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Title: Supersonic molecular beam injection effects on tokamak plasma applied non-axisymmetric magnetic perturbation

Abstract

The change of tokamak plasma behavior by supersonic molecular beam injection (SMBI) was investigated by applying a three-dimensional magnetic perturbation that could suppress edge localized modes (ELMs). From the time trace of decreasing electron temperature and with increasing plasma density keeping the total confined energy constant, the SMBI seems to act as a cold pulse on the plasma. However, the ELM behaviors were changed drastically (i.e., the symptom of ELM suppression has disappeared). The plasma collisionality in the edge-pedestal region could play a role in the change of the ELM behaviors.

Authors:
; ; ; ; ; ;  [1];  [2]
  1. National Fusion Research Institute, Daejeon 34133 (Korea, Republic of)
  2. Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141 (Korea, Republic of)
Publication Date:
OSTI Identifier:
22599893
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 23; Journal Issue: 8; 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; AXIAL SYMMETRY; BEAM INJECTION; DISTURBANCES; EDGE LOCALIZED MODES; ELECTRON TEMPERATURE; MOLECULAR BEAMS; PERTURBATION THEORY; PLASMA DENSITY; PULSES; THREE-DIMENSIONAL CALCULATIONS; TOKAMAK DEVICES

Citation Formats

Han, Hyunsun, E-mail: hyunsun@nfri.re.kr, In, Y., Jeon, Y. M., Hahn, S. H., Lee, K. D., Nam, Y. U., Yoon, S. W., and Lee, H. Y. Supersonic molecular beam injection effects on tokamak plasma applied non-axisymmetric magnetic perturbation. United States: N. p., 2016. Web. doi:10.1063/1.4961433.
Han, Hyunsun, E-mail: hyunsun@nfri.re.kr, In, Y., Jeon, Y. M., Hahn, S. H., Lee, K. D., Nam, Y. U., Yoon, S. W., & Lee, H. Y. Supersonic molecular beam injection effects on tokamak plasma applied non-axisymmetric magnetic perturbation. United States. doi:10.1063/1.4961433.
Han, Hyunsun, E-mail: hyunsun@nfri.re.kr, In, Y., Jeon, Y. M., Hahn, S. H., Lee, K. D., Nam, Y. U., Yoon, S. W., and Lee, H. Y. 2016. "Supersonic molecular beam injection effects on tokamak plasma applied non-axisymmetric magnetic perturbation". United States. doi:10.1063/1.4961433.
@article{osti_22599893,
title = {Supersonic molecular beam injection effects on tokamak plasma applied non-axisymmetric magnetic perturbation},
author = {Han, Hyunsun, E-mail: hyunsun@nfri.re.kr and In, Y. and Jeon, Y. M. and Hahn, S. H. and Lee, K. D. and Nam, Y. U. and Yoon, S. W. and Lee, H. Y.},
abstractNote = {The change of tokamak plasma behavior by supersonic molecular beam injection (SMBI) was investigated by applying a three-dimensional magnetic perturbation that could suppress edge localized modes (ELMs). From the time trace of decreasing electron temperature and with increasing plasma density keeping the total confined energy constant, the SMBI seems to act as a cold pulse on the plasma. However, the ELM behaviors were changed drastically (i.e., the symptom of ELM suppression has disappeared). The plasma collisionality in the edge-pedestal region could play a role in the change of the ELM behaviors.},
doi = {10.1063/1.4961433},
journal = {Physics of Plasmas},
number = 8,
volume = 23,
place = {United States},
year = 2016,
month = 8
}
  • Plasma fueling with high efficiency and deep injection is very important to enable fusion power performance requirements. It is a powerful and efficient way to study neutral transport dynamics and find methods of improving the fueling performance by doing large scale simulations. Furthermore, two basic fueling methods, gas puffing (GP) and supersonic molecular beam injection (SMBI), are simulated and compared in realistic divertor geometry of the HL-2A tokamak with a newly developed module, named trans-neut, within the framework of BOUT++ boundary plasma turbulence code [Z. H. Wang et al., Nucl. Fusion 54, 043019 (2014)]. The physical model includes plasma density,more » heat and momentum transport equations along with neutral density, and momentum transport equations. In transport dynamics and profile evolutions of both plasma and neutrals are simulated and compared between GP and SMBI in both poloidal and radial directions, which are quite different from one and the other. It finds that the neutrals can penetrate about four centimeters inside the last closed (magnetic) flux surface during SMBI, while they are all deposited outside of the LCF during GP. Moreover, it is the radial convection and larger inflowing flux which lead to the deeper penetration depth of SMBI and higher fueling efficiency compared to GP.« less
