2024 – Diagnostic Edge Cases – Physics of q-parallel disagreements

Diagnostic Edge Cases – Physics of q-parallel disagreements

2024 Research Campaign, Diagnostics and Actuators

Purpose of Experiment

The physics for interpreting plasma diagnostics is often as complex as the plasma physics we seek to unravel. DIII-D is equipped with four diagnostics capable of measuring the parallel heat flux to the target, and good agreement is typically found [1,2], but edge cases exist where measurements do not agree [6] including cases where the sheath heat transmission coefficient needed to bring the measurements into mutual agreement are non-physical [3-5]. The purpose of this experiment is to explore the plasma physics for the far more interesting cases where these diagnostics do not agree.

Experimental Approach

This experiment relies on new capabilities being deployed starting in the 2024 campaign; and cannot be performed from archived data. Four diagnostics will be used to measure the parallel heat flux at the R,Z coordinates of DiMES on the outer divertor shelf. Self-Eroding ThermoCouples (SETC) will be installed in DiMES, and upgrades to the target Langmuir Probes will include an increased number of probes on the shelf including a new probe at the R,Z location of DiMES. IRTV views the shelf and a direct view of DiMES is available in low neutron discharges. The edge cases where the diagnostics do not agree will be explored and documented. The hypothesis of non-Maxwellian energy distributions affecting Langmuir probe measurements in high recycling conditions [6-9] will be validated.