RF Sheath-Enhanced Beryllium Sources at JET’s ICRH Antennas

Local beryllium (Be) I and Be II line intensities were measured in the plasma-wall interaction region near an ICRH antenna in JET. The intent was to use these intensities as a measure of the formation of local Radio Frequency (RF) sheath potentials, through RF sheath rectification and potential build up at the end of field lines passing in front of the antenna. Experimetally, it was found that the Be I and Be II emission increase when using the antenna local to the spectroscopic measurement, and increase even more when using a remote antenna that is magnetically connected to the observation point. Magnetic field mapping indicates a magnetic connection between the observation location and the top corner region of the remote antenna and/or its protection limiter. These measurements can be used in support of RF sheath modeling that is an important part of the optimization of antenna design for next generation fusion energy devices, including ITER.
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