Feedback system for divertor impurity seeding based on real-time measurements of surface heat flux in the Alcator C-Mod tokamak

Brunner, D.; Burke, W.; Kuang, A. Q.; LaBombard, B.; Lipschultz, B.; Wolfe, S.

doi:10.1063/1.4941047

Title: Feedback system for divertor impurity seeding based on real-time measurements of surface heat flux in the Alcator C-Mod tokamak

Journal Article · Wed Feb 10 00:00:00 EST 2016 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/1.4941047· OSTI ID:1897622

^[1]; Burke, W. ^[1]; Kuang, A. Q. ^[1]; LaBombard, B. ^[1];

^[2];

^[1]

Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center
Univ. of York, Heslington, York (United Kingdom)

Mitigation of the intense heat flux to the divertor is one of the outstanding problems in fusion energy. One technique that has shown promise is impurity seeding, i.e., the injection of low-Z gaseous impurities (typically N₂ or Ne) to radiate and dissipate the power before it arrives to the divertor target plate. To this end, the Alcator C-Mod team has created a first-of-its-kind feedback system to control the injection of seed gas based on real-time surface heat flux measurements. Surface thermocouples provide real-time measurements of the surface temperature response to the plasma heat flux. The surface temperature measurements are inputted into an analog computer that “solves” the 1-D heat transport equation to deliver accurate, real-time signals of the surface heat flux. The surface heat flux signals are sent to the C-Mod digital plasma control system, which uses a proportional–integral–derivative (PID) algorithm to control the duty cycle demand to a pulse width modulated piezo valve, which in turn controls the injection of gas into the private flux region of the C-Mod divertor. This paper presents the design and implementation of this new feedback system as well as initial results using it to control divertor heat flux.

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Research Organization:: Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center

Sponsoring Organization:: USDOE Office of Science (SC), Fusion Energy Sciences (FES); Wolfson Foundation; UK Royal Society

Grant/Contract Number:: FC02-99ER54512; EP/I501045; FC02-99ER54512-CMOD

OSTI ID:: 1897622

Alternate ID(s):: OSTI ID: 1237773

Journal Information:: Review of Scientific Instruments, Vol. 87, Issue 2; ISSN 0034-6748

Publisher:: American Institute of Physics (AIP)Copyright Statement

Country of Publication:: United States

Language:: English

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Cited by: 24 works

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High-resolution heat flux width measurements at reactor-level magnetic fields and observation of a unified width scaling across confinement regimes in the Alcator C-Mod tokamak Brunner, D.; LaBombard, B.; Kuang, A. Q. Nuclear Fusion, Vol. 58, Issue 9 https://doi.org/10.1088/1741-4326/aad0d6	journal	July 2018
The surface eroding thermocouple for fast heat flux measurement in DIII-D Ren, J.; Donovan, D.; Watkins, J. Review of Scientific Instruments, Vol. 89, Issue 10 https://doi.org/10.1063/1.5038677	journal	October 2018
A volume-averaged model of nitrogen–hydrogen plasma chemistry to investigate ammonia production in a plasma-surface-interaction device Body, Thomas; Cousens, Samuel; Kirby, Juliet Plasma Physics and Controlled Fusion, Vol. 60, Issue 7 https://doi.org/10.1088/1361-6587/aab740	journal	June 2018
Power accounting of plasma discharges in the linear device Proto-MPEX Showers, M.; Piotrowicz, P. A.; Beers, C. J. Plasma Physics and Controlled Fusion, Vol. 60, Issue 6 https://doi.org/10.1088/1361-6587/aab7c8	journal	April 2018

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Title: Feedback system for divertor impurity seeding based on real-time measurements of surface heat flux in the Alcator C-Mod tokamak

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