Skip to main content
Home
Department Of Physics text logo
  • Research
    • Our research
    • Our research groups
    • Our research in action
    • Research funding support
    • Summer internships for undergraduates
  • Study
    • Undergraduates
    • Postgraduates
  • Engage
    • For alumni
    • For business
    • For schools
    • For the public
Menu
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

Influence of the density gradient on turbulent heat transport at ion-scales: an inter-machine study with the gyrokinetic code stella

Nuclear Fusion IOP Publishing 65:1 (2024) 016062

Authors:

H Thienpondt, JM García-Regaña, I Calvo, G Acton, M Barnes

Abstract:

Efficient control of turbulent heat transport is crucial for magnetic confinement fusion reactors. This work discusses the complex interplay between density gradients and microinstabilities, shedding light on their impact on turbulent heat transport in different fusion devices. In particular, the influence of density gradients on turbulent heat transport is investigated through an extensive inter-machine study, including various stellarators such as W7-X, LHD, TJ-II and NCSX, along with the Asdex Upgrade tokamak (AUG) and the tokamak geometry of the Cyclone Base Case (CBC). Linear and nonlinear simulations are performed employing the δf-gyrokinetic code stella across a wide range of parameters to explore the effects of density gradients, temperature gradients, and kinetic electrons. A strong reduction in ion heat flux with increasing density gradients is found in NCSX and W7-X due to the stabilization of temperature-gradient-driven modes without significantly destabilizing density-gradient-driven modes. In contrast, the tokamaks exhibit an increase in ion heat flux with density gradients. Notably, the behavior of ion heat fluxes in stellarators does not align with that of linear growth rates, if only the fastest-growing mode is taken into account. Additionally, this study provides physical insights into the microinstabilities, emphasizing the dominance of trapped-electron-modes (TEMs) in CBC, AUG, TJ-II, LHD and NCSX, while both the TEM and the passing-particle-driven universal instability contribute significantly in W7-X.
More details from the publisher
Details from ORA
More details

Density profiles in stellarators: an overview of particle transport, fuelling and profile shaping studies at TJ-II

Nuclear Fusion IOP Publishing 64:11 (2024) 112018

Authors:

JA Alonso, D Alegre, J Alonso, R Antón, A Arias-Camisón, E Ascasíbar, A Baciero, JM Barcala, M Barnes, E Blanco, L Bueno, A Bustos, S Cabrera, E de la Cal, I Calvo, A Cappa, D Carralero, R Carrasco, B Carreras, R Castro, A de Castro, L Cebrián, M Chamorro, AA Chmyga, P Colino, J Duque, FJ Escoto, T Estrada, A Fernández, J Fraguas, JM Fontdecaba, A Gabriel, L García, I García-Cortés, R García-Gómez, JM García-Regaña, G Godino-Sedano, J Gómez-Manchón, A González, A González-Jerez, V Guisse, J Hernández-Sánchez, J Hernanz, C Hidalgo, P Ivanova, A Jiménez-Denche, D Jiménez-Rey, G Kocsis, M Koepke, AS Kozachek, F Lapayese, M Liniers, D López, D López-Bruna, B López-Miranda, E de la Luna, E Maragkoudakis, F Martín-Díaz, G Martín-Gómez, J Martínez-Fernández, KJ McCarthy, F Medina, D Medina-Roque, M Medrano, P Méndez, FJ Miguel, B van Milligen, A Molinero, G Motojima, S Mulas, M Navarro, I Nedzelskiy, R Nuñez, M Ochando, E Oyarzábal, JL de Pablos, F Palomares, N Panadero, FI Parra, C Pastor, I Pastor, A de la Peña, R Peralta, A Pereira, P Pons-Villalonga, AB Portas, E Poveda, FJ Ramos, GA Rattá, M Redondo, C Reynoso, E Rincón, J de la Riva, C Rodríguez-Fernández, A Ros, E Sánchez, J Sánchez, E Sánchez-Sarabia, JA Sebastián, ER Solano, A Soleto, T Szepesi, FL Tabarés, D Tafalla, H Takahashi, N Tamura, H Thienpondt, A Tolkachev, V Tribaldos, R Unamuno, J Varela, J Vega, JL Velasco, I Voldiner
More details from the publisher
More details

