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Excitation of the centrifugally driven interchange instability in a plasma confined by a magnetic dipolea)
a)Paper NI2 3, Bull. Am. Phys. Soc. 49, 250 (2004).
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10.1063/1.1888685
/content/aip/journal/pop/12/5/10.1063/1.1888685
http://aip.metastore.ingenta.com/content/aip/journal/pop/12/5/10.1063/1.1888685
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

(a) A schematic of the CTX vacuum chamber, depicting the magnetic field lines, equatorial mesh biasing array, several movable probes, and the polar current detector array. The location of the fundamental ECRH resonance is indicated by the dotted line. Photographs of the equatorial bias mesh (b) and the polar detector array (c) are also shown.

Image of FIG. 2.
FIG. 2.

(a) Floating potential measurements with and without external bias and (b) the rotation frequency consistent with floating potential measurements. The dashed lines are model predictions based on classical Pedersen conductivity due to ion-neutral collisions. (c) Profile of the ion saturation current normalized to a fixed edge probe. The marginally stable density profile is indicated by the dotted line.

Image of FIG. 3.
FIG. 3.

(Color). Time-frequency spectrogram of interchange fluctuations upon application of mesh bias. Also shown is the Mach probe measurement of edge ion flow.

Image of FIG. 4.
FIG. 4.

(Color). Interchange fluctuations in plasmas with fastest rotation rates achieved by reducing the dipole magnetic field. When the applied mesh bias becomes more negative than , the interchange mode structure is dominated by .

Image of FIG. 5.
FIG. 5.

(Color). Simultaneous observation of HEI and centrifugal modes during a low density shot. (a) The floating potential fluctuations and the corresponding time-frequency spectrograms are shown from one probe digitized at 200 kHz and (b) another probe sampling at 12.5 MHz displaying one of the HEI instability bursts, with their characteristic frequency sweeping.

Image of FIG. 6.
FIG. 6.

Normalized magnitude of the correlation function between two probes as a function of the radial position of one probe for the , 2, and 3 azimuthal components numbers. Solid lines are computed Fourier components from the nonlinear simulation.

Image of FIG. 7.
FIG. 7.

(Color). (a) Total phase of the correlation function between two probes as a function of the radial position of one probe for the three lowest harmonics. (b) The radial phase for the mode at three different times during a discharge. Solid line is the result of numerical simulation. (c) Reconstructed component of the interchange mode.

Image of FIG. 8.
FIG. 8.

(Color). Measurements using the polar imaging diagnostic. (a) Equilibrium and (b) fluctuations of the polar electron current. The small round circles indicate the detector locations in (a). (c) The frequency spectrum averaged over all detectors. (d) Radial profiles of the normalized amplitude for the three lowest azimuthal components of the fluctuating endloss current.

Image of FIG. 9.
FIG. 9.

(Color). Computed variation of the interchange mode structure as the fraction of energetic electrons and the plasma rotation rate changes. Only the regimes dominated by and are seen experimentally.

Image of FIG. 10.
FIG. 10.

Fractional decrease in the measured soft x-ray signals due to the external bias collimated at three different radial cords through the plasma.

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/content/aip/journal/pop/12/5/10.1063/1.1888685
2005-05-05
2014-04-19
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Excitation of the centrifugally driven interchange instability in a plasma confined by a magnetic dipolea)
http://aip.metastore.ingenta.com/content/aip/journal/pop/12/5/10.1063/1.1888685
10.1063/1.1888685
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