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Experiment to Study Alfven Wave Pulses Along Curved Moving Magnetic Flux Tubes

Author: Mark K Kendall
Requested Type: Poster Only
Submitted: 2011-06-10 14:57:45

Co-authors: P.M. Bellan

Contact Info:
1200 E California Blvd
Pasadena, CA   91125

Abstract Text:
Plasma dynamics in open field line geometry is an active area of great interest to the fusion community. Arched plasma-filled twisted open magnetic flux tubes are generated at Caltech using pulsed power techniques (J.F. Hansen, S.K.P. Tripathi, P.M. Bellan, 2004). The structure and time evolution of these flux tubes exhibit similarities with solar coronal loops, spheromaks, astrophysical jets, and possibly open field line regions near the wall of tokamaks. We are now developing a method to excite propagating torsional Alfven wave modes by superposing a ~10kA, ~100ns current pulse upon the ~50kA, 10µs main discharge current that flows along the ~20cm long, 2cm diameter arched flux tube. To achieve this high power 100ns pulse, a magnetic pulse compression technique based on saturable reactors is employed. In this scheme, the saturable reactors act as passive switches in a pulse-forming network, resonantly discharging a pulse along a series of stages with successively shorter timescales. A low power prototype has been successfully tested, and design and construction of a full-power device is nearing completion. The full-power device will compress an initial 2µs pulse by a factor of nearly 20. The final stage of the device utilizes a coaxial water-filled transmission line with ultra-low inductance to attain the final timescale. The water system is additionally de-gassed to help prevent bubble formation which otherwise could contribute to electrical breakdown between the conductors resulting from the >10kV applied voltage. This new pulse device will subsequently be used to investigate interactions between Alfven waves and the larger-scale loop evolution; one goal will be to directly capture the motion of the propagating wave using high-speed photography capable of resolving the Alfven timescale.

Work supported by the DOE, NSF, and AFOSR.

Characterization: E2

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University of Washington

Workshop on Innovation in Fusion Science (ICC2011) and
US-Japan Workshop on Compact Torus Plasma
August 16-19, 2011
Seattle, Washington

ICC 2011