OXFORD THEORETICAL ASTROPHYSICS AND PLASMA PHYSICS GROUP

   

DPhil PROJECTS IN PLASMA PHYSICS

  starting in October 2025

 Application deadline: 8 January 2025

Oxford Plasma Theory Group welcomes applications for DPhil studies and research in plasma physics in the areas of magnetic confinement fusion (MCF) and plasma astrophysics (including "laboratory astrophysics")

Potential supervisors: Prof Michael Barnes, Dr Archie Bott, Prof Gianluca Gregori, Prof Alexander Schekochihin, Prof Dmitri Uzdensky

Note that the project descriptions given below are not set in stone and we are willing to discuss modifications and adjustments to them that might better reflect your interests and inclinations.

*** PROJECT DESCRIPTIONS MAY BE ADDED/EDITED AND NEW ONES APPEAR IN DUE COURSE. COME BACK AND CHECK! ***

 Size of intake: we expect to take at least 3 fully funded students in 2025.

Projects in Fusion Plasmas and in Fundamental Plasma Theory

MAST

  Our magnetic-confinement-fusion theory projects are offered jointly with researchers at the U.K.A.E.A. Culham Centre for Fusion Energy.

At the application stage, you are not required to (although you may if you wish) indicate which project you prefer --- we will consider all applicants purely on intellectual merit. If you are offered admission, we will strive to give you the opportunity to work on the project of your choice.
1. Spontaneous symmetry breaking and intrinsic rotation in high-beta spherical tokamaks
Supervisor: Prof Michael Barnes
UKAEA co-supervisor: Dr Daniel Kennedy
[for this project, apply to DPhil in Theoretical Physics]

Many current magnetic-confinement-fusion experiments rely on externally induced differential rotation of the plasma to quench large-scale magnetohydrodynamic (MHD) instabilities and to improve plasma confinement by reducing turbulent transport. However, it has also been observed that tokamak plasmas can spin up spontaneously even in the absence of any obvious external sources of momentum. This natural rotation, known as intrinsic rotation, is expected to play an important role in the performance of future devices such as STEP, a next-generation fusion pilot plant being designed a stone's throw from Oxford. While intrinsic rotation is routinely observed in present-day tokamaks, its characteristics are not yet fully understood, and much remains to be explained. A key focus of this project will be to predict the level of intrinsic rotation in next-generation plasmas and likely develop alternative methods for generating rotation. Generating sufficiently strong intrinsic rotation is anticipated to be essential in next-generation fusion devices, where it appears crucial for suppressing electromagnetic instabilities [1,2], especially given that external momentum input is expected to be minimal.
 
We envision exploring several avenues as part of this project, including: (i) developing a theory of intrinsic rotation, which could involve in particular an understanding of its dependence on the isotope mix based on recent observations [3]; (ii) predicting intrinsic rotation for high-beta spherical tokamaks; and (iii) exploring alternative methods for generating rotation. This work will build on previous studies of intrinsic rotation in conventional tokamaks at low beta [4], aiming to determine the amount of rotation that could be generated with the modest applied torques expected for a STEP-like device. Additionally, the study will explore how much rotation can be achieved through up-down-asymmetric flux-surface shapes, edge momentum input, and other 'intrinsic' rotation mechanisms [5]. The project will primarily focus on analytical and numerical work, but there will also be opportunities to engage with various exciting experiments.

Background Reading:
1. M. Giacomin et al., "On electromagnetic turbulence and transport in STEP," PPCF 66, 055010 (2024)
2. D. Kennedy et al., "Electromagnetic gyrokinetic instabilities in STEP," Nucl. Fusion 63, 126061 (2023)
3. M. F. F. Nave et al., "Isotope effects on intrinsic rotation in hydrogen, deuterium and tritium plasmas," Nucl. Fusion 63, 044002 (2023)
4. F. I. Parra & M. Barnes, "Intrinsic rotation in tokamaks: theory", PPCF 57, 045002 (2015)
5. J. Ball et al., "Optimized up-down asymmetry to drive fast intrinsic rotation in tokamaks," Nucl. Fusion 58, 026003 (2017)

