Laboratory studies of spectroscopic markers for the characterization of surface erosion by plasmas
The erosion rates in portions of fusion plasma devices like the ITER tokamak are sufficiently high that nearly real-time information on cumulative removal is needed for control and machine safety. We are developing a digitally--encoded scheme to indicate the depth of erosion at numerous poloidal and toroidal locations around ITER. The scheme uses materials embedded in the walls and divertors, which, when uncovered, present remotely detectable signals. This paper reports laboratory experiments on prototype markers consisting of combinations of up to 5 elements (Au,Pd,Ag,In,Ga) along with Au,Pt, and Ta pure metals. The markers were bonded to 4-D carbon-carbon composite of the type proposed for use in the ITER first wall, and placed in the lower-hybrid-driven plasma of the atomic beam facility at PPL. The paper describes this device Light emission was characterized using a 1 meter Czerny-Turner vacuum ultraviolet monochromator. The samples were characterized both before and after plasma exposure by Auger spectroscopy. We report the time-dependent behavior of the spectra of the visible and ultraviolet light emitted by the plasma when the markers are uncovered by the erosion showing emission lines of the marker elements which are easily distinguished from the background plasma lines. The dependence of the light intensity on bias voltage is compared to the known sputtering yields of the elements. The optical detection method allows exploration of the threshold dependence of these multi-element targets. An exponential dependence of yield above threshold was observed for all of the elements studied.
- Research Organization:
- Princeton Univ., NJ (United States). Plasma Physics Lab.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC02-76CH03073
- OSTI ID:
- 10143191
- Report Number(s):
- PPPL-CFP-2608; CONF-920311-6; ON: DE92012674
- Resource Relation:
- Conference: 10. international conference on plasma-surface interactions in controlled fusion devices,Monterey, CA (United States),30 Mar - 3 Apr 1992; Other Information: PBD: [1992]
- Country of Publication:
- United States
- Language:
- English
Similar Records
Tritium concentration measurements in the JET divertor by optical spectroscopy of a Penning discharge
Erosion of tungsten marker layers in W7-X