Theoretical astrophysics and plasma physics at RPC

Abstract:

Magnetized plasma interactions are ubiquitous in astrophysical and laboratory plasmas. Various physical effects have been shown to be important within colliding plasma flows influenced by opposing magnetic fields, however, experimental verification of the mechanisms within the interaction region has remained elusive. Here we discuss a laser-plasma experiment whereby experimental results verify that Biermann battery generated magnetic fields are advected by Nernst flows and anisotropic pressure effects dominate these flows in a reconnection region. These fields are mapped using time-resolved proton probing in multiple directions. Various experimental, modelling and analytical techniques demonstrate the importance of anisotropic pressure in semi-collisional, high-β plasmas, causing a reduction in the magnitude of the reconnecting fields when compared to resistive processes. Anisotropic pressure dynamics are crucial in collisionless plasmas, but are often neglected in collisional plasmas. We show pressure anisotropy to be essential in maintaining the interaction layer, redistributing magnetic fields even for semi-collisional, high energy density physics (HEDP) regimes.

Abstract:

The ST40 tokamak [1], built and operated by Tokamak Energy, has recently been upgraded with upper and lower divertors to enable double null diverted operations with up to 1MA plasma current and 2MW neutral beam heating. ST40 is a high field spherical tokamak (ST), BT=3T at R0=0.4m with a goal to extend the high field spherical tokamak physics basis. Crucially, transport and confinement in high field, high temperature STs will be explored in support to the design of next step STs [2]. Extensive modelling activities have been undertaken to prepare for the exploitation of ST40. A range of plasma equilibrium in double-null configuration have been designed along with detailed scenario modelling, including 1.5D transport simulations and 2D SOL modelling. Gyrokinetic analysis has been performed to assess the level of expected turbulent transport. Building upon the NSTX pedestal database the pedestal width and height in the high performance ST40 scenarios have been predicted. MHD stability analysis and beta limit have been assessed. ST40 will be initially operated in hydrogen with up to 1.5 MW NBI (0.8MW at 55kV and 0.7MW at 25kV). The heating systems will be upgraded in view of the follow up campaign in deuterium, with 2MW, 55kV NBI and around 1.6MW 105/140GHz ECRH. Careful analysis of the power deposited in the divertor during high performance operation has also been carried out.