2. Interaction of high-energy particles with high-frequency electromagnetic modes in spherical tokamaks
Supervisor: Prof Dmitri Uzdensky
UKAEA co-supervisor: Dr James Oliver 
[for this project, apply to DPhil in Theoretical Physics]
Electromagnetic waves known as Alfven waves are regularly excited in plasma experiments due to their ability to interact resonantly with high-energy ('fast') particles, which provide a source of energy that can drive the waves unstable [1]. In a burning plasma, these fast particles are the alpha particles produced by the D-T fusion reaction (alongside neutrons); in currently existing experiments, there are also other fast particles injected into the plasma for a variety of reasons and by a variety of techniques. Alfven waves excited by these particles can potentially then eject them from the plasma, reducing fusion efficiency and potentially damaging the device as they hit the wall. Recent observations [2] from the MAST-U spherical tokamak---located at UKAEA's Culham Laboratory near Oxford---have demonstrated that high-frequency Alfven waves can indeed significantly degrade the confinement of energetic particles. These high-frequency modes, known as global Alfven eigenmodes, have also been known to degrade electron confinement in other spherical tokamaks [3]. Despite this clear and present danger, we do not have a good theoretical model that would adequately describe global Alfven eigenmodes in spherical tokamaks. In its own right, wave-particle-interaction theory is a challenging and conceptually interesting area of plasma physics. This DPhil project aims to produce a theoretical model of the interaction between global Alfven eigenmodes and fast particles, using numerical and analytical techniques, which will then be tested in MAST-U experiments. The student will develop numerical tools to describe the wave structure, stability and interaction with fast particles. New analytical theory will be developed to describe how global Alfven eigenmodes interact with thermal particle populations. Using these new tools, the student will assess the possible impact of high-frequency waves on particle confinement in the planned UK STEP power plant and develop solutions to improve the confinement of both energetic and thermal particles.

Background Reading:
1. W. W. Heidbrink, "Basic physics of Alfven instabilities driven by energetic particles in toroidally confined plasmas," Phys. Plasmas 15, 055501 (2008)
2. J. F. Rivero-Rodriguez et al., "Overview of fast particle experiments in the first MAST Upgrade experimental campaigns," Nucl. Fusion, 64, 086025 (2024)
3. D. Stutman et al., "Correlation between electron transport and shear Alfven activity in the National Spherical Torus Experiment," Phys. Rev. Lett. 102, 115002 (2009)

3. Modelling macroscopic free-energy sources in high-energy-density plasmas via anomalous microphysical forces
Supervisors: Dr Archie Bott & Prof Gianluca Gregori
[for this project, apply to DPhil in Atomic & Laser Physics]
There is a pressing need to establish new theories that relate macroscopic free-energy sources (e.g., temperature gradients) to transport properties (e.g., heat conductivity) in the hot, dense plasmas commonly present in high-energy-density (HED) physics experiments [1,2]. Measurements of laser-produced plasmas have shown that classical models of transport properties, which only include the effect of Coulomb collisions between a plasma's constituent particles, often fail when applied to HED plasmas [3]. This failure, which is believed to be due to neglecting collective plasma interactions [4], is particularly unfortunate for inertial-confinement-fusion (ICF) research, because accurate modelling of heat transport is crucial for realising high-gain target designs. Other research groups have recently attempted to address this problem using particle-in-cell (PIC) simulations [5-7]; however, these previous efforts only focus on astrophysically relevant plasma conditions and consider specific free-energy sources that cannot be generalised. In this project, a student would learn to use a newly proposed numerical approach that overcomes the latter limitation by modelling free-energy sources in PIC simulations via "anomalous" velocity-dependent forces applied to particles, and then apply it to HED and ICF-relevant plasmas.

