An ion trap facility for experiments with highly-charged heavy ions

The transfer beam line between cooler trap and the experimental area of HITRAP has been decoupled from the low energy transport section from the 4-rod RFQ to the cooler trap. The extracted ion beam from the cooler trap is guided via quadrupole lenses towards the experimental area through this vertical beam line assuming a maximum emittance of 10 mm mrad at 1.7 keV/u. Thus the beam optics elements can be kept compact. Detailed planning for the transfer lines has been extended with focus on vacuum requirements. The vacuum conditions are stringent for very highly charged ions and calculations have shown that the pressure has to be kept on a level of 10^-10 mbar, in order to reduce the losses below 0.1%. A vacuum concept has been worked out, which employs ion- and NEG-getter pumps and sections, which are NEG-coated. The complete low energy beam system including the HITRAP cooler trap will be put into operation at the MAXEBIS test bench at GSI Heckhalle prior to it's installation in the re-injection line. First components of the low energy beam transport lines like valves, pumps and gauges have been ordered. First schematic design drawings are completed. Now detailed design drawings of the beam lines are imminent and first parts will tested in spring 2006 with the Frankfurt MAXEBIS setup at GSI. The complete installation at the test bench of the MAXEBIS is foreseen in August 2006.

A reaction microscope (combined multi-electron recoil ion momentum spectrometer) particularly suitable for charge- transfer collision experiments between highly charged ion (HCI) beams and atomic/molecular gas targets has been developed in Heidelberg. The additional detector required to analyse the charge-state of the projectile has been implemented. The extraction beam-line of the Heidelberg Electron Beam Ion Trap (EBIT) and the necessary beam diagnostics were constructed, assembled, commissioned and tested. Subsequently, the extraction from the trap and the associated beam optics were optimised. The reaction microscope has been installed and successfully tested at the EBIT beam-line by performing electron capture experiments with extracted slow HCI. Data were taken for the following collision systems: (a) F7+, Ne10+, Ar16+ on He and (b) U64+ on He and Ne. Precision spectroscopy not only of light HCI but also, for the first time, of the heavy U64+ ions has been achieved in charge transfer experiments. It is therefore achievable to perform similar studies at HITRAP. A Recoil Ion Momentum Spectrometer (RIMS) allowing multi-fragment coincident detection has been developed and successfully tested by carrying out ion-molecule collision experiments with HCI beams provided from the GANIL accelerator facility. The molecular fragmentation details have been revealed in great detail. Then, coincident multi-electron detection has been implemented in the RIMS to transform it in a so called "reaction microscope". The successful operation and detection of the emitted electrons has been demonstrated in the following experiments performed at GANIL: (i) Coincident Auger electron spectroscopy in slow ion-atom collisions (ii) Electron emission following fast ion-D2 collision. Similar studies of fast ion-H2 collisions have been performed in Heidelberg using the same experimental technique. Another RIMS apparatus, combining imaging and time-of-flight techniques, specifically suitable for ion-surface interaction studies has been developed. Sputtering of secondary ions from LiF and UO2 solid surfaces after HCI impact has been investigated at GANIL for two different impact velocity regimes: (i) for fast ions (10 MeV/u Ca17+) and (ii) for slow ions (17keV/q Xe21+), thus demonstrating the applicability for HITRAP. We have successfully developed reaction microscopes and RIMS as multi-purpose instruments for studying charge-transfer processes between HCI and atoms/molecules/clusters/surfaces. All apparatus are operational and ready to be transferred to the HITRAP facility. In the mean time, they are standalone, integrated in the research program at GANIL or Heidelberg, respectively, and constitute ideal set-ups for short-time training projects as well.

A complete beam dynamics calculation of the HITRAP decelerator from the ESR towards the cooler trap has been performed. The beam dynamics design of the re-buncher, of the IH-structure and of the RFQ have been finalized and the corresponding lay-out of the cavity drift tube structures and the RFQ electrodes respectively has been done. A so-called double drift re-buncher (DDB), which comprises two coaxial resonator structures, has been included in order to increase the efficiency of the phase spread matching of the ion bunch from the ESR into the phase acceptance of the IH-structure. Hence 70% of the particles extracted from the ESR will be transmitted and decelerated. In order to improve the injection efficiency into the HITRAP cooler trap, a low energy de-buncher has been designed and included into the RFQ set-up. Because of the completed beam dynamics design, data of all magnetic quadrupole lenses are available and a call for tender can be done beginning of next year. The rf-design of all decelerator cavities, which comprises the cavity geometry, drift tube structure and the tuning plungers, has been completed. 3-D CAD drawings of the buncher cavities for the production are being done and the call for tender is placed. All geometry data of the IH-structure have been submitted to the GSI design office in order to finalize the cavity design drawings. A call for tender is planned beginning of 2006. The RFQ design and the low energy de-buncher attached to the RFQ, will be performed by the manufacturer, based on a similar cavities built at the IAP Frankfurt. An order has been placed. The preparation work has been done in order to start the HITRAP LINAC assembly in 2006, followed by beam commissioning end of 2006 and beginning of 2007.

