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

Professor Felix Parra Diaz

Visitor

Research theme

  • Plasma physics

Sub department

  • Rudolf Peierls Centre for Theoretical Physics

Research groups

  • Theoretical astrophysics and plasma physics at RPC
felix.parradiaz@physics.ox.ac.uk
Rudolf Peierls Centre for Theoretical Physics
  • About
  • Publications

Linear pedestal ETG

University of Oxford (2020)

Authors:

Jason Parisi, Felix I Parra Diaz, Colin M Roach, Michael Barnes, David R Hatch, William Dorland, Plamen Ivanov, Jon C Hillesheim, Nobuyuki Aiba, Carine Giroud, Justin Ball

Abstract:

Refer to readme.pdf in the repository.
More details from the publisher

Impact of main ion pressure anisotropy on stellarator impurity transport

Nuclear Fusion IOP Publishing 60 (2019) 016035

Authors:

I Calvo, F Parra Diaz, JL Velasco, JM García-Regaña

Abstract:

Main ions influence impurity dynamics through a variety of mechanisms; in particular, via impurity-ion collisions. To lowest order in an expansion in the main ion mass over the impurity mass, the impurity-ion collision operator only depends on the component of the main ion distribution that is odd in the parallel velocity. These lowest order terms give the parallel friction of the impurities with the main ions, which is typically assumed to be the main cause of collisional impurity transport. Next-order terms in the mass ratio expansion of the impurity-ion collision operator, proportional to the component of the main ion distribution that is even in the parallel velocity, are usually neglected. However, in stellarators, the even component of the main ion distribution can be very large. In this article, such next-order terms in the mass ratio expansion of the impurity-ion collision operator are retained, and analytical expressions for the neoclassical radial flux of trace impurities are calculated in the Pfirsch-Schl\"uter, plateau and $1/\nu$ regimes. The new terms provide a drive for impurity transport that is physically very different from parallel friction: they are associated to anisotropy in the pressure of the main ions, which translates into impurity pressure anisotropy. It is argued that main ion pressure anisotropy must be taken into account for a correct description of impurity transport in certain realistic stellarator plasmas. Examples are given by numerically evaluating the analytical expressions for the impurity flux.
More details from the publisher
Details from ORA
More details
Details from ArXiV

Dependence on ion temperature of shallow-angle magnetic presheaths with adiabatic electrons

Journal of Plasma Physics Cambridge University Press 85:6 (2019) 795850601

Authors:

A Geraldini, Felix I Parra, F Militello

Abstract:

The magnetic presheath is a boundary layer occurring when magnetized plasma is in contact with a wall and the angle α between the wall and the magnetic field B is oblique. Here, we consider the fusion-relevant case of a shallow-angle, α 1, electron-repelling sheath, with the electron density given by a Boltzmann distribution, valid for α/√τ + 1 √me/mi, where me is the electron mass, mi is the ion mass, τ = Ti/ZTe,Te is the electron temperature, Ti is the ion temperature and Z is the ionic charge state. The thickness of the magnetic presheath is of the order of a few ion sound Larmor radii ρs = √mi(ZTe + Ti)/ZeB, where e is the proton charge and B = |B| is the magnitude of the magnetic field. We study the dependence on τ of the electrostatic potential and ion distribution function in the magnetic presheath by using a set of prescribed ion distribution functions at the magnetic presheath entrance, parameterized by τ . The kinetic model is shown to be asymptotically equivalent to Chodura’s fluid model at small ion temperature, τ 1, for |ln α| > 3|ln τ | 1. In this limit, despite the fact that fluid equations give a reasonable approximation to the potential, ion gyroorbits acquire a spatial extent that occupies a large portion of the magnetic presheath. At large ion temperature, τ 1, relevant because Ti is measured to be a few times larger than Te near divertor targets of fusion devices, ions reach the Debye sheath entrance (and subsequently the wall) at a shallow angle whose size is given by √α or 1/√τ, depending on which is largest.
More details from the publisher
Details from ORA

Overview of recent TJ-II stellarator results

Nuclear Fusion IOP Publishing 59:11 (2019) 112019

Authors:

E Ascasíbar, D Alba, D Alegre, A Alonso, J Alonso, F de Aragón, A Baciero, JM Barcala, E Blanco, J Botija, L Bueno, S Cabrera, E de la Cal, I Calvo, A Cappa, D Carralero, R Carrasco, B Carreras, F Castejón, R Castro, A de Castro, G Catalán, AA Chmyga, M Chamorro, AW Cooper, A Dinklage, L Eliseev, T Estrada, M Ezzat, F Fernández-Marina, JM Fontdecaba, L García, I García-Cortés, R García-Gómez, JM García-Regaña, A González-Jerez, G Grenfell, J Guasp, J Hernández-Sánchez, J Hernanz, C Hidalgo, E Hollmann, A Jiménez-Denche, P Khabanov, N Kharchev, I Kirpitchev, R Kleiber, AS Kozachek, L Krupnik, F Lapayese, M Liniers, B Liu, D López-Bruna, A López-Fraguas, B López-Miranda, J López-Rázola, U Losada, E de la Luna, A Martín de Aguilera, F Martín-Díaz, M Martínez-Fuentes, G Martín-Gómez, AB Martín-Rojo, J Martínez-Fernández, KJ McCarthy, F Medina, M Medrano, L Melón, AV Melnikov, P Méndez, R Merino, FJ Miguel, B van Milligen, A Molinero, B Momo, P Monreal, S Mulas, Y Narushima, M Navarro, M Ochando, S Ohshima, J Olivares, E Oyarzábal, JL de Pablos, L Pacios, N Panadero, F Parra, I Pastor, A de la Peña, A Pereira, JR Pinzón, AB Portas, E Poveda, JA Quintana, FJ Ramos, GA Rattá, M Redondo, E Rincón, L Ríos, C Rodríguez-Fernández, L Rodríguez-Rodrigo, B Rojo, A Ros, E Rosa, E Sánchez, J Sánchez, M Sánchez, E Sánchez-Sarabia, S Satake, JA Sebastián, R Sharma, C Silva, ER Solano, A Soleto, BJ Sun, FL Tabarés, D Tafalla, H Takahashi, N Tamura, A Tolkachev, J Vega, G Velasco, JL Velasco, S Yamamoto, B Zurro
More details from the publisher

stella: An operator-split, implicit–explicit δf-gyrokinetic code for general magnetic field configurations

Journal of Computational Physics 391 (2019) 365-380

Authors:

M Barnes, FI Parra, M Landreman

Abstract:

Here we present details of an operator-split, implicit–explicit numerical scheme for the solution of the gyrokinetic-Poisson system of equations in the local limit. This scheme has been implemented in a new code called stella, which is capable of evolving electrostatic fluctuations with full kinetic electron effects and an arbitrary number of ion species in general magnetic geometry. We demonstrate the advantages of this mixed approach over a fully explicit treatment and provide linear and nonlinear benchmark comparisons for both axisymmetric and non-axisymmetric magnetic equilibria.
More details from the publisher
More details

Pagination

  • First page First
  • Previous page Prev
  • …
  • Page 3
  • Page 4
  • Page 5
  • Page 6
  • Current page 7
  • Page 8
  • Page 9
  • Page 10
  • Page 11
  • …
  • 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