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Coherent to turbulence transition, enhanced flow and confinement in a simple toroidal plasma
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10.1063/1.3692227
/content/aip/journal/pop/19/3/10.1063/1.3692227
http://aip.metastore.ingenta.com/content/aip/journal/pop/19/3/10.1063/1.3692227
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

A schematic view of cross-section of BETA and diagnostics. Schematic electrical connection is also shown. All the probe measurements are done close to the plane of the limiter and in the horizontal plane z = 0. The radial position indicated by “r” in the rest of the plots is with respect to the minor axis. The toroidal field coils are not shown here.

Image of FIG. 2.
FIG. 2.

Schematic figure of the DLP used for the net flow measurements. This consists of a single electrode, which is a tungsten wire exposed through the open aperture.

Image of FIG. 3.
FIG. 3.

(Color online) Mean radial profiles of (a) density, (b) electron temperature, and (c) plasma potential. Comparative profiles of all the parameters for three values of are shown. The error bars obtained from the multiple measurements at each location are found to be small. A “0” in the subscript indicates the mean value.

Image of FIG. 4.
FIG. 4.

(Color online) Mean radial profiles of floating potential for three values of are shown. The error bars obtained from the multiple measurements at each location are found to be small. A “0” in the subscript indicates the mean value.

Image of FIG. 5.
FIG. 5.

(Color online) Relative “rms” fluctuation profiles of (a) ion saturation current () which are equivalent of relative density fluctuations when fluctuations in are small; (b) floating potential for all three values of are shown. The potential fluctuations are normalized to mean electron temperature.

Image of FIG. 6.
FIG. 6.

(Color online) Mean electric field driven poloidal flow profiles derived from mean plasma potential profiles directly measured using emissive probe. The mean electric field is calculated using finite difference method and B indicates the local toroidal magnetic field.

Image of FIG. 7.
FIG. 7.

(Color online) The fluctuation driven poloidal flux is shown for three values of magnetic field. The HFS values are relatively smaller. Due to short wavelength nature of the fluctuations, measurements close to the minor axis are not reliable and hence not shown here.

Image of FIG. 8.
FIG. 8.

(Color online) The net poloidal flow profiles using measured at the upstream and downstream of the poloidal flow. The measurements shown for 220 G are obtained using Mach probe (taken from Ref. 11), for 440 G and 660 G measurements are obtained using DLP.

Image of FIG. 9.
FIG. 9.

(Color online) Comparative plot of poloidal flow velocities for all three values of ; (a) 220 G, (b) 440 G, and (c) 660 G. For each value net flow is compared with mean electric field driven flow and fluctuation driven flow. The figure (a), used for comparison for different magnetic fields, is taken from Ref. 11.

Image of FIG. 10.
FIG. 10.

(Color online) Typical density and potential auto power spectra on HFS and LFS for all the values of . Frequency is indicated by “f” and power is indicated by and for density and potential, respectively. Figures (a) and (c) are power spectra of and , respectively, at −5 cm. Similarly, (b) and (d) are at +5 cm.

Image of FIG. 11.
FIG. 11.

(Color online) Average poloidal wave number for potential fluctuations on HFS and LFS for all values of ; (a) at −5 cm and (b) +5 cm. The convention for the direction is such that positive indicates wave propagation upwards. The measurements at −5 cm and +5 cm indicate wave propagation in clockwise direction in the poloidal plane of limiter shown in Fig. 1.

Image of FIG. 12.
FIG. 12.

(Color online) Squared bicoherence for fluctuations in at all values of ; (a) 220 G, (b) 440 G, and (c) 660 G. Since the analog bandwidth is 35 kHz, the frequencies beyond this are not shown though the Nyquist frequency is 100 kHz. The statistical significance level for is defined by 1/M 0.003.

Image of FIG. 13.
FIG. 13.

(Color online) Squared bicoherence for fluctuations in at all values of ; (a) 220 G, (b) 440 G, and (c) 660 G. Since the analog bandwidth is 35 kHz, the frequencies beyond this are not shown though the Nyquist frequency is 100 kHz. The statistical significance level for is defined by 1/M 0.003.

Image of FIG. 14.
FIG. 14.

(Color online) Profiles of (a) cross-phase and (b) coherence of density and potential fluctuations for all values of . The values shown correspond to the dominant peaks in the corresponding frequency spectra.

Image of FIG. 15.
FIG. 15.

(Color online) Ratio of relative potential and density fluctuations. The potential fluctuations are those obtained from the floating potential fluctuations. The “rms” indicate the root mean square of fluctuations.

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/content/aip/journal/pop/19/3/10.1063/1.3692227
2012-03-14
2014-04-19
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Coherent to turbulence transition, enhanced flow and confinement in a simple toroidal plasma
http://aip.metastore.ingenta.com/content/aip/journal/pop/19/3/10.1063/1.3692227
10.1063/1.3692227
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