Author: Hillert, W.
Paper Title Page
MOPFI006 A New Load Lock System for the Source of Polarised Electrons at ELSA 294
  • D. Heiliger, W. Hillert, B. Neff
    ELSA, Bonn, Germany
  Funding: supported by DFG (SFB/TR16)
The inverted source of polarized electrons at the electron stretcher accelerator ELSA routinely provides a pulsed beam with a current of 100 mA and a polarization degree of about 80%. One micro-second long pulses with 100 nC charge are produced by irradiating a GaAs strained-layer superlattice photocathode (8 mm in diameter) with laser light. Future accelerator operation requires a significantly higher beam intensity, which can be achieved by using photocathodes with sufficiently high quantum efficiency. Therefore, and in order to enhance the reliability and uptime of the source, a new extreme high-vacuum (XHV) load lock system was installed and commissioned. It consists of a loading chamber in which an atomic hydrogen source is used to remove any remaining surface oxidation, an activation chamber for heat cleaning of the photocathodes and activation with cesium and oxygen and a storage chamber in which up to five different types of photocathodes with various diameters of the emitting surface can be stored under XHV conditions. Additionally, tests of the photocathodes' properties can be performed during accelerator operation.
MOPME006 The New Orbit Correction System at ELSA 479
  • J.-P. Thiry, A. Balling, A. Dieckmann, F. Frommberger, W. Hillert
    ELSA, Bonn, Germany
  ELSA is a fast ramping stretcher ring currently supplying polarized electrons with energies up to 2.4 GeV. To preserve the degree of polarization, the vertical orbit needs to be continuously corrected during beam acceleration. The acceleration is usually performed within 300 ms, with a maximum ramping speed of 6 GeV/s. We aim to achieve a vertical rms deviation not exceeding 50 μm all along the fast energy ramp. In the near future we plan to accelerate polarized electrons up to 3.2 GeV. Therefore, both the power supplies and the corrector magnets have been currently upgraded: first, new power supplies working with a pulsed transistor H-Bridge were developed and successfully installed. Additionally, the existing vertical corrector magnets will now be replaced by newly developed ones. In our contribution, we will present the new correction hardware supplemented by the beam position monitors and their readout electronics.  
MOPME007 High Resolution Synchrotron Light Analysis at ELSA 482
  • S. Zander, F. Frommberger, P. Hänisch, W. Hillert, M.T. Switka
    ELSA, Bonn, Germany
  Funding: Funded by the DFG within the SFB/ TR 16
The Electron Stretcher Facility ELSA provides polarized electrons with energies up to 3.5 GeV for external hadron experiments. In order to suffice the need of stored beam intensities towards 200 mA, advanced beam instability studies need to be carried out. An external diagnostic beamline for synchrotron light analysis has been set up and provides the space for multiple diagnostic tools including a streak camera with time resolution of < 1 ps. Beam profile measurements are expected to identify instabilities and reveal their thresholds. The effect of adequate countermeasures is subject to analysis. The current status of the beamline development will be presented.
MOPWO005 Simulating Spin Dynamics and Depolarization using POLE 891
  • J.F. Schmidt, O. Boldt, F. Frommberger, W. Hillert
    ELSA, Bonn, Germany
  Funding: BMBF
The spin dynamics in circular accelerators with fast energy ramps, or short storage times of up to some seconds, can be investigated with spin tracking appropriately. Additionally, the spin motion of lepton beams is affected significantly by synchrotron radiation. Hence, spin dynamics simulations require spin tracking with a large number of particles to compute the beam polarization and thus take considerably long computing times. Therefore, high efficiency is crucial to perform systematic polarization studies. The new simulation tool POLE provides the ability to balance accuracy against computing time. To that end, adjustable approximations of magnetic fields and synchrotron radiation are implemented. POLE is accessible for a wide range of lepton storage rings because it uses the common MAD-X lattice files and the corresponding particle tracking results.
