| 1. |
- Danielsson, Mathias, et al.
(författare)
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The cross-section and branching fractions for dissociative recombination of the diacetylene cation C4D2
- 2008
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Ingår i: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806 .- 1873-2798. ; 273:3, s. 111-116
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we report the results of a study on the dissociative recombination (DR) of the diacetylene cation, C4D2+, which has been carried out at the ion storage ring CRYRING in Stockholm, Sweden. The energy-dependent absolute DR cross-section as well as the branching fractions at 0 eV collision energy were measured. The DR cross-section was best fitted using the expression σ(E) = (7.5 ± 1.5) × 10−16 × E−(1.29±0.03) cm2 over the collision energy range 1–100 meV. The thermal rate coefficient was deduced from the cross-section to be α(T) = (1.10 ± 0.15) × 10−6 × (T/300)−(0.79±0.03) cm3/s. The reported branching fractions for C4D2+ agree with previous experiments on the DR of C4H2+ performed at the ASTRID storage ring in Aarhus, Denmark, and furthermore, indicate that the DR of C4D2+ possesses only two channels leading to the following products: C4D + D (75%) and C2D + C2D (25%).
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| 2. |
- Hamberg, Mathias, et al.
(författare)
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Experimental Studies of (HCO+)-C-13 Recombining with Electrons at Energies between 2-50 000 meV
- 2014
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 118:31, s. 6034-6049
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Tidskriftsartikel (refereegranskat)abstract
- An investigation into the dissociative recombination process for (HCO+)-C-13 using merged ion-electron beam methods has been performed at the heavy ion storage ring CRYRING, Stockholm, Sweden. We have measured the branching fractions of the different product channels at similar to 0 eV collision energy to be the following: CO + H 87 +/- 2%, OH + C 9 +/- 2%, and O + CH 4 +/- 2%. The formation of electronically excited CO in the dominant reaction channel has also been studied, and we report the following tentative branching fractions for the different CO product electronic states: CO(X (1)Sigma(+)) + H, 54 +/- 10%; CO(a (3)Pi) + H, 23 +/- 4%; and CO(a' (3)Sigma(+)) + H, 23 +/- 4%. The absolute cross section between similar to 2-50 000 meV was measured and showed resonance structures between 3 and 15 eV. The cross section was fitted in the energy range relevant to astrophysics, i.e., between 1 and 300 meV, and was found to follow the expression sigma = 1.3 +/- 0.3 X 10(-16) E-1.29 +/- 0.05 cm(2) and the corresponding thermal rate constant was determined to be k(T) = 2.0 +/- 0.4 X 10(-7)(T/300)(-0.79 +/- 0.05) cm(3) s(-1). Radioastronomical observations with the IRAM 30 m telescope of HCO+ toward the Red Rectangle yielded an upper column density limit of 4 X 10(11) cm(-2) of HCO+ at the 1 sigma level in that object, indicating that previous claims that the dissociative recombination of HCO+ plays an important role in the production of excited CO molecules emitting the observed Cameron bands in that object are not supported.
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| 3. |
- Hamberg, Mathias, et al.
(författare)
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Experimental studies on the dissociative recombination of H13CO+ with electrons at energies between 2 – 50 000 meV
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Determination of dissociative recombination processes of H13CO+ using merged ion-electron beam methods has been performed at the heavy storage ring CRYRING, Stockholm, Sweden. We have measured the branching fractions at ~0 eV as: CO+H 87±2%, OH+C 9±2% and O+CH 4±2%. The channels leading to CO+H have the following branching fractions between the accessible electronic states of CO(X1S+)+H 46±3%, CO(a3Pg)+H 20±1% and CO(a’3S+)+H 34±3% respectively. The reaction cross section was fitted between 1-300 meV and followed the expression σ = 1.2±0.25×10-16 E-1.32±0.02 cm2 and the corresponding thermal rate constant was determined to k(T) = 2.0±0.4×10−7(T/300)−0.82±0.02 cm3s−1. The cross sections between ~2-50 000 meV were investigated showing resonant structures between 3-15 eV.
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| 4. |
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| 5. |
- Vigren, Erik, et al.
(författare)
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Dissociative recombination of fully deuterated protonated acetonitrile, CD3CND+ : Product branching fractions, absolute cross section and thermal rate coefficient
- 2008
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 10, s. 4014-4019
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Tidskriftsartikel (refereegranskat)abstract
- The dissociative recombination of fully deuterated protonated acetonitrile, CD3CND+, has been investigated at the CRYRING heavy ion storage ring, located at the Manne Siegbahn Laboratory, Stockholm, Sweden. Branching fractions were measured at similar to 0 eV relative collision energy between the ions and the electrons and in 65% of the DR events there was no rupture of bonds between heavy atoms. In the remaining 35%, one of the bonds between the heavy atoms was broken. The DR cross-section was measured between similar to 0 eV and 1 eV relative collision energy. In the energy region between 1 meV and 0.1 eV the cross section data were best fitted by the expression sigma = 7.37 x 10(-16) (E/eV)(-1.23) cm(2), whereas sigma = 4.12 x 10(-16) (E/eV)(-1.46) cm(2) was the best fit for the energy region between 0.1 and 1.0 eV. From the cross section a thermal rate coefficient of alpha(T) = 8.13 x 10(-7) (T/300)(-0.69) cm(3) s(-1) was deduced.