Background Reading:
1. R. S. Craxton et al., Phys. Plasmas 22, 110501 (2015)
2. M. A. Barrios et al., Phys. Rev. Lett. 121, 095002 (2018)
3. J. Meinecke et al., Science Adv. 8, eabj6799 (2022)
4. A. F. A. Bott et al., J. Plasma Phys 90, 975900207 (2024)
5. S. Komarov et al., J. Plasma Phys. 84, 905840305 (2018)
6. J. F. Drake et al., Astrophys. J. 923, 245 (2021)
7. E. Yerger et al., arXiv:2405.06481 (2024)

4. Explaining suprathermal ion populations produced in ignited inertial-confinement-fusion plasmas
Supervisors: Dr Archie Bott & Prof Alexander Schekochihin
[for this project, we recommend applying to both DPhil in Atomic & Laser Physics and DPhil in Theoretical Physics]

Recent indirect-drive inertial-confinement-fusion (ICF) experiments at the National Ignition Facility (NIF) have, for the first time, demonstrated ignition in a controlled fusion experiment [1,2]. In such experiments, the plasmas achieved at the centre of the deuterium-tritium capsule (the "hot spot") during its maximum compression are sufficiently hot and dense for heating by fusion-produced alpha particles to overcome other cooling mechanisms, leading to the possibility of high energy gain [3]. A surprising observation from these experiments is a discrepancy between measured neutron spectra and what would be expected if the plasma's underlying ion distribution function obeyed the Maxwell-Boltzmann statistics. Instead, the data suggests that a robust population of suprathermal ions is produced [4]. In this project, a student would investigate various possible explanations for this phenomenon, and in particular, acceleration due to alpha-particle-driven kinetic plasma instabilities and dynamics. Understanding these effects could be vital for realising robust ICF implosions with target gain well beyond unity, and their accurate modelling.

Background Reading:
1. H. Abu-Shawareb et al., Phys. Rev. Lett. 129, 075001 (2022)
2. H. Abu-Shawareb et al., Phys. Rev. Lett. 132, 065102 (2024)
3. A. Zylstra et al., Nature 601, 542 (2022)
4. E.P. Hartouni et al., Nature Phys. 19, 72 (2023) 

5. Kinetic theory of collisionless relaxation and phase-space turbulence in magnetised plasmas
Supervisor: Prof Alexander Schekochihin
[for this project, apply to DPhil in Theoretical Physics]
In recent years, we have made some rapid progress in understanding how (nearly) collisionless plasmas relax to non-Maxwellian, but still, in a certain sense, universal equilibria [1] and what is the underlying structure of their turbulent state, a multi-scale chaos in 6D phase space [2,3]. It turns out that one can construct a statistical mechanics of a collisionless plasma, based on maximising (appropriately defined) entropy subject to Casimir invariants conserved in a collisionless system, and then work out (subject to some assumptions the nature and validity of which are still to be understood) how the plasma relaxes to the maximum-entropy states dynamically, a process controlled by its phase-space turbulence---it then turns out that a small amount of dissipation (collisions or, equivalently, finite-particle-number effects) helps push the system into classes of universal equilibria (a complete analytical theory of this last process is still an unsolved problem, which a student taking up this project might attempt to solve, unless we get it done before October 2025). Much of this understanding is, however, limited to electrostatic plasmas (no magnetic fluctuations) and, in what concerns numerical tests, to 1D models. The plan for this project is to break away from these limitations: thus, a numerically inclined student might attempt to conduct a series of advanced numerical experiments, in 2D and 3D (where electromagnetic effects cannot really be avoided); an analytically inclined one might work on a theory of collisionless relaxation in magnetised plasmas, described by the Vlasov-Maxwell equations, or, in a strong mean field, by gyrokinetic ones [4]. The plan is flexible and will depend on the student's interests and abilities, and also on the state of our understanding in a year's time. Applications range from fusion plasmas (either magnetically or inertially confined) to space physics, high-energy astrophysics, and curious bespoke ones created in a (laser) laboratory---in all of these areas, one encounters particle species whose distributions have non-Maxwellian high-energy tails, embedded in a highly turbulent environment (in some cases, these are the dominant species, in others it is an energetic intruder, e.g., cosmic rays).

