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abstract.pdf2010-02-18 13:51:32Deepak Kumar
talk.pdf2010-02-18 08:47:27Deepak Kumar
abstract_tex.latex2009-12-12 23:23:13Deepak Kumar

Mechanism of helicity injection in the Caltech spheromak experiment

Author: Deepak Kumar
Requested Type: Consider for Invited
Submitted: 2009-12-10 00:49:12

Co-authors: A. Moser, P. Bellan

Contact Info:
Applied Physics, Caltech
1200 E. California Blvd.,
Pasadena, CA   91125

Abstract Text:
Collimated plasma jets flowing away from co-planar electrodes are produced in the Caltech spheromak formation experiment. The jet formation stage precedes the spheromak formation and serves as a mechanism for feeding particles, magnetic helicity, energy and toroidal flux into the system.
The experiment uses a size A ignitron to switch a 59 μF capacitor bank (charged up to 8 kV) across the co-planar electrodes. Typical power levels are ∼ 200 MW for a duration of ∼ 10 μs. Careful analysis of the discharge circuit reveals that the combined impedance of the size A ignitron and the cables is significantly larger than the plasma impedance. This causes the discharge circuit to behave as a current source with low energy transfer efficiency. Such behavior is expected to be common to other helicity injection experiments as well (D. Kumar, A. Moser and P. M. Bellan, IEEE Trans. Plasma Sci., to appear).
The plasma jet is observed to be extremely collimated. Detailed time of flight measurements of hydrogen and deuterium plasma jets have revealed that the flow in the jet is Alfvenic with respect to the the toroidal magnetic field produced by the axial current within the plasma (D. Kumar and P. M. Bellan, Phys. Rev. Lett., 105003 (2009)). Plasma density measurements from a HeNe interferometer have also shown that the jet has a dense core (β ∼ 1). The visual images of the jet reveal that the dense core has a radial extent of ∼ 3 cm. However, magnetic field measurements show that the current and poloidal flux in the jet has a radial extent of ∼ 10 cm. Thus the dense core is surrounded by almost force free (β → 0) plasma towards the periphery of the jet. An MHD analysis successfully predicts the flow properties and the density structure of these jets.

Characterization: E11

Please consider the abstract for an invited talk. If it is not possible to do so, then please place the poster next to Prof. Paul Bellan's poster.

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Innovative Confinement Concepts Workshop
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