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Ions in cold electrostatic storage devices
Stockholm University, Faculty of Science, Department of Physics.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

We have constructed a compact purely electrostatic ion-beam trap, ConeTrap, which we have mounted inside a double-walled vacuum chamber. In the inner vacuum chamber, we can obtain ultra-high vacuum (UHV) conditions and reach thermal equilibrium at well controlled temperatures down to 10 K. The chamber was constructed partly with the purpose of making high-precision measurements in ConeTrap, but also as a test-chamber for testing components (such as the detector-assembly tested and described in this thesis and paper III) to be used in the DESIREE (Double ElectroStatic Ion Ring ExpEriment) facility. The latter is a double electrostatic ion storage-ring being constructed at Stockholm University, in which the conditions are meant to mimic the environment in the interstellar medium. The interaction between two oppositely charged ions at very low relative velocities (controlled collision energies down to 10 meV) may then be studied in a section of the storage device where the two ion beams merge.

The lifetime of loosely bound electronic systems, for example He-, is, at room temperature (and even at much lower temperatures), significantly affected by photons from blackbody radiation from the experimental device and its surroundings. The cryogenic temperature and low pressure obtained in the test chamber have made it possible to use ConeTrap to make the first correction-free lifetime measurement of the long-lived J=5/2 fine-structure level of the metastable 1s2s2p 4Po state of He-. Under the assumption of a statistical population of the fine-structure levels, at the time when the ions are created, we have also deduced the lifetimes of the short-lived J=1/2 and J=3/2 fine-structure levels. Furthermore, we have used ConeTrap to measure the pressure dependent storage lifetimes of He+ and Ar+ ions over wide ranges of temperatures and pressures, and we have thus been able to store positive ions with storage lifetimes of tens of seconds.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2010. , 89 p.
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-32659ISBN: 978-91-7155-983-8 (print)OAI: oai:DiVA.org:su-32659DiVA: diva2:281282
Public defence
2010-01-29, FA32, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Available from: 2010-01-07 Created: 2009-12-15 Last updated: 2009-12-15Bibliographically approved
List of papers
1. Precision lifetime measurements of He- in a cryogenic electrostatic ion-beam trap
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2009 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, no 21, 213002- p.Article in journal (Refereed) Published
Abstract [en]

We have developed a small purely electrostatic ion-beam trap which may be operated in thermal equilibrium at precisely controlled temperatures down to 10 K. Thus, we avoid magnetic field induced mixing of quantum states and may effectively eliminate any influence from absorption of photons from black-body radiation. We report the first correction free measurements of the lifetimes of the 1s2s2p 4PoJ state of 4He- and the high precision result 359.0±0.7 μs for the J=5/2 level. The lifetimes for the J=3/2 and J=1/2 levels are determined to be 12.3±0.5 and 7.8±1.0 μs, respectively.

National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-32636 (URN)10.1103/PhysRevLett.103.213002 (DOI)
Available from: 2009-12-15 Created: 2009-12-15 Last updated: 2017-12-12Bibliographically approved
2. Cryogenic keV ion-beam storage in ConeTrap - a tool for ion-temperature control
Open this publication in new window or tab >>Cryogenic keV ion-beam storage in ConeTrap - a tool for ion-temperature control
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2010 (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. 621, no 1-3, 83-90 p.Article in journal (Refereed) Published
Abstract [en]

We have tested the ion-storage capabilities of the compact triple-electrode electrostatic ion-beam trap, ConeTrap, down to cryogenic temperatures. The low-temperature operation of this electrostatic storage device is an important test for the double electrostatic ion-ring experiment, DESIREE, which is presently under construction at Stockholm University. In the present work we measured the pressure dependent storage lifetimes of 2.5 keV He+ and 2.8 keV Ar+ ion beams in ConeTrap at temperatures down to 28 K and pressures down to 1.3·10-10 mbar. The so far longest measured ion storage lifetime using this system is 21.5±3.8 s for Ar+ ions. The present combination of ConeTrap and the cryogenic experimental chamber was recently applied in the first black-body correction-free measurement of the lifetime of the metastable He- ion at 10 K [Phys. Rev. Lett. 103, 213002(2009)].

Place, publisher, year, edition, pages
Elsevier B.V., 2010
Keyword
Electrostatic ion-beam storage
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-32645 (URN)10.1016/j.nima.2010.06.008 (DOI)
Available from: 2009-12-15 Created: 2009-12-15 Last updated: 2017-12-12Bibliographically approved
3. Operating a triple stack microchannel plate-phosphor assembly for single particle counting in the 12-300 K temperature range
Open this publication in new window or tab >>Operating a triple stack microchannel plate-phosphor assembly for single particle counting in the 12-300 K temperature range
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2007 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 78, no 11, 113301- p.Article in journal (Refereed) Published
Abstract [en]

An assembly consisting of a stack of three microchannel plates (MCPs) and a phosphor screen anode has been operated over the temperature range from 300 to 12 K. We report on measurements at 6.4 kHz (using an alpha source) and with dark counts only (15 Hz). Without any particle source,  the MCP bias current decreased by a factor of 2.1×103 when the temperature was lowered from 300 to 12 K. Using the alpha source, and a photomultiplier tube (PMT) to monitor the phosphor screen anode, we first observed an increase in the decay time of the phosphor from 12 to 45 μs when the temperature was decreased from 300 to 100 K while the decay time then decreased and reached a value of 5 μs at 12 K. The pulse height distribution from the PMT was measured between300 and 12 K and shows a spectrum typical for a MCP phosphor setup at 300 K and 12 K but is strongly degraded for intermediate temperatures. We conclude that the present MCP-phosphor detector assembly is well suited for position-sensitive particle counting operation at temperatures down to at least 12 K even for count rates beyond 6 kHz. This result is crucial and an important part of ongoing developments of new instrumentation for investigations of, e.g., interactions involving complex molecular ions with internal quantum state control.

Place, publisher, year, edition, pages
American Institute of Physics, 2007
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-32613 (URN)10.1063/1.2814030 (DOI)000251325900012 ()
Available from: 2009-12-15 Created: 2009-12-14 Last updated: 2017-12-12Bibliographically approved
4. DESIREE as a new tool for interstellar ion chemistry
Open this publication in new window or tab >>DESIREE as a new tool for interstellar ion chemistry
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2008 (English)In: International Journal of Astrobiology, ISSN 1473-5504, E-ISSN 1475-3006, Vol. 7, no 3-4, 205-208 p.Article in journal (Refereed) Published
Abstract [en]

A novel cryogenic electrostatic storage device consisting of two ion-beam storage rings with a common straight section for studies of interactions between oppositely charged ions at low and well-defined relative velocities is under construction at Stockholm University. Here we consider the prospect of using this new tool to measure cross-sections and rate coefficients for mutual neutralization reactions of importance in interstellar ion chemistry in general and specifically in cosmic pre-biotic ion chemistry.

National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-32615 (URN)10.1017/S1473550408004229 (DOI)000273383100003 ()
Available from: 2009-12-15 Created: 2009-12-14 Last updated: 2017-12-12Bibliographically approved

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