

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