First results from the implementation of the ITER diagnostic residual gas analyzer prototype at Wendelstein 7-X

Schlisio, G.; Harris, J. H.; Biewer, T. M.; Winters, V.; Wenzel, U.; Kornejew, P.; Laqua, H. P.; Krychowiak, M.; Team, West

doi:10.1063/1.5098125

Cited by 5 publications

(5 citation statements)

References 16 publications

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“…One example is the carbon chemistry on the large carbon surface of the first wall, carbohydrates as well as carbon oxides can be regularly observed in the exhaust gas in small quantities, e.g. by means of a residual gas analyser (RGA) [15]. With increasing tungsten surface [16] and continued nitrogen seeding [17] ammonia formation [18] could become a noticeable phenomenon in W7-X as well.…”

Section: Concepts Methodology and Assumptionsmentioning

confidence: 99%

The evolution of the bound particle reservoir in Wendelstein 7-X and its influence on plasma control

et al. 2021

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The investigation of fuel retention in fusion experiments is important in view of plasma density control as well as tritium inventory for future fusion reactors. We present a first gas balance of the stellarator Wendelstein 7-X with its inertially cooled graphite divertor. The gas balance is used to estimate the wall inventory and it is found that the wall plays an important and dynamic role, absorbing or releasing particles depending on the plasma conditions. Several different scenarios are presented and the effect of fueling and heating on the wall inventory is assessed. We find that the record duration plasma experiment of 100 s required previous shorter plasmas to be successfully conducted.

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Section: Concepts Methodology and Assumptionsmentioning

confidence: 99%

The evolution of the bound particle reservoir in Wendelstein 7-X and its influence on plasma control

et al. 2021

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“…The P-DRGA, outfitted with a sampling tube, operated for first integral tests of the DRGA system [4] in the W7-X initial divertor experiment campaign, OP1.2. In the upcoming experiment campaign, OP2, W7-X will operate a new fully water cooled first wall from carbon fiber composite, the so-called high-heat-flux (HHF) divertor, allowing for higher plasma performance and thus higher subdivertor pressure.…”

Section: W7-x Subdivertor Changesmentioning

confidence: 99%

“…The previously installed gauge shielding, consisting of a two-layer strapped-on permalloy foil wound cylindrically around the device, was found to be insufficient, and the P-DRGA suffered from magnetic interference during its campaign in 2018 as reported in [4]. The maximum ambient magnetic field of up to 5 mT leads to saturation of the foil and subsequent disturbance of the measurement process, which is based on free streaming charged particles in carefully controlled electric fields.…”

Section: Magnetic Shieldingmentioning

confidence: 99%

“…Here, it is used to confirm analytical calculations from the design phase of the sampling tube [4] as well as measurements from the initial measurement campaign, especially the gas propagation time through the system [time of flight (TOF)] as well as yielded pressures at the measurement position. A similar analysis has been performed for the ITER DRGA in [9].…”

Section: Monte Carlo Flow Analysismentioning

confidence: 99%

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Improvements on the Diagnostic Residual Gas Analyzer at Wendelstein 7-X

Schlisio

Ravelli

Harris

et al. 2022

IEEE Trans. Plasma Sci.

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Exhaust gas analysis provides key information on fusion processes, divertor operation, and wall state in fusion experiments and future reactors. The diagnostic residual gas analyzer (DRGA) concept has been developed for ITER with a focus on fast helium and hydrogen isotope detection. The first operation of the prototype DRGA (P-DRGA) at the stellarator Wendelstein 7-X showed potential for improvement in terms of magnetic sensor shielding, data acquisition automation, and potential new additions to the cluster of sensors on the P-DRGA. More recently, a Monte Carlo simulation of the flow of the mixed gas species effluent from the pressure-reducing orifice, down to about 8-m sampling tube and into the analysis region of the sensors, has been found to generally agree with previous calculations and measurements but revealed potential backstreaming effects for light gases, with impact on detection limits both for the prototype and for the ITER DRGA currently in design. For the upcoming campaign of the prototype, an enhanced soft iron shield will safeguard the gauges against magnetic stray field influence. The newly introduced shielding has been tested for its effect on magnetic stray fields and found to reduce the inside residual field by about two orders of magnitude.

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“…These gases were analyzed using a diagnostic residual gas analyzer (DRGA) at a port in half-module 40. The details of the DRGA measurement set-up (see figure 7) in W7-X are presented in [35]. Two additional mass spectrometers were operated in half-modules 21and 40 but since these were not calibrated, for the present analysis the DRGA data have been used.…”

Section: Exhaust Of Volatile Carbon Oxides and Hydrocarbonsmentioning

confidence: 99%

Plasma-wall interaction studies in W7-X: main results from the recent divertor operations

Dhard

Brezinsek²,

Mayer

et al. 2021

Phys. Scr.

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Wendelstein 7-X (W7-X) is an optimized stellarator with a 3-dimensional five-fold modular geometry. The plasma-wall-interaction (PWI) investigations in the complex 3D geometry of W7-X were carried out by in situ spectroscopic observations, exhaust gas analysis and post-mortem measurements on a large number of plasma-facing components extracted after campaigns. The investigations showed that the divertor strike line areas on the divertor targets appeared to be the major source of carbon impurities. After multistep erosion and deposition events, carbon was found to be deposited largely at the first wall components, with thick deposits of >1 μm on some baffle tiles, moderate deposits on toroidal closure tiles and thin deposits at the heat shield tiles and the outer wall panels. Some amount of the eroded carbon was pumped out via the vacuum pumps as volatile hydrocarbons and carbon oxides (CO, CO2) formed due to the chemical processes. Boron was introduced by three boronizations and one boron powder injection experiment. Thin boron-dominated layers were found on the inner heat shield and the outer wall panels, some boron was also found at the test divertor unit and in redeposited layers together with carbon. Local erosion/deposition and global migration processes were studied using field-line transport simulations, analytical estimations, 3D-WallDYN and ERO2.0 modeling in standard magnetic field configuration.

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First results from the implementation of the ITER diagnostic residual gas analyzer prototype at Wendelstein 7-X

Cited by 5 publications

References 16 publications

The evolution of the bound particle reservoir in Wendelstein 7-X and its influence on plasma control

The evolution of the bound particle reservoir in Wendelstein 7-X and its influence on plasma control

Improvements on the Diagnostic Residual Gas Analyzer at Wendelstein 7-X

Plasma-wall interaction studies in W7-X: main results from the recent divertor operations

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