Spectroscopic measurements of tungsten erosion in the ASDEX Upgrade divertor

109

Operation with all tungsten plasma facing components has become routine in ASDEX Upgrade. The conditioning of the device is strongly simplified and short glow discharges are used only on a daily basis. The long term fuel retention was reduced by more than a factor of 5 as demonstrated in gas balance as well as in post mortem analyses. Injecting nitrogen Preprint submitted to Elsevier 23 November 2012for radiative cooling, discharges with additional heating power up to 23 MW have been achieved, providing good confinement (H98 y2 = 1), divertor power loads around 5 MW m −2 and divertor temperatures below 10 eV. ELM mitigation by pellet ELM pacemaking or magnetic perturbation coils reduces the deposited energy during ELMs, but also keeps the W density at the pedestal low. As a recipe to keep the central W concentration sufficiently low, central (wave) heating is well established and low density H-Modes could be re-established with the newly available ECRH power of up to 4 MW. The ICRH induced W sources could be strongly reduced by applying boron coatings to the poloidal guard limiters.

Section: W Sourcesmentioning

confidence: 99%

Overview on plasma operation with a full tungsten wall in ASDEX Upgrade

Neu¹,

Kallenbach²,

Balden³

et al. 2013

109

“…Since two of the parameters, the yield factor and the threshold energy, needed for the calculation of boron sputtering of molybdenum were not available, a fit of the boron yield from available molybdenum sputtering data on H, D, T, 4 He and C [20] was used.…”

Section: Source Modelmentioning

confidence: 99%

“…The study of high-Z materials with this method is somewhat limited [3,4]. Source rate calculations have also been routinely made, especially in tokamaks with low-Z plasma interaction surfaces [5,6].…”

mentioning

confidence: 99%

Molybdenum sources and transport in the Alcator C-Mod tokamak

Pappas

Lipschultz

LaBombard

et al. 1999

Atomic molybdenum influxes in the Alcator C-Mod tokamak have been monitored using visible spectroscopy. Measured source rates from the outer divertor, the largest source location, are compared to rates calculated from a standard physical sputtering model utilizing divertor Langmuir probe data. Comparison of the sputtering model with the measured molybdenum source rate shows good agreement during the Ohmic phase of the discharges examined. During the rf phase, the sputtering model consistently underestimates the molybdenum source rate. Analysis of a number of discharges shows no strong dependence of the divertor source on the plasma density for both L-modes and H-modes. The same source rates can be used to follow the screening of Mo from the core plasma. The penetration factor, PF ≡ N core /Φ, i.e. the ratio of the total number of Mo ions in the plasma core to the particle source rate, is higher for limited than diverted portions of discharges. The PF for Mo is found to be lower than another non-recycling impurity, nitrogen, during L-mode diverted plasmas.

“…Studies of high-Z sources have been performed on limiter [2][3][4][5] and divertor tokamaks [6][7][8][9]. The issue of impurity penetration to the core has often been separately addressed through examination of recycling [10][11][12][13] and nonrecycling elements [11,12,[14][15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

Molybdenum sources and transport in Alcator C-Mod

Lipschultz

Pappas

LaBombard

et al. 2001

We present a characterization of molybdenum sources, Γ Mo , core Mo density, n Mo , and their dependencies on Alcator C-Mod operational regimes. This includes sources from the divertor, the inner wall and the ICRF antenna limiters. We also present information characterizing the penetration of these impurities into the core plasma under different conditions based on penetration factors, PF=n Mo /Γ Mo (seconds). In general the inner wall Mo source is large (~10 18 /sec) but is found to be relatively uncorrelated with the core Mo level in diverted plasmas.The outer divertor source is of similar order to that from the inner wall and has a penetration factor in the range 10 -5 -2x10 -3 seconds depending on density and confinement mode. The antenna limiter Mo sources are typically smaller, but with higher penetration factors -10 -3 -2x10 -2 seconds. The behavior of the antenna limiter sources is consistent with physical sputtering due to the influence of RF sheath rectification.