Author: Hillert, W.
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MOPMB010 Compton Polarimetry at ELSA - Beamline and Detector Optimization 95
  • R. Koop, W. Hillert, M.T. Switka
    ELSA, Bonn, Germany
  Funding: Work supported by DFG within CRC TRR16
The Electron Stretcher Facility ELSA provides a polarized electron beam with energies of 0.5 - 3.2 GeV for double polarization hadron physics experiments. Monitoring the vertical electron polarization by Compton polarimetry in the stretcher ring has several advantages over the established polarization measurement by Moeller polarimetry. The Compton polarimeter setup presented consists of a 40 W cw disk laser featuring two polarized photon beams colliding head-on with the stored electron beam in ELSA. A silicon strip detector measures the vertical intensity profile of the backscattered photons. The reversal of handedness of the laser beam's circular polarization results in a polarization dependent vertical shift of this profile. From a calibration using time dependent polarization build-up due to the Sokolov-Ternov effect, the polarization degree of the electron beam can be extracted. After recent laser repairs as well as beamline and detector modifications, first measurement attempts of the electron's polarization degree were conducted. The performance of the beamline and first measurements are presented.
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPMB010  
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MOPOR046 Studies on Depolarization by Synchrotron Radiation using Elegant Particle Tracking 695
  • J.F. Schmidt, W. Hillert
    ELSA, Bonn, Germany
  Funding: BMBF
Spin dynamics in circular electron accelerators are significantly influenced by the emission of synchrotron light. In storage rings, Sokolov-Ternov polarization build-up and radiative depolarization have crucial impact on equilibrium polarization. On shorter timescales, as in damping rings or synchrotrons with fast energy ramp, the temporal development of polarization depends on spin decoherence caused by stochastic momentum changes. Thus, especially longitudinal beam dynamics affect depolarization. This contribution presents the implementation of particle tracking with synchrotron radiation from Elegant in an in-house developed spin tracking code. Exemplary results on depolarization including synchrotron radiation are shown.
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR046  
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MOPOR047 Numerical and Experimental Substantiation of the Ion Density Beam Transfer Function Measurements 698
  • D. Sauerland, W. Hillert
    ELSA, Bonn, Germany
  Funding: Funded by the BMBF, Germany under grant 05K13PDA
In the ELSA stretcher ring electrons are accelerated to a beam energy of 3.2 GeV utilizing a fast energy ramp of 6 GeV/s. Ions being generated by collision with the residual gas molecules accumulate inside the beam potential, causing incoherent tune shifts and coherent beam instabilities. Since the ion induced incoherent tune shift rises linearly with the beam neutralisation, it offers a suitable approach for evaluating the efficiency of several ion clearing measures. It was indirectly measured using a new experimental approach: By measuring the beam transfer function using a broadband transversal kicker, one was able to perceive a shift and broadening of the tune peak. Both effects could be adequately parameterized providing a quantity proportional to the incoherent tune shift and thus the average neutralisation. The impact of incoherent effects to the coherent electron beam response during the measurement has not been subject to intensive theoretical attention yet. This leaves the obtained quantity unscaled. Here new numerical simulations and experimental investigations will be presented in order to further substantiate the results of this new method.
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR047  
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WEPOR011 Lattice Matching with Elegant at ELSA 2690
  • J.-P. Thiry, W. Hillert
    ELSA, Bonn, Germany
  The electron stretcher ring ELSA provides a beam of polarized electrons of up to 3.2 GeV energy. To preserve the initial degree of polarization, several depolarizing resonances have to be compensated during the fast energy ramp of 6 GeV/s. Beam depolarization, caused by crossing these resonances is studied using comprehensive numerical calculations. These depend essentially on a precise model of the actual magnetic field distributions, explicitly taking into account misalignments. Hence it is necessary to match the theoretical lattice to the actual accelerator. In a first step the alignment of all magnets has been examined and improved. This was done by using standard survey equipment and precise electronic spirit levels. In a second step the concept of response matrix fitting is used for further, beam based, lattice matching. Particle tracking and optics calculations are carried out using elegant, a fully 6D accelerator toolbox. Lattice matching is done by repeatedly calling elegant and utilizing a modified Levenberg-Marquardt optimizer. In this contribution we will describe our lattice fitting implementation.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPOR011  
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THPOW029 Single Electron Extraction at the ELSA Detector Test Beamline 4002
  • F. Frommberger, N. Heurich, W. Hillert, T. Schiffer, M.T. Switka
    ELSA, Bonn, Germany
  The Electron pulse Stretcher Facility ELSA delivers polarized and non-polarized electrons with an adjustable beam energy of 0.5 - 3.2 GeV to external experimental stations. Extraction currents available range down from 1 nanoampere to several atto-amperes provided by single electron extraction. Especially the high energy physics community requires detector test stations with electron tagging rates between 100 Hz to 100 kHz, imposing particular requirements for stable minimum-current extraction from the storage ring. These requirements are met with the implementation of a low-injection mode for the booster synchrotron and photomultiplier-based stored current monitoring, providing feedback for a selectable limit of the injected current. A homogeneous extraction current with duty factor > 80% is routinely granted by the excitation of a 3rd integer optical resonance. The setup of the low-current injection system and measurements of the extraction properties at the preliminary detector test beamline are presented.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPOW029  
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THPOY001 Implementation of a New Ramp Computation Scheme for the Magnet Power Supplies at ELSA 4085
  • D. Proft, W. Hillert
    ELSA, Bonn, Germany
  At the ELSA electron stretcher facility new power supply control units have been commissioned. These require a new software interface for set-point calculation based on the accelerator and timing model. Goal of the new scheme is a strict separation of the bidirectional ramp computation into an accelerator model dependent, a magnet dependent and a power supply dependent part. This introduces possible calibration/correction factors on each layer, thus allowing easy component replacement of the power supplies, the control units or even the magnets without the need for recalibration of the whole chain. In this contribution we will provide insights into the implementation of the new modeling scheme.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPOY001  
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THPOY002 The New External Beamline for Detector Tests at ELSA 4088
  • N. Heurich, F. Frommberger, P. Hänisch, W. Hillert
    ELSA, Bonn, Germany
  At the electron accelerator ELSA, a new external beam line has been constructed whose task is to provide a primary electron beam for detector tests. Using a slow resonance extraction method, it is possible to extract a quasi continuous electron beam with a maximum energy of 3.2 GeV to the test area. An external beam current of 100 pA to 1 fA can be realized. A further reduction of the beam current is envisaged as well. The beam width can be changed in both transverse directions from 1 mm to 8 mm. To dump and simultaneously measure the current of the electron beam behind the detector components a Faraday cup consisting of depleted uanium is used. The residual radiation leaving the cup is absorbed in a concrete casing. The radiation protection concept for the entire area of the new beamline was designed with the help of the Monte Carlo simulation program Fluka. In addition to the concrete casing, radiation protection walls were built to allow a safe working environment in the neighboring control room.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPOY002  
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