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Title: Temporal and spatial evolution of runaway electrons at the instability moments in Damavand tokamak

Abstract

The time and position behavior of runaway electrons at the Parail–Pogutse instability moments has been investigated using experimental observations in plasma current, loop voltage, the Hard X-ray (HXR) radiations, and 18 poloidal pickup coils signals received by data acquisition system simultaneously. The conditional average sampling (CAS) method was used to analyze the output data. Moreover, a filament current code was modified to study the runaway electrons beam movement in the event of instabilities. The results display a rapid drift of runaway beam toward the inner wall of the vacuum vessel and the collision with the wall components at the instability moments. The existence of the collisions in these experiments is evident in the HXR bursts which are considered as the main trigger for CAS Analysis. Also, the variation of HXR bursts with the toroidal magnetic field shows that the hard X-ray bursts drop with increase in the toroidal magnetic field and runaway electrons confinement quality.

Authors:
 [1];  [2]; ;  [3]
  1. Department of Nuclear Engineering, Faculty of Advance Sciences and Technologies, University of Isfahan, P.O. Box 81747-73441, Isfahan (Iran, Islamic Republic of)
  2. Department of Physics, Faculty of Science, University of Isfahan, P.O. Box 81747-73441, Isfahan (Iran, Islamic Republic of)
  3. Plasma Physics and Nuclear Fusion Research School, Nuclear Science and Technology Research Institute, AEOI, P.O. Box 14155-1339, Tehran (Iran, Islamic Republic of)
Publication Date:
OSTI Identifier:
22600072
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 23; Journal Issue: 7; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; COLLISIONS; DATA ACQUISITION; DATA ACQUISITION SYSTEMS; ELECTRIC CURRENTS; ELECTRIC POTENTIAL; ELECTRON BEAMS; FILAMENTS; HARD X RADIATION; MAGNETIC FIELDS; PLASMA; PLASMA INSTABILITY; RUNAWAY ELECTRONS; SIGNALS; TOKAMAK DEVICES; WALLS

