Spectroscopic imaging of limiter heat and particle fluxes and the resulting impurity sources during Wendelstein 7-X startup plasmas

Abstract

A combined IR and visible camera system [G. A. Wurden et al., "A high resolution IR/visible imaging system for the W7-X limiter," Rev. Sci. Instrum. (these proceedings)] and a filterscope system [R. J. Colchin et al., Rev. Sci. Instrum. 74, 2068 (2003)] were implemented together to obtain spectroscopic data of limiter and first wall recycling and impurity sources during Wendelstein 7-X startup plasmas. Both systems together provided excellent temporal and spatial spectroscopic resolution of limiter 3. Narrowband interference filters in front of the camera yielded C-III and H photon flux, and the filterscope system provided H, H, He-I, He-II, C-II, and visible bremsstrahlung data. The filterscopes made additional measurements of several points on the W7-X vacuum vessel to yield wall recycling fluxes. The resulting photon flux from both the visible camera and filterscopes can then be compared to an EMC3-EIRENE synthetic diagnostic [H. Frerichs et al., "Synthetic plasma edge diagnostics for EMC3-EIRENE, highlighted for Wendelstein 7-X," Rev. Sci. Instrum. (these proceedings)] to infer both a limiter particle flux and wall particle flux, both of which will ultimately be used to infer the complete particle balance and particle confinement time τ.

Error field measurement, correction and heat flux balancing on Wendelstein 7-X a

“…The effect of a perturbing n = 1 EX/P5-5 trim coil field on the limiter temperatures was examined. In figure 1 a stereotypical limiter IR camera image is shown [6,7]. Three lines are drawn across the limiter from which temperature data is extracted.…”

“…The effect of error fields on limiter heat loads were also explored with the trim coils. A high resolution infrared camera [6,7] gave detailed imagery of the limiters during the pulse. Low limiter temperatures limited the range of diagnostic coverage during this first campaign.…”

Overview of diagnostic performance and results for the first operation phase in Wendelstein 7-X (invited)

“…The filtered visible camera provided absolutely calibrated measurements of carbon and hydrogen light, and therefore inputs to particle balance calculations. 22 The infrared camera was used to derive space and time resolved power fluxes, as well as in a calorimeter mode to infer total energy deposited on the limiter. measurements of limiter temperatures, heat flux density has been derived with the help of the THEODOR code.…”

“…10). The versatile gas injection system has been used for injection of helium for measurement of local edge n e and T e profiles 28 and effective particle confinement time τ p * He , 22 neon for development of a collisional radiative model to extend the parameter range and accuracy of the diagnostic helium beam, 28,29 argon for impurity transport studies as well as nitrogen for radiative edge cooling. Perpendicular observation of the gas emission at the upper plasma edge was done along 8 los, using quartz fibers and an imaging spectrometer with a CCD camera.…”

Reconstruction of recycling flux from synthetic camera images, evaluated for the Wendelstein 7-X startup limiter

“…W7-AS [4,5], W7-X [6,7], LHD [8,9], HSX [10,11]) and tokamaks (e.g. DIII-D [12,13], NSTX [14,15], TEXTOR-DED [16,17]), yet their interpretation in terms of local quantities can be challenging due to line of sight integration effects.…”