Stockholm University

Development of Diagnostics for DESIREE 

ER:  Susanta Das (das@msl.se)
Supervisor:  Anders Kaellberg (kallberg@msl.se)

The Double Electrostatic Ion Ring Experiment (DESIREE) consists of two electrostatic storage rings with a common straight section where merged-beams experiments on positive/negative ion collisions can be performed. The two rings are housed in a single double walled vacuum chamber built like a cryostat with a radiation screen and several layers of super insulation in between the two chambers. The inner chamber, which holds all optical elements, is cooled by cryogenerators attached to the bottom of this chamber. The whole accelerator structure is cooled to temperatures below 20 K. This low temperature in combination with the unique double ring structure results in a very powerful machine for studying interactions between cold molecular ions close to zero relative energy.

In experiments for which the primary objective is to determine the absolute cross section for the process under investigation, it is a necessity to have reliable and accurate diagnostic tools for determination of the absolute currents stored and the position, width and shape of the two beams in the merger section. The main ingredients necessary for this have been identified to be electrostatic pick-up electrodes, position-sensitive detection of neutralized particles from residual-gas collisions and a system of beam scrapers. The fact that all diagnostics inside DESIREE has to be compatible with the cryogenic environment as well as the ultra-high vacuum requirements is a challenge to the design.

Within this DITANET project, key diagnostics components have been developed. In addition to the before-mentioned instrumentation a secondary emission monitor has been designed and successfully tested with beam. Investigations into applications for medical accelerators, as well as for other electrostatic storage ring projects complemented this project. During the project, close collaboration took place with partners at HIT/Germany, the Max Planck Institute for Nuclear Physics in Heidelberg/Germany and the University of Liverpool/UK.