Laser Thomson scattering measurements in fusion-relevant magnetised plasma (plasma strand project)

Supervisor/s – Professor James Bradley & Dr Mark Bowden (University of Liverpool)

At the University of Liverpool, we have developed a world-class magnetically confined plasma experiment, furnished with an array of optical and electrical diagnostic tools. The system allows us to study anomalous electron transport in magnetised plasmas, relevant to fusion.

Using Laser Thomson Scattering (LTS) [1] we can gain valuable information on the electron energy distribution functions (eedf’s) at different orientations to the magnetic field. The LTS system is a highly accurate diagnostic technique, that is non-perturbing to the plasma and has the benefit of straightforward and unambiguous data interpretation. LTS is used on many Tokamaks (including MAST-U) as the “gold standard” for electron density and temperature acquisition.

In the first stage of this project, tokamak edge conditions will be replicated using a magnetron discharge plasma. Electron properties will be measured using both conventional Langmuir probes and laser Thomson Scattering. The latter is an ideal technique to bench-mark plasma-perturbing Langmuir probe measurements. For the Langmuir probe measurements, orbital motion current-collection theories [2] will be applied to the data to obtain electron temperature and density measurements and the eedf’s will be calculated using the Druyvesteyn method. These results will then be calibrated using the more accurate LTS method.

As the project develops, LTS and Langmuir probe measurements will be made in the magnetron operated in a recently developed “bipolar pulsed” mode in which a positive voltage pulse follows the negative (plasma creating) pulse. We will seek to measure anisotropies in the eedf’s in different parts of the pulse, including strong E x B drift speeds, due to the crossed E and B fields in the plasma source. More sophisticated probe theories will be developed to allow better interpretation of the probe characteristics. Some redesign of the plasma source may be possible to achieve higher magnetic field strengths enabling us to study the effect of magnetised ions on the Langmuir probe characteristics.

The overall aims of this project are to: 1) study anomalous (Bohm-like) cross-field electron transport, applicable to fusion plasmas, 2) to increase the applicability of Langmuir probes in tokamak edge plasmas and 3) develop skills in laser Thomson Scattering diagnostics.

[1] K. Muraoka and M. Maeda ‘Laser-Aided Diagnostics of Plasmas and Gases’, IOP Publishing UK, (2000).
[2] F. F. Chen, “Langmuir Probe Diagnostics”, https://www.seas.ucla.edu/~ffchen/Publs/Chen210R.pdf

The project will be based at the University of Liverpool and supervised by Prof. James Bradley and Dr. Mark Bowden. The results will be directly relevant to on-going research at CCFE (MAST-U) including computer simulations of the edge plasma and Langmuir probe data interpretation. Focused visits to CCFE (MAST-U staff) will be made.

The project also offers the opportunity to collaborate with fusion and low-temperature laboratories world-wide involved in advanced probe development and the understanding of electron transport in magnetised plasmas.

This project is offered by The University of Liverpool. For further information please contact: Professor James Bradley (J.W.Bradley@liverpool.ac.uk).

This project may be compatible with part time study, please contact the project supervisors if you are interested in exploring this.