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Student Design Project: The eSPS at CERN

One of the biggest mysteries in modern physics is the nature of so called dark matter particles. The illusive particles are thought to make up about 27% of the mass in the universe but their detection has so far evaded scientists. A new facility planned at CERN, the eSPS, seeks to change that. The facility, based around CERN’s Super Proton Synchrotron (SPS), will provide electron beams of up to 18 GeV to the Light Dark Matter eXperiment (LDMX), which would search for dark matter in the mass range we find most ordinary matter, a few MeV to GeV.

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Beyond searching for dark matter, the eSPS facility enables physics research into a wide range of topics, ranging from neutrino oscillations beyond the Standard Model, to accelerator R&D such as demonstrating CLIC (Compact LInear Collider), 800 MHz super-conducting cavity technology, and plasma wakefield accelerators. The eSPS beams are produced by a compact X-band linac with the ability to accelerate electrons to 3.5 GeV using up to 100 MV/m accelerating gradients developed for CLIC. Using existing infrastructure, the beams are sent to the SPS, where they are accelerated to 16 GeV in the SPS ring. The electrons are then slow-extracted to provide the low-current, high EOT (electrons on target) beam required to sustain searches for dark matter at the LDMX.

The current first year PhD students at the John Adams Institute were tasked with completing a design study on how existing tunnels and technology (such as magnets and superconducting RF cavities) could be ‘re-used’ to develop the SPS into a facility that can once again accelerate electrons. The aim of the project was to build this in the least invasive way possible, allowing CERN to switch between electron and proton acceleration with minimal down-time between runs whilst also minimising the cost associated with building new infrastructure and components.
The students split into three groups, one group working on the lattice design of the transfer beamlines, one group looking at the magnets in these transfer lines, and the third looking at the 800 MHz superconducting cavities used to accelerate the electron beam in the SPS. The design study progressed over 7 weeks, with each team feeding back their work at weekly meetings with experts in accelerator physics. The results of the study were presented virtually at a graduate symposium at Oxford. In addition to this, the team may or may not be heading out to CERN to present their results in the near future, depending on the ever-evolving state of a global pandemic!

The accelerator design project is a requirement of the JAI accelerator physics PhD course and is a great way for students to put the theoretical concepts behind accelerator design into practice, alongside strengthening their ability to collaborate in groups.