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Description
Linear plasma devices can generate steady state long duration plasma and are ideal for lifetime plasma exposure studies on plasma-facing materials (PFM) in a fusion reactor. The plasma exposures are followed by in-situ and ex-situ measurements on surface erosion and fuel retention respectively. Additional possibilities such as sample biasing and sample temperature variation enable a wide scenario of experimental conditions on PFM. JULE-PSI is a hot cathode-based linear plasma device, specifically designed to operate in a radiation compatible hot cell environment. Its main objective is the study of plasma-wall interactions on irradiated PFM with in-situ measurements of fuel retention.
The integration and operation of a linear plasma device in a radiation environment is challenging and requires extensive modification of the machine as compared presently operated linear plasma devices. Hence, presently the machine alongside modifications is being characterised on a test-stand outside the radiation area for machine stability and plasma performance. The plasma is characterized through a single tip Langmuir probe and a segmented dump with current measurement capabilities. A series of experiments using argon, neon, helium and hydrogen gas have been run under steady state conditions with the aim to achieve stable plasma with a top hat profile, electron density of ~1017-1019 m-3, an electron temperature of 3-10 eV and an ion flux to the target of ~1021-1023 m-2s-1. Optical spectroscopy using an overview spectrometer (OES, wavelength range 300-890 nm) was used in conjunction to the Langmuir probe for verification of the plasma profile.
In this contribution, results from different magnetic configurations measured using the Langmuir probe and the segmented dump will be presented. A stable plasma configuration is seen in the cross-field discharge configuration as compared to a direct arc magnetic configuration. The optical spectroscopy results show a good agreement with the Langmuir probe results and will be detailed alongside hyperspectral imaging results. Additionally, the results from JULE-PSI test-stand will be compared to the existing linear plasma device PSI-2, which has a cylindrical hollow LaB6 cathode. The differences in the Langmuir probe results, highlight the influence of cathode geometry in plasma profile and transport. Lastly, an outlook to the project alongside integration into the hot cell environment is discussed.