Introduction
There are more than forty thousand particle accelerators currently in use worldwide. Despite only 3% of those accelerators being dedicated to scientific research, over thirty Nobel Prizes have resulted from their use. The remaining 97% deliver far-reaching impact in areas such as medicine, energy, and the environment. However, the beam time available is generally saturated by users, with the high demand for more facilities constrained by traditional radio-frequency accelerator technology, which makes them large and costly.
Plasma-wakefield accelerators overcome these limitations by harnessing the enormous electric fields experienced at atomic scales, utilised by ploughing a density wave using an intense particle beam, allowing a second particle beam to surf behind in the wake. This exciting method of acceleration offers the potential to reduce the accelerator arm of these facilities a thousand-fold, from the length of a football field to a side of A4 paper, enabling a new generation of accelerators to be used both for scientific research as well as pressing societal needs such as particle-based cancer therapy.
To enable this revolution, the plasma acceleration process must be repeated many thousands of times per second — thousands of times faster than the current world record. We recently demonstrated that plasma accelerators can in principle operate at 10 MHz repetition rates, thus meeting the demands of linear colliders such as the HALHF scheme that we recently proposed. The next step in development is to realise this promise by building a plasma accelerator that can operate as close to this upper limit as possible.
The major scientific question currently preventing us from doing so, however, is an insufficient understanding of how the plasma evolves over the relatively long timescales between acceleration events. More specifically, how does the plasma heat up due to the cumulative energy deposition from multiple acceleration events and how does that temperature evolve in time? Understanding this, through the development of novel plasma-temperature diagnostics as well as high-performance computing codes to simulate the fundamental effects, is the major goal of our group.