Plasma Dynamical Processes and Turbulence Studies using Advanced Microwave Diagnostics
Field-line pitch angle measurement
Background: Both tokamak and stellarator devices use helical magnetic fields to confine the plasma, via external coils and internal plasma currents. The field line pitch and its shearing (i.e. radial variation) affect the confinement, thus a measurement of the pitch profile (the local safety factor or q-profile) is extremely important. Conventional methods, such as the motional Stark effect have limited accuracy in the plasma edge, and as with other spectroscopic techniques will be difficult to implement in future devices.
Approach: There are a couple of microwave techniques that could potentially be employed. For example, using the fact that the plasma turbulence aligns with the magnetic field, i.e. k_para << k_perp, and propagates across the field lines, the pitch angle can be estimated from the ratio of the turbulence propagation times poloidal and toroidal directions using cross correlation techniques and signals from a multi-antennae array - see project.1
Alternatively, it may be possible to measure the ellipticity of the reflected beam cross-section (the axis is aligned with the magnetic field) using coherent detection techniques with two orthogonal components.
Goal: The applicability of these methods are to be developed and their reliability tested, first in the lab. then in present fusion devices under varying plasma scenarios. Here, the availability of the various devices operated by the partners (ASDEX Upgrade, TCV, TEXTOR, W7-X) are well suited.
Project lead by IPP in collaboration with IPF, TUM and FZJ: MSc student (t.b.a.) Dr. Garrard Conway Dr. Andreas Kraemer-Flecken