Background Reading:
1. R. J. Ewart et al., "Collisionless relaxation of a Lynden-Bell plasma,'' J. Plasma Phys. 88, 925880501 (2022); "Non-thermal particle acceleration and power-law tails via relaxation to universal Lynden-Bell equilibria," J. Plasma Phys. 89, 905890516 (2023) ; "Relaxation to universal non-Maxwellian equilibria in a collisionless plasma," arXiv:2409.01742; see also A. Schekochihin's MMathPhys Lecture Notes, sec. 10-11.
2. A. A. Schekochihin et al., "Phase mixing vs. nonlinear advection in drift-kinetic plasma turbulence," J. Plasma Phys. 82, 905820212 (2016)
3. M. L. Nastac et al., "Phase-space entropy cascade and irreversibility of stochastic heating in nearly collisionless plasma turbulence," Phys. Rev. E 109, 065210 (2024); see also A. Schekochihin's MMathPhys Lecture Notes, sec. 12
4. M. W. Kunz et al., "Astrophysical gyrokinetics: turbulence in pressure-anisotropic plasmas at ion scales and beyond,'' J. Plasma Phys. 84, 715840201 (2018)


Projects in Plasma Astrophysics and Laser Plasmas



Candidates interested in any of these projects or generally in plasma astrophysics, astrophysical turbulence and/or dynamo theory are welcome to get in touch with prospective supervisors for further information. A more bespoke project can be designed to align with the inclinations and interests of the student (for example how much emphasis is placed on analytical vs. numerical methods or kinetic theory vs. fluid dynamics, etc., is negotiable).  

6. Generating and sustaining radio filaments in astrophysical plasmas
Supervisors: Dr Archie Bott & Prof Alexander Schekochihin
[for this project, we recommend applying to both DPhil in Astrophysics and DPhil in Theoretical Physics]

One of the most intriguing findings from recent high-resolution astronomical observations of radio emission in astrophysical objects, such as galaxy clusters (as well as our own Galaxy), is the presence of collimated filaments of plasma [1-6]. These structures, which can extend from tens [2] to hundreds [4] of kiloparsecs, pose a significant theoretical challenge: how they are formed and persist are open questions. If the evolution of these plasma filaments were modelled accurately by hydrodynamics, they would quickly break up due to the Kelvin-Helmholtz and Rayleigh-Taylor instabilities. Yet they are there, and they shine with synchrotron radiation---which suggests that both the fluid instabilities are suppressed, and also that the filaments are capable of channelling high-energy cosmic rays, thought to produce the observed radio emission. A plausible hypothesis is that these filaments are threaded by magnetic fields with energy densities comparable to the thermal energy density of the plasma. However, the mechanism by which such strong magnetic fields could be generated in the low-density, high-temperature plasma typical of intergalactic space is a mystery. In this DPhil project, we will investigate how (or whether) strong compression and shearing of intergalactic plasma can lead to emergence of a "two-phase" intracluster medium: strongly and weakly magnetised, with a particular focus on the nonlinear evolution of the so-called mirror instability [7-9]. The research will involve analytical work, as well as fluid and kinetic simulations of astrophysical plasmas.

Background Reading:
1. R. J. van Weeran et al., Space Sci. Rev. 215, 16 (2019)
2. M. Brienza et al., Nature Astron. 5, 1261 (2021)
3. L. Rudnick et al., Astrophys. J. 935, 168 (2022)
4. K. Rajpurohit et al., Astrophys. J. Lett. 927, L80 (2022)
5. F. Yusef-Zadeh et al., Astrophys. J. Lett. 939, L21 (2022)
6. E. Churazov et al., Astron. Astrophys. 686, A14 (2024)
7. M. W. Kunz et al., Phys. Rev. Lett. 112, 205003 (2014)
8. F. Rincon et al., MNRAS 447, L45 (2015)
9. S. Melville et al., MNRAS 459, 2701 (2016)

