Ehresmann, A.

Knie, A.

Ozga, C.

Reiß, P.

Schmidt, P.

GSI Repository

Development of a VUV-VIS-spectropolarimeter for target characterisationPh. Reiß∗1, Ph. Schmidt∗1, A. Knie1, Ch. Ozga1, and A. Ehresmann†11Institute of Physics and CINSaT, University of Kassel, Heinrich-Plett-Str. 40, 34132 Kassel, GermanyThe interaction of highly charged ions with with atomicor molecular gases and free electrons has been thoroughlystudied in the past by means of x-ray and particle spec-troscopy. In these experiments, processes like radiativeelectron capture and dielectronic recombination have beeninvestigated and compared to theory. The calculations,however, have been performed by averaging over all possi-ble channels involving different electronic states of neutralatoms and ions, and then comparing the results with theexperiments.Advantages of Fluorescence SpectrometryDispersed fluorescence spectrometry, however, offersthe possibility to detect state-specific fluorescence transi-tions in the projectile or target atoms. In coincidence withx-ray or particle spectrometry, this allows the investigationand testing of different processes during or following theinteraction. The technique may also be used in experi-ments on radiative electron capture, the time-reversed pro-cess of photoionization, where an electron is captured fromthe continuum to a bound state while emitting a photonto be detected, or on dielectronic recombination, when thecapture of a free electron leads to the excitation of anotherelectron in the ion. The involved states can be identified bysubsequent dipole transitions. Also, time-dependent fluo-rescence measurements have been shown to pose a monitorfor longitudinal beam profiles. In order to evaluate the ap-plicability of the technique, a pilot experiment for fluores-cence spectrometry has been carried out at the GSI.Experimental setupThe experiment has been carried out at the gas targetof the ESR storage ring at the GSI, where a jet of neu-tral Xe atoms crossed a beam of Xe52+ and Xe54+ ions at200 MeV/u. For the fluorescence measurements, a Seya-Namioka-type spectrometer has been used as depicted infig. 1. The dispersive element is an optical grating witha concave radius of 1 m and a line density of 600 l/mm,the opening angle between entrance and exit arm is 70.15◦,which is characteristic for this type of spectrometer. Thedetector is a commercial 1” micro-channel-plate detectorfrom Quantar Technology that uses an S-20 Bialkali pho-tocathode and a resistive anode for position encoding. Inthis tentative experiment, a view port with a borosilicateviewport was in the path of the fluorescence, restricting thelowest observable wavelength to 200 nm.∗Work supported by the HGS-HIRe for FAIR† ehresmann@physik.uni-kassel.deFigure 1: Scheme of the used spectrometer setup. Fluo-rescence light from the interaction volume passes throughthe entrance slit of the spectrometer and is dispersed by aspherical reflection grating that projects the dispersed flu-orescence onto the surface of a position-sensitive detec-tor. This enables the measurement of a certain fluorescencewavelength range. The width of which depends on the linedensity of the grating and the size of the detector.First resultsThe wavelength range from 200 nm to 650 nm hasbeen scanned and a number of individual fluorescence linescould be measured, most likely stemming from Xe2+ andXe3+ ions in the gas target, as shown in fig. 2. A conclusiveevaluation is in progress. The experiment showed that theapplication of fluorescence spectometry at heavy-ion stor-ange rings is feasible. For future experiments, an optimisedspectrometer for the use at CRYRING@ESR is planned.Figure 2: Example for the measured fluorescence spec-trum from the Xe gas target, excited by Xe54+ ions at200 MeV/u.GSI SCIENTIFIC REPORT 2014 APPA-MML-AP-34DOI:10.15120/GR-2015-1-APPA-MML-AP-34 249

Development of a VUV-VIS-spectropolarimeter for target characterisation

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Development of a VUV-VIS-spectropolarimeter for target characterisation

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