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Student Design Project: A Rapid Cycling Synchrotron for a Muon Collider

Despite the success of the Standard Model, many fundamental questions still remain in particle physics. Why is there an asymmetry between the amount of matter and anti-matter we observe in the universe? How do the fundamental forces of nature work and how are they connected? What is the nature of dark matter? One way to investigate these questions is to probe the energy frontier with high energy particle colliders.

Throughout the past 60 years several colliders have been used to fulfil this purpose, culminating in our greatest existing tool for probing the high energy frontier, the Large Hadron Collider (LHC). Many possible replacements have been proposed to further our understanding of these fundamental questions, including the Compact Linear Collider (CLIC), the International Linear Collider (ILC) and the Future Circular Collider (FCC). However, the type of particles that each project will accelerate, electrons and protons, put a fundamental limit on their effectiveness, raising their cost and size.

A possible alternative to these large, expensive colliders is a more compact muon collider. Muons are 207 times more massive than electrons, therefore, they do not suffer from the same energy losses due to synchrotron radiation as electrons. Yet they are still leptons so allow high precision measurements to be done, unlike proton collisions of a similar energy. Both of these points could allow a compact muon circular collider to be built, with a good level of physics potential, yet a low cost.

The current first year PhD students at the John Adams Institute were tasked with completing a design study on the acceleration stage for a 3 TeV centre-of-mass energy muon collider. Their proposed design accelerated muons to a top energy of 1.5 TeV in two Rapid Cycling Synchrotrons (RCSs). The design utilized the existing Super Proton Synchrotron (SPS) tunnel at CERN to significantly save on construction costs.

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The students split into three groups, one group working on the design of the magnets used to bend the beam around the accelerator, one worked on the accelerating cavities used to give energy to the beam and another on the arrangement of these cavities and magnets in the SPS tunnel. Alongside these groups, an additional student also looked into the radiation considerations for a 3 TeV muon collider, as muons decay into electrons and neutrinos, causing potentially problematic amounts of radiation.

The design study progressed over two months, with each team feeding back their work at weekly meetings with experts in accelerator physics. The results of the study were presented at a graduate symposium at Oxford and the team will also be heading out to CERN to present their results to the muon collider community in the near future.

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.