Electron cooling of heavy ions

Steck, M.; Bisoffi, G.; Blum, Monika; Friedrich, Alexander; Geyer, C.; Grieser, M.; Hölzer, B.; Jaeschke, E.; Jung, Matthias; Krämer, D.; Matl, K.; Ott, W.; Repnow, R.

doi:10.1016/0168-9002(90)91817-u

Cited by 38 publications

(22 citation statements)

References 2 publications

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“…Along their closed orbit with a circumference of 55.4 m, the residual gas pressure is below 1×10 −10 mbar. As in previous experiments [26] at this facility, the ions were merged on each turn in the ring with collinear, velocity-matched or slightly velocity-detuned electron beams of ∼1.5 m length in two straight sections of the TSR: the electron cooler [27][28][29], and the electron target section (ETS) [30].…”

Section: Methodsmentioning

confidence: 99%

Assignment of resonances in dissociative recombination of HD+ions: High-resolution measurements compared with accurate computations

et al. 2011

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The collision-energy resolved rate coefficient for dissociative recombination of HD + ions in the vibrational ground state is measured using the photocathode electron target at the heavy-ion storage ring TSR. Rydberg resonances associated with ro-vibrational excitation of the HD + core are scanned as a function of the electron collision energy with an instrumental broadening below 1 meV in the low-energy limit. The measurement is compared to calculations using multichannel quantum defect theory, accounting for rotational structure and interactions and considering the six lowest rotational energy levels as initial ionic states. Using thermal equilibrium level populations at 300 K to approximate the experimental conditions, close correspondence between calculated and measured structures is found up to the first vibrational excitation threshold of the cations near 0.24 eV. Detailed assignments, including naturally broadened and overlapping Rydberg resonances, are performed for all structures up to 0.024 eV. Resonances from purely rotational excitation of the ion core are found to have similar strengths as those involving vibrational excitation. A dominant low-energy resonance is assigned to contributions from excited rotational states only. The results indicate strong modifications in the energy dependence of the dissociative recombination rate coefficient through the rotational excitation of the parent ions, and underline the need for studies with rotationally cold species to obtain results reflecting low-temperature ionized media.

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Section: Methodsmentioning

confidence: 99%

Assignment of resonances in dissociative recombination of HD+ions: High-resolution measurements compared with accurate computations

et al. 2011

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“…The average pressure in the storage ring was 5-10 × 10 −11 mbar during the present measurements. The TSR electron cooler [40,41] was used to apply phase space cooling to the stored He + 2 ion beam [42] and to perform the electron-ion recombination experiments [32,33]. The electron beam is guided by a longitudinal magnetic field (∼0.04 T) and has a diameter of 29.5 mm in the region where the electron and ion beam overlap collinearly, surrounded by a 1.5 m long solenoid magnet.…”

Section: A Ion Beam and Detector Setupmentioning

confidence: 99%

Dissociative recombination and low-energy inelastic electron collisions of the helium dimer ion

et al. 2005

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The dissociative recombination (DR) of 3 He 4 He + has been investigated at the heavy-ion Test Storage Ring (TSR) in Heidelberg by observing neutral products from electron-ion collisions in a merged beams configuration at relative energies from near-zero (thermal electron energy about 10 meV) up to 40 eV. After storage and electron cooling for 35 s, an effective DR rate coefficient at nearzero energy of 3 × 10 −9 cm 3 s −1 is found. The temporal evolution of the neutral product rates and fragment imaging spectra reveals that the populations of vibrational levels in the stored ion beam are non-thermal with fractions of ∼0.1-1% in excited levels up to at least v = 4, having a significant effect on the observed DR signals. With a pump-probe-type technique using DR fragment imaging while switching the properties of the electron beam, the vibrational excitation of the ions is found to originate mostly from ion collisions with the residual gas. Also, the temporal evolution of the DR signals suggests that a strong electron induced rotational cooling occurs in the vibrational ground state, reaching a rotational temperature near or below 300 K. From the absolute rate coefficient and the shape of the fragment imaging spectrum observed under stationary conditions, the DR rate coefficient from the vibrational ground state is determined; converted to a thermal electron gas at 300 K it amounts to (3.3 ± 0.9) × 10 −10 cm 3 s −1 . The corresponding branching ratios from v = 0 to the atomic final states are found to be (3.7 ± 1.2)% for 1s2s 3 S, (37.4 ± 4.0)% for 1s2s 1 S, (58.6 ± 5.2)% for 1s2p 3 P , and (2.9 ± 3.0)% for 1s2p 1 P . A DR rate coefficient in the range of 2 × 10 −7 cm 3 s −1 or above is inferred for vibrational levels v = 3 and higher. As a function of the collision energy, the measured DR rate coefficient displays a structure around 0.2 eV. At higher energies, it has one smooth peak around 7.3 eV and a highly structured appearance at 15-40 eV. The small size of the observed effective DR rate coefficient at near-zero energy indicates that the electron induced rotational cooling is due to inelastic electron-ion collisions and not due to selective depletion of rotational levels by DR.

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“…When a collinear electron beam [24] is merged with the ion beam (see Fig. 1), electron-ion collisions occur at rest-frame collision energies that can be controlled through the velocity difference between both beams and hence, assuming the ion velocity fixed, through the electron acceleration voltage.…”

Section: Twin Electron Beams In a Magnetic Storage Ringmentioning

confidence: 99%

Progress in stored ion beam experiments on atomic and molecular processes

et al. 2006

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Stored fast ion beams in atomic and molecular collision experiments are discussed with an emphasis on electron-ion interactions at low relative energies. Recent progress was obtained in electron collision spectroscopy using an electroncooled stored ion beam and a separate electron target in the same storage ring; from a cryogenic photocathode, electron beams with internal temperatures of 5 to 10 K were produced. Results are presented for dielectronic recombination resonances, resolving the hyperfine structure of stored lithiumlike scandium ions and obtaining precise results for the fine structure splitting of these ions, and for ro-vibrational resonances in the recombination of electrons with hydrogen molecular ions, revealing sharp structures down to 2 meV. An overview of the cryogenic storage ring (CSR) project in Heidelberg is given.

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Electron cooling of heavy ions

Cited by 38 publications

References 2 publications

Assignment of resonances in dissociative recombination of HD+ions: High-resolution measurements compared with accurate computations

Assignment of resonances in dissociative recombination of HD+ions: High-resolution measurements compared with accurate computations

Dissociative recombination and low-energy inelastic electron collisions of the helium dimer ion

Progress in stored ion beam experiments on atomic and molecular processes

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