Universal linear accelerator

Abstract: Swift heavy ions (SHI) of MeV–GeV energy lead to the creation of nanometric surface structures as well as modifications in the bulk along the ion penetration depth. Recently, similar surface modifications have been observed for the impact of individual slow highly charged ions (HCI). Non-amorphizable ionic-halide single crystals, like KBr, CaF2 and BaF2, are considered as the most intensively studied materials after irradiation with HCI. In this contribution we study the creation of surface nanostructures in an amorphizable material, namely SiO2 quartz after irradiation with slow highly charged Xe ions from the Electron Beam Ion Trap at Helmholtz Zentrum Dresden-Rossendorf and swift xenon ions from Universal Linear Accelerator at GSI in Darmstadt. After irradiation at room temperature, the crystals were investigated by scanning force microscopy. For both SHI and HCI, the created nanostructures exhibit the shape of hillocks. Moreover UV–VIS spectroscopy was performed to identify the defects created by ion irradiation at high fluence. The results are discussed in terms of the creation mechanisms driven by the dependence on both potential and kinetic energies of the ions.

Abstract: As part of an intensity upgrade program, a new Radio Frequency Quadrupole (RFQ) has been commissioned at the high charge state injector (HLI), one of the two injector linacs of GSI’s UNIversal Linear ACcelerator UNILAC. The main feature of this RFQ is its continuous wave (cw) operation capability. Besides, improved beam quality as well as increased beam transmission are persued. The HLI mainly provides beam for the super heavy element research, which is one of the major physics experiments at GSI. At the Separator for Heavy Ion reaction Products (SHIP) six new chemical elements have been discovered; moreover nuclear chemical experiments with transactinides were recently performed with the TransActinide Separator and Chemistry Apparatus (TASCA). This experimental program strongly benefits from high average beam intensities. In the past beam currents were raised significantly by a number of improvements. The present upgrade program comprises the installation of a second, superconducting (sc) 28 GHz Electron Cyclotron Resonance (ECR) ion source and a new frontend (Low Energy Beam Transport (LEBT) and Radio Frequency Quadrupole (RFQ)). For the short term, the new RFQ will raise the useable duty cycle by a factor of two, limited by the following rf cavities. The setup of the RFQ as the major upgrade of the 20 year old high charge state injector was finished in January 2010, the commissioning went on until April. This paper reports on the challenging rf and beam commissioning.

Abstract: The irradiation with fast ions with kinetic energies of > 10 MeV leads to the deposition of a high amount of energy along their trajectory (up to several ten keV/nm). The energy is mainly transferred to the electronic subsystem and induces different secondary processes of excitations which result in significant material modifications. A new setup to study these ion induced effects on surfaces will be described in this paper. The setup combines a variable irradiation chamber with different techniques of surface characterizations like scanning probe microscopy, time-of-flight secondary ion and neutral mass spectrometry, as well as low energy electron diffraction under ultra high vacuum conditions, and is mounted at a beamline of the universal linear accelerator (UNILAC) of the GSI facility in Darmstadt, Germany. Here, samples can be irradiated with high-energy ions with a total kinetic energy up to several GeVs under different angles of incidence. Our setup enables the preparation and in-situ analysis of different types of sample systems ranging from metals to insulators. Time-of-flight secondary ion mass spectrometry enables us to study the chemical composition of the surface, while scanning probe microscopy allows a detailed view into the local electrical and morphological conditions of the sample surface down to atomic scales. With the new setup particle emission during irradiation as well as persistent modifications of the surface after irradiation can thus be studied. We present first data obtained with the new setup, including a novel measuring protocol for time-of-flight mass spectrometry with the GSI UNILAC accelerator.

Abstract: At GSI's accelerator facilities ion beam intensities usually are observed and measured with various types of current transformers (CT), matched to the special requirements at their location in the machines. In the universal linear accelerator (UNILAC), and the high charge state injector (HLI) as well, active transformers with 2nd-order feedback are used, while passive pulse CTs and two DC-CTs based on the magnetic modulator principle are implemented in the heavy ion synchrotron (SIS) and the experimental storage ring (ESR). In the high energy beam transfer lines (HEBT) the particle bunch extraction/reinjection is monitored with resonant charge-integrating types. Since more than 10 years number and significance of beam current transformers for operating GSI's accelerators have grown constantly. Due to increased beam intensities following the last UNILAC upgrade, transmission monitoring and beam loss supervision with CTs have become the main tools for machine protection and radiation security purposes. All CTs have been constructed and developed at GSI, since no commercial products or were available, when solutions were needed.