WEPFI006 Broad and Narrow Band Feedback Systems at ELSA 2714
  • M. Schedler, F. Frommberger, P. Hänisch, W. Hillert, C. Reinsch
    ELSA, Bonn, Germany
  At the Electron Stretcher Facility ELSA of Bonn University, an upgrade of the maximum stored beam current from 20 mA to 200 mA is planned. The storage ring operates applying a fast energy ramp of 6 GeV/s from 1.2 GeV to 3.5 GeV. The intended upgrade is mainly limited due to the excitation of multibunch instabilities. As a countermeasure, we succesfully commissioned state-of-the-art bunch by bunch feedback systems in the longitudinal and the two transverse dimensions. In addition, a narrow band cavity based feedback system for damping the most harmful longitudinal multi bunch mode caused by a HOM of the accelerating cavities is under construction.  
WEPFI007 Amplitude, Phase and Temperature Stabilization of the ELSA RF System 2717
  • D. Sauerland, W. Hillert, A. Roth, M. Schedler
    ELSA, Bonn, Germany
  • D. Teytelman
    Dimtel, San Jose, USA
  In the stretcher ring of the accelerator facility ELSA electrons are accelerated to a maximum energy of 3.2 GeV applying a fast energy ramp of up to 6 GeV/s. In order to be able to offer higher external beam currents one has to increase the current of the internal beam in ELSA accordingly. The beam current is limited due to excitation of multi bunch instabilities which are mainly caused by higher order modes of the two PETRA cavities used for particle acceleration in the stretcher ring. To control the resonance frequency of these modes, a variable bypass of the cavities' cooling system has been installed which allows a stabilization of their temperature. With this modification, it is possible to vary the temperature of the cavities between 26 °C and 65 °C and thus to shift the higher order modes by hundreds of kHz in frequency. Additionally, first operational studies with a prototype of a FPGA based LLRF system (Dimtel) have been performed which in future will be used to stabilize the amplitude and phase of the accelerating RF fields of the cavities.  
THPEA002 The Accelerator Control System at ELSA 3149
  • D. Proft, F. Frommberger, W. Hillert
    ELSA, Bonn, Germany
  To fulfill the new requirements of the post-accelerator mode of the electron stretcher facility ELSA, a new computer control system was developed during the early 1990s. Providing capabilities to control and monitor the facility, it represents the top layer of a distributed control system composed of HP workstations, VME and field bus processors as well as linux based personal computer s. In addition to regular updates and improvements, the HP-UX operated part of the control system recently was ported to linux, so the outdated HP workstations could be replaced by a single linux PC. All reference values, for example the betatron tune or the extraction energy, can be specified using a window-based graphical user front end. They are directly computed to hardware compatible representations. Vice versa, measured beam parameters, e.g. the transversal beam emittance, are displayed for easy user access, allowing real time diagnostics. This abstraction layer allows for an intuitive approach to machine operation, requiring no detailed knowledge of the hardware implementation. In this contribution, the design principles and implementation at different layers of the control system are presented.  
THPFI006 A New External Beamline for Detector Tests 3300
  • N. Heurich, F. Frommberger, P. Hänisch, W. Hillert, S. Patzelt
    ELSA, Bonn, Germany
  At the electron accelerator ELSA, a new external beamline is under construction, whose task is to provide a primary electron beam for detector tests. In the future, the accelerator facility will not only be offering an electron beam to the currently installed double polarization experiments for baryon spectroscopy, but to the new "Research and Technology Center Detector Physics" as well. This institution will be established near the accelerator in Bonn and is charged with the development of detectors for particle and astroparticle physics. The requirement for the new beamline is to be able to vary the beam parameters such as beam current and width over a wide range. With the resonance extraction method, it is possible to extract electrons with a maximum energy of 3.2 GeV slowly to the test area. A quasi-continuous external beam current of 1 fA to 100 pA can be offered. A further reduction of the beam current can be realized by utilizing the single-pulse operation mode at ELSA. The beam width can be changed in both transverse directions from 1 mm to 8 mm.