Search

We have used the Cryogenic Storage Ring (CSR) at the Max Planck Institute for Nuclear Physics to study long-lived metastable states of the silicon anion. A ${\mathrm{Si}}^{\ensuremath{-}}$ beam of 58 keV kinetic energy was stored in the ultrahigh cryogenic vacuum of the CSR, employing only electrostatic deflection elements. We used laser systems at various wavelengths to infer information on the decay of the metastable anionic states by selective photodetachment. Our results give evidence of an excited anionic state for which we determine the extremely long lower lifetime limit of 5.7 h at 90% confidence level, consistent with theoretical predictions for the $^{2}D$ term. Furthermore, we find an average lifetime of $\ensuremath{\tau}=(22.2\ifmmode\pm\else\textpm\fi{}2.5)$ s for the weakly bound $^{2}P$ states, employing coincidence counting with a pulsed nanosecond laser at 2.45 $\ensuremath{\mu}\mathrm{m}$. Using a laser depletion technique, we produce a pure ground term $^{4}S_{3/2}\phantom{\rule{4pt}{0ex}}{\mathrm{Si}}^{\ensuremath{-}}$ beam, and we quantify the fraction of ions in metastable states in our initial ion sample. We combine our experimental efforts with state-of-the-art multiconfiguration Dirac-Hartree-Fock calculations for the radiative lifetimes of all metastable levels of ${\mathrm{Si}}^{\ensuremath{-}}$. We find these calculations to be in excellent agreement with our measurements and to improve previous efforts considerably.

Photodetachment thermometry on a beam of OH$^-$ in a cryogenic storage ring cooled to below 10 K is carried out using two-dimensional, frequency and time dependent photodetachment spectroscopy over 20 minutes of ion storage. In equilibrium with the low-level blackbody field, we find an effective radiative temperature near 15 K with about 90% of all ions in the rotational ground state. We measure the J = 1 natural lifetime (about 193 s) and determine the OH$^-$ rotational transition dipole moment with 1.5% uncertainty. We also measure rotationally dependent relative near-threshold photodetachment cross sections for photodetachment thermometry., Manuscript LaTeX with 5 pages, 3 figures, and 1 table plus LaTeX supplement with 12 pages, 3 figures and 3 tables. This article has been accepted by Physical Review Letters

We have used a single-particle detector system, based on secondary electron emission, for counting low-energetic (~keV/u) massive products originating from atomic and molecular ion reactions in the electrostatic Cryogenic Storage Ring (CSR). The detector is movable within the cryogenic vacuum chamber of CSR, and was used to measure production rates of a variety of charged and neutral daughter particles. In operation at a temperature of ~6 K, the detector is characterised by a high dynamic range, combining a low dark event rate with good high-rate particle counting capability. On-line measurement of the pulse height distributions proved to be an important monitor of the detector response at low temperature. Statistical pulse-height analysis allows to infer the particle detection efficiency of the detector, which has been found to be close to unity also in cryogenic operation at 6 K., Accepted to Nuclear Inst. and Methods in Physics Research, A

An electrostatic cryogenic storage ring, CSR, for beams of anions and cations with up to 300 keV kinetic energy per unit charge has been designed, constructed and put into operation. With a circumference of 35 m, the ion-beam vacuum chambers and all beam optics are in a cryostat and cooled by a closed-cycle liquid helium system. At temperatures as low as (5.5 $\pm$ 1) K inside the ring, storage time constants of several minutes up to almost an hour were observed for atomic and molecular, anion and cation beams at an energy of 60 keV. The ion-beam intensity, energy-dependent closed-orbit shifts (dispersion) and the focusing properties of the machine were studied by a system of capacitive pickups. The Schottky-noise spectrum of the stored ions revealed a broadening of the momentum distribution on a time scale of 1000 s. Photodetachment of stored anions was used in the beam lifetime measurements. The detachment rate by anion collisions with residual-gas molecules was found to be extremely low. A residual-gas density below 140 cm$^{-3}$ is derived, equivalent to a room-temperature pressure below 10$^{-14}$ mbar. Fast atomic, molecular and cluster ion beams stored for long periods of time in a cryogenic environment will allow experiments on collision- and radiation-induced fragmentation processes of ions in known internal quantum states with merged and crossed photon and particle beams., PDFLaTeX with 17 pages, 16 figures, 2 tables. This article has been accepted by Review of Scientific Instruments. After it is published, it will be found at http://scitation.aip.org/content/aip/journal/rsi

We have studied the photodissociation of CH^{+} in the Cryogenic Storage Ring at ambient temperatures below 10 K. Owing to the extremely high vacuum of the cryogenic environment, we were able to store CH^{+} beams with a kinetic energy of ∼60 keV for several minutes. Using a pulsed laser, we observed Feshbach-type near-threshold photodissociation resonances for the rotational levels J=0-2 of CH^{+}, exclusively. In comparison to updated, state-of-the-art calculations, we find excellent agreement in the relative intensities of the resonances for a given J, and we can extract time-dependent level populations. Thus, we can monitor the spontaneous relaxation of CH^{+} to its lowest rotational states and demonstrate the preparation of an internally cold beam of molecular ions.

