Design and fabrication of emissive biased limiter and its effect on tokamak plasma

Abstract

In this paper, an emissive-biased limiter (EBL) was designed and fabricated then the magneto hydrodynamic activity was investigated based on Mirnov oscillations and hard X-ray spectroscopy through the tokamak plasma biasing. The EBL is positioned at r/a=0.92, and the biased voltage, which is varied from−250 to 250 V, applied between the head of the emissive limiter and vacuum chamber. Furthermore, the effects of the biased limiter for both negative and positive applied voltages are measured, and the results are compared with cold-biased limiter. As the results of IR-T1 tokamak suggest, in emissive negative polarity, the duration of plasma current is increased, compared with no bias, cold positive and emissive positive polarities. The amplitude of Mirnov fluctuations in emissive negative polarity is larger and more regular, compared with emissive positive polarity. The amplitude of the hard X-ray fluctuation in emissive negative polarity is very low compared with cold negative, cold positive and emissive positive polarities which leads to minimum energy loss.

Keywords:

• emissive limiter bias
• IR-T1 tokamak
• Mirnov oscillations
• hard X-ray emission

Acknowledgements

The authors acknowledge support for this project from the Iran National Science Foundation (INSF) and Messrs. Reza Arvin, Ali Nik Mohammadi, and Siamak Mohammadi.