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Studies of Heavy Ion Induced Desorption in the Energy Range 5-100 MeV/u
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Nuclear and Particle Physics.
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 [en]
Physics, Heavy Ion Induced Desorption, Ultra High Vacuum, NEG Coating, Heavy Ion Accelerators, Test Particle Monte-Carlo, Gas Flow, Throughput, Laser Refractometry, Metrology
Keyword [sv]
Fysik
Identifiers
URN: urn:nbn:se:uu:diva-8654ISBN: 978-91-554-7168-2 (print)OAI: oai:DiVA.org:uu-8654DiVA: diva2:171866
Public defence
2008-05-09, Siegbahnsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15
Opponent
Supervisors
Available from: 2008-04-18 Created: 2008-04-18Bibliographically approved
List of papers
1. Heavy-Ion-Induced Electronic Desorption of Gas from Metals
Open this publication in new window or tab >>Heavy-Ion-Induced Electronic Desorption of Gas from Metals
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2007 (English)In: Physical Review Letters, ISSN 0031-9007, Vol. 98, no 6, 064801- p.Article in journal (Refereed) Published
Abstract [en]

During heavy-ion operation in several particle accelerators worldwide, dynamic pressure rises of orders of magnitude were triggered by lost beam ions that bombarded the vacuum chamber walls. This ion-induced molecular desorption, observed at CERN, GSI, and BNL, can seriously limit the ion beam lifetime and intensity of the accelerator. From dedicated test stand experiments we have discovered that heavy-ion-induced gas desorption scales with the electronic energy loss (dEe/dx) of the ions slowing down in matter; but it varies only little with the ion impact angle, unlike electronic sputtering.

Keyword
Positive-ion beams, Interactions of atoms and molecules with surfaces; photon and electron emission; neutralization of ions, Atomic, molecular, and ion beam impact and interactions with surfaces
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-97073 (URN)10.1103/PhysRevLett.98.064801 (DOI)000244117400034 ()
Available from: 2008-04-18 Created: 2008-04-18 Last updated: 2011-02-14Bibliographically approved
2. A new test stand for heavy ion induced gas desorption measurements at TSL
Open this publication in new window or tab >>A new test stand for heavy ion induced gas desorption measurements at TSL
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2008 (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. 586, no 3, 377-381 p.Article in journal (Refereed) Published
Abstract [en]

In several experiments at CERN, GSI and BNL it has been found that the lifetime of highly energetic heavy ions in synchrotrons decreases with increasing number of injected ions. This phenomenon occurs due to the collisions of beam ions and residual gas molecules leading to the change of charge of the ions and their loss on the vacuum chamber walls, which in turn cause ion-induced gas desorption and further pressure increase. To gain a deeper understanding of the ion-induced desorption process in the energy range 5-45 MeV/u, a dedicated test stand was built at the end of the K beamline at The Svedberg Laboratory (TSL) in Uppsala, Sweden. The energy range was chosen due to the fact that the injection energy of the heavy ion synchrotron SIS18 at GSI will be 10 MeV/u, and that there are insufficient data in this energy range. A Test Particle Monte-Carlo model of the experimental set-up was build-up, run and analysed for different sample configurations. An important result is that for the same sample material the desorption yield from a flat sample causes a 1.58 times larger pressure increase than that of a tubular sample. A detailed explanation of the set-up is presented.

Keyword
ultrahigh vacuum, heavy-ion-induced desorption, test particles Monte-Carlo
National Category
Physical Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-97074 (URN)10.1016/j.nima.2007.12.020 (DOI)000253960800001 ()
Available from: 2008-04-18 Created: 2008-04-18 Last updated: 2016-04-12Bibliographically approved
3. Ar ion induced desorption yields at the energies 5-17.7 MeV/u
Open this publication in new window or tab >>Ar ion induced desorption yields at the energies 5-17.7 MeV/u
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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.

Keyword
Ultra high vacuum, Heavy ion induced desorption, Heavy ion accelerators
National Category
Physical Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-97075 (URN)10.1016/j.nima.2008.09.052 (DOI)000263205100001 ()
Available from: 2008-04-18 Created: 2008-04-18 Last updated: 2016-04-14Bibliographically approved
4. Energy Scaling of the Ion-Induced Desorption Yield for Perpendicular Collisions of Ar and U with Stainless Steel in the Energy Range between 5 and 100 MeV/u
Open this publication in new window or tab >>Energy Scaling of the Ion-Induced Desorption Yield for Perpendicular Collisions of Ar and U with Stainless Steel in the Energy Range between 5 and 100 MeV/u
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2009 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 27, no 2, 245-247 p.Article in journal (Refereed) Published
Abstract [en]

For the GSI future project Facility for Antiproton and Ion Research a beam intensity of 10(12)U(28+)ions/s is planned to be extracted from the GSI heavy ion synchrotron SIS18. Measurements performed in 2001 showed that the beam lifetime of the ions in the synchrotron is decreasing with increasing number of injected particles due to vacuum   instabilities caused by ion-induced desorption. The injection energy for the SIS18 is about 10 MeV/u and U28+ ions are accelerated to 200 MeV/u limited by the magnetic rigidity for the low charge state. The aim of this work was to measure the desorption yield as a function of   the impact energy from injection to extraction of SIS18 at GSI. Low energy yields at 5.0, 9.7, and 17.7 MeV/u were measured at the Cyclotron of The Svedberg Laboratory in Uppsala. High energy yields at 40, 80, and 100 MeV/u were measured at SIS18 of GSI in a different   setup. It was found that the desorption yield scales with the electronic energy loss (dE/dx)(el)(n), with n between 2 and 3, decreasing for increasing impact energy above the Bragg maximum.