We have studied the photodissociation of CH+ in the Cryogenic Storage Ring at ambient temperatures below 10 K. Owing to the extremely high vacuum of the cryogenic environment, we were able to store CH+ beams with a kinetic energy of ∼60 keV for several minutes. Using a pulsed laser, we observed Feshbach-type near-threshold photodissociation resonances for the rotational levels J=0–2 of CH+, exclusively. In comparison to updated, state-of-the-art calculations, we find excellent agreement in the relative intensities of the resonances for a given J, and we can extract time-dependent level populations. Thus, we can monitor the spontaneous relaxation of CH+ to its lowest rotational states and demonstrate the preparation of an internally cold beam of molecular ions.

Monitoring of beam currents in particle accelerators without affecting the beam guiding elements, interrupting the beam or influencing its profile is a major challenge in accelerator technology. A solution to this problem is the detection of the magnetic field generated by the moving charged particles. We present a non-destructive beam monitoring system for particle beams in accelerators based on the Cryogenic Current Comparator (CCC) principle. The CCC consists of a high-performance low-temperature DC superconducting quantum interference device (LTS DC-SQUID) system, a toroidal pick-up coil, and a meander-shaped superconducting niobium shield. This device allows the measurement of continuous as well as pulsed beam currents in the nA-range. The resolution and the frequency response of the detector strongly depend on the toroidal pick-up coil and its embedded ferromagnetic core. Investigations of both the temperature and frequency dependence of the relative permeability and the noise contribution of several nanocrystalline ferromagnetic core materials are crucial to optimize the CCC with respect to an improved signal-to-noise ratio and extended transfer bandwidth.

Ultra-thin (⩽1 μg/cm2) diamond-like carbon (DLC) foils prepared by sputtering and supported by high-transmission meshes, have proven advantageous over standard carbon foils for timing and stripping of low-energy ions in many accelerator experiments. Specifically manufacture support mesh permits the use of much thinner, smoother and larger foils that can be accomplished without it. The main limitation of fine mesh as a mechanical support appears to be interaction of transmitting ions with the mesh that might affect both energy and angle distributions of primary ion beams under some irradiation conditions. As an alternative, collodion coatings can be used to support a foil during the mounting and handling, but later such coatings must be removed completely. In this work, process of removal of collodion coating from ultra-thin DLC foils by using ion beam bombardment in the energy range 6–15 MeV was investigated with the main emphasis given to determination of the minimal beam intensity sufficient to remove collodion, and to the measurement of the thickness of possible residual deposits. Removing of collodion was monitored online by measuring the energy of ions penetrating the foils. This was performed with high-resolution magnetic and electrostatic analyzers available at the beam lines of the Heidelberg MP-Tandem, and VERA-Tandem, respectively. In addition, preliminary results are presented of lifetime measurements for the collodion-reinforced very thin DLC foils in the thickness range of 0.6–5 μg/cm2. The results were obtained for a 20 MeV, 63Cu ion beam.

The one-neutron transfer reaction Li-9 + H-2 -> Li-8 + t has been investigated in an inverse kinematics experiment by bombarding a deuterated polypropylene target with a 2.36 MeV/u Li-9 beam from the post-accelerator REX-ISOLDE at CERN. Excitation energies in Li-8 as well as angular distributions of the tritons were obtained and spectroscopic factors deduced. (c) 2006 Elsevier B.V. All rights reserved.

A novel cryogenic electrostatic storage ring is planned to be built at the Max-Planck Institute for Nuclear Physics in Heidelberg. The machine is expected to operate at low temperatures (∼ 2K) and to store beams with kinetic energies between 20 to 300 keV. An electron target based on cooled photocathode technology will serve as a major tool for the study of reactions between molecular ions and electrons. Moreover, atomic beams can be merged and crossed with the stored ion beams allowing for atom molecularion collision studies at very low up to high relative energies. The proposed experimental program, centered around the physics of cold molecular ions, is shortly outlined.