7. Magnetic-field amplification by the fluctuation dynamo in astrophysical plasmas
Supervisors: Dr Archie Bott & Prof Alexander Schekochihin
[for this project, we recommend applying to both DPhil in Astrophysics and DPhil in Theoretical Physics]

Understanding cosmic magnetism is a long-standing problem in astrophysics. Astronomical observations of various astrophysical environments---for example, those of our own galaxy by the MeerKAT telescope [1] or of more distant galaxy clusters [2]---reveal the presence of finely structured magnetic fields of sufficient strength to affect the dynamics of such systems. A possible mechanism for explaining the presence and characteristics of these magnetic fields is the so-called fluctuation dynamo, whereby stochastic or turbulent motions of the plasma in which these magnetic fields are embedded amplify and maintain them [3]. The fluctuation dynamo has mostly been studied using simplified magnetohydrodynamic (MHD) plasma models whose key transport properties (viz., resistivity and viscosity) do not depend on macroscopic plasma properties such as density, temperature, and the magnetic field [4,5]. However, the plasmas found in the astrophysical systems of interest are often weakly collisional, and current theories for the transport properties of such plasmas typically do predict a dependence on macroscopic plasma properties [6]. It is an outstanding question whether "anomalous" transport properties can explain why certain predictions of the simplified theory of the fluctuation dynamo are at odds with astronomical observations (for example, that the energy-containing scale of the magnetic field is macroscopic). In this project, a student would explore how more realistic models of transport properties affect the fluctuation dynamo using both theory and numerical simulations, and then attempt to identify key differences with simplified dynamo theories that could be detected in astronomical observations.

Background Reading:
1. I. Heywood et al., Nature 573, 235 (2019)
2. C. L. Carilli & G. B. Taylor, Annu. Rev. Astron. Astrophys. 40, 319 (2002)
3. F. Rincon, J. Plasma Phys. 85, 205850401 (2019) 
4. A. A. Schekochihin et al., Astrophys. J. 612, 276 (2004)
5. A. K. Galishnikova et al., PRX 12, 041027 (2022)
6. A. A. Schekochihin, S. C. Cowley, Phys. Plasmas 13, 056501 (2006)
7. A. F. A. Bott et al., PNAS 118, e2015729118 (2021)
8. Magnetised plasma turbulence: from laser lab to galaxy clusters
Supervisors: Prof Gianluca Gregori, Dr Archie Bott, & Prof Alexander Schekochihin
[for this project, we recommend applying to both DPhil in Astrophysics and DPhil in Atomic & Laser Physics]
There are a number of possibilities within this project to design, take part in, and theorise about laboratory experiments employing laser-produced plasmas to model astrophysical phenomena and basic, fundamental physical processes in turbulent plasmas. Recent examples of our work in this field include turbulent generation of magnetic fields ("dynamo") [1,2], supersonic turbulence mimicking star-forming molecular clouds [3], diffusion and acceleration of particles by turbulence [4,5], suppression of thermal conduction in galaxy-cluster-like plasmas [6]. Our group has access to several facilities (including the National Ignition Facility, the largest laser system in the world). Students will also have access to a laser laboratory on campus, where initial experiments can be fielded. Depending on the student's inclinations, it is also possible to pursue a project focused on theory and/or numerical modelling of plasma phenomena in astrophysical and laboratory-astrophysical environments.
Background Reading:
1. P. Tzeferacos et al., "Laboratory evidence of dynamo amplification of magnetic fields in a turbulent plasma," Nature Comm. 9, 591 (2018)
2. A. F. A. Bott et al., "Time-resolved fast turbulent dynamo in a laser plasma," PNAS 118, e2015729118 (2021)
3. T. G. White et al.,"Supersonic plasma turbulence in the laboratory," Nature Comm. 10, 1758 (2019)
4. A. F. A. Bott et al., "Proton imaging of stochastic magnetic fields," J. Plasma Phys. 83, 905830614 (2017)
5. L. E. Chen et al., "Transport of high-energy charged particles through spatially intermittent turbulent magnetic fields," Astrophys. J. 892, 114 (2020)
6. J. Meinecke et al., "Strong suppression of heat conduction in a laboratory analogue of galaxy-cluster turbulent plasma," Science Adv. 8, eabj6799 (2022)

