Particle source impact on fusion plasma density profile in JET experiments

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http://urn.fi/URN:NBN:fi:hulib-202104071828
Title: Particle source impact on fusion plasma density profile in JET experiments
Author: Kirjasuo, Anu
Other contributor: Helsingin yliopisto, Matemaattis-luonnontieteellinen tiedekunta
University of Helsinki, Faculty of Science
Helsingfors universitet, Matematisk-naturvetenskapliga fakulteten
Publisher: Helsingin yliopisto
Date: 2021
Language: eng
URI: http://urn.fi/URN:NBN:fi:hulib-202104071828
http://hdl.handle.net/10138/328798
Thesis level: master's thesis
Degree program: Materiaalitutkimuksen maisteriohjelma
Master's Programme in Materials Research
Magisterprogrammet i materialforskning
Specialisation: Kokeellinen materiaalifysiikka
Experimental Material Physics
Experimentell materialfysik
Abstract: Despite a vast body of knowledge that has already been accumulated on particle transport at both theoretical and experimental level, a simple method for estimating particle source impact on plasma density profile peaking has been lacking. Fable et al. presented a parameter for calculating the source strength (Sstr, the S parameter) in [1]. The parameter is derived from particle flux continuity equation, and after approximations takes as input parameters only the information on neutral beam injection (NBI) power, beam ions injection energy, effective core heat transport diffusivity and plasma density, radius, and volume together with a fitted coefficient from an ASDEX Upgrade experiment. The formula was applied to a database of 165 pulses in both high and low confinement mode, mostly with neutral beam heating, in JET, Joint European Torus, fusion experiment. The results appear reasonable considering the fitted parameter and the approximations in the formula. In addition to the S parameter values, also normalised density gradient dependence on neutral beam heating power and collisionality were investigated, to compare the results with those obtained at ASDEX Upgrade in [1]. Detailed studies of six gas puff modulation shots [2, 3, 4] at JET are used as reference. In [2] the source contribution for the H-mode shots was 50-60% and low confinement mode shots 10-20%. This is further validated in [3] and the high confinement mode shots are compared to similar shots DIII-D fusion experiment in [4], where the source impact on density peaking was negligible. Observed differences are attributed to different dominant turbulent environments. The average calculated level of S parameter values suggest mostly non-negligible source contribution to density peaking, and the values differ for high and low confinement mode plasmas, in line with [2, 3, 4]. However, the results imply that the coefficient 2000 is not constant across the database, and while a scalar correction to fit the coefficient to JET may be possible for low confinement mode plasmas, the high confinement mode plasmas require further research.
Subject: fusion
fusion energy
tokamak
neutral beam heating
plasma density peaking
particle transport


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