The Radioactive beam EXperiment (REX) at CERN-ISOLDE has been commissioned and the first experiments successfully completed during 2002 and 2003. The concept used for post-acceleration has proven to be flexible and the experimental program has therefore been extended during the past year. This paper relays some experiences drawn from using the machine in the current program and also conveys some plans for the future.

4 pages, 4 figures.-- Issue title: Proceedings of the 8th International Conference on Clustering Aspects of Nuclear Structure and Dynamics (Nara, Japan, Nov 24-29, 2003)., The particle unbound nucleus Li-10 has been investigated at the newly constructed post-accelerator REX-ISOLDE at CERN via the Li-9 +d --> Li-10 +p reaction at 2.36 MeV/u. We present here the preliminary analysis of our first data from REX-ISOLDE.

We have investigated the autodetachment of electrons from rovibrationally hot SF${}_{6}{}^{\ensuremath{-}}$ anions using a cryogenic ion-beam trap. Extremely low residual gas densities of ${10}^{4}$ cm${}^{\ensuremath{-}3}$ provided undisturbed observation of the neutralization rates due to vibrational autodetachment (VAD) over almost five orders of magnitude and over times up to 100 ms. We successfully explain our experimental decay curves using statistical rate theory combined with electron attachment data and vibrational frequencies calculated for a ${C}_{4v}$-distorted SF${}_{6}{}^{\ensuremath{-}}$. The unprecedented sensitivity of the experiment to the decay constants at the VAD threshold allows us to infer from the data the adiabatic electron affinity of SF${}_{6}$ to be $(0.91\ifmmode\pm\else\textpm\fi{}0.07)$ eV and to confirm the recently predicted ${C}_{4v}$ symmetry of SF${}_{6}{}^{\ensuremath{-}}$.

The Radioactive Beam Experiment REX-ISOLDE [1-3] is a pilot experiment at ISOLDE (CERN) testing the new concept of post acceleration of radioactive ion beams by using charge breeding of the ions in a high charge state ion source and the efficient acceleration of the highly charged ions in a short LINAC using modern ion accelerator structures. In order to prepare the ions for the experiments singly charged radioactive ions from the on-line mass separator ISOLDE will be cooled and bunched in a Penning trap, charge bred in an electron beam ion source (EBIS) and finally accelerated in the LINAC. The LINAC consists of a radiofrequency quadrupole (RFQ) accelerator, which accelerates the ions up to 0.3 MeV/u, an interdigital H-type (IH) structure with a final energy between 1.1 and 1.2 MeV/u and three seven gap resonators, which allow the variation of the final energy. With an energy of the radioactive beams between 0.8 MeV/u and 2.2 MeV/u a wide range of experiments in the field of nuclear spectroscopy, astrophysics and solid state physics will be addressed by REX-ISOLDE.

REX-ISOLDE [1] is an experiment at ISOLDE/CERN with a twofold aim: (i) to demonstrate a novel efficient scheme for the acceleration of radioactive ions from the online mass separator ISOLDE to energies around the Coulomb barrier. (ii) to perform first nuclear physics experiments by studying the structure of the neutron-rich (N = 20, N = 28) nuclei by Coulomb excitation and neutron transfer reactions. An overview on the different components of the radioactive beam accelerator is given with special emphasis on the separation possibilities and ion number capabilities of the system.

At the MPI fur Kernphysik, a new type of accelerator is under construction which consists of a CHORDIS ion source [1] , two RFQ and eight 7-gap resonators [2] . The High Current Injector will deliver 1–3 orders of magnitude higher intensities in comparison to the existing tandem-postaccelerator combination. The RFQ is designed to accelerate ions with a minimum charge to mass ratio of q / m =1:9 up to an energy of 0.478 MeV/u. Both resonators operate at a frequency of 108.48 MHz with a pulsed power of 90 kW (25% duty factor (DF)). By means of an optimizing algorithm, it was possible to lower the electrode voltage of the RFQ-accelerator from 71 kV to 60 kV maintaining a slightly reduced final energy and a particle transmission of about 80% with ion currents of 10 mA [3] . A new electrode profile was developed in order to combine sufficient cooling with good mechanical stability. Moreover the fabrication process of the RFQ-stems and the electrodes were simplified and optimized. Both resonators are tuned and tested with low level measurements and under high power with a H + 2 -ion beam.