9. Microphysics of gamma-ray bursts
Supervisors: Prof Gianluca Gregori, Prof Subir Sarkar, & Prof Dmitri Uzdensky
[for this project, we recommend applying to both DPhil in Astrophysics and DPhil in Atomic & Laser Physics]
Gamma-ray bursts (GRBs) are among the most energetic events in the Universe. They occur at cosmological distances and are the result of the collapse of massive stars or neutron stars mergers, with emission of relativistic "fireballs" of electron-positron pairs. From astrophysical observations, a wealth of information has been gleaned about the mechanism that leads to such strong emission of radiation, with leading models predicting that this is due to the disruption of the beam as it blasts through the surrounding plasma. This produces shocks and hydromagnetic turbulence that generate synchrotron emission, potentially accelerating to ultra-high energies the protons which are observed on Earth as cosmic rays. However, there is no direct evidence of the generation of either magnetic fields or cosmic rays by GRBs. Estimates are often based on crude energy equipartition arguments or idealised numerical simulations that struggle to capture the extreme plasma conditions. We propose to address this lacuna by conducting laboratory experiments at accelerator facilities to mimic the jet propagation through its surrounding plasma. Our intial work [1] has demonstrated that we can create enormous beams of electron-positron plasmas that have properties very similar to GRB Fireballs. We are now planning new experiments at CERN as well as at Laboratori Nazionali Frascati (INFN, Italy) to characterise fully the interaction of these beams with a surrounding (ambient) plasma. Such experiments will enable in-situ measurement of the plasma properties, with exquisite details that cannot be achieved elsewhere. The experiments also complement numerical simulations by providing long measurement times extending into the non-linear regime where numerical simulations are not possible today. The proposed experiments will study fundamental physics processes, unveil the microphysics of GRBs, and provide a new window in high-energy astrophysics using novel Earth-based laboratory tools.

 Background Reading:
1. C. D. Arrowsmith et al., "Laboratory realisation of relativistic pair-plasma beams," Nature Comm. 15, 5029 (2024)

10. Free-energy flows and universal equilibria in turbulent astrophysical plasmas
Supervisors: Prof Alexander Schekochihin & Prof Michael Barnes
[for this project, we recommend applying to both DPhil in Astrophysics and DPhil in Theoretical Physics]

In magnetised astrophysical plasmas, there is a turbulent cascade of electromagnetic fluctuations carrying free energy from large to small scales. The energy is typically extracted from large-scale sources (e.g., in the solar wind, the violent activity in the Sun's corona; in accretion discs, the Keplerian shear flow; in galaxy clusters, outbursts from active galactic nuclei) and deposited into heat---the internal energy of ions and electrons. In order for this dissipation of energy to happen, the energy must reach small scales---in weakly collisional plasmas, these are small scales in the 6D kinetic phase space, i.e., what emerges is large spatial gradients of electric and magnetic fields and large gradients of the particle distribution functions with respect to velocities. This prompts two fundamental questions: (1) how does the energy flow through the 6D phase space and what therefore is the structure of the fluctuations in this space: their spectra, phase-space correlation functions etc. [1,2,3] (these fluctuations are best observed in the solar wind, but we can measure density and magnetic fluctuations even in extragalactic plasmas, via X-ray and radio observations); (2) when turbulent fluctuations are dissipated into particle heat, how is their energy partitioned between various species of particles that populate the plasma: electrons, bulk ions, minority ions, fast non-thermal particles (e.g., cosmic rays) [4,5]. The latter question is particularly important for extragalactic plasmas because all we can observe is radiation from the particles and knowing where the internal energy of each species came from is key to constructing and verifying theories both of turbulence and of macroscale dynamics and thermodynamics. This project has an analytical and a numerical dimension (which of these will dominate depends on the student's inclinations). Analytically, we will work out a theory of phase-space cascade at spatial scales between the ion and electron Larmor scales. Numerically, we will simulate this cascade using "gyrokinetic" equations---an approach in which we average over the Larmor motion and calculate the distribution function of "Larmor rings of charge" rather than particles (this reduces the dimension of phase space to 5D, making theory more tractable and numerics more affordable).