Optimisation of gyrokinetic microstability using adjoint methods

Journal of Plasma Physics Cambridge University Press 90:4 (2024) 905900406

Authors:

Georgia Acton, Michael Barnes, S Newton, H Thienpondt

Abstract:

Microinstabilities drive turbulent fluctuations in inhomogeneous, magnetised plasmas. In the context of magnetic confinement fusion devices, this leads to an enhanced transport of particles, momentum and energy, thereby degrading confinement. In this work, we describe an application of the adjoint method to efficiently determine variations of gyrokinetic linear growth rates on a general set of external parameters in the local δf-gyrokinetic model. We then offer numerical verification of this approach. When coupled with gradient-based techniques, this methodology can facilitate the optimisation process for the microstability of the confined plasmas across a high-dimensional parameter space. We present a numerical demonstration wherein the ion-temperature-gradient instability growth rate in a tokamak plasma is minimised with respect to flux surface shaping parameters. The adjoint method approach demonstrates a significant computational speed-up compared with a finite-difference gradient calculation.
More details from the publisher
Details from ORA
More details

Linearised Fokker–Planck collision model for gyrokinetic simulations

Plasma Physics and Controlled Fusion IOP Publishing 66:10 (2024) 105016

Authors:

A von Boetticher, FI Parra, M Barnes

Abstract:

We introduce a gyrokinetic, linearised Fokker–Planck collision model that satisfies conservation laws and is accurate at arbitrary collisionalities. The differential test-particle component of the operator is exact; the integral field-particle component is approximated using a spherical harmonic and a modified Laguerre polynomial expansion developed by Hirshman and Sigmar (1976 Phys. Fluids 19 1532). The numerical methods of the implementation in the δf-gyrokinetic code stella (Barnes et al 2019 J. Comput. Phys. 391 365–80) are discussed, and conservation properties of the operator are demonstrated. The collision model is then benchmarked against the collision model of the gyrokinetic solver GS2 in the limiting cases of a reduced test-particle collision operator and energy- and momentum-conserving operator. The accuracy of the full collision model is investigated by solving the parallel Spitzer-Härm problem for the transport coefficients. It is shown that retaining collisional energy flux and higher-order terms in the field-particle operator reduces errors in the transport coefficients from 10%–25% for a simple momentum- and energy-conserving model to under 1%.
More details from the publisher
Details from ORA
More details

Saturation of magnetised plasma turbulence by propagating zonal flows

(2024)

Authors:

Richard Nies, Felix Parra, Michael Barnes, Noah Mandell, William Dorland
More details from the publisher

Pagination

  • First page First
  • Previous page Prev
  • Page 1
  • Current page 2
  • Page 3
  • Page 4
  • Page 5
  • Page 6
  • Page 7
  • Page 8
  • Page 9
  • …
  • Next page Next
  • Last page Last

Footer Menu

  • Contact us
  • Giving to the Dept of Physics
  • Work with us
  • Media

User account menu

  • Log in

Follow us

FIND US

Clarendon Laboratory,

Parks Road,

Oxford,

OX1 3PU

CONTACT US

Tel: +44(0)1865272200

University of Oxfrod logo Department Of Physics text logo
IOP Juno Champion logo Athena Swan Silver Award logo

© University of Oxford - Department of Physics

Cookies | Privacy policy | Accessibility statement

Built by: Versantus

  • Home
  • Research
  • Study
  • Engage
  • Our people
  • News & Comment
  • Events
  • Our facilities & services
  • About us
  • Current students
  • Staff intranet