The Radioactive Beam Experiment at ISOLDE (REX-ISOLDE-Experiment) which presently is being developed and under construction at CERN serves to investigate exotic, very neutron rich, radioactive nuclei [1] (Radioactive beam EXperiment at ISOLDE: Coloumb Excitation and Neutron Transfer Reactions of Exotic Nuclei, Proposal to the ISOLDE commitee, CERNSIC94-25). A linear accelerator delivers radioactive ions which are produced by the isotope separator ISOLDE with energies between 0.85 and 2.2 MeV/u. The Linac will consist of a RFQ-accelerator, an interdigital H-Structure (IH) and three 7-gap-resonators with variable energy. While the LMU Munich is responsible for the frontpart of the accelerator, the backpart is being built by the MPI [2] (H. Podlech, Master Thesis, MPI-H-V21-1997, Heidelburg, 1997). After estimation of the voltage of one resonator to 1.75 MV at 90 kW, the design velocities were fixed to 5.4%, 6.0% and 6.6% of the velocity of light. Three downscaled models (1:2.5) were built in order to optimize the shuntimpedance and the field-distribution at the operation frequency of the amplifiers of 101.28 MHz. The optimization of all low power resonators is now successfully finished. Extensive beam dynamic calculations were made in order to optimize the transmission of the beam up to the target. It turned out that final energies between 0.85 and 2.2 MeV/u with nearly 100% transmission can be achieved. The acceptance in the x-plane is 1.2π mm mrad (norm.) and in the y-plane 3.0π mm mrad (norm.). The bunchlength of the fully accelerated beam (2.2 MeV/u) is 2.4 ns at the target. The development of the resonators was accompanied by extensive MAFIA calculations. It could be demonstrated that spiral-resonators like 7-gap-resonators can be calculated with MAFIA with an accuracy of 1% in comparison with experimental results. Presently, the tanks and the half shells of the power type resonators are manufactured in the workshops of the MPI.

REX-ISOLDE [1] is a pilot experiment at ISOLDE/CERN with the aim to study the nuclear structure of neutron-rich nuclei using radioactive ion beams. Radioactive ions with the charge state 1+, which are delivered by the on-line mass separator ISOLDE, are post-accelerated. A new concept is being employed, where the ions are first accumulated in a Penning trap, then converted to highly charged ions in an EBIS ion source and finally accelerated in a short linear accelerator to an energy of 2.2 MeV/u.

We propose to install a storage ring at an ISOL-type radioactive beam facility for the first time. Specifically, we intend to setup the heavy-ion, low-energy ring TSR at the HIE-ISOLDE facility in CERN, Geneva. Such a facility will provide a capability for experiments with stored secondary beams that is unique in the world. The envisaged physics programme is rich and varied, spanning from investigations of nuclear ground-state properties and reaction studies of astrophysical relevance, to investigations with highly-charged ions and pure isomeric beams. The TSR might also be employed for removal of isobaric contaminants from stored ion beams and for systematic studies within the neutrino beam programme. In addition to experiments performed using beams recirculating within the ring, cooled beams can also be extracted and exploited by external spectrometers for high-precision measurements. The existing TSR, which is presently in operation at the Max-Planck Institute for Nuclear Physics in Heidelberg, is well-suited and can be employed for this purpose. The physics cases as well as technical details of the existing ring facility and of the beam and infrastructure requirements at HIE-ISOLDE are discussed in the present technical design report. ispartof: European Physical Journal. Special Topics vol:207 issue:1 pages:1-117 status: published

A new and technologically challenging project, the electrostatic Cryogenic Storage Ring CSR, is presently under construction at the Max-Planck-Institute for Nuclear Physics in Heidelberg. Applying liquid helium cooling, the CSR, with 35 m circumference, will provide a low temperature environment of only a few Kelvin and an extremely high vacuum of better than 10 −13 mbar. To realize these conditions the mechanical design has been completed and now the first quarter section is in the construction phase. For the onion skin structure of the cryogenic system we have at the outer shell the cryostat chambers, realized by welded rectangular stainless steel frames with aluminum plates. The next two shells are fabricated as aluminum shields kept at 80 and 40 K. The inner vacuum chambers for the experimental vacuum consist of stainless steel chambers cladded with external copper sheets connected to the LHe lines for optimized thermal equilibration and cryopumping. Additional large surface 2 K units are installed for cryogenic pumping of H 2 . The mechanical concepts and the realization will be presented in detail.