With a theory of plasma turbulence in hand, it is possible to attack what is probably the most fundamental question of the field: in the absence of collisions, are there universal equilibria, or classes of equilibria, independent of initial conditions, that a turbulent plasma will want to converge to? There is some recent progress indicating that the answer is yes and that one can predict statistical-mechanically the emergence of universal power-law (in particle energy) distributions [6]---this is exciting both on its own merits and because of the astrophysical challenge of explaining theoretically power-law distributions that are observed for, e.g., cosmic rays or solar-wind electrons. How to construct a theory of that for a magnetised, turbulent plasma is an open and exciting question. Attempting to do this will again involve kinetic theory and/or kinetic simulations.  

Background Reading:
1. A. A. Schekochihin et al., "Astrophysical gyrokinetics: kinetic and fluid turbulent cascades in magnetized weakly collisional plasmas," Astrophys. J. Suppl. 182, 310 (2009)
2. A. A. Schekochihin et al., "Phase mixing vs. nonlinear advection in drift-kinetic plasma turbulence," J. Plasma Phys. 82, 905820212 (2016)
3. R. Meyrand et al., "Fluidization of collisionless plasma turbulence," PNAS 116, 1185 (2019)
4. Y. Kawazura et al., "Thermal disequilibration of ions and electrons by collisionless plasma turbulence," PNAS 116, 771 (2019)
5. J. Squire et al., "High-frequency heating of the solar wind triggered by low-frequency turbulence," Nature Astron. 6, 715 (2022)
6. R. J. Ewart et al., "Relaxation to universal non-Maxwellian equilibria in a collisionless plasma," arXiv:2409.01742; see also A. Schekochihin's MMathPhys Lecture Notes, sec. 10-11

11. Nonthermal particle acceleration in extreme plasmas around black holes
Supervisors: Prof Dmitri Uzdensky
[for this project, we recommend applying to both DPhil in Astrophysics and DPhil in Theoretical Physics]
Accreting supermassive black holes (SMBHs) residing in active galactic nuclei (AGN) at the centres of many galaxies, including the Milky Way, are arguably the most fascinating and enigmatic objects in the Universe. These black holes, and the powerful relativistic jets emanating from them, often exhibit spectacular, violent phenomena, such as bright high-energy flares with nonthermal X-ray and gamma-ray spectra. They are also the most likely generators of highly energetic non-electromagnetic observational "messengers": extremely relativistic cosmic rays and ultra-high-energy neutrinos. All these observational signals indicate that BH environments are very efficient relativistic-particle accelerators. Understanding how these cosmic accelerators work is an outstanding problem in high-energy astrophysics. Nonthermal particle acceleration is believed to be a natural product of collective kinetic nonlinear plasma processes, such as magnetic reconnection, shocks, and magnetised turbulence. How these processes operate under the extreme physical conditions in the exotic relativistic plasmas of accreting black holes is not well understood because the underlying physics is much richer than in more traditional plasmas (like ones in the solar system): special- and general-relativistic effects, strong interaction of the plasma with radiation, and quantum-electrodynamic effects such as pair creation all come into play in nontrivial ways. Elucidating the complex interplay of these effects with collective plasma processes and, consequently, their impact on particle acceleration and radiation presents an exciting theoretical challenge and is a vibrant frontier of modern plasma astrophysics research. This project will explore these fundamental plasma-theoretical questions and their observational implications through a combination of analytical and computational methods, with the balance between theory and computation to be decided based on the student's preferences.