The Frontiers of Plasma Physics colloquium is jointly sponsored by PPPL and the Journal of Plasma Physics.
A full list of upcoming colloquia can be found on the JPP Frontiers of Plasma Physics Colloquium Upcoming Talks webpage.
Alexander Ivanov, Budker Institute of Nuclear Physics, Novosibirsk, RussiaThe gas dynamic trap (GDT) was invented by Vladimir Mirnov and Dmitrii Ryutov in Novosibirsk in the late 1970s. It is basically a version of a magnetic mirror which is characterized by a long mirror-to-mirror distance exceeding the effective mean free path of ion scattering into a loss cone, a large mirror ratio (R ~ 100) and axial symmetry. Under these conditions the plasma confined in a GDT is isotropic and Maxwellian. The plasma loss rate out of the end mirrors is governed by a set of simple gas-dynamic equations, hence the device's name. Plasma magnetohydrodynamic stability in GDT can be achieved through a favorable averaged pressure-weighted curvature of the magnetic field lines, as was initially proposed, or, alternatively through a sheared plasma rotation at periphery induced by electrically biased electrodes at the end wall. A high flux volumetric neutron source based on a GDT is proposed, which benefits from the high β achievable in magnetic mirrors. Axial symmetry also makes the GDT neutron source more maintainable and reliable, and technically simpler. This review discusses the results of a conceptual design of the GDT-based neutron source which can be used for fusion materials development and as a driver of fission–fusion hybrids. The main physics issues related to plasma confinement and heating in a GDT are addressed by the experiments at the GDT device in Novosibirsk. The review concludes by updating the experimental results obtained, a discussion about the limiting factors in the current experiments and a brief description of the design of a future experimental device for more comprehensive modeling of the GDT-based neutron source. Conceivable approaches to improvement of plasma confinement in a GDT are also considered which would allow to consider the concept application in a fusion reactor.
Matt Kunz, Princeton UniversityMany space and astrophysical plasmas are so hot and dilute that they cannot be rigorously described as fluids. These include the solar wind, low-luminosity black-hole accretion flows, and the intracluster medium of galaxy clusters. All of these plasmas are magnetized and weakly collisional, with plasma beta parameters of order unity or even much larger (“high-beta”). In this regime, deviations from local thermodynamic equilibrium ("pressure anisotropies") and the kinetic instabilities they excite can dramatically change the material properties of such plasmas and thereby influence the macroscopic evolution of their host systems. This talk outlines an ongoing programme of kinetic calculations aimed at elucidating from first principles the physics of waves, turbulence, and transport under these conditions. Three key results will be featured. (1) Shear-Alfvén waves “interrupt” themselves at sufficiently large amplitudes by adiabatically driving a field-biased pressure anisotropy that both nullifies the restoring tension force and excites a sea of ion-Larmor-scale instabilities. (2) Ion-acoustic waves in a collisionless, high-beta plasma similarly excite Larmor-scale instabilities, which ultimately aid the waves' propagation by rendering the plasma more fluid-like and, therefore, incapable of Landau damping. (3) Pressure anisotropy generated either by turbulent fluctuations or by global expansion (as in the solar wind) qualitatively change the properties of magnetized turbulence, affecting plasma heating and the so-called “critical balance”. Contact with observations of the near-Earth solar wind and the intracluster medium of galaxy clusters will be made.
Howard Wilson, University of York, UKSTEP – the Spherical Tokamak for Electricity Production – aims to deliver a prototype power plant by 2040 that will deliver net electricity at the 100MW level. This is a challenging timescale, that will require disruptive changes to how we design and regulate. The plasma scenario presents some of the biggest challenges, and this talk will discuss some of them. A spherical tokamak plasma has some advantages over one at conventional aspect ratio, allowing access to high elongation and beta (ratio of thermal plasma pressure to magnetic field pressure), in a compact geometry. Therefore, while much of the physics in the two designs is similar, there are also key differences. For example, the compact nature means there is little space for a solenoid, so non-inductive current drive is essential; the low magnetic field and high density require novel radio frequency methods for this current drive; the high beta affects the micro-instabilities that drive plasma turbulence and influence confinement; magnetohydrodynamic instabilities must be controlled to limit disruptions while achieving high fusion power and bootstrap current fraction; novel systems are required to manage the exhaust power loads, especially for the inner divertor leg. This talk will explore progress and challenges in modelling these key physics issues in support of STEP.
TAE Technologies, Inc. (TAE) is a privately funded company pursuing a novel approach to magnetic confinement fusion, which relies on Field-Reversed Configuration (FRC) plasmas composed of mostly energetic and stable particles. This advanced FRC-based system simplifies the reactor design and could offer a path forward to clean, safe, and economical aneutronic p-B11 fusion. To validate the science behind the FRC-based approach to fusion, an active experimental program is underway at TAE’s state-of-the-art plasma research facility in Orange County, California. The core of the facility is the world’s largest FRC device named Norman. In Norman, tangential injection of variable energy neutral beams (15 – 40 keV hydrogen, up to 20 MW total), coupled with plasma edge biasing, active plasma control, and advanced surface conditioning, led to production of steady-state, hot FRC plasmas dominated by fast ion pressure. High-performance, advanced beam-driven FRCs were produced,1-4 characterized by (1) macroscopic stability, (2) steady-state plasma sustainment, and (3) dramatically reduced transport rates (more than an order of magnitude improvement over conventional FRCs). Collectively, these accomplishments represent a strong argument validating the FRC-based approach to fusion power. This talk will provide a comprehensive overview of the TAE experimental program.
