The electron accelerator

The Mainz Energy-Recovering Superconducting Accelerator MESA will be the world's first superconducting energy-recovering accelerator dedicated to research. "With the high intensity and quality of its beam, MESA provides a unique platform for a forward-looking experimental program to study and test the limits of currently known phenomena in elementary particle physics. This is one of the core objectives of PRISMA," said Professor Hartmut Wittig, Spokesperson for the PRISMA Cluster of Excellence, from whose resources the development and construction of MESA is funded.

Electrons are provided by a photo-gun and are pre-accelerated to 5 MeV with a beam time structure of 1.3 GHz (quasi continuous wave beam). The heart of the accelerator, however, are the two cryomodules each with two superconducting cavities. With each pass the electrons gain up to 25 MeV more energy. Actually, the accelerator has two different operating modes.

In extracted-beam mode, the beam can be directed to the so-called P2 experiment after up to three circulations. Main objective of this parity-violation experiment is to precisely measure the weak mixing angle. Behind P2, the beam is then stopped in a massive beam dump. One may reinterprete this beamdump also as a massive target for production of dark matter particles, which may subsequently be detected by our dedicated beam dump experiment, DarkMESA.

There is also a small-scale beamdump that can be used for MAGIX in external beam mode ‒ particularly advantageous during the accelerator's early stage or when deploying thick targets. However, the real beauty of that accelerator lies in its ability to be operated in energy-recovering mode. In this mode, the beam is directed back to the cavities with a 180-degree phase shift after traversing the MAGIX target. Consequently, instead of being accelerated, the electrons undergo deceleration, leading to the restoration of energy to the accelerating structures! Again, up to 25 MeV for each pass. The beam makes up to two turns until it reaches 5 MeV and is then disposed in a tiny beam dump situated a considerable distance away from our experimental site ‒ excellent for a minimal background situation. Overall, this energy recovery mode provides a very energy efficient acceleration, and in return enormous beam currents of 1000 uA or more (up to 10000 uA in the later stages...!) can be achieved. To achieve this, it is crucial that the beam is not excessively disrupted by the target during interaction, which necessitates the use of a low-density target. Just like the gas jet target we have developed for this very purpose, which provides a very compact interaction zone between the electron beam and the target nuclei.

Are you eager to learn more about the accelerator? Then have a look at the ⇒ MESA group's website, where you'll discover detailed information and exciting insights into this groundbreaking technology.