Feasibility of electron Bernstein wave coupling via O-X-B mode conversion in the RFX-mod reversed field pinch device

Bilato, R.; Volpe, F.; Köhn, A.; Paccagnella, R.; Farina, D.; Poli, E.; Brambilla, M.

doi:10.1088/0029-5515/49/7/075020

Cited by 17 publications

(16 citation statements)

References 29 publications

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“…The shape of B(r) profiles is nearly fixed through the relaxation process that generates the equilibrium [12], with magnitude proportional to the plasma current. Current driven instabilities lead to strong edge density fluctuations that can diminish coupling efficiency to the EBW using OXB conversion [13]. Multiple internal resonant modes lead to a stochastic magnetic field over much of the plasma minor radius.…”

Section: O I : P a C S N U M B E R Smentioning

confidence: 99%

Observation of Electron Bernstein Wave Heating in a Reversed Field Pinch

et al. 2017

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The first observation of rf heating in a reversed field pinch (RFP) using the electron Bernstein wave (EBW) is demonstrated on the Madison Symmetric Torus. Propagation across and heating in a stochastic magnetic field is observed. Novel techniques are required to measure the suprathermal electron tail generated by EBW heating in the presence of intense Ohmic heating. rf-heated electrons directly probe the edge transport properties in the RFP; measured loss rates imply a large noncollisional radial diffusivity.

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Section: O I : P a C S N U M B E R Smentioning

confidence: 99%

Observation of Electron Bernstein Wave Heating in a Reversed Field Pinch

et al. 2017

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“…Plasma density and background magnetic field profiles of arbitrary shape can be treated on a 2D grid. The code has been used previously to study the O-X-B mode conversion process in detail [7,8] and to investigate microwave heating scenarios [9] . The code allows for spatial variations of the background plasma parameters in two dimensions.…”

Section: The Full-wave Code Ipf-fdmcmentioning

confidence: 99%

Influence of density fluctuations on the O–X mode conversion and on microwave propagation

Köhn

Williams

Vann

et al. 2015

EPJ Web of Conferences

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Abstract. Full-wave simulations are performed in order to investigate the interaction of plasma density perturbations and microwaves. The perturbations are divided into two cases: A single blob-like structure and a fully turbulent density profile. The resulting scattering of a microwave beam and the effect on the O-X mode conversion are presented for both cases. Quantitative analyses are performed as a function of the average size and position of the perturbations. The usage of spatial coordinates normalized to the vacuum wavelength of the microwave allows to easily adopt the results to a specific problem.

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“…Since RFPs typically operate with overdense plasmas (ω pe /Ω ce ≫ 1, with ω pe = (e 2 n e /(ε 0 m e )) 1/2 the electron plasma angular frequency and Ω ce = e B/m e the electron cyclotron angular frequency), except for a thin layer at the edge, the efforts have been oriented to lower hybrid and electron Bernstein waves [1,2]. However, none of the usual rf schemes can access the plasma core of typical RFP plasmas, except for high plasma current discharges (I p > 1.5 MA) recently obtained in the RFX-mod device with an extended set of active control coils [3].…”

Section: -Introductionmentioning

confidence: 99%

“…According to the µ&p model (see Eq. (6) of [2] for a simplified version), for typical RFX-mod equilibria 2.2 < δ d < 2.6. Hereafter, we assume δ d = 2.3, which implies B 0[T] ≈ I p [MA] .…”

Section: -Introductionmentioning

confidence: 99%

Electron Cyclotron Heating in RFP plasmas

Bilato

Volpe²,

Poli

et al. 2009

AIP Conference Proceedings

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Abstract. Reversed field pinches (RFP) plasmas are typically overdense (ω pe > Ω ce ) and thus not suitable for conventional electron cyclotron (EC) heating and current drive. In recent high plasma current discharges (I p > 1.5 MA), however, the RFX-mod device was operated in underdense conditions (ω pe < Ω ce ) for the first time in an RFP. Thus, it is now possible to envisage heating the RFP plasma core by conventional EC at the 2nd harmonic, in the ordinary or extraordinary mode. We present a preliminary study of EC-heating feasibility in RFX-mod with the use of beamtracing and full-wave codes. Although not competitive -as a heating system -with multi-MW Ohmic heating in an RFP, EC might be useful for perturbative transport studies, even at moderate power (hundreds of kW), and, more generally, for applications requiring localized power deposition. Keywords -Introduction.There is an ongoing interest in using radio-frequency (rf) waves in RFPs in order to control the current density profile in the plasma periphery. Since RFPs typically operate with overdense plasmas (ω pe /Ω ce ≫ 1, with ω pe = (e 2 n e /(ε 0 m e )) 1/2 the electron plasma angular frequency and Ω ce = e B/m e the electron cyclotron angular frequency), except for a thin layer at the edge, the efforts have been oriented to lower hybrid and electron Bernstein waves [1,2]. However, none of the usual rf schemes can access the plasma core of typical RFP plasmas, except for high plasma current discharges (I p > 1.5 MA) recently obtained in the RFX-mod device with an extended set of active control coils [3].The confining magnetic field on axis scales with the plasma current [MA] , with a = 0.46 m the RFX-mod minor radius and δ d the RFP paramagnetic amplification factor. According to the µ&p model (see Eq.(6) of [2] for a simplified version), for typical RFX-mod equilibria 2.2 < δ d < 2.6. Hereafter, we assume δ d = 2.3, which implies B 0[T] ≈ I p [MA] . Consequently, the nth EC harmonic frequency on the plasma axis scales with I p like f [GHz] = 28 n I p [MA] . For I p > 1.5 MA the 2nd EC (i.e. n = 2) harmonic in the plasma core is above 80 GHz. At this range of frequencies, the wave accessibility constraint on the plasma density is not particularly severe. In fact, if we make use of the dimensionless density X = ω 2 pe /ω 2 and magnetic field Y = Ω ce /ω, where ω = 2π f is the angular frequency of the injected waves, the cutoffs of O-and X-mode are X = 1 and X = (1 − Y )(1 − N 2 ) = (n − 1)/n (1 − N 2 ), respectively, with N the parallel component of the refractive index. Hereafter we

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Feasibility of electron Bernstein wave coupling via O-X-B mode conversion in the RFX-mod reversed field pinch device

Cited by 17 publications

References 29 publications

Observation of Electron Bernstein Wave Heating in a Reversed Field Pinch

Observation of Electron Bernstein Wave Heating in a Reversed Field Pinch

Influence of density fluctuations on the O–X mode conversion and on microwave propagation

Electron Cyclotron Heating in RFP plasmas

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