2025 – Impact of high opaqueness at lower collisionality on fueling efficiency and neutral penetration

Impact of high opaqueness at lower collisionality on fueling efficiency and neutral penetration

2025 Research Campaign, Thrust: High Opacity and Density Operation

Purpose of Experiment

The purpose of this experiment is to study the impact of opaqueness on fueling efficiency using both gas puff and pellet injection at low collisionality and provide data to develop and validate models to predict the plasma edge density profile for Fusion Power Plants concepts (FPP). This experiment will scan opaqueness, at low collisionality leveraging the new Shape and Volume Rise (SVR). High opaqueness plasmas are predicted to have reduced neutral penetration and enhance main chamber fueling, reducing poloidal neutral asymmetries. The data obtained will be used to validate 1D and 2D edge models such as SOLPS-ITER and KN1D and along with prior experiments at lower opaqueness and/or higher collisionality, this data will be used to develop simplistic models that can be used both for the design of an FPP as well as the development of control algorithms.

Experimental Approach

Step 1: Reproduce the reference shot 201573 with high IP ~ 1.5 MA and PNBI ~11 MW (no gas reference) (1-2 shots) – Good ref. shot for optimal LLAMA coverage without losing the benefits of SVR. Adapt current ramp and NBI injection allow for current profile evolution and development of a stable, high IP ~1.6 MA, high power PNBI ~ 15MW during 2s long SVR flat top. – Contingency: Reproduce shot reference and work with the reference shot engineering parameters for Ip~1.5MA, Bt ~-2.1T, and Pnbi~11MW and proceed to perform the gas puffing and pellet scans with this ref shot sacrificing the highest value set for the gas puffing and pellet scan. Step 2: Gas puffing scans (4-5 shots). – Using the new target shot developed in Step 1, puff D2 gas at 11.1 torr.L.s-1 during flattop ~ 2.1 s. Puff for 1s from LFS (Gas A valve) and 1s from HFS (CPMID). Match starting injection time with shot 201574 @3.0s (2.0 torr.L.s-1) – Repeat D2 gas puffing for 18.5, 31.5 and 37 torr.L.s-1 during flattop ~2.1s. Puff for 1s from LFS (Gas A valve) and 1s from HFS (CPMID) Step 3: Pellet injection scans (4-5 shots) -Using the new target shot developed in Step 1, inject D2 pellets (length = diameter = 1.8 mm) at 3 Hz during flattop ~ 2.1 s -> dt = [3.0 , 5.0](s) – Repeat D2 pellets injection for 5, 8.5, and 10 Hz during flattop ~2.1s – Values might be adjusted to match the gas puffing rate in step 2.

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