Pedestal and Equilibrium (PEEQ)
The PEEQ group investigates tokamak physics ranging from the plasma edge to the global equilibrium, seeking to understand and optimise plasma performance.
The pedestal and equilibrium group covers two important aspects of tokamak physics. Firstly, we calculate the plasma equilibrium state using a range of plasma diagnostics which are integrated in interpretive codes. These calculations form the basis of (almost) all plasma data evaluation; if we don’t know what the magnetic structure of the plasma looks like, we can’t do much further work.
Secondly, the group has a strong focus on the so-called pedestal region. This is a small layer at the plasma edge which acts as an insulator to keep the rest of the plasma hot and dense and thus create the optimal conditions for fusion. Our interests and expertise range from data collection to analysis and modelling.
The primary activities and interests of the group are:
Magnetic data collection
The magnetic field and flux sensors which are critical for the real-time operation of ASDEX Upgrade are maintained and operated by the PEEQ group.
Plasma equilibrium reconstruction
The starting point for all detailed plasma analysis is an understanding of the magnetic geometry of the plasma. Various levels of fidelity are used to reconstruct the equilibrium. The most basic uses only the magnetic data, and runs quickly. A next step involves adding measurements of the plasma temperature and density. The current state of the art in equilibrium reconstruction is realised via integrated data analysis (see below).
Plasma density measurements
The edge plasma density can be measured via emission spectroscopy on injected lithium ions. This diagnostic can provide not only density profile measurements, but also information on fluctuations on fast time scales. This is one of the key inputs for integrated data analysis on ASDEX Upgrade.
Integrated data analysis
Combining a multitude of diagnostic measurements that inform radial profiles of density and temperature within a Bayesian statistical framework delivers exceptionally well characterised profile data. The same framework is also used for calculating the magnetic equilibrium, including magnetic measurements, profiles and a current diffusion model. The development continues ...
Pedestal structure analysis
Understanding the physics of the pedestal structure (its gradient and radial extent) is critical for interpretation of present day experiments and projecting to future tokamaks. The group works on data evaluation at ASDEX Upgrade and in collaboration with tokamaks around the world.
Linear edge stability analysis
An important part of understanding the physics of the plasma edge is understanding the various instabilities that can occur. The group uses a range of linear magnetohydrodynamic stability codes to calculate the limits on the edge pressure and current on several tokamaks, with a focus on ASDEX Upgrade.