Ultrahigh-frequency Methods of Plasma Heating

Golant, V.E.

doi:10.1070/pu1972v014n04abeh004749

Cited by 64 publications

(94 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…(4)], des Diffusions-und Anregungskoeffizienten. Die theoretischen Rechnungen [9][10][11][12][13][14][15][16][17][18][19] füllen diese Lücke nur unbefriedigend aus. Eine detaillierte Berechnung ist nur in einem kleinen Feldstärkebereich für Helium und Neon durchgeführt worden 16 .…”

Section: Introductionunclassified

Elektronentransport in nichtthermischen Edelgasplasmen

Lehrke¹,

Müller²

1976

Zeitschrift Für Naturforschung A

View full text Add to dashboard Cite

Transport of Electrons in Non-Thermal Noble Gas PlasmaFor the transport of electrons in a non-thermal, weakly ionized plasma an analytical model and a detailed numerical calculation is presented. The following transport coefficients: mean energy, characteristic energy, mobility, diffusion coefficient, excitation and ionization coefficient for He, Ne, Ar, Kr, Xe are calculated in the region of reduced electric field 0.01 V/cm Torr < Elp < 100 V/cm Torr. The parameters of the model are developed using the existing experimental and our numerical data. With increasing £/p the dominant energy loss of the electrons changes from elastic to inelastic collisions and here from constant to increasing effective excitation energy. Three model regions of Elp result, in which the transport coefficients can be described as a power of £/p. The data presented here provide a starting point for further investigations of similarity rules and models of nonthermal plasmas.

show abstract

Section: Introductionunclassified

Elektronentransport in nichtthermischen Edelgasplasmen

Lehrke¹,

Müller²

1976

Zeitschrift Für Naturforschung A

View full text Add to dashboard Cite

show abstract

“…However, an anomalous loss of current drive efficiency has nevertheless been observed in a number of tokamaks even though 0 / (0) > 2 and the accessibility condition [7] was well satisfied [8,9]. For example, an efficient current drive regime [10][11][12] on Alcator C-Mod (R0 ≈ 67 cm, a ≈ 22 cm) [13] is found to exist only below the line-averaged density ( ̅ ) of ≈ 1 × 10 20 −3 [14][15][16], for which 0 / (0) = 3 and the accessibility condition assures core LH penetration up to ̅ ≈ 1.5 × 10 20 −3 for the typical launched parallel refractive index, || = 2, and BT =5.4 T. Here, || = || / 0 is the ratio of the speed of light to the parallel phase velocity of the wave.…”

Section: Introductionmentioning

confidence: 99%

High density LHRF experiments in Alcator C-Mod and implications for reactor scale devices

et al. 2015

View full text Add to dashboard Cite

Abstract. Parametric Decay Instabilities (PDI) appear to be an ubiquitous feature of Lower Hybrid Current Drive (LHCD) experiments at high density. In density ramp experiments in Alcator C-Mod and other machines the onset of PDI activity has been well correlated with a decrease in current drive efficiency and production of fast electron Bremsstrahlung. However whether PDI is the primary cause of the "density limit", and if so by exactly what mechanism (beyond the obvious one of pump depletion) has not been clearly established. In order to further understand the connection, the frequency spectrum of PDI activity occurring during Alcator C-Mod LHCD experiments has been explored in detail by means of a number of RF probes distributed around the periphery of the C-Mod tokamak including a probe imbedded in the inner wall. The results show that i) the excited spectra consists mainly of a few discrete ion cyclotron quasi-modes, which have higher growth than the ion sound branch; ii) PDI activity can begin either at the inner or outer wall, depending on magnetic configuration; iii) the frequencies of the IC quasi-modes correspond to the magnetic field strength close to the LFS or HFS separatrix; and iv) although PDI activity may initiate near the inner separatrix, the loss in fast electron Bremsstrahlung is best correlated with the appearance of IC quasimodes characteristic of the magnetic field strength near the LFS separatrix. These data, supported by growth rate calculations, point to the importance of the LFS SOL density in determining PDI onset and degradation in current drive efficiency. By minimizing the SOL density it is possible to extend the core density regime over which PDI can be avoided, thus potentially maximizing the effectiveness of LHCD at high density. Increased current drive efficiency at high density has been achieved in FTU and EAST through lithium coating and special fueling methods, and in recent C-Mod experiments by operating at higher plasma current. Another approach would be to locate the launcher in the inner wall with double null operation. This would reduce the SOL density by an order of magnitude or more and greatly mitigate the effects of PDI as well as other parasitic losses.

show abstract

“…Additionally, there are some restrictions on the wave for accessibility to a given plasma density. These restrictions have been discussed by Golant 33 and StixM and studied experimentally by Motley et al 35 Kinetic theory 38 yields a complex dispersion relation with a temporal damping rate for the waves given by y ::::v + 11'l' 2 wa 3 exp(-a The first contribution to (3) is v, which represents the collisional damping, e.g., electron-ion and electron-neutral collisions, while the second term is the Landau damping contribution. For a wave launched at a given location, this damping can also be viewed as a damping of each ku component of the wave in space as it propagates away from the antenna.…”

Section: Theory a Wave Propagationmentioning

confidence: 99%