The envisaged objective was to design and construct a particle detector for use with the Hitrap facility, offering a large range of flexibility for different kinds of application. The design focussed on the problem of low particle intensities expected from the Hitrap facility. In close collaboration with the Ioffe institute in St. Petersburg, a new type of electrostatic spectrometer for ion and electron detection was designed and constructed. A classical electrostatic analyser design with two bended plates (condenser-configuration) was unsuited since it either leads to very small opening angles and thus to low detection efficiencies, or to an unsatisfactory energy resolution. The final spectrometer construction follows the Einzellens-principle, allowing for a large solid angle of 2Sr. This results in 10^4 higher efficiencies. The achieved energy resolution is with 1-2% by far satisfactory for the desired applications. As particle detector in the final version, an MCP assembly is foreseen. By this, the spectrometer size will be kept small in order to allow rotation around the collision centre inside the chamber. The spectrometer can detect particles with energies up to 3 keV/q. Slight changes regarding the electrical isolations allow the detection of 5 keV/q. These specifications make the detector well suited for measuring Auger and auto-ionization electrons from highly charged ions interacting with matter. A high vacuum version of the detector is build and tested by the group at Ioffe institute. First tests with electron beams confirmed the simulated energy resolution. The construction of the UHV version is finished by now, all required detector components are ordered, and the spectrometer will be ready for testing and calibration at the KVI beginning 2006.

Monte Carlo calculations of ion trajectories for designing a scattering chamber for ion-surface interactions were performed. The so-called trampoline effect was studied in order to find out whether a reflection of incompletely neutralized projectiles will take place due to the surface charge resulting from the electron capture by the very same projectile. It was found that for charge states up to q = 10 such an effects is very unlikely. Simulations for transmission through nanocapillaries based on the classical transport theory were performed. The discharge characteristics from the macroscopic properties of the nanocapillary material could be incorporated. The bulk discharge time or bulk diffusion constant as well as the surface charge diffusion constant were estimated from surface and bulk conductivity data for Mylar. This approach represents a mean-field classical trajectory theory based on a microscopic classical-trajectory Monte Carlo (CTMC) simulation for the ion transported, self-consistently coupled to the charge-up of and charge diffusion near the internal capillary walls. This has lead to a satisfactory description of the experimental data from the Stockholm node of this network (Vikor, Schuch et al.) for the angular dependent transmission probability. Furthermore, inconsistencies of an earlier non-linear model (Stolterfoht et al.) could be resolved.

We designed a trap to perform laser spectroscopy of trapped and cooled highly charged heavy ions. This trap is a cylindrical open-end cap Penning trap which combines resistive cooling and the rotating wall technique with high-precision laser spectroscopy. We have performed detailed calculations in order to optimise the trap design so that good fluorescence rates can be expected. The results of these calculations have been incorporated in the trap design and this work is also published (Rev. Sci. Instrum.). We aim to measure ground state hyperfine splitting in highly charged heavy ions, such as hydrogen-like lead and lithium-like bismuth, by laser spectroscopy. These ions will be delivered by the HITRAP re-injection channel (from the cooler trap), and trapped, cooled and compressed in our spectroscopy trap. By using laser spectroscopy it is possible to obtain high-accuracy results, which are 3 orders of magnitude better than the previous ones. For pilot experiments at Imperial College in London (2006/2007), we will use our existing super conducting magnet (warm bore, no radial access) and design and build a simple ion source that can produce singly/doubly charged ions, which have magnetic dipole transitions in the visible range. For the final measurements at GSI in Darmstadt (2007/2008), we will use the super conducting magnet from the RETRAP experiment (cold bore, radial access). Our spectroscopy trap has been designed to be compatible with both magnet systems. The electrodes of our Penning trap are being constructed in our workshop and, by the end of 2005, the spectroscopy trap will be ready for first test measurements at Imperial College. Final measurements on highly charged ions can only be performed once the HITRAP set up in the re-injection channel has been completed, which is anticipated to be near the end of 2007. Unfortunately, most of the advanced techniques used in our trap, i.e. electronic cooling and detection and the rotating wall technique, can only be tested effectively when the trap is operated at cryogenic temperatures (RETRAP magnet) and highly charged ions, coming from the HITRAP re-injection channel, are used. We have also carried out studies of new designs for scalable Penning traps and constructed a prototype permanent magnet Penning trap, which is currently under test. Our recent experiments involving laser spectroscopy and laser cooling of singly-charged ions in Penning traps have led to a deeper understanding of the dynamics of ions in traps under excitation from quadrupole fields, which is highly relevant for the operation of the HITRAP Penning trap. These experiments have also given us more experience of laser spectroscopic techniques including detection of low levels of light, which is important for the planned experiments at HITRAP.

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