The Cryogenic Storage Ring (CSR), presently under construction at the Max-Planck-Institute for Nuclear Physics, will allow the storage of large ionic molecules under optimum experimental conditions. The electrostatic beam optics and the presence of a low-energy electron cooler will allow highly-precise recombination experiments with molecular ions of 160 atomic mass units per charge state. The all-cryogenic design of the storage ring will provide unprecedented vacuum conditions and assure long storage times even for very heavy ion beams. Suppression of the black body radiation background of the beam pipe in combination with electron cooling will give access to internal ion temperatures of 10K and allow state-selective experiments on infrared-active species, impossible in present-day room-temperature storage rings. We give an overview of the CSR project, point out the scientific opportunities arising from its unique design, and give an outlook on possible first molecular recombination experiments after commissioning of the storage ring.

A high current injector for the heavy ion storage ring TSR in Heidelberg is under construction. As a part of the injector eight seven-gap resonators with high shunt impedance are being developed. These resonators ( ƒ 0 = 108.48 MHz ) are designed for the synchronous velocities of β s = 3.7, 4.5, 5.1 and 5.7%. Low power models with scaling factors of 1:2.5 were built in order to study the characteristics of these new resonators. Following low level measurements to optimize the voltage distribution and eigenfrequency, a first power resonator was built and successfully tested at 80 kW (duty cycle of 25%). At this power, the resonator generated a maximum voltage (summation of all gap amplitude voltages) of 1.75 MV. This paper describes the design of the resonators and gives some details of the measurements.

The existing accelerator facility at the Max-Planck-Institute in Heidelberg consists of a 12 MV tandem Van de Graaff accelerator, a post-accelerator and a heavy ion cooler storage ring TSR. Many experiments at the TSR, especially laser cooling, are limited by the low current delivered by the MP tandem. A new injector consisting of a high current source, two RFQs and eight seven-gap resonators will increase the currents for singly charged ions by up to three orders of magnitude. In a second phase, an ECR source for highly charged ions will be added and the high current injector will be used in combination with the Heidelberg heavy ion post-accelerator. This new system will deliver beams up to uranium with energies above the Coulomb barrier of the heaviest elements. In this paper the design and the status of the project are presented.

We report on the realization and operation of a fast ion beam trap of the linear electrostatic type employing liquid helium cooling to reach extremely low blackbody radiation temperature and residual gas density and, hence, long storage times of more than 5 min which are unprecedented for keV ion beams. Inside a beam pipe that can be cooled to temperatures15 K, with 1.8 K reached in some locations, an ion beam pulse can be stored at kinetic energies of 2-20 keV between two electrostatic mirrors. Along with an overview of the cryogenic trap design, we present a measurement of the residual gas density inside the trap resulting in only 2 x 10(3) cm(-3), which for a room temperature environment corresponds to a pressure in the 10(-14) mbar range. The device, called the cryogenic trap for fast ion beams, is now being used to investigate molecules and clusters at low temperatures, but has also served as a design prototype for the cryogenic heavy-ion storage ring currently under construction at the Max-Planck Institute for Nuclear Physics.

The cryogenic and vacuum concepts for the electrostatic Cryogenic ion Storage Ring (CSR), under construction at the Max-Planck-Institut fur Kernphysik in Heidelberg, is presented. The ring will operate in a broad temperature range from 2 to 300 K and is required to be bakeable up to 600 K. Extremely high vacuum and low temperatures are necessary to achieve long lifetimes of the molecular ions stored in the ring so that the ions will have enough time to cool by radiation to their vibrational and rotational ground states. To test cryogenic and vacuum technological aspects of the CSR, a prototype is being built and will be connected to the commercial cryogenic refrigerator recently installed, including a specialized 2-K connection system. The first results and the status of current work with the prototype are also presented.

The cryogenic storage ring (CSR) for positive and negative atomic, molecular and cluster ions is starting operation at the Max Planck Institute for Nuclear Physics in Heidelberg.

A network of ion sources is being developed on the 300-kV acceleration platform of the cryogenic storage ring (CSR) at the Max-Planck-Institut fur Kernphysik. It consists of several types of sources like a metal ion sputtering source (MISS), a Penning source, a laser vaporization (LVAP) source, and an electrospray ionization (ESI) source to produce a large variety of ions which can be studied for photon and electron interaction in a ro-vibrationally cold environment. Furthermore a storage device such as a radiofrequency quadrupole (RFQ) is foreseen for internal state cooling and accumulation of rarely produced species.

The Cryogenic Storage Ring (CSR) is currently under construction at MPI‐K in Heidelberg. The CSR is an electrostatic ring with a total circumference of about 34 m, straight section length of 2.5 m and will store ions in the 20 ∼ 300 keV energy range (E/Q). The cryogenic system in the CSR is expected to cool the inner vacuum chamber down to 2 K. The CSR will be equipped with an electron cooler which has also to serve as an electron target for high resolution recombination experiments. In this paper we present the results of numerical investigations of the CSR lattice with finite element calculations of the deflection and focusing elements of the ring. We also present a layout of the CSR electron cooler which will have to operate in low energy mode to cool 20 keV protons in the CSR, as well as numerical estimations of the cooling times to be expected with this device.

