Andelkovic, Z.

Birkl, G.

Hannen, V.

König, K.

Martin, A.

Murböck, T.

Nörtershäuser, W.

Schmidt, S.

Scholl, S.

Segal, D.

Thompson, R.

Vogel, M.

Vollbrecht, J.

Weinheimer, C.

GSI Repository

Highly charged ions at SpecTrap∗T. Murbo¨ck1, G. Birkl1, A. Martin1, M. Vogel1, K. Ko¨nig2, W. No¨rtersha¨user2, S. Schmidt2, S. Scholl2,Z. Andelkovic3, V. Hannen4, J. Vollbrecht4, C. Weinheimer4, D. Segal5, and R. Thompson51IAP, TU Darmstadt; 2IKP, TU Darmstadt; 3GSI, Darmstadt; 4Westfa¨lische Wilhems-Universita¨t, Mu¨nster; 5ImperialCollege LondonThe SpecTrap collaboration aims at high precision laserspectroscopy of forbidden transitions in highly chargedions (HCIs). Similar experiments performed to date withions stored in an EBIT or in a storage ring still suffer fromDoppler broadening or the difficulties in wavelength con-version between the laboratory frame and the rest frame[1, 2]. Therefore, the SpecTrap experiment employs acryogenic Penning trap suitable for trapping externally pro-duced ions and sympathetically cooling them with lasercooled Mg+ ions [3]. Cooling of HCI to the mK-regimewill dramatically reduce the Doppler broadening of the flu-orescence signal and allow the measurement of the hyper-fine splitting of the HCI with an expected relative accuracyof 10−8 for a stringent test of bound state QED.In 2013, a new beamline was installed at the HITRAP plat-form to connect a commercial EBIT with the SpecTrapPenning trap [4]. This EBIT can be used to produce ar-gon ions with any desired charge state up to bare Ar. SinceAr13+ is a suitable candidate for a laser-accessible, forbid-den transition in a HCI, the beamline has been optimisedfor maximum transmission of this charge state. Several 104Ar13+ ions have been transported with a kinetic energy of4 keV/q to the SpecTrap experiment. Because of the maxi-mum voltage that can be applied to the trap electrodes onlylow energy ions with kinetic energies of a few hundredseV/q can be trapped in the SpecTrap-Penning trap whereasmuch lower transport energies would be desirable. Un-fortunately, intra-beam scattering and electron capture setsconstraints to the minimum transport energy of the beamand further reduction of the current value of 4 keV/q wouldlead to much lower transport efficiency from the EBIT tothe trap. Therefore, a pulsed drift tube has been installedclose to the trap and used to decelerate several 104 Ar13+ions in a single bunch to energies as low as 600 eV/q. Ionswith this energy can be easily trapped with the Penningtrap’s electrodes and the number of Ar13+ ions even inone single bunch is now sufficient for the designated spec-troscopy experiments at SpecTrap.Prior to the installation of the HITRAP beamline, the ex-periment had been connected to two different ion sourcessimultaneously. The first source supplied the experimentwith singly charged magnesium, the second one with Ar+and Ar2+. With this setup, alternating trapping of Mg+and Ar+ was demonstrated, being the first step for simulta-neous storage and sympathetic cooling of HCI. Ar+ trans-ported with a kinetic energy of 600 eV has been trapped and∗This work has been supported financially by BMBF (05P12RDFA4,06DA9020I), DFG, EPSRC, GSI, HGS-HiRe and HIC for FAIR.electronically detected with the resonant circuit attached tothe endcaps of the SpecTrap Penning trap. Furthermore,resistive cooling of Ar+ with the resonant circuit has beendemonstrated as well. Different ion species and chargestates were identified via their axial and radial oscillationfrequencies. To this end, the trap parameters that influencethe axial oscillation frequency have been determined withthe species Mg+ and Ar+. Resonant excitation of differention species has been performed and detected by changes inthe fluorescence signal of 24Mg+ (see Fig. 1). This demon-strates the potential for non-destructive detection and iden-tification of arbitrary ion species.With these tools at hand, the SpecTrap experiment is readyfor trapping and detection of HCI like Ar13+. In a first stepthe storage time, resistive, and sympathetic cooling and theinteraction between Ar13+ and Mg+ will be investigated.As soon as a cold and dense ion cloud of Ar13+ is avail-able, the forbidden transition of Ar13+ will be measured ina high precision laser spectroscopy experiment, followedby experiments with different ion species like Ca14+ andBi82+ once HITRAP is fully operational.Excitation Frequency [kHz]Fluorescence Signal ofMg+2424Mg+25Mg+26Mg+Resonances ofThree Mg IsotopesFigure 1: Reduced cyclotron frequencies νc of 24−26Mg+isotopes. Excitation of νc changes the state of the ioncloud and therefore increases the fluorescence signal re-ceived from 24Mg isotopes.References[1] Ma¨ckel et al., Phys. Rev. Lett. 107, 143002 (2011)[2] Lochmann et al., arXiv:1401.8224 (2013)[3] Murbo¨ck et al., Phys. Scr. T156 (2013)[4] Andelkovic et al., GSI Scientific Report (2013)GSI SCIENTIFIC REPORT 2013 PNI-AP-14doi:10.15120/GR-2014-1-PNI-AP-14 171

Highly charged ions at SpecTrap

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Highly charged ions at SpecTrap

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