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Theoretical physicists working at a blackboard collaboration pod in the Beecroft building.
Credit: Jack Hobhouse

Prof Michael Barnes

Professor in Theoretical Physics

Sub department

  • Rudolf Peierls Centre for Theoretical Physics

Research groups

  • Theoretical astrophysics and plasma physics at RPC
michael.barnes@physics.ox.ac.uk
Telephone: 01865 (2)73960
Rudolf Peierls Centre for Theoretical Physics, room 50.10
  • About
  • Publications

Phase-space entropy cascade and irreversibility of stochastic heating in nearly collisionless plasma turbulence

(2023)

Authors:

Michael L Nastac, Robert J Ewart, Wrick Sengupta, Alexander A Schekochihin, Michael Barnes, William D Dorland
More details from the publisher
Details from ArXiV

Prevention of core particle depletion in stellarators by turbulence

Physical Review Research American Physical Society 5:2 (2023) L022053

Authors:

H Thienpondt, Jm García-Regaña, I Calvo, Ja Alonso, Jl Velasco, A González-Jerez, M Barnes, K Brunner, O Ford, G Fuchert, J Knauer, E Pasch, L Vanó

Abstract:

In reactor-relevant plasmas, neoclassical transport drives an outward particle flux in the core of large stellarators and predicts strongly hollow density profiles. However, this theoretical prediction is contradicted by experiments. In particular, in Wendelstein 7-X, the first large optimized stellarator, flat or weakly peaked density profiles are generally measured, indicating that neoclassical theory is not sufficient and that an inward contribution to the particle flux is missing in the core. In this Research Letter, it is shown that the turbulent contribution to the particle flux can explain the difference between experimental measurements and neoclassical predictions. The results of this Research Letter also prove that theoretical and numerical tools are approaching the level of maturity needed for the prediction of equilibrium density profiles in stellarator plasmas, which is a fundamental requirement for the design of operation scenarios of present devices and future reactors.
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Details from ORA
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Isotope effects on intrinsic rotation in hydrogen, deuterium and tritium plasmas

Nuclear Fusion IOP Publishing 63:4 (2023) 044002

Authors:

MFF Nave, E Delabie, J Ferreira, J Garcia, D King, M Lennholm, B Lomanowski, F Parra, PR Fernandez, J Bernardo, M Baruzzo, M Barnes, F Casson, JC Hillesheim, A Hubber, E Joffrin, A Kappatou, CF Maggi, A Mauriya, L Meneses, M Romanelli, F Salzedas, JET Contributors
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3D magnetic field measurements and improvements at the negative ion source BATMAN Upgrade

Fusion Engineering and Design Elsevier 189 (2023) 113471

Authors:

G Orozco, M Barnes, M Froeschle, N den Harder, B Heinemann, J Kolbinger, A Oberpriller, R Nocentini, C Wimmer, U Fantz
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New linear stability parameter to describe low-β electromagnetic microinstabilities driven by passing electrons in axisymmetric toroidal geometry

Plasma Physics and Controlled Fusion IOP Publishing 65:4 (2023) 045011

Authors:

Mr Hardman, Fi Parra, Bs Patel, Cm Roach, J Ruiz Ruiz, M Barnes, D Dickinson, W Dorland, Jf Parisi, D St-Onge, H Wilson

Abstract:

In magnetic confinement fusion devices, the ratio of the plasma pressure to the magnetic field energy, β, can become sufficiently large that electromagnetic microinstabilities become unstable, driving turbulence that distorts or reconnects the equilibrium magnetic field. In this paper, a theory is proposed for electromagnetic, electron-driven linear instabilities that have current layers localised to mode-rational surfaces and binormal wavelengths comparable to the ion gyroradius. The model retains axisymmetric toroidal geometry with arbitrary shaping, and consists of orbit-averaged equations for the mode-rational surface layer, with a ballooning space kinetic matching condition for passing electrons. The matching condition connects the current layer to the large scale electromagnetic fluctuations, and is derived in the limit that β is comparable to the square root of the electron-to-ion-mass ratio. Electromagnetic fluctuations only enter through the matching condition, allowing for the identification of an effective β that includes the effects of equilibrium flux surface shaping. The scaling predictions made by the asymptotic theory are tested with comparisons to results from linear simulations of micro-tearing and electrostatic microinstabilities in MAST discharge #6252, showing excellent agreement. In particular, it is demonstrated that the effective β can explain the dependence of the local micro-tearing mode (MTM) growth rate on the ballooning parameter θ 0-possibly providing a route to optimise local flux surfaces for reduced MTM-driven transport.
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