Divertor erosion in DIII-D
- Univ. of California, San Diego, CA (United States)
- Sandia National Labs., Albuquerque, NM (United States)
- Argonne National Lab., IL (United States)
- General Atomics, San Diego, CA (United States)
- TRINITI Lab. (United States)
Net erosion rates of carbon target plates have been measured in situ for the DIII-D lower divertor. The principal method of obtaining this data is the DiMES sample probe. Recent experiments have focused on erosion at the outer strike-point (OSP) of two divertor plasma conditions: attached (T{sub e} > 40 eV) ELMing plasmas, and detached (T{sub e} < 2 eV) ELMing plasmas. For the attached cases, the erosion rates exceed 10 cm/exposure-year, even with incident heat flux < 1 MW/m{sup 2}. In this case, measurements and modeling agree for both gross and net carbon erosion, showing the near-surface transport and redeposition of the carbon is well understood. In the attached cases, physical sputtering (with enhancement from self-sputtering and oblique incidence) is dominant, and the effective sputtering yield, Y, is greater than 10%. In ELM-free discharges, the total OSP net erosion rate is equal to the rate of carbon accumulation in the core plasma. For the detached divertor cases, the cold incident plasma eliminates physical sputtering. Attempts to measure chemically eroded hydrocarbon molecules spectroscopically indicate an upper limit of Y {le} 0.1% for the chemical sputtering yield. Net erosion is suppressed at the outer strike-point, which becomes a region of net redeposition ({approximately} 4 cm/exposure-year). The private flux wall is measured to be a region of net redeposition with dense, high neutral pressure, attached divertor plasmas. Leading edges intercepting parallel heat flux ({approximately} 50 MW/m{sup 2}) have very high net erosion rates at the OSP of an attached plasma ({approximately} 10 {micro}m/s > 1,000x erosion rate of aligned surfaces). Leading edge erosion, and subsequent carbon redeposition, caused by tile gaps can account for half of the deuterium codeposition in the DIII-D divertor.
- Research Organization:
- Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Argonne National Lab. (ANL), Argonne, IL (United States); General Atomics, San Diego, CA (United States); Univ. of California, San Diego, CA (United States)
- Sponsoring Organization:
- USDOE Office of Energy Research, Washington, DC (United States)
- DOE Contract Number:
- AC04-94AL85000; W-31109-ENG-38; AC03-98ER54411; FG03-95ER54294
- OSTI ID:
- 291094
- Report Number(s):
- GA-A-22858; CONF-980560-; ON: DE99000497; BR: AT601020E; AT601020F; AT101014D; AT101015A; TRN: 99:002289
- Resource Relation:
- Conference: 13. international conference on plasma surface interactions, San Diego, CA (United States), 18-22 May 1998; Other Information: PBD: Aug 1998
- Country of Publication:
- United States
- Language:
- English
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