Hye-Sook Park, Lawrence Livermore National Laboratory, USA
Collisionless shocks are ubiquitous in astrophysical environments such as in supernova remnants, jets in active galactic nuclei and gamma ray bursts and are known to be responsible for cosmic ray acceleration. While the theory of diffusive, or Fermi, shock acceleration (DSA) is well-established, the plasma microphysics responsible for the generation of the shocks, the nature of their resulting magnetic turbulence residue, and the injection of particles into DSA is not yet well understood. With the advent of high-power lasers, laboratory experiments with high-Mach number, collisionless plasma flows can provide critical information to help understand the mechanisms of shock formation by plasma instabilities and self-generated magnetic fields. A series of experiments were conducted on Omega and the National Ignition Facility to observe: the filamentary Weibel instability that seeds microscale magnetic fields [1, 2]; collisionless shock formation (seen by an abrupt ~4x increase in density and ~6x increase in temperature); and electron acceleration distributions that deviated from the thermal distributions . Experimental results along with theoretical interpretations aided by particle-in-cell simulations will be discussed.  H.-S. Park et al., High Energy Density Phys. 8, 38 (2012);  C. Huntington et al., Nat. Phys. 11, 173 (2015);  F. Fiuza et al., Nat. Phys. 16, 916 (2020).
Uri Shumlak, University of Washington, USA and Zap Energy, Inc.
The equilibrium Z pinch is a novel approach to magnetic confinement fusion because it does not rely on external magnetic field coils. Equilibrium conditions are reached through the use of sheared plasma flows, which enhance stability and provide a path to thermonuclear fusion. Simple geometry and strong scaling of fusion gain with pinch current form the cornerstones of this compact fusion device. The sheared-flow-stabilized Z pinch has been developed through integrated computational and experimental investigations at the University of Washington in collaboration with Lawrence Livermore National Laboratory. Experimental results demonstrate plasma stabilization, sustained thermonuclear fusion, and agreement with theoretical and computational predictions. Building on these advances, Zap Energy Inc. is developing a low-cost fusion reactor core based on the equilibrium Z pinch.
In the EU Roadmap to Fusion Electricity, DEMO is the step between ITER and a commercial power plant. It is supposed to generate net electricity and have a self-sufficient fuel cycle. The pre-conceptual studies carried out for a tokamak-based DEMO show that the plasma scenario cannot be simply transferred from the ITER Q=10 scenario. We will discuss the physics issues encountered and possible solutions how to overcome them. The focus of the talk will be on the plasma physics aspects, not on reactor integration, and therefore meant to be exciting for plasma physicists from all fields.
After a review and summary of the observational evidence for random flows and rotation at large altitudes (1-10 kpc) above the discs of spiral galaxies, I discuss the physical parameters of the off-planar gas and the energy sources of the random motions. I argue that the effects of the turbulent viscosity on large-scale gas flows are significant and propose an exploratory model of the viscous coupling of the rotating galactic disc and the corona.
A growing body of evidence suggests that the solar wind is powered to a large extent by an Alfven-wave energy flux that is generated by convective motions on the surface of the Sun. The solar wind and solar corona are also affected by the flux of heat, including conductive losses into the radiative lower solar atmosphere. Numerical simulations that account for the above physics are increasingly able to reproduce remote observations of the corona and solar wind. On the other hand, we still lack an analytic theory that provides formulas for key quantities such as the solar mass-loss rate. Analytic treatments are needed for several reasons. They deepen our understanding by distilling complex processes into their most essential elements, they show how different quantities scale with one another, and they encapsulate our understanding into a portable form that can be applied to other systems and used by anyone. In this talk, I will present a recently developed analytic theory of coronal heating and solar-wind acceleration that provides analytic formulas and intuitive explanations for the solar mass-loss rate, the solar-wind speed far from the Sun, the coronal temperature, the heat flux from the corona into the lower solar atmosphere, and the plasma density at the base of the corona.
Upcoming deuterium-tritium tokamak experiments are expected to have large energetic alpha particle populations. These experiments can be used to study the interaction between these alpha particles and perturbations to the tokamak’s electric and magnetic fields. In this talk, I will first describe why this behavior is important and interesting. Then, I will discuss a new drift kinetic theory to calculate the alpha heat flux resulting from a wide range of perturbation frequencies and periodicities. This theory suggests that the alpha heat flux caused by toroidal field ripple, one type of perturbation, is small. Applied to the toroidal Alfvén eigenmode (TAE), another type of perturbation, the theory suggests a significant alpha heat flux that scales with the square of the TAE amplitude. The TAE amplitude calculated from one saturation condition suggests that TAEs in SPARC, one upcoming deuterium-tritium experiment, will not cause significant alpha transport via the mechanisms in this theory. However, saturation above the level suggested by the simple condition, but within numerical and experimental experience, could cause significant transport.