ELM frequency enhancement and discharge modification through lithium granule injection into EAST H-modes

Lunsford, R. ; Hsu, J. S.; Sun, Z. ; Maingi, R. ; Mansfield, D. K. ; Xu, W.; Zuo, G. Z.; Huang, M.; Diallo, A. ; Osborne, T.; Tritz, K.; Canik, J.; Meng, X. C.; Gong, X. Z.; Wan, B. N.; Li, J. G.
Issue date: 2018
Creative Commons Attribution 4.0 International (CC BY)
Cite as:
Lunsford, R., Hsu, J. S., Sun, Z., Maingi, R., Mansfield, D. K., Xu, W., Zuo, G. Z., Huang, M., Diallo, A., Osborne, T., Tritz, K., Canik, J., Meng, X. C., Gong, X. Z., Wan, B. N., & Li, J. G. (2018). ELM frequency enhancement and discharge modification through lithium granule injection into EAST H-modes [Data set]. Princeton Plasma Physics Laboratory, Princeton University. https://doi.org/10.11578/1562100
  author      = {Lunsford, R. and
                Hsu, J. S. and
                Sun, Z. and
                Maingi, R. and
                Mansfield, D. K. and
                Xu, W. and
                Zuo, G. Z. and
                Huang, M. and
                Diallo, A. and
                Osborne, T. and
                Tritz, K. and
                Canik, J. and
                Meng, X. C. and
                Gong, X. Z. and
                Wan, B. N. and
                Li, J. G.},
  title       = {{ELM frequency enhancement and discharge
                modification through lithium granule inj
                ection into EAST H-modes}},
  publisher   = {{Princeton Plasma Physics Laboratory, Pri
                nceton University}},
  year        = 2018,
  url         = {https://doi.org/10.11578/1562100}

The injection of impurity granules into fusion research discharges can serve as a catalyst for ELM events. For sufficiently low ELM frequencies, and granule sizes above a threshold, this can result in full control of the ELM cycle, referred to as ELM pacing. For this research, we extend the investigation to conditions where the natural ELM frequency is too high for ELM pacing to be realized. Utilizing multiple sizes of lithium granules and classifying their effects by granule size, we demonstrate that ELM mitigation through frequency multiplication can be used at ELM triggering rates that nominally make ELM pacing unrealizable. We find that above a size threshold, injected granules promptly trigger ELMs and commensurately enhance the ELM frequency . Below this threshold size, injection of an individual granule does not always lead to the prompt triggering of an ELM; however, collective ablation in the edge pedestal region does enhance the ELM frequency. Specifically, Li granules too small to individually trigger ELMs were injected into EAST H-mode discharges at frequencies up to 2.3 kHz; collectively the granules were observed to enhance the natural ELM frequency up to 620 Hz, resulting in a ~2.4x multiplication of the natural ELM frequency and a 50% decrease of the ELM size.

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