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Beat-wave Seeding of Magnetic Feld in an Accelerated Compact Toroid

Author: Robert D. Horton
Requested Type: Poster Only
Submitted: 2009-12-04 11:57:16

Co-authors: D.Q.Hwang, F.Liu, B.Zhu

Contact Info:
University of California, Davis
L-661, Eastgate Drive
Livermore,, CA   94550

Abstract Text:
An experiment is being developed on the CTIX compact-toroid injector to test beat-wave interaction of electromagnetic waves with plasma. By launching high-power “pump” waves at differing frequencies, a wave at the beat (difference) frequency is created within a region of plasma. The beat wave method has several advantages compared to linear methods of wave-plasma interaction, including near-transparency of the target plasma to the pump waves outside the region of overlap, precise control of the position and velocity of electrons interacting with plasma, and the ability to make large changes in beat frequency by making small changes in pump frequency. The beat wave is efficiently damped, and electron current generated, if the beat frequency is close to local plasma frequency, and if phase velocity is close to electron thermal velocity. In contrast to previous experiments at microwave pump frequencies and low plasma density [1], the CTIX experiment will make use of two TEA CO2 lasers operating at mid-infrared optical wavelengths (f ~ 30 THz) and high power (~100 MW). By selecting among the numerous available CO2 laser wavelengths near 10.6 microns, beat frequencies between 45 GHz and 4.7 THz can be chosen, corresponding to a wide range of plasma densities, 1e14 cm-3 to 1e19 cm-3. A particular application of the beat-wave method with optical pump waves is current generation by transfer of energy from the asymmetric beat-wave velocity spectrum into thermal plasma electrons. This method may provide a reasonably efficient means for standoff current generation in initially unmagnetized target plasmas. In the magnetized target fusion (MTF) concept, the target plasma is then compressed, multiplying the initial magnetic field strength and enhancing particle confinement.
The CTIX experiment will test basic physics of the beat wave process, including models of wave mixing, modification of the transmitted pump waves by nonlinear interaction, and quasilinear modification of the electron velocity distribution. The tunable TEA laser system, and modifications to CTIX to deliver highly reproducible plasma targets, are currently being developed; preliminary results will be presented. [1] Rogers, J. H. and Hwang, D. Q., Phys. Rev. Lett. v68 p3877 (1992).‏

Characterization: E5,E8


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