Cyclotrons2013 - List of Authors (van Goethem, M.J.)

Paper

Title

Page

Transmission of Heavy Ion Beams in the AGOR Cyclotron

420

A. Sen, S. Brandenburg, M.A. Hofstee
KVI, Groningen, The Netherlands
M.J. van Goethem
UMCG, Groningen, The Netherlands

During the acceleration of intense low energy heavy ion beams in the AGOR cyclotron feedback between beam intensity and pressure, driven by beam loss induced desorption, is observed. This feedback limits the attainable beam intensity. Calculations and measurements of the pressure dependent transmission for various beam agree reasonably well. Calculation of the trajectories of ions after a charge change shows that the desorption is mainly due to ions with near extraction energies, hitting the outer wall at a shallow angle of incidence. For heavy ions like ²⁰⁶Pb²⁷⁺ several charge exchanges are needed before the orbit becomes unstable. Our calculations indicate that these ions make thousands of turns before finally hitting the wall. They therefore are a large fraction of the circulating ions and may contribute to vacuum degradation through restgas ionization. Ion induced desorption for relevant ions and materials has been measured; it explains the observations in the cyclotron semi-quantitatively.
This work has been financially supported by the Foundation FOM, the Dutch funding agency NWO and the EU-FP7, Grant Agreement n° 262010 - ENSAR.

Slides WE3PB04 [5.272 MB]

Paper	Title	Page
WE3PB04	Transmission of Heavy Ion Beams in the AGOR Cyclotron	420
	A. Sen, S. Brandenburg, M.A. Hofstee KVI, Groningen, The Netherlands M.J. van Goethem UMCG, Groningen, The Netherlands
	During the acceleration of intense low energy heavy ion beams in the AGOR cyclotron feedback between beam intensity and pressure, driven by beam loss induced desorption, is observed. This feedback limits the attainable beam intensity. Calculations and measurements of the pressure dependent transmission for various beam agree reasonably well. Calculation of the trajectories of ions after a charge change shows that the desorption is mainly due to ions with near extraction energies, hitting the outer wall at a shallow angle of incidence. For heavy ions like ²⁰⁶Pb²⁷⁺ several charge exchanges are needed before the orbit becomes unstable. Our calculations indicate that these ions make thousands of turns before finally hitting the wall. They therefore are a large fraction of the circulating ions and may contribute to vacuum degradation through restgas ionization. Ion induced desorption for relevant ions and materials has been measured; it explains the observations in the cyclotron semi-quantitatively. This work has been financially supported by the Foundation FOM, the Dutch funding agency NWO and the EU-FP7, Grant Agreement n° 262010 - ENSAR.
	Slides WE3PB04 [5.272 MB]