Diagnostics

In modern tokamaks, sophisticated diagnostic systems together with accompanying interpretative models are vital in advancing understanding. Increasingly the standard is for a comprehensive awareness of plasma behaviour, in order to definitively identify processes and explain the effects observed in particular measurements. This is also critical to measurement of plasma properties in order to identify parameter dependencies and scaling of effects. As devices move towards operation close to and above limits for instabilities, and seek to control detailed transport properties of the plasma, the integration of diagnostics into real time reconstruction, identification and control systems becomes increasingly important.

This is a challenging field, as all measurements of a fusion plasma must be made remotely, with at most, probes inserted a few millimetres into the edge of the plasma. UKAEA produces a range of world class diagnostics for the MAST and JET devices, often pioneering novel techniques and combining disparate measurements to assist physics investigation. Techniques are based on a wide variety of principles. These include:

• magnetic measurement of instabilities and reconstruction of plasma geometry and energy
• spectroscopic diagnostics for a wide range of internal and edge plasma parameters such as density and temperature
• probes to measure heat and particle fluxes at the edge of the plasma
• visible/infra-red cameras to observe general behaviour and heating effects
• radio/microwave emission to measure temperature profiles
• neutral particle analysis for measurement of (non-maxwellian) particle distributions
• soft X ray for temperature-density profiles
• hard X rays to identify potentially damaging energetic electrons
• neutron detectors

Typically diagnostic experts will be involved in the analysis of their data, and play a role in physics programmes that depend on them as key data, sometimes leading experiments. It is important to provide a good support for relevant experiments, and reliable data with quantification of errors. The understanding behind diagnostic techniques goes well beyond mainstream plasma physics, and will involve many disparate areas, such as atomic physics, electrical effects, Fourier techniques, statistical analysis, radio-frequency physics, etc.

Candidates should have a good experimental background. Grounding in specifically relevant physics or diagnostic expertise is welcome, but not essential as there are opportunities at Culham to develop this. However, a good understanding of the physics fundamentals behind a given area of interest is useful, together with experience of practicalities of experimental work. Expertise with electronics or data acquisition systems can also be of benefit.