Physics
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsa11a0303t&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SA11A-0303
Physics
0654 Plasmas, 2151 Neutral Particles (7837), 2423 Ionization Processes (7823), 2463 Plasma Convection (2760), 7815 Electrostatic Structures
Scientific paper
A vortex is observed in a cylindrical magnetized plasma. The characteristic feature of this vortex is that the direction of rotation is opposite to that of ExB drift, which is usually dominant mechanism for driving plasma rotation. This result suggests that there exists a force acting on the ion fluid and it exceeds the ambipolar electric field. To clarify the origin of anti-ExB rotation, detailed experiments have been carried out to find that the anti-ExB vortex always accompanies with a deep density hole in the background neutrals. The density depletion causes a flow of neutrals due to steep density gradient. When the ion energy is of the order or less than 1 eV, ions interact with neutrals through charge exchange collisions. Then, momentum possessed by the neutral flow can be transferred to the ions, and consequently an effective force against the ions arises. If this force is opposite to and dominates the electric field, the anti-ExB rotation is possible. To experimentally verify the above-mentioned mechanism, a direct observation of neutral flow is the key issue, for which we have been developing a laser induced fluorescence (LIF) spectroscopy system using a tunable diode laser. Since the neutral flow is expected to be very slow (several m/s), the spectrum of the laser should be very narrow, which is the reason why we use a tunable diode laser. We have observed the expected neutral flow with a velocity of 80m/s by using the newly developed LIF spectroscopy system. Our experimental result shows that the dynamical behavior of ions is drastically changed by the interaction with neutral flow. This mechanism provides a new route to vortex formation in magnetized plasmas. It is emphasized that charge exchange process plays an essential role in the transport of momentum.
Etoh S.
Mitsutoshi A.
Ogiwara K.
Tanaka Masayoshi Y.
Yoshimura Shunsuke
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