Andelkovic, Z.

Fedotova, S.

Herfurth, F.

Kotovskiy, N.

Maaß, B.

Neidherr, D.

Steinmann, J.

Votobyev, G.

GSI Repository

Deceleration of ions in the HITRAP facilityZ. Andelkovic1, S. Fedotova1, F. Herfurth1, N. Kotovskiy1, B. Maaß2, D. Neidherr1, J. Steinmann3, G.Vorobyev1, and the HITRAP collaboration11GSI Darmstadt; 2Technische Universita¨t Darmstadt; 3Hochschule DarmstadtThe major challenge for experiments with low-energyhighly charged ions (HCI) remains their preparation in suf-ficient quantities. As the only facility of its kind in theworld, HITRAP aims to take advantage of the high inten-sities of HCI production by in-flight stripping of electronsin an accelerator facility for low-energy experiments. Byreducing the energy in several steps from production at 400down to 4 MeV/u and finally to sub-eV in a trap, a bunch ofsome 105 cold HCI can be forwarded with a chosen trans-port energy to different experiments.The first stage of the linear decelerator, an interdigital H-type structure (IH), decelerates ions from 4 to 0.5 MeV/uand was successfully commissioned several years ago withdeceleration efficiencies close to the theoretical maximum[1]. The commissioning of the second deceleration stage,the radio-frequency quadrupole (RFQ), has proven to bemore challenging because of the very large parameter spacecombined with a relatively low acceptance of the device.An attempt to improve on this brought a new design ofthe electrodes [2] and offline tests at MPIK in Heidelberg[3]. The modified RFQ was reinstalled at GSI and com-missioned during three beamtimes in 2014. Figure 1 showsthe signal of the HCI decelerated from 500 to 6 keV by theRFQ, obtained after systematic scans and optimization ofthe system parameters during the first two beamtimes. TheFigure 1: The ion beam from the RFQ after the energy analyser.The thin, red line is the reference signal from the offline tests andthe thick, blue line is the online signal from July 2014. The lowenergy part, i.e. the decelerated ions’ signal is the peak to the left.The peak to the right is the undecelerated part of the beam.ions leaving the RFQ were sent through a magnetic fieldof a permanent magnet with integrated slits. As a result,the ions with smaller energy get a larger deflection angle(the left peak in Fig. 1) and can be distinguished from thenon-decelerated ions. The last HITRAP beamtime of theyear was used for systematic tests of deceleration, as wellas to transport the decelerated ions through the low energybeamline towards the cooling trap.The synchrotron cooling of trapped electrons for elec-tron cooling was investigated for the last deceleration stageof HITRAP, the cooling trap. Electrons emitted from aGaAs surface after irradiation with UV light were guided tothe trap and stored for extended amounts of time. The cool-ing effect by synchrotron radiation in the strong magneticfield of the trap was experimentally verified [4]. Furtherimprovements include improvements of the vacuum, theoptimization of the ion and electron capture process as wellas their mixing and cooling. Detailed simulations of thetrapping and the cooling process in the cooling trap havebeen conducted to that end and show promising results [5].Figure 2: Synchrotron cooling of electrons in the cooling trap.The measured cooling constant of the trapped electrons reduceswith the increasing magnetic field. The full, red line shows thevalue expected from theory.References[1] F. Herfurth, et al.: HITRAP - Heavy, Highly-Charged Ions atRest - A Status Report, GSI Scientific Reports 2011[2] S. Yaramyshev, et al.: A new Design of the RFQ-Deceleratorfor HITRAP, GSI Scientific Reports 2012[3] M. Maier, at al.: Offline commissioning of the old and newHITRAP RFQ, GSI Scientific Reports 2012[4] B. Maaß: Geladene Teilchen in der Ku¨hlfalle, Master’s thesis,TU Darmstadt, 2014[5] J. Steinmann, PhD Thesis, University Erlangen-Nu¨rnberg, tobe submitted, 2015FG-GENERAL-12 GSI SCIENTIFIC REPORT 2014430 DOI:10.15120/GR-2015-1-FG-GENERAL-12

Deceleration of ions in the HITRAP facility

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Deceleration of ions in the HITRAP facility

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