A cryogenic electrostatic ion storage ring CSR is under development at the Max‐Planck Institute for Nuclear Physics in Heidelberg, Germany. Cooling of the ultrahigh vacuum chamber is envisaged to lead to extremely low pressures as demonstrated by cryogenic ion traps. The ring will apply electron cooling with electron beams of a few eV up to 200 eV. Through long storage times of 1000 s as well as through the low wall temperature, internal cooling of infrared‐active molecular ions to their rotational ground state will be possible and their collisions with merged collinear beams of electrons and neutral atoms can be detected with high energy resolution. In addition storage of slow highly charged ions is foreseen. Using a fixed in‐ring gas target and a reaction microscope, collisions of the stored ions at a spead of the order of the atomic unit can be kinematically reconstructed. The layout and the cryogenic concept are introduced.

At the Max‐Planck‐Institut fur Kernphysik in Heidelberg a next generation electrostatic storage ring for cryogenic temperatures is under development. The main focus of this unique machine is the research on ions, molecules and clusters up to bio molecules in the energy range of 20–300 keV at low temperatures down to 2 Kelvin. The achievement of this low temperature for all material walls seen by the ions in the storage ring will allow novel experiments to be performed, such as rotational and vibrational state control of molecular ions and their interaction with ultra‐low energy electrons and laser radiation. The low temperature of the storage ring not only causes a strong reduction of black body radiation incident onto the stored particles, but also acts as a large cryopump, expected to lead to a vacuum in the 10–15 mbar range. In this paper the cryogenic concept of the storage ring and the related vacuum design will be presented.

We report on the first radioactive beam experiment performed at the recently commissioned REX-ISOLDE facility at CERN in conjunction with the highly efficient γ spectrometer MINIBALL. Using Mg-30 ions accelerated to an energy of 2.25 MeV/u together with a thin Ni-nat target, Coulomb excitation of the first excited 2(+) states of the projectile and target nuclei well below the Coulomb barrier was observed. From the measured relative deexcitation γ-ray yields the B(E2;0(gs)(+)R 2(1)(+)) value of Mg-30 was determined to be 241(31)e(2) fm(4). Our result is lower than values obtained at projectile fragmentation facilities using the intermediate-energy Coulomb excitation method, and confirms the theoretical conjecture that the neutron-rich magnesium isotope Mg-30 resides outside the "island of inversion."

19 pages, 12 figures, 2 tables.-- PACS nrs.: 25.60.-t; 25.45.-z; 27.20.+n.-- et al. ISOLDE Collaborattion and REX-ISOLDE Collaboration., At the newly constructed postaccelerator REX-ISOLDE (Radioactive beam Experiment at ISOLDE) we have investigated reactions induced by a Li-9 beam incident on a deuterium target at an energy of 2.36 MeV/u. Most reaction channels were recorded. From one-neutron transfer the differential cross-section for the low lying Li-10 spectrum is found. The results from the other channels demonstrate the great applicability and many possibilities that REX-ISOLDE opens up.

After the successful commissioning of the Radioactive beam EXperiment (REX) at ISOLDE (CERN) in 2002, first physics experiments were performed in 2003 which focussed on the neutron-rich Mg isotopes in the vicinity of the “island of inversion”. After introducing the REX facility and the modern γ spectrometer MINIBALL first preliminary results will be presented showing the high potential and physics opportunities offered by this new radioactive beam facility.

In previous experiments, diamond-like carbon (DLC) foils which are being produced at Kurchatov Institute, have proven well suited as long-lived stripper foils for high-energy heavy-ion tandem accelerators and ultra-thin secondary-electron (SE) emitting foils for TOF spectrometers. This paper presents the recent advances in DLC targetry with main emphasis given to development and applications of ultra thin foils (maximum diameter up to 70 mm) with high uniformity and minimal possible effective thickness, the latter has been evaluated by measurements of both energy loss and angular scattering of heavy ions transmitting through the foils. Comparative lifetimes of DLC stripper foils irradiated with high intensity (150 μA) He + beams at 2 MeV are reported, which demonstrate the favorable use of DLC foils as supplemental strippers at RFQ linacs. In conclusion, the attractive results of application of ultra-thin DLC foils to TOF detectors for heavy ion AMS as well as to compact tandem accelerators are presented.

