Speaker
Description
Research on fundamental plasma physics in the divertor region for DEMO divertor design has required divertor simulation experiments using linear devices. Existing linear devices are still unable to fully replicate DEMO-class divertor plasmas. To address this limitation, we have constructed a new linear device, the Pilot GAMMA PDX-SC (PGX-SC), designed to verify high-density plasma sources and heating system for the DEMO divertor simulation test facility. PGX-SC has two superconducting coils that generate a steady mirror magnetic field of up to 1.5 T and uses a hot-cathode arc discharge to produce high-density, large-diameter hydrogen plasmas. We are tackling the generation of large-diameter, high-density plasma, which has been difficult to achieve until now, using a hot-cathode arc discharge plasma source which incorporates a 150 mm diameter LaB6 cathode, five intermediate floating electrodes, and a copper anode. The inner diameters of the floating electrodes and the anode are tailored to follow the magnetic field lines generated by the superconducting coils. The large cathode size, aligned with the magnetic-field geometry, also plays a key role in achieving a large-diameter plasma.
So far, hydrogen plasmas generated by the plasma source have had electron densities of approximately 1019 m-3. To reach the target density of 1020 m-3, further improvements to the plasma source are underway. In recent discharge experiments, the end plate potential has played a crucial role in drawing plasma into the end region, and it is expected to also play an essential role in achieving higher plasma density.
In addition, two heat load measurement systems were installed in the end region of PGX-SC: a calorimeter located in front of the end plate and a thermocouple-based system to evaluate heat load from the end-plate temperature. As an initial result, the heat load to the end plate during ICRF heating was successfully measured. These measurement systems constitute essential experimental infrastructure for future DEMO-class divertor simulation experiments and studies of plasma–wall and plasma–surface interactions.
This presentation reports on the status of plasma source development and initial results from end-plate heat-load measurements.
This work was partly supported by the NIFS Collaboration Research program (NIFS23KUGM174, NIFS25KFFT001), JST SPRING, Grant Number JPMJSP2124.