AVS 58th Annual International Symposium and Exhibition
    Vacuum Technology Division Tuesday Sessions
       Session VT-TuP

Paper VT-TuP7
Cryogenic Viscous Compressor Design and Development for the ITER Vacuum System

Tuesday, November 1, 2011, 6:00 pm, Room East Exhibit Hall

Session: Vacuum Technology Poster Session & Student Poster Competition
Presenter: Steven Meitner, Oak Ridge National Laboratory
Authors: S.J. Meitner, Oak Ridge National Laboratory
L.R. Baylor, Oak Ridge National Laboratory
C.N. Barbier, Oak Ridge National Laboratory
S.K. Combs, Oak Ridge National Laboratory
R.C. Duckworth, Oak Ridge National Laboratory
T.D. Edgemon, Oak Ridge National Laboratory
M.P. Hechler, Oak Ridge National Laboratory
D.A. Rasmussen, Oak Ridge National Laboratory
R. Kersevan, ITER International Organization, France
M. Dremel, ITER International Organization, France
R.J.H. Pearce, ITER International Organization, France
Correspondent: Click to Email
A specialized cryopump known as a cryogenic viscous compressor (CVC) is being developed for the ITER vacuum system to pump the regenerated, hydrogenic, fusion reaction gases from the torus cryopumps and neutral beam cryopumps, to the tritium exhaust processing facility. Several of these pumps will operate in parallel and are staged to maintain continuous pumping during plasma operation. The CVC’s regenerate at a higher pressure (500 mbar) than the torus and neutral beam cryopumps, which allows the regenerated gas to be pumped by a tritium compatible scroll pump train, with sufficient speed to maintain the regeneration duty cycle. The CVC’s are cooled to operating temperatures by precooling the inlet gas with a 80K helium cooled chevron heat exchanger, followed by a tube bank heat exchanger cooled with supercritical helium at 4.5K. Hydrogenic gas is frozen on the inner tube bank walls while helium impurity gas, a byproduct of the fusion reactions, passes through the CVC and is pumped by conventional vacuum pumps.

A conceptual design of the CVC has been developed and a representative prototype has been designed, fabricated, and is undergoing testing to verify the concept of a full scale CVC before detailed design is completed. While cooling is provided by either cold helium gas or supercritical helium, hydrogen with trace amounts of helium gas is introduced into the central column of the cryopump at 100 Pa and 80 K at flow rates of 8 mg/s. Heat transfer between the laminar flowing gas and the cold pump tube is being enhanced with the use of internal petal fins. Temperature and pressure measurements are made along the pump gas stream in order to benchmark with design heat transfer characteristics. Comparison with a fluid dynamics code is under way. Modeling of the gas flowing into the pump and through the precooler heat exchanger and freezing zones is accomplished with the CFX computational fluid dynamics code [1]. The flows into the pump are at low pressure (~ 1mbar) and are in a laminar, low Reynolds number regime, (Re < 300) that is handled well with the CFX code. As the gas begins to desublimate in the cold zone of the pump, it reaches a rarified gas regime where the CFX model for flow and heat transfer breaks down. The modeling results are being compared with the prototype testing and will be used to further optimize and ensure reliable operation of the full CVC in the ITER application.

[1] ANSYS CFX, ANSYS, Inc., Canonsburg, PA 15317, USA

* This work was supported by the Oak Ridge National Laboratory managed by UT-Battelle, LLC for the U.S. Department of Energy under Contract No. DE-AC05-00OR22725.