University of Liverpool

Beam Stability and Life Time in Low Energy Storage Rings 

Trainee: Bianca Veglia
Supervisor: Carsten P. Welsch

ELENA at CERN’s AD and FLAIR will provide cooled beams of antiprotons at lower energies than currently achievable anywhere in the world. It will be crucial to have detailed knowledge about the achievable stability of the beam in the storage ring and the expected beam life times. Existing low energy storage rings, operating at keV beam energies, found strong limitations on beam intensity and reduced life time in experimental studies. The nature of these effects had not been fully understood for a very long time and only recently causes of these limits to beam current and life time were identified and reproduced in simulations.

The Fellow developed realistic models for beam transport, storage, deceleration and cooling from storage rings through beam lines to experiments. This will allow to investigate the effects impacting on beam stability and emittance. They will also help establish realistic models of beam storage and cooling. Using data collected during measurements with Low Energy Ion Ring (LEIR), the Fellow developed cooling maps describing how the cooling efficiency of the electron cooler varies with increasing distance from the beam centre.

Further data analysis provided elements to accurately simulate the cooling process that can be expected for ELENA. The simulation tools developed by the Fellow enabled start-to-end simulations of antiproton pulses through electrostatic low energy beam lines.

A DMD based Beam Halo and Emittance Monitor 

Trainee: Milena Vujanovic
Supervisor: Carsten P. Welsch

The exact measurement of the beam profile in any accelerator is of great importance for a full understanding of the physical processes happening in the beam. Of particular relevance is the detection of particles in the tail distribution of a beam, the so-called ‘beam halo’. This requires the detection of small quantities of light which is often difficult because other parts of the beam yield much higher signal levels.

As changes in beam halo are usually associated with emittance growth, particle losses, and even damage to accelerator components, it is essential to have a method in place which allows non-invasive, high dynamic range measurements of full profile which includes the halo.

A (digital micro mirror device) DMD-based Beam Halo Monitor allows to restrict any measurement to specific ‘regions of interest’ and is therefore a promising tool for imaging of beam parts. The Fellow adapted this imaging method for advanced measurements that could not be achieved with any other technique so far. The Fellow imaged the visible component of the synchrotron radiation onto a DMD which allowed it to serve as an optical mask to block the light coming from the beam core, enabling measurement of the halo. As a result, the dynamic range of the camera has been increased by two orders of magnitude.

6-D studies into beam motion in low energy storage rings 

Trainee: Volodymyr Rodin 
Supervisor: Carsten P. Welsch

The study of the collision dynamics of correlated quantum systems can be done by crossing a gas jet target with a beam of low energy antiprotons. Antiproton (projectile) energies between 20 keV and some MeV correspond to interaction strength between a weekly perturbed system (where approximation theories can be applied) and strong perturbation (where all details of the interaction need to be taken into account in theoretical models).

However, this requires beam compression to a diameter of around 1 mm and a pulse length of 1-2 ns or a highly optimized compact recycler ring. 

The Fellow developed a comprehensive simulation framework which shall enable these studies under both ELENA and FLAIR conditions. Compression of the beam is based on higher order harmonic bunching and phase space ‘gymnastics’ and, for the first time, extended to a full 3D description of bunches motion which has now been shown for one of ELENA’s transfer lines. All relevant effects on the beam are considered, such as intra-beam scattering, phase space rotation, scattering and cooling.

Studies of in-ring schemes have been done along (quasi) single-pass setups where the spectrometer was installed in an external beam line or a dedicated small storage ring. Another achievement was the benchmarking of state-of-art Micro-Electro-Mechanical-Systems (MEMS) sensor technology on beamline optics. Good agreement within beam tracking simulation tools confirmed the possibility of bunch compression within ELENA storage ring as well as in transfer lines. Ongoing research will focus on the impact of bunch compression on beam stability and a proposal of the best experimental setups to detect secondaries after beam collision with gaseous target.