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22-27 October 2018
Mahatma Mandir Conference Centre
Asia/Kolkata timezone
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A nonlinear 2-fluid study of the effect of pellet injection on ELM dynamics

26 Oct 2018, 09:50
20m
Mahatma Mandir Conference Centre

Mahatma Mandir Conference Centre

Gandhinagar (nearest Airport: Ahmedabad), India
Oral THS - Magnetic Confinement Theory and Modelling: Stability EX/7-TH/5 Active ELM Control

Speaker

Dr Debasis Chandra (Institute For Plasma Research, INDIA)

Description

We report on nonlinear simulation studies of the dynamical behavior of ELMs under the influence of repetitive injection of pellets using the nonlinear 2-fluid code CUTIE. ELMs are excited by introducing a particle source in the confinement region and a particle sink in the edge region. High density pellets are injected repeatedly near the edge with different duty cycles, where a duty cycle refers to the ratio of `on’ time and `off’ time of localized density perturbations. A combination of various duty cycles and different densities of the pellets have been used and comparative studies of the time series in edge density and temperature perturbations both in the absence and presence of pellets have been made. We find that the pellets significantly influence both the frequency and amplitude of the ELMs and the results are sensitive to the duty cycle and the density of the pellets. For pellets with density that are twice the normal edge density and injected with a duty cycle of 1:2, the ELMs are generated on an average at a faster rate (~twice the rate of normal ELMs) and with reduced amplitudes (~50% of the average height of ELMs without pellets). These changes lead to significant improvements in the plasma beta indicative of an improvement in the energy confinement due to pellet injection. Furthermore, advanced spectral analysis of the data shows that in the presence of pellets there is an inward shift in the radial location of the ELMs and a spectral shift of the mode energy towards longer wavelengths. The shifts in the fluctuation spectrum with pellets are opposite to those of earlier RMP results in that pellets induce an inverse cascade while RMPs lead to a direct cascade of the energy. Both mechanisms however lead to an overall improvement in the plasma beta.
Country or International Organization India
Paper Number TH/5-1

Primary author

Dr Debasis Chandra (Institute For Plasma Research, INDIA)

Co-authors

Prof. Abhijit Sen (Institute for Plasma Research) Dr Anantanarayanan Thyagaraja (Astrophysics Group, University of Bristol, Bristol, BS8 1TL, UK)

Presentation Materials

Paper