2024 – Test modulation schemes for helicon heating and current drive evaluation

Test modulation schemes for helicon heating and current drive evaluation

2024 Research Campaign, Heating and Current Drive

Purpose of Experiment

The goal of this experiment is to perform preliminary tests for experiments which will measure the efficiency of heating and current drive with the newly installed helicon system for validation of theoretical models. The results will inform the feasibility of using such a system in future reactors.

Background: Steady-state advanced tokamak reactors, such as a next generation Fusion Power Plant (FPP) or tokamaks beyond ITER, require a source of external current drive to support a fraction on the order of 10-20% of the plasma current. Several current drive systems currently in use may not be effective in the high-density plasmas envisioned for reactors. Helicon current drive, also called fast wave current drive in the lower hybrid range of frequencies, has long been regarded as a promising current drive tool for reactor grade high-beta plasmas. Helicon current drive is predicted to be effective at high densities and high electron temperatures. To date the concept lacks experimental verification, which this work is intended to provide.

Experimental Approach

The project makes use of a 1.2 MW klystron RF-source operating at 476 MHz. The klystron powers a traveling wave antenna installed in the DIII-D vessel, which launches waves with the appropriate wave length and polarization into the plasma. The absorbed RF power will be inferred from measured changes in the electron temperature. The current driven by that absorbed power will be deduced from measurements of the motional Stark effect diagnostic. The experiment will be repeated in plasmas with varying core temperatures and densities. Measured efficiencies for helicon heating and current drive will be compared to theoretical estimates.

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