First measurements of energetic protons in Mega Amp Spherical Tokamak Upgrade (MAST-U)

What is it about?

In this work we present the first measurements of proton production rates from deuterium-deuterium (DD) fusion reactions occurring in the Mega Amp Spherical Tokamak Upgrade (MAST-U). Our project is part of an international collaboration with the United Kingdom Atomic Energy Authority (UKAEA) involving experiments at the Culham Campus in the United Kingdom. Our proton detector (PD) detects energetic protons (3 MeV) and tritons (1 MeV) emitted by a plasma heated by high-energy particle beams. Injection of these beams into the plasma results in the presence of a population of energetic ions, which account for nearly all of the DD fusion reactions. Detection of the charged products of these reactions provides information about the energetic ions producing them. We want to find out where in the plasma these fusion products originate from, what their production rates are and how they change with time. Using collimated silicon detectors and a diamond detector simultaneously has allowed us to directly compare the performance of these two detector types.

Featured Image

Photo by Hal Gatewood on Unsplash

Photo by Hal Gatewood on Unsplash

Why is it important?

Neutrons emitted during DD fusion reactions are typically measured to obtain information on energetic ions in hot deuterium plasmas and are detected using relatively large instruments located outside the tokamak vessel. Charged fusion reaction products, such as protons, can be measured using compact detector systems which have a much better intrinsic energy resolution and can be used to determine the energy distribution of charged fusion products, which contains additional information on energetic ion and plasma parameters. This technique requires that the detectors must be located inside the vacuum vessel and are thus exposed to the very hostile plasma environment. In our study we showed that diamond detectors have the potential to be uniquely suited to detect charged fusion products as they promise to be much more radiation resistant and much less sensitive to temperature variations than silicon detectors. We were able to identify high energy protons, measuring proton count rates of up to 200-300 kHz, and show that the diamond detector can be used to study various plasma instabilities and their effects on plasma confinement and heating.

Perspectives