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

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

Journal Article · Tue Feb 09 23:00:00 EST 2016 · Review of Scientific Instruments

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

^[1]; Burke, W. ^[2]; Kuang, A. Q. ^[2]; LaBombard, B. ^[2]; ^[3]; ^[2]

Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center; OSTI
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.

View Accepted Manuscript (DOE)

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

OSTI ID:: 1897622

Alternate ID(s):: OSTI ID: 1237773

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

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

Country of Publication:: United States

Language:: English

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