  • As a new fueling method, supersonic molecular beam injection (SMBI) has been successfully developed and used in the HL-1M tokamak and HT-7 superconducting tokamak. SMBI can enhance penetration depth and fueling efficiency. It can be considered a significant improvement over conventional gas puffing. In recent experiments, hydrogen clusters have been found in the beam produced by high working gas pressure. The hydrogen particles of the beam have penetrated into the plasma center region, in which the average velocity of the injected beam is >1200 m/s. The rate of increase of electron density for SMBI, d[bar]n{sub e}/dt, approaches that of smallmore » ice pellet injection (PI). The plasma density increases step by step after multipulse SMBI, just as with the effects of multipellet fueling. Comparison of fueling effects was made between SMBI and small ice PI in the same shot of ohmic discharge in HL-1M.« less
  • In the present paper, it is reported that a large production of runaway electrons has been observed during the flattop phase of electron cyclotron resonance heating (ECRH) discharges and in the presence of supersonic molecular beam injection (SMBI) in the HuanLiuqi-2A (commonly referred to as HL-2A) [Q. W. Yang, Nucl. Fusion 47, S635 (2007)] tokamak. For the set of discharges carried out in the present experiment, the ranges of ECRH power and plasma electron density are 0.8-1.0 MW and (3.0-4.0)x10{sup 19} m{sup -3}, respectively. A large number of superthermal electrons are produced through the avalanche effect [A. Lazaros, Phys. Plasmasmore » 8, 1263 (2001)] during ECRH. The loop voltage increase due to SMBI gives rise to a decline in the critical runaway energy, which leads to that many superthermal electrons could be converted into runaway region. Therefore, this phenomenon may come from the synergetic effects of ECRH and SMBI. That is, the superthermal electrons created by ECRH are accelerated into runaway regime via the Dreicer process which is triggered by SMBI. The experimental results are in well agreement with the calculational ones based on the superthermal electron avalanche effect and the Dreicer runaway theory.« less
  • A method of the particle transport study using supersonic molecular beam injection (SMBI) and microwave reflectometry is reported in this paper. Experimental results confirm that pulsed SMBI is a good perturbation source with deeper penetration and better localization than the standard gas puffing. The local density modulation is induced using the pulsed SMBI and the perturbation density is measured by the microwave reflectometry. Using Fourier transform analysis for the local density perturbation, radial profiles of the amplitude and phase of the density modulation can be obtained. The experimental results in HL-2A show that the particle injected by SMBI is locatedmore » at about r/a=0.65-0.75. The position of the main particle source can be determined through three aspects: the minimum of the phase of the first harmonic of the Fourier transform of the modulated density measured by microwave reflectometry; the H{sub a} intensity profile and the local density increase ratio. The maximum of the amplitude of the first harmonic shifts often inward relative to the particle source location, which indicates clearly there is an inward particle pinch in this area. Good agreement has been found between the experimental results and the simulation using analytical transport model. The particle diffusivity D and the particle convection velocity V have been obtained by doing this simulation. The sensitivity in the transport coefficients of the amplitude and the phase of the density modulation has been discussed.« less
  • Plasma fueling with high efficiency and deep injection is very important to enable fusion power performance requirements. It is a powerful and efficient way to study neutral transport dynamics and find methods of improving the fueling performance by doing large scale simulations. Two basic fueling methods, gas puffing (GP) and supersonic molecular beam injection (SMBI), are simulated and compared in realistic divertor geometry of the HL-2A tokamak with a newly developed module, named trans-neut, within the framework of BOUT++ boundary plasma turbulence code [Z. H. Wang et al., Nucl. Fusion 54, 043019 (2014)]. The physical model includes plasma density, heatmore » and momentum transport equations along with neutral density, and momentum transport equations. Transport dynamics and profile evolutions of both plasma and neutrals are simulated and compared between GP and SMBI in both poloidal and radial directions, which are quite different from one and the other. It finds that the neutrals can penetrate about four centimeters inside the last closed (magnetic) flux surface during SMBI, while they are all deposited outside of the LCF during GP. It is the radial convection and larger inflowing flux which lead to the deeper penetration depth of SMBI and higher fueling efficiency compared to GP.« less