Extraordinary mode absorption at the electron cyclotron harmonic frequencies as a tokamak electron temperature diagnostic

Pachtman, A.; Wolfe, S.; Hutchinson, I. H.

doi:10.1088/0029-5515/27/8/009

Cited by 14 publications

(9 citation statements)

References 21 publications

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“…Calculations of the theoretical absorption with the ray tracing code TORAY-GA, assuming an isotropic, Maxwellian velocity distribution, are in fair agreement with the experimental results corresponding to ECH (φ = 0 • ) preheating. This observation is also in agreement with X3 absorption measurements made by Pachtman et al [26]. However, the measured X3 absorption exceeds that predicted by TORAY-GA by a factor of up to 2 for the CNT-and CO-ECCD cases.…”

supporting

confidence: 92%

Full absorption of third harmonic ECH in TCV tokamak plasmas in the presence of second harmonic ECCD

et al. 2002

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An experimental study of the extraordinary mode (X mode) absorption at the third electron cyclotron harmonic frequency has been performed on the TCV tokamak in plasmas preheated by X mode at the second harmonic. Full single pass absorption of injected X3 power was measured with X2 preheating in co-current drive (CO-ECCD). The measured absorption exceeds that predicted by the linear ray tracing code TORAY-GA by more than a factor of 2 for the CO-ECCD case. Experimental evidence indicates that a large fraction of the X3 power is absorbed by electrons in an energetic tail created by the X2 ECCD preheating.

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supporting

confidence: 92%

Full absorption of third harmonic ECH in TCV tokamak plasmas in the presence of second harmonic ECCD

et al. 2002

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“…Calculations of the theoretical absorption with the TORAY ray tracing code [5], which makes the assumption of an isotropic Maxwellian velocity distribution, are in fair agreement with the experimental results corresponding to ECH preheating. This observation is also in agreement with X3 absorption measurements made by Pachtman et al [21]. However, the measured X3 absorption exceeds that predicted by TORAY by a factor of up to 3 for the CNTR-and CO-ECCD cases.…”

Section: Full Absorption Of Ech Power At the Third Electron Cyclotron...supporting

confidence: 92%

Overview of TCV results

et al. 2001

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The TCV tokamak (R = 0.88 m, a < 0.25 m, BT < 1.54 T) is equipped with six 0.5 MW gyrotron sources operating at 82.7 GHz for second harmonic X mode ECH. By distributing the ECCD current sources over the discharge cross section, fully driven stationary plasmas with Ip = 210 kA, ne0 = 2 × 10 19 m −3 , Te0 ≈ 4 keV, were obtained for the full discharge duration of 2 s. Highly peaked electron temperature profiles with Te0 up to 12 keV were obtained in central counter-current drive scenarios with off-axis ECH. Absorption measurements using a 118 GHz gyrotron have demonstrated the importance of suprathermal electrons for third harmonic absorption. A coupled heat-particle transport phenomenon known as 'density pumpout', which leads to the expulsion of particles from the plasma core, has been linked to the presence of m = 1 modes, suggesting that it is due to the existence of locally trapped particles associated with the loss of axisymmetry. Highly elongated discharges have been developed with ohmic heating (κ < 2.8) and off-axis ECH. The latter exhibit considerably improved vertical stability due to current profile broadening. A 'gateway' for ELMy H modes has been discovered, which allows stationary ohmic ELMy H mode operation over a wide range of elongation, triangularity and density. Divertor detachment experiments suggest the existence of recombination pathways other than three body or radiative processes.

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“…Good agreement with theory has also been obtained in these experiments, under different injection geometries (see, e.g., Ref. [9] for the case where the diagnostic beam is injected in the horizontal plane and Ref. [10] for the case of vertical propagation, along B const, in tokamak geometry; the influence of the different launching scenarios on absorption will be briefly addressed in Section 2.2).…”

Section: Experimental Databasesupporting

confidence: 64%

High harmonic electron cyclotron resonance heating in the Large Helical Device

et al. 1998

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During the initial experimental phase, LHD, a stellarator of the heliotron/torsatron variety presently under construction, will operate at a magnetic field lower than the nominal one. In this scenario, the frequency of the available gyrotrons (chosen in view of second harmonic heating at full field operation) will be resonant with the third or the fourth harmonic of the electron gyrofrequency. The aim of this article is to analyse the electron cyclotron resonance heating (ECRH) at these high harmonics. By using linear absorption theory, together with transport predictions, good absorption is found over a wide density range for third harmonic heating. In the case of the fourth harmonic, the conditions for absorption are considerably more critical, but non-negligible heating (single pass absorption ≳ 10%) is expected in very low density, high temperature target plasmas. Owing to the strong temperature dependence of the absorption mechanism, heating at higher harmonics presents some peculiar characteristics. Quasi-linear effects are found to improve the absorption properties (as compared with those of linear theory), and bifurcation phenomena, as well as a critical power threshold, might appear. The physical origin and the consequences of these effects are discussed.

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Extraordinary mode absorption at the electron cyclotron harmonic frequencies as a tokamak electron temperature diagnostic

Cited by 14 publications

References 21 publications

Full absorption of third harmonic ECH in TCV tokamak plasmas in the presence of second harmonic ECCD

Full absorption of third harmonic ECH in TCV tokamak plasmas in the presence of second harmonic ECCD

Overview of TCV results

High harmonic electron cyclotron resonance heating in the Large Helical Device

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