The radioactive beam experiment REX-ISOLDE, a pilot experiment testing a new concept of post acceleration of radioactive ions at ISOLDE/CERN is in progress. Singly charged radioactive ions delivered by the online mass separator ISOLDE are accumulated in a Penning trap (REX trap), charge bred in an electron beam ion source (EBIS), separated from the residual gas in a mass separator and then accelerated in a linac with output energies between 0.8 and 2.2 MeV/u. The REX trap is in operation, a first test beam was already injected. The design phase of the EBIS is finished and the construction has been started. The superconducting magnet is delivered. The linac consists of a radiofrequency quadrupole (RFQ) accelerator, an interdigital IH-structure and 3 seven gap resonators to vary the final energy.

The REX-ISOLDE-experiment which is presently being under construction at CERN is intended to investigate exotic, very neutron rich, radioactive nuclei. A linear accelerator will deliver radioactive beams which are produced by the isotope separator ISOLDE, with energies between 0.85 and 2.2 MeV/u. The Linac will consist of a RFQ accelerator, an interdigital H-structure (IH) and three 7-gap-resonators for variable final energy. Assuming an acceleration voltage of one 7-gap-resonator to be 1.75 MV at 90 kW rf power, the design velocities of the three resonators were chosen to be 5.4%, 6.0% and 6.6% of the velocity of light. Three downscaled models (1:2.5) were built in order to optimize the shunt impedance and the field distribution for the operating frequency of the amplifiers of 101.28 MHz. The development of the resonators was accompanied by extensive MAFIA calculations. It could be demonstrated that spiral-resonators like 7-gap-resonators can be calculated with MAFIA. Important quantities like frequency, shunt impedance, quality factor and field distribution were compared between simulation and measurement. The first two power type resonators (5.4% and 6.0%) are finished, frequency tuning and low power measurements were done. The Q-values are about 5560 and 5280, respectively, the shunt impedance 71 M/spl Omega//m and 68 M/spl Omega//m, respectively, and are in very good agreement with the model measurements. After preparation for high power tests a beam test for the voltage calibration is planned. In this paper the status of the production of the 7-gap-resonators is reported.

The post accelerator REX‐ISOLDE is installed at the ISOLDE facility at CERN, where a broad variety of radioactive ions can be addressed. Since the end of 2001 beams at the final energy of 2.2 MeV/u are available. REX‐ISOLDE uses a unique system of beam bunching and charge breeding. First a Penning trap accumulates and bunches the ions, which are delivered as a quasi‐continuous beam from the ISOLDE target‐ion‐source, and then an electron beam ion source (EBIS) charge‐breeds them to a mass‐to‐charge ratio below 4.5. This enables a very compact design for the following LINAC, consisting of a 4 rod RFQ, an IH structure and three 7‐gap‐resonators. The later ones allow a variation of the final energy between 0.8 and 2.2 MeV/u. Although the machine is still in the commissioning phase, first physics experiments have been done with neutron rich Na and Mg isotopes and 9Li. A total efficiency of several percent has already been obtained.

In 2001 the linear accelerator of the Radioactive beam EXperiment (REX-ISOLDE) delivered for the first time accelerated radioactive ion beams, at a beam energy of 2 MeV/u. REX-ISOLDE uses the method of charge-state breeding, in order to enhance the charge state of the ions before injection into the LINAC. Radioactive singly-charged ions from the on-line mass separator ISOLDE are first accumulated in a Penning trap, then charge bred to an A/q < 4.5 in an electron beam ion source (EBIS) and finally accelerated in a LINAC from 5 keV/u to energies between 0.8 and 2.2 MeV/u. Dedicated measurements with REXTRAP, the transfer line and the EBIS have been carried out in conjunction with the first commissioning of the accelerator. Thus the properties of the different elements could be determined for further optimization of the system. In two test beam times in 2001 stable and radioactive Na isotopes (Na-23-Na-26) have been accelerated and transmitted to a preliminary target station. There Ni-58- and Be-9- and H-2-targets have been used to study exited states via Coulomb excitation and neutron transfer reactions. One MINIBALL triple cluster detector was used together with a double sided silicon strip detector to detect scattered particles in coincidence with gamma-rays. The aim was to study the operation of the detector under realistic conditions with gamma-background from the beta-decay of the radioactive ions and from the cavities. Recently for efficient detection eight tripple Ge-detectors of MINIBALL and a double sided silicon strip detector have been installed. We will present the first results obtained in the commissioning experiments and will give an overview of realistic beam parameters for future experiments to be started in the spring 2002.

