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Ar ion induced desorption yields at the energies 5-17.7 MeV/u
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Nuclear and Particle Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
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2009 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 599, no 1, 1-8 p.Article in journal (Refereed) Published
Abstract [en]

Particle accelerators have, during operation with heavy ion beams, shown a significant pressure rise when the intensity of the beam is increased. This pressure rise is due to ion induced desorption, which is the result of beam ions colliding with residual gas atoms in the beam pipe, where they undergo charge exchange. This causes them to hit the vacuum chamber after the next dipole magnet and gas to be released. For the upgrade of the SIS18 synchrotron at GSI the intensity has to be a few orders of magnitude higher than it is today at the injection energy of 10 MeV/u. The aim of this experiment is to measure desorption yields, η, (released molecules per incident ion) from materials commonly used in accelerators: 316LN stainless steel, Cu, etched Cu, gold coated Cu and Ta, using an Ar beam at impact energies in the range of 5–17.7 MeV/u for perpendicular incidence. The measured initial desorption yields vary for the same material from sample to sample: up to 4.5 times for stainless steel and up to 3 times for etched Cu. Therefore more samples should be studied to have better statistics. Beam conditioning at lower energy does not significantly reduce the desorption yield at higher energy. There is a significant difference of up to a few times in desorption yield between flat and tubular samples. The desorption yield from a Cu sample at grazing incident angle of 125 mrad was an order of magnitude larger than at normal incident angle. It was found that the total number of positively and negatively charged secondary particles, emitted from the surface bombarded with heavy ions, does not exceed 40 secondary particles per impact heavy ion. The current of negatively charged particles was about 2.3 times larger than the current for positively charged particles. The impact from secondary particles on dynamic gas pressure was not possible to investigate.

Place, publisher, year, edition, pages
2009. Vol. 599, no 1, 1-8 p.
Keyword [en]
Ultra high vacuum, Heavy ion induced desorption, Heavy ion accelerators
National Category
Physical Sciences Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-97075DOI: 10.1016/j.nima.2008.09.052ISI: 000263205100001OAI: oai:DiVA.org:uu-97075DiVA: diva2:171861
Available from: 2008-04-18 Created: 2008-04-18 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Studies of Heavy Ion Induced Desorption in the Energy Range 5-100 MeV/u
Open this publication in new window or tab >>Studies of Heavy Ion Induced Desorption in the Energy Range 5-100 MeV/u
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

During operation of heavy ion accelerators a significant pressure rise has been observed when the intensity of the high energy beam was increased. The cause for this pressure rise is ion induced desorption, which is the result when beam ions collide with residual gas molecules in the accelerator, whereby they undergo charge exchange. Since the change in charge state will affect the bending radius of the particles after they have passed a bending magnet, they will not follow the required trajectory but instead collide with the vacuum chamber wall and gas are released. For the Future GSI project FAIR (Facility for Antiproton and Ion Research) there is a need to upgrade the SIS18 synchrotron in order to meet the requirements of the increased intensity. The aim of this work was to measure the desorption yields, η, (released molecules per incident ion) from materials commonly used in accelerators: 316LN stainless steel, Cu, Etched Cu, gold coated Cu, Ta and TiZrV coated stainless steel with argon and uranium beams at the energies 5-100 MeV/u. The measurements were performed at GSI and at The Svedberg Laboratory where a new dedicated teststand was built. It was found that the desorption yield scales with the electronic energy loss to the second power, decreasing for increasing impact energy above the Bragg Maximum. A feasibility study on the possibility to use laser refractometry to improve the accuracy of a specific throughput system was performed. The result was an improvement by up to 3 orders of magnitude, depending on pressure range.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 65 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 425
Keyword
Physics, Heavy Ion Induced Desorption, Ultra High Vacuum, NEG Coating, Heavy Ion Accelerators, Test Particle Monte-Carlo, Gas Flow, Throughput, Laser Refractometry, Metrology, Fysik
Identifiers
urn:nbn:se:uu:diva-8654 (URN)978-91-554-7168-2 (ISBN)
Public defence
2008-05-09, Siegbahnsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15
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Available from: 2008-04-18 Created: 2008-04-18Bibliographically approved

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