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| 6. |
- Vigren, Erik, et al.
(författare)
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Dissociative recombination of the deuterated acetaldehyde ion, CD3CDO+ : product branching fractions, absolute cross sections and thermal rate coefficient
- 2007
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - 1463-9076 .- 1463-9084. ; 9:22, s. 2856-2861
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Tidskriftsartikel (refereegranskat)abstract
- Dissociative recombination of the deuterated acetaldehyde ion CD3CDO+ has been studied at the heavy-ion storage ring CRYRING, located at the Manne Siegbahn Laboratory, Stockholm, Sweden. Product branching fractions together with absolute DR cross-sections were measured. The branching fractions were determined at a relative collision energy between the ions and the electrons of 0 eV. With a probability of 34% the DR events resulted in no ruptures of bonds between heavy atoms (i.e. no breakage of the C–C bond or the CO bond). In the remaining 66% of the events one of the bonds between the heavy atoms was broken. The energy-dependent cross-section for the DR reaction was measured between 0 and 1 eV relative kinetic energy. In the energy region between 1 meV and 0.2 eV the absolute cross section could be fitted by the expression σ(E) = 6.8 × 10−16E−1.28 cm2, whereas in the energy interval between 0.2 and 1 eV the data were best fitted by σ(E) = 4.1 × 10−16E−1.60 cm2. From these cross section data the thermal rate coefficient (as a function of the electron temperature), α(T) = 9.2 × 10−7 (T/300)−0.72 cm3 s−1 was obtained.
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| 7. |
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| 8. |
- Angelova, G., et al.
(författare)
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Observation of two-dimensional longitudinal-transverse correlations in an electron beam by laser-electron interactions
- 2008
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Ingår i: Physical Review Special Topics - Accelerators and Beams. - 1098-4402. ; 11:7
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Tidskriftsartikel (refereegranskat)abstract
- During the preparatory work for the optical-replica synthesizer experiment in the free-electron laser FLASH at DESY, we were able to superimpose a short, approximately 200 fs long pulse from a frequencydoubled mode-locked erbium laser with titanium-sapphire amplifier and an approximately 20 ps long electron bunch in an undulator. This induces an energy modulation in a longitudinal slice of the electron bunch. A magnetic chicane downstream of the undulator converts the energy modulation into a density modulation within the slice that causes the emission of coherent optical transition radiation from a silver-coated silicon screen. Varying the relative timing between electron and laser, we use a camera to record two-dimensional images of the slices as a function of the longitudinal position within the electron bunch.
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| 9. |
- Chlouba, Tomas, et al.
(författare)
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Diamond-based dielectric laser acceleration
- 2022
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Ingår i: Optics Express. - 1094-4087. ; 30:1, s. 505-510
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Tidskriftsartikel (refereegranskat)abstract
- The field of dielectric laser accelerators (DLA) garnered a considerable interest in the past six years as it offers novel opportunities in accelerator science and potentially transformative applications. Currently, the most widespread approach considers silicon-based structures due to their low absorption and high refractive index in the infrared spectral region and the well-developed silicon processing technology. In this paper we investigate a diamond as an alternative to silicon, mainly due to its considerably higher damage threshold. In particular, we find that our diamond grating allows a three times higher acceleration gradient (60 MeV/m) compared to silicon gratings designed for a similar electron energy. Using more complex geometries, GeV/m acceleration gradients are within reach for subrelativistic electrons.
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| 10. |
- Fahlström, Simon, et al.
(författare)
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Simulations of Magnetic Fields and Forces in Highly Adjustable Magnet (HAM) Undulator Concept Using COMSOL
- 2019
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A design for a new type of undulator insertion device has been proposed. The undulator would consist of a stack of disks that each contain a pair of magnet structures, each disk being a half period of the minimum planar case. The disks could rotate independently about the beam axis, and the distance of the magnets from the center line is adjustable, so the magnetic field is adjustable in magnitude and orientation within the transverse plane along the beam axis. This would allow the undulator to be configured for generating a wide variety of radiation. Plane polarization would be attained with undulator periods as integer multiples of the base period. In the base case the direction of magnetization alternates between each disk, and for the case of multiple periods the magnetization alternates each M:th disk. Helical polarization would be attained with a period greater than two times the base period such that an integer number of periods fit inside the undulator structure. Initial numerical simulations have been made, and are reported in this paper. Building on a previous study [1] further simulations were requested to study the behavior of the magnets closer, and to calculate the forces acting on the magnet structures for use in feasibility assessment. In the previous study simple magnetic structures with uniform direction of magnetization were simulated. In this study a more complex structure was also investigated: a type of partial transverse Halbach configuration. This structure would concentrate the magnetic flux along the beamline and could lead to a more compact design, and limit the magnetic field outside the device.The simulations were made using COMSOL Multiphysics modelling software.
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