Determination of the suprathermal electron distribution function during lower hybrid current drive in JET

Brusati, M.; Bartlett, D.V.; Froissard, P.; Airoldi, A.; Ramponi, G.; Silva, R.P. da; Peysson, Y.

doi:10.1088/0029-5515/34/1/i02

Cited by 39 publications

(49 citation statements)

References 16 publications

(2 reference statements)

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“…The upper limit of the of super thermals are set to 0.5 % because logically we are not expecting more than this value. Even in JET the maximum possible fraction is about 0.12 % (see reference [15]). So at present we do not expect super thermal electrons more than 0.5 % in ITER.The energy range of super thermals are initially bracketed in a range between 100 KeV and 250 KeV.…”

Section: Parametric Regimementioning

confidence: 99%

Computational studies on ECE spectrum for ITER, in the presence of a small fraction of non-thermals and radial resolution evolution for oblique view

Subhash

Ghai

Pandya

et al. 2015

EPJ Web of Conferences

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Abstract. In tokamaks, the temperature measurement using different techniques like Electron Cyclotron Emission (ECE), Thomson scattering etc. shows differences because of various phenomena. The physical reasons for this are not entirely understood. Thus to have comprehensive understanding of these difference, the contribution from each phenomenon needs to be individually understood. The phenomenon affecting radial temperature profile measurement includes harmonics overlap, relativistic down shifting, presence of non-thermals etc. For ITER like plasma, radial temperature profiles can be obtained from the first harmonics ordinary (O) mode or second harmonic extra-ordinary(X) mode of ECE spectrum. It is possible that, higher harmonics produced from the non-thermals can be relativistically downshifted to second harmonics and results a deviation in the measured temperature profile. We performed a parametric study on the e ffect of non-thermal electrons on measured ECE temperature for ITER scenario-2. All the numerical calculations reported in this paper are performed using NOTEC computer code which is capable of handling non-thermal populations. After proper validation of numerical methods using normal electron population (without non-thermals) a parametric study with non-thermals is performed. In the parametric study radial locations of non-thermals, energy of non-thermals and fraction of non-thermals are considered. This study is initially performed for normal view and later extended in to oblique views. The range of deviation of temperature over the examined parametric regime as well as the possible physical reasons will be presented. The effect of parallel component of non-thermal energy is also examined. Finally results of one set of study for oblique view (where the detector is not exactly normal to the magnetic field) with non-thermal electrons are also presented. In ITER apart from an Electron Cyclotron Emission (ECE) detector placed normal to magnetic field an oblique view detector is planned to grab information about non-thermal electrons. Usefulness of such an additional detector for a better radial resolution is examined. The differences in the ECE spectrum from a tokamak plasma between a direct LOS (normal to toroidal magnetic field) and a slightly oblique LOS have been modelled. A typical ITER tokamak scenario has been chosen in this study. The intensities of radiation, as observable from the low-field side, covering the first harmonic O-mode spectral frequencies 105-230 GHz have been compared. The physical reasons for the code-predicted results, regarding the differences between the direct and oblique spectra, are elucidated. Finally, signatures of the presence of non-thermals from a comparison of normal view and oblique view are also examined.

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Section: Parametric Regimementioning

confidence: 99%

Computational studies on ECE spectrum for ITER, in the presence of a small fraction of non-thermals and radial resolution evolution for oblique view

Subhash

Ghai

Pandya

et al. 2015

EPJ Web of Conferences

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“…Similarly an upper bound is also exist at upper cut-off frequency. For the case of emission perpendicular to the magnetic field frequency of emission is given by [5] …”

Section: Selection Of Parametric Regimementioning

confidence: 99%

“…It should be noted that amount of down shifting will be determined by relativistic parameter γ. Considering electron rest energy of 511 KeV the above equation can be re written to obtain the radius of emission as [5].…”

Section: -P3mentioning

confidence: 99%

Effects of Non-thermal Electrons from ECCD on ECE Temperature Measurements for ITER

Subhash

Pandya

Kumar

et al. 2012

EPJ Web of Conferences

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Abstract. In tokamaks, the radial temperature profile measured using Electron Cyclotron Emission (ECE) diagnostics are affected by many phenomena like harmonics overlap, relativistic down shifting, presence of non-thermals etc. In this paper we have estimated effects of a small non-thermal electron population on measured temperature profile for ITER-Scenario 2. For ITER like plasma, radial temperature profiles can be obtained from the second harmonic ECE spectrum. It is possible that, higher harmonics produced from the non-thermals can be relativistically downshifted to second harmonics and introduce error in the measured temperature profile. Generally Non-thermals are produced from Electron Cyclotron Resonance heating (ECRH), Electron Cyclotron Current Drive (ECCD) etc. In the present study the non-thermals are assumed to be produced from proposed ECCD, which is being considered for suppressing Neoclassical Tearing Modes (NTM). We have ignored any other source of non-thermals in the present study. All the numerical calculations reported in this paper is performed using NOTEC computer code which is capable of handling non-thermal populations. The locations and spatial extents of non-thermals are taken from previous report on optimization study of the ITER ECRH top launcher. The non-thermals are assumed to be centered around safety points q=1, q=1.5 and q=2, where the ECCD is expected to be used for suppressing the NTMs. The main results of the present study are summarized below. In the first part of the paper we present the results for temperature measurement with out non-thermal populations for the purpose of validation. Secondly the rage of higher harmonic frequencies (due to nonthermals) which possibly reach antenna and induce error in the temperature measurement are identified and the corresponding energies of non-thermal populations are calculated analytically. This calculations are further checked by simulations using NOTEC code. Finally non-thermal populations are seeded in the plasma with fraction and energies of non-thermals are varied in a parametric form. The parametric range of energies are initially bracketed by the analytical calculations explained above. The resultant temperature profiles and error in the measured temperatures will be presented.

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“…19 These early measurements were based on scintillator technology. Materials such as NaI, 6,12,14,15,20,21 CsI, 7,16 and BGO 22 were used in scintillators coupled to photomultipliers and image intensifiers 7,23 ͑see Fig. 3͒.…”

Section: Hard-x-ray Bremsstrahlungmentioning

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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Determination of the suprathermal electron distribution function during lower hybrid current drive in JET

Cited by 39 publications

References 16 publications

Computational studies on ECE spectrum for ITER, in the presence of a small fraction of non-thermals and radial resolution evolution for oblique view

Computational studies on ECE spectrum for ITER, in the presence of a small fraction of non-thermals and radial resolution evolution for oblique view

Effects of Non-thermal Electrons from ECCD on ECE Temperature Measurements for ITER

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

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