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Diagnostics for lab and astrophysical plasmas

Author: Jennifer K. Baerny
Requested Type: Poster Only
Submitted: 2009-12-06 22:00:56

Co-authors: S. Woodruff, C. Smith

Contact Info:
Woodruff Scientific Inc
4501 Shilshole Ave NW
Seattle, WA   98107
USA

Abstract Text:
In order to obtain strong magnetic fields in the spheromak, it is necessary to obtain conditions with low radiated power, full ionization, and low density. This argument follows from basic considerations of helicity injection and build-up, where the limit to the obtainable field strength is set by dissipation. The experimental campaign during the next year for the Pulsed Build-up Experiment (PBX) [1] and the Adiabatic Compression experiment (ACE) will include vacuum conditioning such as bake, glow and Ti gettering. To monitor effects of vacuum conditioning, we are currently building three radiation diagnostics: a HeNe heterodyne interferometer, Bolometer, and Hydrogen-alpha detector. The HeNe interferometer to be is based on the 2008 interferometer used for the Caltech spheromak formation experiment [2]. The interferometer will measure the line average refractive index of the plasma, enabling us to obtain the average line density. The bolometer is being designed like ones used on SSPX [3] and the HBT-EP tokamak [4]. The bolometer will be a soft x-ray/UV detector used to directly measure the radiation loss from photons, allowing us to ignore neutral particle energy loss. The Hydrogen-alpha detector is also based on the one on SSPX. Using the detector, we will be able to detect the amount of Hydrogen-alpha being emitted by the plasma as a function of time, thus gauging the neutral density.

These same concepts are also used to study astrophysical plasmas, with slightly different approaches. Interferometry is used either as radio telescope pairs or arrays such as the VLBA. These radio telescopes allow astronomers higher resolution images and more precise measurements of celestial objects. Spectroscopy is also frequently used in astronomy to determine composition, temperature, and distance to an object using Doppler shift. The overlap between diagnostics / detectors for lab and astrophysical plasmas will be discussed.

[1] S. Woodruff, A.I.D. Macnab, T.M. Ziemba, and K.E. Miller. Spheromak Formation and Current Sustainment Using a Repetitively Pulsed Source. Journal of Fusion Energy, 28 (2): 229-234, June 2009.
[2] Deepak Kumar. Experimental investigations of magnetohydrodynamic plasma jets. Dissertation, California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-04092009-163047, 2009.
[3] H.S. McLean et al. Plasma Diagnostics for the Sustained Spheromak Physics Experiment. Rev. Sci. Instruments, 72(1):556-561, January 2001.
[4] Qingjun Xiao and Gerald Navratil. A photodiode for the measurement of soft x-ray radiation from plasma. Rev. Sci. Instrument, 67(9):3334-3335, September 1996.
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Work supported by Department of Energy under subcontract numbers DE-FG02-06ER84449 and DE-FG02-07ER84924. *JKB is a Masters student at UW.

Characterization: A1,A3

Comments:
Please place with Woodruff Scientific Inc posters:
1. Woodruff
2. Mattor
3. Baerny
4. Stoulil