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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

Centrifugal-mirror confinement with strong azimuthal magnetic field

Plasma Physics and Controlled Fusion 67:9 (2025)

Authors:

T Stoltzfus-Dueck, FI Parra

Abstract:

One practical challenge for the centrifugal-mirror confinement concept is the large radial voltage necessary to drive supersonic azimuthal rotation. In principle, the addition of a strong azimuthal field could reduce the required voltage, since the simple azimuthal E × B drift would be replaced by more rapid azimuthal trapped-particle precession. Also, if the mirror ratio is large enough, newly ionized ions are accelerated to the necessary parallel velocities in their first bounce orbit, both confining and significantly heating them. Unfortunately, MHD analysis shows that the centrifugal-force-confining plasma current is purely azimuthal. This implies that only the axial magnetic field contributes to the confining magnetic pressure, severely limiting the usefulness of the azimuthal magnetic field in a beta-limited plasma scenario.
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Strong gradient effects on neoclassical electron transport and the bootstrap current in large aspect ratio tokamaks

Journal of Plasma Physics Cambridge University Press (CUP) 91:4 (2025) e97

Authors:

Silvia Trinczek, Felix I Parra, Peter J Catto

Abstract:

Standard approaches to neoclassical theory do not extend into regions of strong gradients in tokamaks such as the pedestal and internal transport barriers. Here, we calculate the modifications to neoclassical electron physics inside strong gradient regions of large aspect ratio tokamaks in the banana regime. We show that these modifications are due to the different ion flow and the strong poloidal variation of the potential. We also provide a physical interpretation of the mechanisms that drive poloidal asymmetries and hence a poloidal electric field. We apply our model to two specific example cases of pedestal profiles, calculating the neoclassical electron flux and the bootstrap current. We find that, depending on the ion flow, weak gradient neoclassical theory overestimates or underestimates the neoclassical electron transport and the bootstrap current in regions with strong gradients. We show that the determination of the mean parallel flow is more complex than in weak gradient neoclassical theory. For vanishing turbulence, we can determine the radial electric field for a given flow profile in the pedestal.
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Enhanced Collisional Losses from a Magnetic Mirror Using the Lenard-Bernstein Collision Operator

Journal of Plasma Physics Cambridge University Press (CUP) (2025) 1-24

Authors:

Maxwell H Rosen, W Sengupta, I Ochs, FI Parra, GW Hammett
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Beam focusing and consequences for Doppler backscattering measurements

Journal of Plasma Physics Cambridge University Press (CUP) 91:2 (2025) e60

Authors:

J Ruiz Ruiz, FI Parra, VH Hall-Chen, N Belrhali, C Giroud, JC Hillesheim, NA Lopez, JET contributors
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Measurement of Zero-Frequency Fluctuations Generated by Coupling between Alfvén Modes in the JET Tokamak.

Physical review letters American Physical Society (APS) 134:9 (2025) 95103

Authors:

J Ruiz Ruiz, J Garcia, M Barnes, M Dreval, C Giroud, Vh Hall-Chen, Mr Hardman, Jc Hillesheim, Y Kazakov, S Mazzi, Bs Patel, Fi Parra, Aa Schekochihin, Ž Štancar, JET Contributors and the EUROfusion Tokamak Exploitation Team

Abstract:

We report the first experimental detection of a zero-frequency fluctuation that is pumped by an Alfvén mode in a magnetically confined plasma. Core-localized Alfvén modes of frequency inside the toroidicity-induced gap (and its harmonics) exhibit three-wave coupling interactions with a zero-frequency fluctuation. The observation of the zero-frequency fluctuation is consistent with theoretical and numerical predictions of zonal modes pumped by Alfvén modes, and is correlated with an increase in the deep core ion temperature, temperature gradient, confinement factor H_{89,P}, and a reduction in the main ion heat diffusivity. Despite the energetic particle transport induced by the Alfvén eigenmodes, the generation of a zero-frequency fluctuation that can suppress the turbulence leads to an overall improvement of confinement.
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