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

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 m{sup 2} 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 themore » 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 {ell}/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.« less

Authors:
; ; ; ; ; ; ; ; ; ;  [1];  [2]
  1. General Atomics, San Diego, CA (United States)
  2. Oak Ridge National Lab., TN (United States)
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States); Oak Ridge National Lab., TN (United States)
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
10190778
Report Number(s):
GA-A-21396; CONF-931018-20
ON: DE94001106; TRN: 93:025477
DOE Contract Number:  
AC03-89ER51114; AC05-84OR21400
Resource Type:
Conference
Resource Relation:
Conference: Symposium on fusion engineering,Hyannis, MA (United States),11-15 Oct 1993; Other Information: PBD: Oct 1993
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; DOUBLET-3 DEVICE; PUMPED LIMITERS; DESIGN; PERFORMANCE TESTING; PLASMA DENSITY; EDDY CURRENTS; INDUCTION; CRYOPUMPS; HEAT FLUX; 700420; PLASMA-FACING COMPONENTS

Citation Formats

Smith, J P, Schaubel, K M, Baxi, C B, Campbell, G L, Hyatt, A W, Laughon, G J, Mahdavi, M A, Reis, E E, Schaffer, M J, Sevier, D L, Stambaugh, R D, and Menon, M M. Installation and initial operation of the DIII-D advanced divertor cryocondensation pump. United States: N. p., 1993. Web.
Smith, J P, Schaubel, K M, Baxi, C B, Campbell, G L, Hyatt, A W, Laughon, G J, Mahdavi, M A, Reis, E E, Schaffer, M J, Sevier, D L, Stambaugh, R D, & Menon, M M. Installation and initial operation of the DIII-D advanced divertor cryocondensation pump. United States.
Smith, J P, Schaubel, K M, Baxi, C B, Campbell, G L, Hyatt, A W, Laughon, G J, Mahdavi, M A, Reis, E E, Schaffer, M J, Sevier, D L, Stambaugh, R D, and Menon, M M. 1993. "Installation and initial operation of the DIII-D advanced divertor cryocondensation pump". United States. https://www.osti.gov/servlets/purl/10190778.
@article{osti_10190778,
title = {Installation and initial operation of the DIII-D advanced divertor cryocondensation pump},
author = {Smith, J P and Schaubel, K M and Baxi, C B and Campbell, G L and Hyatt, A W and Laughon, G J and Mahdavi, M A and Reis, E E and Schaffer, M J and Sevier, D L and Stambaugh, R D and Menon, M M},
abstractNote = {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 m{sup 2} 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 {ell}/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.},
doi = {},
url = {https://www.osti.gov/biblio/10190778}, journal = {},
number = ,
volume = ,
place = {United States},
year = {1993},
month = {10}
}

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