Runaway losses in current ramp-up with lower hybrid waves

Jukka Heikkinen, Timo Pättikangas, Seppo Karttunen, Seppo Sipilä

Research output: Contribution to journalArticleScientificpeer-review

1 Citation (Scopus)

Abstract

The effects of fast electron confinement and plasma temperature on the lower hybrid current ramp-up efficiency are investigated. The production of reverse runaways in a toroidal geometry is calculated with a Monte Carlo particle following code, which includes collisions and both neoclassical and relativistic effects. When anomalous fast electron diffusion in the configuration space is taken into account, the ramp-up efficiency is found to be enhanced for increasing loss rate of runaway electrons. The enhancement is in accordance with a simple analytical model that expresses the efficiency as a function of the average runaway electron confinement time and the runaway fraction of current carrying electrons. A larger runaway production rate is found for the electrons orbiting on outer magnetic surfaces, because their trapping region in velocity space is wider. The runaway rate is also significantly enhanced, as the thermal velocity is increased up to and above one sixth of the runaway velocity vR. The range of the phase velocity spectrum where the waves efficiently ramp up the current in large tokamaks is limited by these effects to velocities below 1.3vR
Original languageEnglish
Pages (from-to)887 - 894
Number of pages8
JournalNuclear Fusion
Volume33
Issue number6
DOIs
Publication statusPublished - 1993
MoE publication typeA1 Journal article-refereed

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ramps
electron diffusion
electrons
plasma temperature
relativistic effects
phase velocity
trapping
collisions
augmentation
geometry
configurations
temperature

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Heikkinen, Jukka ; Pättikangas, Timo ; Karttunen, Seppo ; Sipilä, Seppo. / Runaway losses in current ramp-up with lower hybrid waves. In: Nuclear Fusion. 1993 ; Vol. 33, No. 6. pp. 887 - 894.
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abstract = "The effects of fast electron confinement and plasma temperature on the lower hybrid current ramp-up efficiency are investigated. The production of reverse runaways in a toroidal geometry is calculated with a Monte Carlo particle following code, which includes collisions and both neoclassical and relativistic effects. When anomalous fast electron diffusion in the configuration space is taken into account, the ramp-up efficiency is found to be enhanced for increasing loss rate of runaway electrons. The enhancement is in accordance with a simple analytical model that expresses the efficiency as a function of the average runaway electron confinement time and the runaway fraction of current carrying electrons. A larger runaway production rate is found for the electrons orbiting on outer magnetic surfaces, because their trapping region in velocity space is wider. The runaway rate is also significantly enhanced, as the thermal velocity is increased up to and above one sixth of the runaway velocity vR. The range of the phase velocity spectrum where the waves efficiently ramp up the current in large tokamaks is limited by these effects to velocities below 1.3vR",
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Runaway losses in current ramp-up with lower hybrid waves. / Heikkinen, Jukka; Pättikangas, Timo; Karttunen, Seppo; Sipilä, Seppo.

In: Nuclear Fusion, Vol. 33, No. 6, 1993, p. 887 - 894.

Research output: Contribution to journalArticleScientificpeer-review

TY - JOUR

T1 - Runaway losses in current ramp-up with lower hybrid waves

AU - Heikkinen, Jukka

AU - Pättikangas, Timo

AU - Karttunen, Seppo

AU - Sipilä, Seppo

N1 - Project code: YDI0030

PY - 1993

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N2 - The effects of fast electron confinement and plasma temperature on the lower hybrid current ramp-up efficiency are investigated. The production of reverse runaways in a toroidal geometry is calculated with a Monte Carlo particle following code, which includes collisions and both neoclassical and relativistic effects. When anomalous fast electron diffusion in the configuration space is taken into account, the ramp-up efficiency is found to be enhanced for increasing loss rate of runaway electrons. The enhancement is in accordance with a simple analytical model that expresses the efficiency as a function of the average runaway electron confinement time and the runaway fraction of current carrying electrons. A larger runaway production rate is found for the electrons orbiting on outer magnetic surfaces, because their trapping region in velocity space is wider. The runaway rate is also significantly enhanced, as the thermal velocity is increased up to and above one sixth of the runaway velocity vR. The range of the phase velocity spectrum where the waves efficiently ramp up the current in large tokamaks is limited by these effects to velocities below 1.3vR

AB - The effects of fast electron confinement and plasma temperature on the lower hybrid current ramp-up efficiency are investigated. The production of reverse runaways in a toroidal geometry is calculated with a Monte Carlo particle following code, which includes collisions and both neoclassical and relativistic effects. When anomalous fast electron diffusion in the configuration space is taken into account, the ramp-up efficiency is found to be enhanced for increasing loss rate of runaway electrons. The enhancement is in accordance with a simple analytical model that expresses the efficiency as a function of the average runaway electron confinement time and the runaway fraction of current carrying electrons. A larger runaway production rate is found for the electrons orbiting on outer magnetic surfaces, because their trapping region in velocity space is wider. The runaway rate is also significantly enhanced, as the thermal velocity is increased up to and above one sixth of the runaway velocity vR. The range of the phase velocity spectrum where the waves efficiently ramp up the current in large tokamaks is limited by these effects to velocities below 1.3vR

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