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Title: Experimental Observation of Convective Cell Formation due to a Fast Wave Antenna in the Large Plasma Device

Authors:
; ; ; ;
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1409226
Grant/Contract Number:
DOE DE-FC02-07ER54918:0016
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 119; Journal Issue: 20; Related Information: CHORUS Timestamp: 2017-11-17 10:07:43; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society
Country of Publication:
United States
Language:
English

Citation Formats

Martin, M. J., Gekelman, W., Van Compernolle, B., Pribyl, P., and Carter, T.. Experimental Observation of Convective Cell Formation due to a Fast Wave Antenna in the Large Plasma Device. United States: N. p., 2017. Web. doi:10.1103/PhysRevLett.119.205002.
Martin, M. J., Gekelman, W., Van Compernolle, B., Pribyl, P., & Carter, T.. Experimental Observation of Convective Cell Formation due to a Fast Wave Antenna in the Large Plasma Device. United States. doi:10.1103/PhysRevLett.119.205002.
Martin, M. J., Gekelman, W., Van Compernolle, B., Pribyl, P., and Carter, T.. 2017. "Experimental Observation of Convective Cell Formation due to a Fast Wave Antenna in the Large Plasma Device". United States. doi:10.1103/PhysRevLett.119.205002.
@article{osti_1409226,
title = {Experimental Observation of Convective Cell Formation due to a Fast Wave Antenna in the Large Plasma Device},
author = {Martin, M. J. and Gekelman, W. and Van Compernolle, B. and Pribyl, P. and Carter, T.},
abstractNote = {},
doi = {10.1103/PhysRevLett.119.205002},
journal = {Physical Review Letters},
number = 20,
volume = 119,
place = {United States},
year = 2017,
month =
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on November 17, 2018
Publisher's Accepted Manuscript

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  • Asymmetry in density peaks on either side of an m = +1 half helical antenna is observed both in terms of peak position and its magnitude with respect to magnetic field variation in a linear helicon plasma device [Barada et al., Rev. Sci. Instrum. 83, 063501 (2012)]. The plasma is produced by powering the m = +1 half helical antenna with a 2.5 kW, 13.56 MHz radio frequency source. During low magnetic field (B < 100 G) operation, plasma density peaks are observed at critical magnetic fields on either side of the antenna. However, the density peaks occurred at differentmore » critical magnetic fields on both sides of antenna. Depending upon the direction of the magnetic field, in the m = +1 propagation side, the main density peak has been observed around 30 G of magnetic field. On this side, the density peak around 5 G corresponding to electron cyclotron resonance (ECR) is not very pronounced, whereas in the m = -1 propagation side, very pronounced ECR peak has been observed around 5 G. Another prominent density peak around 12 G has also been observed in m = -1 side. However, no peak has been observed around 30 G on this m = -1 side. This asymmetry in the results on both sides is explained on the basis of polarization reversal of left hand polarized waves to right hand polarized waves and vice versa in a bounded plasma system. The density peaking phenomena are likely to be caused by obliquely propagating helicon waves at the resonance cone boundary.« less
  • A large-area planar plasma source with a resonant cavity type launcher driven by a 915 MHz ultra-high frequency wave was developed. Theoretical analysis with the three-dimensional finite difference time-domain simulation was carried out to determine the optimized launcher structure by analyzing the resonant transverse magnetic mode in the resonant cavity. Numerical result expects that the resonant electric field distribution inside the cavity dominantly consists of the TM{sub 410} mode. The resonant cavity type launcher having 8 holes in an octagonal geometry was designed to fit the resonant transverse magnetic mode. Adjusting 8 hole positions of the launcher to the fieldmore » pattern of the resonant TM{sub 410} mode, we found that the plasma density increased about 40%∼50% from 1.0∼1.1 × 10{sup 11} cm{sup −3} to ∼1.5 × 10{sup 11} cm{sup −3} at the same incident power of 2.5 kW, compared with the previous results with the launcher having 6 holes in the hexagonal geometry. It is also noted that the electron density changes almost linearly with the incident wave power without any mode jumps.« less
  • Spatially resolved two-dimensional Langmuir-probe measurements of energy-resolved electron fluxes have been performed in an inductively coupled radio-frequency plasma. A flux pattern reminiscent of a ''convection cell'' in energy-configuration space has been observed. The measurements are interpreted in terms of a total-energy picture of the plasma electrons. (c) 2000 American Institute of Physics.
  • A wave detector, a newly designed magnetic probe, is installed in the large helical device (LHD). This wave detector is a 100-turn loop coil with electrostatic shield. Comparing a one-loop coil to this detector, this detector has roughly constant power coupling in the lower frequency range of 40 MHz, and it can easily detect magnetic wave in the frequency of a few megahertz. During high-harmonic fast wave heating, lower frequency waves (<10 MHz) were observed in the LHD for the first time, and for the power density threshold of lower frequency wave excitation (7.5 MHz) the power density of excitedmore » pumped wave (38.47 MHz) was approximately -46 dBm/Hz. These lower frequencies are kept constant for electron density and high energy particle distribution, and these lower frequency waves seem to be ion cyclotron waves caused by nonlinear wave-particle interaction, for example, parametric decay instability.« less
  • Asymmetry in the transverse wave number spectrum of the radiated power of a screenless fast wave antenna at an ion cyclotron range of frequencies is calculated with a model that takes into account the nonsymmetry of the plasma surface impedance matrix for an inhomogeneous tokamak plasma in front of the antenna. The directivity of the wave number spectrum transverse to the ambient magnetic field caused by the asymmetry in the surface impedance is found to be strongly asymmetric with respect to the parallel wave number by the effect of the nonperpendicular angle between the antenna current strap and the magneticmore » field. The latter is shown to be responsible also for the asymmetry in the parallel wave number spectrum of an undirected antenna, and can lead to deviations of order {le}30% in the corresponding spectrum of a phased antenna array with directivity. The consequences of the observed effects to the antenna performance in the current drive applications as well as in excitation of poloidally asymmetric spectra are discussed. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.« less