A newly designed radio frequency cavity was used at the storage ring TSR in Heidelberg to accelerate stored /sup 12/C/sup 6+/ (E/sub 0/=73.3 MeV) beams. It was possible to accelerate about 90% of the stored particles by more than a factor of three in kinetic energy (E/sub fin/ /spl ap/240 MeV). A new operating mode of the machine close to the transition energy was also investigated. Up to 10 /spl mu/A /sup 12/C/sup 6+/ and protons could be stored, however the beams were susceptive to longitudinal instabilities. For 21 MeV protons (/spl gamma/=1.02) a /spl gammasub tr/ parameter of 1.04 could be reached. A new method to produce a beam of polarized ions, based on spin selective attenuation by a polarized atomic hydrogen target was successfully proved with 23 MeV protons. To minimize losses of the beam particles the TSR was operated in the low-beta mode. After one hour a beam polarisation of 0.014 was achieved. >

The accelerator facilities at the Max-Planck-Institut fur Kernphysik in Heidelberg will be upgraded by a new high current injector which is under development. The first phase will consist of a high current ion source (CHORDIS) for singly charged ions, two 4-ROD-RFQ-resonators and eight 7-gap-resonators. The ion source has already delivered the design current of several mA Li/sup +/. New 'vane-like' electrodes with good cooling properties and good mechanical stability allow the operation of the RFQ-resonators at high power level and duty cycle. The eight 7-gap-resonators were constructed and tested. The final energy of the injector (E=1.8 MeV/u) is matched to the existing post-accelerator. By adding an ECR-or an EBIS-source, the new injector-post accelerator system will be able to deliver beams up to uranium with energies above the Coulomb barrier. The progress of the project will be described.

The Radioactive beam Experiment (REX-ISOLDE)(1,2,3) at ISOLDE/CERN is under progress and first tests are carried out with some of the structures. The radioactive ions from the online mass separator ISOLDE will be cooled and bunched in a Penning trap, charge bred in an electron beam ion source (EBIS) and finally accelerated in a short LINAC to a target energy between 0.8 and 2.2 MeV/u. The LINAC consists of a radio frequency quadrupole (RFQ) accelerator, which accelerates the ions up to 0.3 MeV/u, an interdigital H-type (IH) structure with a final energy between 1.1 and 1.2 MeV/u and three seven gap resonators, which allow the variation of the final energy. All components of the experiment are now in production or undergo first test measurements. Such measurements are ion capture tests of the trap, electron beam tests of the EBIS, low level measurements and first power tests of the RFQ and the first 7-gap resonator. In this paper the status of the experiment, and the proposed schedule are presented.

At the Max-Planck-Institut fur Kernphysik, a new type of accelerator is under operation which consists of a CHORDIS and an ECR ion source, two directly coupled 4-Rod-RFQ and eight 7-gap resonators. The RFQs are designed to accelerate ions with a minimum charge to mass ratio of q/A=1:9 up to an energy of 0.478 MeV/u. Both RFQ resonators operate at a frequency of 108.48 MHz with a maximum pulsed power of 90 kW (25% duty factor). The development of the RFQ resonators was accompanied by extensive numerical simulations with the code MAFIA. We present the results of electrostatic calculations with modulated electrodes and the results of electrodynamic simulations of RFQ resonators.

The ISOLDE RIB-facility at CERN has today been producing a vast range of radioactive beams since more than 30 years. The low-energy beams of ISOLDE will be complemented by a post-accelerator, REX-ISOLDE, currently being assembled. In order to convert the pseudo-DC, singly-charged beam from the ISOLDE mass separators into a cooled and bunched beam at higher charge states, a novel scheme of trapping, cooling, and charge-state breeding has been devised, using a linear Penning trap and an Electron Beam Ion Source (EBIS). This allows for subsequent acceleration by a short, cost-effective LINAC consisting of an RFQ, an IH-structure and three seven-gap resonators, reaching 0.8–2.2 MeV/u. The installation of REX-ISOLDE is well underway and the first post-accelerated radioactive beams are expected to be obtained during late 2000.

The radioactive beam experiment (REX-ISOLDE) is now in the commissioning phase. REX-ISOLDE is a pilot experiment for testing a new concept of post acceleration at ISOLDE/CERN. The concept of REX-ISOLDE using a Penning trap-EBIS combination as a charge breeder and a compact linac for post acceleration requires detailed tests of all components in order to get a high efficiency. First measurements with REXTRAP, the transfer beam line and the REXEBIS have been done as well as first acceleration of stable beams from the EBIS with use of REXRFQ.