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Charge and mass-dependence of ion heating in merged CT plasmas

Author: Mike Brown
Requested Type: Poster Only
Submitted: 2009-12-04 13:56:27

Co-authors: T. Gray, B. Gerber-Siff

Contact Info:
Swarthmore College
500 College Ave.
Swarthmore, PA   19081
USA

Abstract Text:
Ion heating due to magnetic reconnection is measured in the SSX compact torus merging device for a variety of ion masses and charge states with a high resolution ion Doppler spectrometer. The velocity resolution of the instrument is $le 5~km/s$. Peak ion temperatures of $100~eV$ have been recorded during reconnection events as well as flows up to $40~km/s$. Spheromak merging in a new slightly prolate flux conserver ($R=0.2~m, L=0.4~m$) often results in excitation of several unstable MHD modes with a dynamical evolution to a preferred final state. Massive ions are doped at the $1%$ level in a hydrogen plasma. After reconnection and instability, we measure a period of reconnection-driven ion heating with peak temperatures for argon $(Ar^{+++})~T_{Ar} cong 15~eV$, for carbon $(C^{++})~T_C cong 40~eV$, and for helium $(He^+)~T_{He} cong 75~eV$ (averaged over many shots). Ion temperatures in the turbulent high corona and solar wind are known to scale with the ion mass ($T_i propto M_i$). Laboratory measurements of ion temperature during reconnection-driven events in the MST reversed field pinch have a particular scaling ($T_i propto sqrt{M_i}$) whereas impulsive events in the SSX reconnection device have another scaling ($T_i propto Z/M_i$). Computer simulations are being planned to help sort out the discrepancies but evidently, different physics pertains in each system. It seems likely that turbulent, reconnection-driven ion heating depends on details like the fluctuation spectrum of turbulence and waves, the spatial extent of the heating zone, and the duration of the reconnection event(s).

Characterization: E4

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