Non-invasive Beam Profile Monitor – An Accelerator Physicists’ Dream

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Supersonic gas jet based beam profile monitor.

Beam profile measurement is very important for any particle accelerator to monitor how the beam moves and optimise the experimental output. Measuring the beam profile with high precision without affecting the primary beam’s motion has always been the dream of beam diagnostics experts from around the world. Beams with ever high intensity and high power as they will be found for example in the High Luminosity upgrade of the Large Hadron Collider (HLLHC), today create totally new challenges, due to their destructive nature. This makes the development of a method suited for beam profile diagnostics at range of different energies and a variety of particle species a very challenging task.

Researchers from the QUASAR Group have now experimentally demonstrated a new type of monitor that can provide a universal solution to this problem. Compared with traditional beam profile measurements using scintillating screens such as phosphor or YAG, this monitor uses a supersonic gas jet curtain which on the one hand will not be fragile, because it can be reproduced many times. On the other hand, this monitor will not interfere with the projectile beam very much as the interaction rate can be controlled via the gas jet density and thickness.

The detection system of this diagnostic shares some basic ideas with commonly used ionisation beam profile monitors. These use the residual gas inside a vacuum chamber to monitor the primary beam. Both methods are non-invasive and rely on the detection of ions that are produced by the primary beam to be measured, however, the properties of the supersonic gas jet such as its density, low internal temperature and high directional speed give access to a better detection efficiency and resolution while maintaining much better vacuum conditions than what can be realised with an IPM.

An open access paper just published in the APS journal Physical Review Accelerators and Beams describes the detailed monitor design, underlying diagnostic principle and also presents first experimental results. The monitor is currently being redesigned to meet the specific challenges of the HLLHC project even better and a second gas jet setup will be established at the Cockcroft Institute later in 2017.

Further information:

V. Tzoganis, et al., Design and first operation of a supersonic gas jet based beam profile monitor, Phys. Rev. Accel. Beams 20, 062801 (2017).