One of the work packages, led by the ISIS Low Energy Beams Group (LEBG), is looking into how to improve the beam transport from an ion source into a radio frequency quadrupole (RFQ) accelerator.

“It is common to think that the hydrogen ions simply pass through the low energy beam transport in vacuum but that's not the case", says Erin Flannigan, a postdoctoral researcher in the LEBG. “The beam ions repel each other but they also pass through a background of hydrogen, ionising the hydrogen molecules. These slow charged particles then reduce the repulsion between the beam ions making it easier to transport the beam."

This dynamic process, called space charge compensation, affects the beam transport but is not well-understood, especially for H^- beams like those used at ISIS. The STFC-DAE project is developing diagnostics to measure the time it takes for the compensation to build up until it reaches a steady state and beam transport can be controlled accurately.

“We use optical diagnostics and particle monitors for these experiments and work with STFC's Scientific Computing to run complex particle-in-cell simulations to model the compensation process. The goal is to find techniques to make the compensation faster until we reach full compensation and can control the beam divergence," continues Erin.

In October 2025, the LEBG hosted Deepak Mathad from Bhabha Atomic Research Centre (BARC), a large-scale DAE facility in Mumbai, for experiments using the Ion Source Development Rig and Front End Test Stand facilities at ISIS. The purpose of these experiments was to complete a technology transfer of ISIS-developed optical diagnostics equipment from ISIS to BARC, where the experiments will be continued with proton beams.

“Comparing the results of the space charge compensation experiments with both H^- and H⁺ beams using the same diagnostics techniques is a unique opportunity. It helps us to build better low energy beamlines for high-current beams," Deepak says. “At BARC we are developing a proton accelerator for a next-generation accelerator-driven nuclear power plant. This will use a spallation neutron target to drive the nuclear reactions, allowing us to use thorium fuel, which is abundant in India. Improving the beam transport in the low energy beamline where significant beam losses occur is crucial."

The ISIS-developed optical diagnostics device can measure very weak light emission, invisible to human eye. It was developed by Erin Flannigan and Dean Morris, a graduate electrical engineer in the LEBG. The next step for the collaboration and the technology transfer is an experimental campaign at BARC, assisted by the LEBG team.

The STFC-DAE accelerator technology project is led by ASTeC and has received around £1.5 million from the International Science Partnerships Fund (ISPF).