Installation and initial operation of the DIII-D advanced divertor cryocondensation pump

J. P. Smith, K. M. Schaubel, C. B. Baxi, G. L. Campbell, A. W. Hyatt, G. J. Laughon, M. A. Mahdavi, E. E. Reis, M. J. Schaffer, D. L. Sevier, R. D. Stambaugh, M. M. Menon

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

3 Scopus citations

Abstract

Phase two of a divertor cryocondensation pump, the Advanced Divertor Program, is now installed in the DIII-D tokamak at General Atomics and complements the phase one biasable ring electrode. The installation consists of a 10 m long cryocondensation pump located in the divertor baffle chamber to study plasma density control by pumping of the divertor. The design is a toroidally electrically continuous liquid helium-cooled panel with 1 m2 of pumping surface. The helium panel is single point grounded to the nitrogen shield to minimize eddy currents. The nitrogen shield is toroidally continuous and grounded to the vacuum vessel in 24 locations to prevent voltage potentials from building up between the pump and vacuum vessel wall. A radiation/particle shield surrounds the nitrogen-cooled surface to minimize the heat load and prevent water molecules condensed on the nitrogen surface from being released by impact of energetic particles. Large currents (>5000 A) are driven in the helium and nitrogen panels during ohmic coil ramp up and during disruptions. The pump is designed to accommodate both the thermal and mechanical loads due to these currents. A feedthrough for the cryogens allows for both radial and vertical motion of the pump with respect to the vacuum vessel. Thermal performance measured on a prototype verified the analytical model and thermal design of the pump. Characterization tests of the installed pump show the pumping speed in deuterium is 42,000 ℓ/sec for a pressure of 5 mTorr. Induction heating of the pump (at 300 W) resulted in no degradation of pumping speed. Plasma operations with the cryopump show a 60% lower density in H-mode.

Original languageEnglish
Title of host publicationProceedings - Symposium on Fusion Engineering
PublisherPubl by IEEE
Pages1043-1046
Number of pages4
ISBN (Print)0780314131
StatePublished - 1993
Externally publishedYes
EventProceedings of the 15th IEEE/NPSS Symposium on Fusion Engineering. Part 2 (of 2) - Hyannis, MA, USA
Duration: Oct 12 1993Oct 12 1993

Publication series

NameProceedings - Symposium on Fusion Engineering
Volume2

Conference

ConferenceProceedings of the 15th IEEE/NPSS Symposium on Fusion Engineering. Part 2 (of 2)
CityHyannis, MA, USA
Period10/12/9310/12/93

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