National Category
Physical Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-97076 (URN)10.1116/1.3065979 (DOI)000264017500012 ()
Available from: 2008-04-18 Created: 2008-04-18 Last updated: 2016-04-14Bibliographically approved
5. Heavy-Ion Induced Desorption of a TiZrV Coated Vacuum Chamber Bombarded with 5 MeV/u Ar8+ beam at grazing incidence
Open this publication in new window or tab >>Heavy-Ion Induced Desorption of a TiZrV Coated Vacuum Chamber Bombarded with 5 MeV/u Ar8+ beam at grazing incidence
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2009 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 27, no 1, 139-144 p.Article in journal (Refereed) Published
Abstract [en]

TiZrV nonevaporable getter (NEG) coated vacuum chambers is a new vacuum technology which is already used in many particle accelerators worldwide. This coating is also of interest for heavy-ion accelerator vacuum chambers. Heavy-ion desorption yields from an activated as well as a CO saturated NEG coated tube have been measured with 5 MeV/u Ar8+ beam. The sticking probability of the NEG film was obtained by using the partial pressure ratios on two sides of the NEG coated tube. These ratios were compared to results of modeling of the experimental setup with test particle Monte Carlo and angular coefficient methods. The   partial pressures inside the saturated NEG coated tube bombarded with heavy ions were up to 20 times larger than those inside the activated one. However, the partial pressure of methane remained the same. The value of the total desorption yield from the activated NEG coated tube is 2600 molecules/ion. The desorption yields after saturation for CH4, H-2, and CO2 were found to be very close to the yields measured after the activation, while CO increased by up to a factor of 5. The total desorption yield for the saturated tube is up to 7000 molecules/ion. The large value of the desorption yield of the activated NEG coated   tube, an order of magnitude higher than the desorption yield from a stainless steel tube at normal incident angle, could be explained by the grazing incident angle.

Keyword
carbon compounds, desorption, hydrogen, ion beam effects, metallic thin films, Monte Carlo methods, titanium alloys, vanadium alloys, zirconium alloys
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-97077 (URN)10.1116/1.3032914 (DOI)000264017300019 ()
Available from: 2008-04-18 Created: 2008-04-18 Last updated: 2010-08-12Bibliographically approved
6. Improved determination of the gas flow rate for UHV and leak metrology with laser refractometry
Open this publication in new window or tab >>Improved determination of the gas flow rate for UHV and leak metrology with laser refractometry
2006 (English)In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 17, no 10, 2767-2772 p.Article in journal (Refereed) Published
Abstract [en]

A system often used for vacuum metrology purposes in order to calibrate vacuum gauges in the UHV region and to calibrate gas leak rates is the throughput system, employing the continuous ( or dynamic) expansion method. An important component in such systems is the flowmeter, which has to deliver a pure and well-determined gas flow into the system. To determine the generated gas flow, a number of factors including the pressure inside the flowmeter have to be determined. However, it has turned out that the calibration uncertainty when measuring the pressure in the flowmeter gives a main contribution to the total uncertainty (of typically about 0.1%) for the generated flow, thereby limiting the accuracies of the generated vacuum pressure as well as gas leak rates in UHV metrology. A feasibility study is reported in this paper about the possibility of using laser refractometry to monitor dynamic gas density in situ in the flowmeter, as an alternative and possibly more accurate means of determining the generated gas flow, thereby potentially improving the calibration gas leak rates in the range 10(-8) - 10(-4) Pa m(3) s(-1).

Keyword
laser refractometry, gas flow, metrology, throughput, UHV
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-97078 (URN)10.1088/0957-0233/17/10/031 (DOI)000241989700033 ()
Available from: 2008-04-18 Created: 2008-04-18 Last updated: 2011-05-12Bibliographically approved
7. Addendum to ‘Improved determination of the gas flow rate for UHV and leak metrology with laser refractometry’
Open this publication in new window or tab >>Addendum to ‘Improved determination of the gas flow rate for UHV and leak metrology with laser refractometry’
2007 (English)In: Measurement science and technology, ISSN 0957-0233, Vol. 18, no 11, 3661-3663 p.Article in journal (Refereed) Published
Abstract [en]

Clarification is provided for certain expressions quoted in Hedlund and Pendrill (2006 Meas. Sci. Technol. 17 2767-72).

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-97079 (URN)10.1088/0957-0233/18/11/052 (DOI)
Available from: 2008-04-18 Created: 2008-04-18 Last updated: 2010-03-05Bibliographically approved

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