Reduction of hydrogen content in deuterium plasma with mixed graphite and tungsten divertors in EAST
- Chinese Academy of Sciences (CAS), Hefei (China). Inst. of Plasma Physics
- Chinese Academy of Sciences (CAS), Hefei (China). Inst. of Plasma Physics; CAS Key Lab. of Photovoltaic and Energy Conservation Materials, Hefei (China)
- Hunan Univ., Changsha (China). Dept. of Applied Physics
- Chinese Academy of Sciences (CAS), Hefei (China). Inst. of Plasma Physics; Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
- Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
- Johns Hopkins Univ., Baltimore, MD (United States)
Reduction of hydrogen content in deuterium-fueled fusion plasmas is important not only to avoid diluting reacting core deuterons but also so as to allow the optimization of hydrogen-minority-heating efficiency in those fusion devices which employ ion-cyclotron-radio-frequency heating systems. In EAST, the amount of hydrogen released from plasma-facing components has been shown to depend strongly on both their composition and their temperature. In this paper, as measured by thermal desorption spectroscopy, the hydrogen inventory in graphite – used in EAST as lower divertor material – has been determined to be >25 times larger than that of tungsten which comprises the upper divertor. This difference in hydrogen inventory is attributed mostly to the intrinsically porous nature of bulk graphite. Thus the main source of hydrogen release into EAST discharges was identified as the graphite tiles used in the lower divertor. The hydrogen content in EAST plasmas were clearly reduced by first employing a high-temperature vacuum baking of all graphite tiles and then renewing a 100–200 μm thick SiC coating before an EAST experimental run campaign. Subsequent active surface conditioning of all wall components with elemental silicon and then with elemental lithium were seem to again reduce the plasma hydrogen content significantly – with lithium proving to be more effective than silicon. Combining these several techniques, H/(H + D) levels as low as ~3% have been achieved in EAST discharges. Additionally, the effects of lithium thickness on H surface implantation and retention has been re-examined semi-quantitatively using data from a previous run campaign. These data suggest that relatively thick Li films coated on the first wall can effectively isolate the rich source of hydrogen stored in the porous bulk of the underlying graphite from the deuterium-fueled plasma so as to minimize hydrogen release. In conclusion, an operational maneuver whereby a diverted plasma is repetitively switched from an upper single null configuration to a lower single null configuration is presented. This switching maneuver has been shown to suppress hydrogen influx into a 35s-long EAST discharge by alternately mitigating the rise in divertor temperature.
- Research Organization:
- Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Chinese Academy of Sciences (CAS), Hefei (China); Hunan Univ., Changsha (China)
- Sponsoring Organization:
- USDOE; National Key Research and Development Program of China; National Natural Science Foundation of China (NSFC)
- Grant/Contract Number:
- AC02-09CH11466; 2017YFA0402500; 11775261; 11625524; 11605246; 11075185; 11021565
- OSTI ID:
- 1459546
- Journal Information:
- Fusion Engineering and Design, Vol. 131; ISSN 0920-3796
- Publisher:
- ElsevierCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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