Zhu, Hao, Dendy, R. O., Chapman, Sandra C. and Inagaki, S. (2015) A quantitative model for heat pulse propagation across Large Helical Device plasmas. Physics of plasmas, 22 (6). 062308 . doi:10.1063/1.4923307 ISSN 1070-664X.

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Abstract

It is known that rapid edge cooling of magnetically confined plasmas can trigger heat pulses that propagate rapidly inward. These can result in large excursion, either positive or negative, in the electron temperature at the core. A set of particularly detailed measurements was obtained in Large Helical Device(LHD) plasmas [S. Inagaki et al, Plasma Phys. Control. Fusion 52 (2010) 075002], which are considered here. By applying a travelling wave transformation, we extend the model of R. O. Dendy, S. C. Chapman and S. Inagaki, Plasma Phys. Control. Fusion 55 (2013) 115009, which successfully describes the local time-evolution of heat pulses in these plasmas, to include also spatial dependence. The new extended model comprises two coupled nonlinear first order differential equations for the (x, t) evolution of the deviation from steady state of two inde- pendent variables: the excess electron temperature gradient and the excess heat flux, both of which are measured in the LHD experiments. The mathematical structure of the model equations implies a formula for the pulse velocity, defined in terms of plasma quantities, which aligns with empirical expectations and is within a factor of two of the measured values. We thus model spatio-temporal pulse evolution, from first principles, in a way which yields as output the spatiotemporal evolution of the electron temperature, which is also measured in detail in the experiments. We compare the model results against LHD datasets using appropriate initial and boundary conditions. Sensitivity of this nonlinear model with respect to plasma parameters, initial conditions and boundary conditions is also investigated. We conclude that this model is able to match experimental data for the spatio-temporal evolution of the temperature profiles of these pulses, and their propagation velocities, across a broad radial range from r/a ~ 0.5 to the plasma core. The model further implies that the heat pulse may be related mathematically to soliton solutions of the Korteweg-de Vries-Burgers equation.

Item Type:	Journal Article
Alternative Title:
Subjects:	Q Science > QC Physics
Divisions:	Faculty of Science, Engineering and Medicine > Science > Physics
Library of Congress Subject Headings (LCSH):	Plasma waves, Heat pulses
Journal or Publication Title:	Physics of plasmas
Publisher:	American Institute of Physics
ISSN:	1070-664X
Official Date:	June 2015
Dates:	Date Event June 2015 Published 14 June 2015 Accepted 4 March 2015 Submitted
Volume:	22
Number:	6
Number of Pages:	7
Article Number:	062308
DOI:	10.1063/1.4923307
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Open Access (Creative Commons)
Copyright Holders:	AIP
Date of first compliant deposit:	29 December 2015
Date of first compliant Open Access:	29 December 2015
Funder:	Research Councils UK (RCUK), Horizon 2020 (European Commission) (H2020), Purazuma Kakuyūgō Gakkai‏ (JSPF), Kakuyūgō Kagaku Kenkyūjo‏ (NIFS)
Grant number:	EP/I501045 (RCUK), 633053 (H2020), 23244113 (JSPF), 21224014 (JSPF), 23360414 (JSPF), NIFS13KOCT001 (NIFS)

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