Ansgar Simonsson

CRYRING — a synchrotron, cooler and storage ring

Abstract CRYRING is a small synchrotron and storage ring equipped with electron cooling. Highly charged ions from the electron beam ion source CRYSIS or singly charged ions from the plasmatron source MINIS are injected via an RFQ into the ring. The facility is in the commissioning phase. Full design energy has been achieved and electron cooling demonstrated both for atomic and molecular ions. The experimental program started in August with two projects, dissociative recombination of H+3 ions and radiative recombination to deuterons. The status as of September 20, 1992, is reported.

First storage of ion beams in the Double Electrostatic Ion-Ring Experiment: DESIREE

We report on the first storage of ion beams in the Double ElectroStatic Ion Ring ExpEriment, DESIREE, at Stockholm University. We have produced beams of atomic carbon anions and small carbon anion molecules (C(n)(-), n = 1, 2, 3, 4) in a sputter ion source. The ion beams were accelerated to 10 keV kinetic energy and stored in an electrostatic ion storage ring enclosed in a vacuum chamber at 13 K. For 10 keV C2 (-) molecular anions we measure the residual-gas limited beam storage lifetime to be 448 s ± 18 s with two independent detector systems. Using the measured storage lifetimes we estimate that the residual gas pressure is in the 10(-14) mbar range. When high current ion beams are injected, the number of stored particles does not follow a single exponential decay law as would be expected for stored particles lost solely due to electron detachment in collision with the residual-gas. Instead, we observe a faster initial decay rate, which we ascribe to the effect of the space charge of the ion beam on the storage capacity.

DISSOCIATIVE RECOMBINATION OF NITRILE IONS: DCCCN + AND DCCCND +

Branching ratios and absolute cross sections have been measured for the dissociative recombination of DCCCN+ and DCCCND+ using the CRYRING ion storage ring. In the case of DCCCN+ the dissociation y ...

Dissociative recombination of protonated methanol

The branching ratios of the different reaction pathways and the overall rate coefficients of the dissociative recombination reactions of CH3OH2+ and CD3OD2+ have been measured at the CRYRING storage ring located in Stockholm, Sweden. Analysis of the data yielded the result that formation of methanol or deuterated methanol accounted for only 3 and 6% of the total rate in CH3OH2+ and CD3OD2+, respectively. Dissociative recombination of both isotopomeres mainly involves fragmentation of the C-O bond, the major process being the three-body break-up forming CH3, OH and H (CD3, OD and D). The overall cross sections are best fitted by sigma = 1.2 +/- 0.1 x 10(-15) E(-1.15 +/- 0.02) cm2 and sigma = 9.6 +/- 0.9 x 10(-16) E(-1.20 +/- 0.02) cm2 for CH3OH2+ and CD3OD2+, respectively. From these values thermal reaction rate coefficients of k(T) = 8.9 +/- 0.9 x 10(-7) (T/300)(-0.59 +/- 0.02) cm3 s(-1) (CH3OH2+) and k(T) = 9.1 +/- 0.9 x 10(-7) (T/300)(-0.63 +/- 0.02) cm3 s(-1) (CD3OD2+) can be calculated. A non-negligible formation of interstellar methanol by the previously proposed mechanism via radiative association of CH3+ and H2O and subsequent dissociative recombination of the resulting CH3OH2+ ion to yield methanol and hydrogen atoms is therefore very unlikely.

Studies of electron cooling with a highly expanded electron beam

Abstract The electron cooler at CRYRING is now operating with a superconducting gun solenoid and an electron beam that is adiabatically expanded with a factor of up to 100. This paper describes the new gun solenoid and electron gun. It presents measurements made on longitudinal cooling forces with different expansion factors, electron densities, magnetic field strengths and beam alignments. It also presents studies of a transverse beam instability that appears when a misalignment is introduced between ion and electron beams. Finally, some measurements of dielectronic recombination that directly yield transverse and longitudinal electron temperatures are discussed.

Experimental determination of dissociative recombination of CH2OH+, CD2OD+, and CD2+

Measurements of the cross-sections and branching ratios of the dissociative recombination of the ions CH2OH þ, CD2OD þ and CD2OD þ 2 have been performed at the CRYRING storage ring located in Stockholm, Sweden. Evaluation of the data yielded reaction rate coefficients of: 7.0 10 (T/300) 0.78 cmmol 1 s 1 for CH2OH; 7.5 10 (T/300) 0.70 cmmol 1 s 1 for CD2OD þ and 1.51 10 (T/300) 0.66 cmmol 1 s 1 for CD2OD2 . Calculation of the branching ratios for CH2OH þ and its deuterated isotopologue gave the following results for the DR reaction channels involving C–O bond fissure: H2OþCH (2.2%) and CH2þOH (5.5%) in the reaction of CH2OH þ as well as D2OþCD (5%) and CD2þOD (18%) for the dissociative recombination of CD2OD þ. The remainder of the reaction flux kept the C–O bond intact: 92% for CH2OH þ and 77% for CD2OD þ, respectively. Other recent measurements on the CH3OH þ 2 ion indicate dominating bond breaking between the heavy atoms, which is in contrast to this experiment. For CD2OD þ 2 CO-bond breaking was observed for 43% of the reaction flux.Measurements of the cross-sections and branching ratios of the dissociative recombination of the ions CH2OH+, CD2OD+ and CD2OD2+ have been performed at the CRYRING storage ring located in Stockholm, Sweden. Evaluation of the data yielded reaction rate coefficients of: 7.0 x 10-7( T/300) -0.78 cm3mol-1s -1 for CH2OH+; 7.5 x 10-7(T/300) -0.70 cm3 mol-1s-1 for CD2OD+ and 1.51 x 10-6(T/300)-0.66 cm3 mol-1s-1 for CD2OD2+. Calculation of the branching ratios for CH2OH+ and its deuterated isotopologue gave the following results for the DR reaction channels involving C-O bond fissure: H2O+CH (2.2%) and CH2+OH (5.5%) in the reaction of CH2OH+ as well as D2O+CD (5%) and CD2+OD (18%) for the dissociative recombination of CD2OD+. The remainder of the reaction flux kept the C-O bond intact: 92% for CH2OH+ and 77% for CD2OD+, respectively. Other recent measurements on the CH3OH2+ ion indicate dominating bond breaking between the heavy atoms which is conversely to this experiment. For CD2OD2+ CO-bond breaking was observed for 57% of the reaction flux.

Experimental studies of the dissociative recombination processes for the dimethyl ether ions CD3OCD2+ and (CD3)2OD+

Aims: Determination of branching fractions, cross sections and thermal rate coefficients for the dissociative recombination of CD3OCD2+ (0-0.3 eV) and (CD3)2OD+ (0-0.2 eV) at the low relative kinet ...

DESIREE as a new tool for interstellar ion chemistry

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-de ...

One-dimensional ordering in coasting and bunched beams

The sudden reduction of momentum spread, and under certain conditions also of Schottky-noise power, that has been observed with electron-cooled coasting beams of highly charged ions at several storage rings, has been interpreted as the effect of a one-dimensional ordering of the beams. At CRYRING, first observations of a momentum-spread reduction have also been made with bunched beams. We discuss models of one-dimensional ordering and compare model predictions of Schottky-noise power, and in the case of bunched beams the bunch length, with experimental results from CRYRING.

Two-site double-core-hole states formed when fast protons capture electrons from aligned N2

We report on an experimental investigation of 1.04 MeV H++N2 electron transfer collisions. The fast protons were stored in the electron-cooler ion-storage ring, CRYRING and the molecular nitrogen t ...