Absolute calibration of sniffer probes on Wendelstein 7-X

Abstract

Moseev, D.; Laqua, H.P.; Marsen, S.; Stange, T.; Braune, H.; Erckmann, V.; Gellert, F.J.; Oosterbeek, J.W. Published in:Review of Scientific Instruments DOI:10.1063/1.4960349Published: 01/08/2016 Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers)Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Here we report the first measurements of the power levels of stray radiation in the vacuum vessel of Wendelstein 7-X using absolutely calibrated sniffer probes. The absolute calibration is achieved by using calibrated sources of stray radiation and the implicit measurement of the quality factor of the Wendelstein 7-X empty vacuum vessel. Normalized absolute calibration coefficients agree with the cross-calibration coefficients that are obtained by the direct measurements, indicating that the measured absolute calibration coefficients and stray radiation levels in the vessel are valid. Close to the launcher, the stray radiation in the empty vessel reaches power levels up to 340 kW/m 2 per MW injected beam power. Furthest away from the launcher, i.e., half a toroidal turn, still 90 kW/m 2 per MW injected beam power is measured. [http://dx

Advanced electron cyclotron heating and current drive experiments on the stellarator Wendelstein 7-X

“…5 shows an overview of the W7-X torus indicating the position of the ECRH launchers and some important diagnostics, which were commissioned during OP1.1. Safety relevant diagnostics like the stray radiation probes (sniffer) [5], indicating the ECRH absorption, and the electron cyclotron emission diagnostic (ECE) [6], measuring the electron temperature, were available from the first day of operation. A detailed description of all diagnostics is given in [7].…”

Collective Thomson scattering diagnostic at Wendelstein 7-X

“…Stray radiation from ECE is not taken into account because of its insignificance in the W7-X plasmas. 28 The distribution of stray radiation in the port plugin and in the transmission line from the port in the triangular cross section to the ECRH tower in module 1 is calculated using a multicavity model. 29 The model has proven its validity in the OP1.1 campaign 30 and is used to simulate the stray radiation loads in ITER.…”

Inference of the microwave absorption coefficient from stray radiation measurements in Wendelstein 7-X

“…Operating at such high power, the knowledge of the microwave absorption is crucial for understanding the physics of heating and for the machine safety. Wendelstein 7-X is equipped with five absolutely calibrated sniffer probes, equally toroidally distributed in the machine [4]. Sniffer probes measure the distribution of ECRH stray radiation energy flux in the machine.…”