Measurement of suprathermal electrons in tokamaks via electron cyclotron transmission

Kirkwood, R. K.; Hutchinson, I. H.; Luckhardt, S.C.; Squire, Jared P.

doi:10.1088/0029-5515/30/3/005

Cited by 37 publications

(32 citation statements)

References 14 publications

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“…This technique was first implemented by Kirkwood. 23 Previous electron cyclotron absorption measurements have used X-mode waves on MIT's Versator II to determine the fraction of the parallel current drive carried by suprathermal electrons. 24,25 Since the electron plasma frequency f pe ¼ 9.0 GHz is greater than the electron cyclotron frequency jf ce j ¼ 5:0 GHz, the LAPD plasma is overdense f pe > jf ce j.…”

Section: A Overview Of the Wwadmentioning

confidence: 99%

Linear theory and measurements of electron oscillations in an inertial Alfvén wave

et al. 2017

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The physics of the aurora is one of the foremost unsolved problems of space physics. The mechanisms responsible for accelerating electrons that precipitate onto the ionosphere are not fully understood. For more than three decades, particle interactions with inertial Alfv en waves have been proposed as a possible means for accelerating electrons and generating auroras. Inertial Alfv en waves have an electric field aligned with the background magnetic field that is expected to cause electron oscillations as well as electron acceleration. Due to the limitations of spacecraft conjunction studies and other multi-spacecraft approaches, it is unlikely that it will ever be possible, through spacecraft observations alone, to confirm definitively these fundamental properties of the inertial Alfv en wave by making simultaneous measurements of both the perturbed electron distribution function and the Alfv en wave responsible for the perturbations. In this laboratory experiment, the suprathermal tails of the reduced electron distribution function parallel to the mean magnetic field are measured with high precision as inertial Alfv en waves simultaneously propagate through the plasma. The results of this experiment identify, for the first time, the oscillations of suprathermal electrons associated with an inertial Alfv en wave. Despite complications due to boundary conditions and the finite size of the experiment, a linear model is produced that replicates the measured response of the electron distribution function. These results verify one of the fundamental properties of the inertial Alfv en wave, and they are also a prerequisite for future attempts to measure the acceleration of electrons by inertial Alfv en waves. Published by AIP Publishing.

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Section: A Overview Of the Wwadmentioning

confidence: 99%

Linear theory and measurements of electron oscillations in an inertial Alfvén wave

et al. 2017

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“…Figure 1 also shows two whistler probes that are a part of the Whistler Wave Absorption Diagnostic (WWAD) [Thuecks et al, 2012]. This diagnostic measures the suprathermal (v z > v te ) portion of g e (v z ) and is based on a principle that was first implemented by Kirkwood et al [1990]. A whistler mode wave is transmitted between the two whistler probes (1 ′′ dipole antennas immersed in the plasma), and the attenuation of the received signal is used to determine the damping of the wave.…”

Section: 1002/2016gl068865mentioning

confidence: 99%

Direct measurement of electron sloshing of an inertial Alfvén wave

Schroeder

Skiff

Kletzing

et al. 2016

Geophysical Research Letters

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We report laboratory measurements of the parallel current carried by suprathermal electrons associated with inertial Alfvén wave excitation in the laboratory. The experiments presented here use a novel wave absorption diagnostic that measures the suprathermal tails of the electron distribution parallel to the mean magnetic field. The diagnostic is used to probe the electron distribution as an inertial Alfvén wave propagates along the mean magnetic field. These results identify, for the first time, the periodic motion of suprathermal electrons participating in the inertial Alfvén wave itself, in agreement with predictions from linear kinetic theory.

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“…98 With an appropriate choice of parameters, a nearly one-to-one correspondence between major radius ͑or frequency͒ and parallel velocity can be achieved, surrendering spatial resolution. 99 In particular, information on the average skewness of the parallel distribution can be obtained readily by comparing similar measurements with opposite k ʈ , in which all effects attributable to the bulk plasma, such as refraction and scattering, are equal. This type of setup, illustrated by Fig.…”

Section: F501-5mentioning

confidence: 99%

“…7, is naturally attractive for the investigation of LHCD plasmas, and most of the implementations have accordingly been in conjunction with LHCD experiments. [99][100][101][102][103][104][105][106] A variant of this approach consists of launching the waves from the LFS in an oblique, approximately horizontal direction, and measuring the power reflected back from a cutoff layer. The relative attenuation is then attributed to ECA by resonant electrons situated on the LFS of the cutoff, which for appropriate choices of parameters can be selected to be suprathermal within a particular range of velocities.…”

Section: F501-5mentioning

confidence: 99%

Diagnostic techniques for measuring suprathermal electron dynamics in plasmas (invited)

Coda

2008

Review of Scientific Instruments

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Plasmas, both in the laboratory and in space, are often not in thermodynamic equilibrium, and the plasma electron distribution function is accordingly non-Maxwellian. Suprathermal electron tails can be generated by external drives, such as rf waves and electric fields, or internal ones, such as instabilities and magnetic reconnection. The variety and importance of the phenomena in which suprathermal electrons play a significant role explains an enduring interest in diagnostic techniques to investigate their properties and dynamics. X-ray bremsstrahlung emission has been studied in hot magnetized plasmas for well over two decades, flanked progressively by electron-cyclotron emission in geometries favoring the high-energy end of the distribution function ͑high-field-side, vertical, oblique emission͒, by electron-cyclotron absorption, by spectroscopic techniques, and at lower temperatures, by Langmuir probes and electrostatic analyzers. Continuous progress in detector technology and in measurement and analysis techniques, increasingly sophisticated layouts ͑multichannel and tomographic systems, imaging geometries͒, and highly controlled suprathermal generation methods ͑e.g., perturbative rf modulation͒ have all been brought to bear in recent years on an increasingly detailed, although far from complete, understanding of suprathermal electron dynamics.

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Measurement of suprathermal electrons in tokamaks via electron cyclotron transmission

Cited by 37 publications

References 14 publications

Linear theory and measurements of electron oscillations in an inertial Alfvén wave

Linear theory and measurements of electron oscillations in an inertial Alfvén wave

Direct measurement of electron sloshing of an inertial Alfvén wave

Diagnostic techniques for measuring suprathermal electron dynamics in plasmas (invited)

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