Citation Formats

Pourshahab, B., Abdi, M. R., Sadighzadeh, A., and Rasouli, C.. Temporal and spatial evolution of runaway electrons at the instability moments in Damavand tokamak. United States: N. p., 2016. Web. doi:10.1063/1.4955218.
Pourshahab, B., Abdi, M. R., Sadighzadeh, A., & Rasouli, C.. Temporal and spatial evolution of runaway electrons at the instability moments in Damavand tokamak. United States. doi:10.1063/1.4955218.
Pourshahab, B., Abdi, M. R., Sadighzadeh, A., and Rasouli, C.. 2016. "Temporal and spatial evolution of runaway electrons at the instability moments in Damavand tokamak". United States. doi:10.1063/1.4955218.
@article{osti_22600072,
title = {Temporal and spatial evolution of runaway electrons at the instability moments in Damavand tokamak},
author = {Pourshahab, B. and Abdi, M. R. and Sadighzadeh, A. and Rasouli, C.},
abstractNote = {The time and position behavior of runaway electrons at the Parail–Pogutse instability moments has been investigated using experimental observations in plasma current, loop voltage, the Hard X-ray (HXR) radiations, and 18 poloidal pickup coils signals received by data acquisition system simultaneously. The conditional average sampling (CAS) method was used to analyze the output data. Moreover, a filament current code was modified to study the runaway electrons beam movement in the event of instabilities. The results display a rapid drift of runaway beam toward the inner wall of the vacuum vessel and the collision with the wall components at the instability moments. The existence of the collisions in these experiments is evident in the HXR bursts which are considered as the main trigger for CAS Analysis. Also, the variation of HXR bursts with the toroidal magnetic field shows that the hard X-ray bursts drop with increase in the toroidal magnetic field and runaway electrons confinement quality.},
doi = {10.1063/1.4955218},
journal = {Physics of Plasmas},
number = 7,
volume = 23,
place = {United States},
year = 2016,
month = 7
}
  • In this work several studies have been conducted on hard x-ray emissions of Damavand tokamak based on radiation dosimetry using the Thermoluminescence method. The goal was to understand interactions of runaway electrons with plasma particles, vessel wall, and plasma facing components. Total of 354 GR-200 (LiF:Mg,Cu,P) thermoluminescence dosimeter (TLD) crystals have been placed on 118 points – three TLDs per point – to map hard x-ray radiation doses on the exterior of the vacuum vessel. Results show two distinctive levels of x-ray radiations doses on the exterior of the vessel. The low-dose area on which measured dose is about 0.5more » mSv/shot. In the low-dose area there is no particular component inside the vessel. On the contrary, on high-dose area of the vessel, x-ray radiations dose exceeds 30 mSv/shot. The high-dose area coincides with the position of limiters, magnetic probe ducts, and vacuum vessel intersections. Among the high-dose areas, the highest level of dose is measured in the position of the limiter, which could be due to its direct contact with the plasma column and with runaway electrons. Direct collisions of runaway electrons with the vessel wall and plasma facing components make a major contribution for production of hard x-ray photons in Damavand tokamak.« less
  • Some experiments for studying the runaway electron (RE) effects have been performed using the poloidal magnetic probes system installed around the plasma column in the Damavand tokamak. In these experiments, the so-called runaway-dominated discharges were considered in which the main part of the plasma current is carried by REs. The induced magnetic effects on the poloidal pickup coils signals are observed simultaneously with the Parail–Pogutse instability moments for REs and hard X-ray bursts. The output signals of all diagnostic systems enter the data acquisition system with 2 Msample/(s channel) sampling rate. The temporal evolution of the diagnostic signals is analyzedmore » by the conditional average sampling (CAS) technique. The CASed profiles indicate RE collisions with the high-field-side plasma facing components at the instability moments. The investigation has been carried out for two discharge modes—low-toroidal-field (LTF) and high-toroidal-field (HTF) ones—related to both up and down limits of the toroidal magnetic field in the Damavand tokamak and their comparison has shown that the RE confinement is better in HTF discharges.« less
  • Set of experiments has been developed to study existing runaway electrons in ''Damavand'' tokamak plasma upon characteristics of hard x-ray emissions produced by collision of the runaway electrons with the plasma particles and limiters. As a first step, spatial distribution of hard x-ray emissions on the equatorial plane of the torus was considered. Obtained spectra of hard x-ray emissions for different alignments of shielded detector indicate isotropic emissivity in the equatorial plane. This is in agreement with wide angle cone of bremsstrahlung radiations, deduced from the mean value of energy of the runaway electrons. The mean energy was calculated frommore » the slope of the energy spectrum of hard x-ray photons. In the second stage in order to investigate time evolution of energy of the runaway electrons, similar technique were applied to obtain hard x-ray energy in every 3 ms intervals, from the beginning to the end of plasma. The mean energy of the runaway electrons increases during the ramp up phase and reaches its maximum between 3 and 9 ms after plasma formation. Also considering the time dependence of the counted photons in each energy range shows that energetic photons are emitted during the ramp up phase of the plasma current in Damavand tokamak.« less
  • Results are presented from investigations of the nonmonotonic spatial distributions of charge-exchange neutral fluxes and optical radiation from plasma in the DAMAVAND tokamak. It is shown that, during ohmic heating of the plasma, the regions with enhanced confinement of both the background plasma particles and heavy impurity ions arise near rational magnetic surfaces with q = 1 and 2. These regions are characterized by enhanced emission of accelerated charge-exchange neutrals and optical radiation from impurity ions.
  • The anisotropy of the distribution of runaway electrons in velocity space has been studied experimentally in the TM-3 tokamak during the instability of the runaway-electron beam (the ''fan'' instability). The anisotropy is estimated by comparing the experimental and calculated x-ray spectra (10 keV