Title: Wisconsin In Situ Penning (WISP) gauge: A versatile neutral pressure gauge to measure partial pressures in strong magnetic fields

Abstract

A new type of in-vessel Penning gauge, the Wisconsin In Situ Penning (WISP) gauge, has been developed and successfully operated in the Wendelstein 7-X (W7-X) island divertor baffle and vacuum vessel. The capacity of the quantitative measurements of the neutral reservoir for light impurities, in particular, helium, is important for tokamaks as well as stellarator divertors in order to avoid fuel dilution and radiative energy loss. Penning gauges assisted by spectroscopy are a powerful tool to obtain the total neutral pressure as well as fractional neutral pressures of specific impurities. The WISP gauge is a miniaturized Penning gauge arrangement, which exploits the ambient magnetic field of magnetic confinement fusion experiments to establish the Penning discharge. Then, in situ spectroscopy is conducted to separate the fractional neutral pressures of hydrogen, helium, and possibly also other impurities. The WISP probe head was qualified using the magnetic field of the Magnetized Dusty Plasma Experiment at Auburn University between 0.25 T and 3.5 T [E. Thomas et al., J. Plasma Phys. 81, 345810206 (2015)]. The in-depth quantitative evaluation for hydrogen and helium will be shown as well as an exploration of nitrogen, argon, and neon. A power law scaling between current I and pressuremore » p, I = f (Gas,V) p^{n⁽Gas, B⁾}, was shown. The factor f is gas and anode potential dependent, while n is gas and magnetic field strength dependent. Pressure measurements from 0.1 mbar and down to 1 × 10^-5 mbar were achieved, demonstrating a reliable operating range for relevant pressure levels in the divertor and main vessel regions in current and future fusion devices, with a time resolution of up to 1 kHz. The lowest achievable pressure measurement increases with an increase in B and can be shifted with the anode potential V. At W7-X, the WISP probe head was mounted on an immersion tube setup that passes through the cryostat and places the probe head close to the plasma. Two probe heads were positioned in different divertor pump gaps, top and bottom, and one close to the plasma on the midplane in one module. The gauges were in situ calibrated together with the ASDEX pressure gauges [G. Haas and H.-S. Bosch, Vacuum 51, 39 (1998)]. Data were taken during the entire operation phase 1.2b, and measurements were coherent with other neutral gas pressure gauges. For the spectroscopic partial pressure measurements, channels of a spectroscopic detection system based on photo-multipliers, a so-called filterscope [R. J. Colchin et al., Rev. Sci. Instrum. 74, 2068 (2003)], provided by the Oak Ridge National Lab were used.« less

Authors:

Kremeyer, T.  ^[1];

• Search DOE PAGES for author "Kremeyer, T."
• Search DOE PAGES for ORCID "0000-0002-6383-944X"

Flesch, K. ^[1]; Schmitz, O.  ^[1];

• Search DOE PAGES for author "Schmitz, O."
• Search DOE PAGES for ORCID "0000-0002-9580-9149"

Schlisio, G.  ^[2];

• Search DOE PAGES for author "Schlisio, G."
• Search DOE PAGES for ORCID "0000-0002-5430-0645"

Wenzel, U.  ^[2]

• Search DOE PAGES for author "Wenzel, U."
• Search DOE PAGES for ORCID "0000-0002-4107-9291"

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+ Show Author Affiliations

1. Univ. of Wisconsin, Madison, WI (United States)
2. Max Planck Institute for Plasma Physics, Greifswald (Germany)

Publication Date:

Thu Apr 02 00:00:00 EDT 2020

Research Org.:

Univ. of Wisconsin, Madison, WI (United States); Auburn Univ., AL (United States)

Sponsoring Org.:

USDOE Office of Science (SC); National Science Foundation (NSF); Euratom

Contributing Org.:

W7-X Team

OSTI Identifier:

1802586

Alternate Identifier(s):

OSTI ID: 1608151

Grant/Contract Number:  

SC0014210; SC0016330; SC0019176; PHY-1613087; OIA-1655280; NSF-1126067; 633053

Resource Type:

Accepted Manuscript

Journal Name:

Review of Scientific Instruments

Additional Journal Information:

Journal Volume: 91; Journal Issue: 4; Journal ID: ISSN 0034-6748

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

47 OTHER INSTRUMENTATION; Instruments & Instrumentation; Physics