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Infrastructure Upgrades to the PFRC Facility

Author: S. A. Cohen
Requested Type: Poster Only
Submitted: 2009-12-04 12:42:12

Co-authors: B. Berlinger, A. Brooks, C. Brunkhorst, D. Farley, H. Feder, J. Gumbas, C. Myers, G. McQuay, H. White

Contact Info:
Princeton Plasma Physics Laboratory
PO Box 451, Forrestal Campus,
Princeton, NJ   08543
USA

Abstract Text:
We describe plans to upgrade the PFRC facility to allow the attainment of longer duration, higher energy-density, lower collisionality plasmas. In the present PFRC (PFRC-I), electron energies are already so high (Te > 200 eV) that first-orbit losses are likely. A stronger bias field and larger radius plasma are both needed to allow higher energy electrons while maintaining low collisionality at higher density. To achieve these goals requires: 1) increased RMF heating power; 2) larger radius vacuum vessel and flux conservers (FCs); 3) longer skin-time FCs; and 4) stronger bias magnetic field. Polycarbonate is chosen as the vacuum vessel material to allow RMF penetration from external antenna, multiple ports for diagnostic access, UHV conditions, and improved safety. The 23-cm inner diameter (ID) of the vessel requires unusually thick (ca. 1.6 cm) walls to reduce deformation under vacuum forces. Novel molding techniques required for the fabrication of this non-standard polycarbonate pipe will be described. The flux conservers will consist of 1st generation, high temperature superconducting (G1-HTS) tapes embedded in LN2-cooled 16-cm ID Cu rings placed inside the vacuum vessel. Insulating shields will cover the FCs, to reduce radiation and plasma heat loads on the Cu rings and sputter contamination of the plasma. Tests on prototype FCs have shown a skin-time increase from 3.4 ms for room temperature Cu to over 12 sec for 77K Cu rings with embedded G1-HTS. Under these conditions, the G1-HTS retains its critical current of 150 A/tape. Each of the 8 flux conservers for the PFRC upgrade (PFRC-II) will need 14 tapes to sustain the 2 kA currents expected at full bias field, ca. 1 kG. The cryogenic system for cooling the FCs will be described as will be the RF system for providing the required increase in RMF power from 20 to 200 kW. With these upgrades, the electron temperature is expected to exceed 1 keV at a density of 10^13 cm^-3 while the ratio S*/E remains below 1, implying continued stability against the internal tilt.

Characterization: A3,A4

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