Multiple awards for accelerator physicist Sarah Schröder

PhD project paves the way for more precision in plasma accelerators

Helmholtz president Otmar Wiestler handing over the award to Sarah Schröder. Image: Helmholtz, Marco Urban

For her excellent PhD thesis in the field of plasma accelerator physics, DESY scientist Sarah Schröder has not only been awarded the Doctoral Prize of the German Physical Society in the section Matter and Cosmos, but also the Helmholtz Doctoral Prize for Mission-Oriented Research in the Field of Matter. The Helmholtz prize ceremony took place on 28 April. The Research Foundation awards this prize to young researchers who combine the search for knowledge and possible applications in their research.

When your first ever scientific publication gets published in Nature Communications, you can count that as a good omen for a steep scientific career. This happened to DESY researcher Sarah Schröder: for her PhD thesis on the FLASHForward experiment, she had developed a collimator apparatus, a metallic filter with which an electron beam can be split into two finely tuned, successive electron beams before they are focused into a plasma. During the commissioning of the collimators, she discovered that they can also be used to precisely measure the accelerating fields in the plasma - a basic requirement for optimising the acceleration process.

"Because the accelerator structure in the plasma is so tiny, measuring it is not that easy," Sarah Schröder explains. "We need a resolution of one thousandth of a millimetre. With the new measurement method, we were able to measure the enormous electric fields of a plasma accelerator in detail for the first time and ultimately even adjust them precisely." The newly developed optimisation method is now routinely used at FLASHForward and is a cornerstone of the unprecedented quality of acceleration achieved there.

Plasma accelerators could allow future particle accelerators to be built more compactly and thus more cost-effectively. A plasma accelerator could achieve the same particle energies in just a few metres that current accelerators achieve over a length of several hundred to thousand metres. A charged particle bundle - in the case of FLASHFoward, these are electrons - is shot into a plasma, a gaseous material consisting of free electrons and ions. Behind the electron beam, a wave of plasma electrons forms in whose wake a second electron beam can be accelerated.

Plasma expert Jens Osterhoff, who supervised Schröder's doctorate, is full of praise: "Sarah is a remarkable scientist. Her success is absolutely deserved and it is a great stroke of luck that she decided to contribute her great talents to the field of plasma accelerator research. With colleagues like Sarah, the field will be in fantastic hands in the future."

She will remain with DESY for a while: since her PhD, which she completed in August 2021, she has been continuing her work at FLASHForward as part of a DESY Fellowship. Her research focus now turns to the next big topic in plasma acceleration: acceleration at high repetition rates. This area is still quite uncharted, both theoretically and experimentally as well as in respect to the available simulation programmes. She will play a leading role in exploring technical and fundamental physical limitations - exciting and challenging times are ahead. By 2024, the researchers want to demonstrate successive acceleration of electron bunches with a spacing of only a millionth of a second. "All applications for beam-driven plasma acceleration need such high repetition rates," Schröder explains. "There are only a few experiments in the world that are dedicated to beam-driven plasma acceleration in a very fundamental way. Of these, FLASHForward is currently the only experiment that allows research on high repetition rates. So the next few years here will be groundbreaking for the entire research field."