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Decking, W.

Paper Title Page
MOPD087 Error Emittance and Error Twiss Functions in the Problem of Reconstruction of Difference Orbit Parameters by Usage of BPM's with Finite Resolution 903
 
  • V. Balandin, W. Decking, N. Golubeva
    DESY, Hamburg
 
 

The problem of errors, arising due to finite BPM resolution in the reconstructed orbit parameters, is one of the standard problems of the accelerator physics. Even so for the case of uncoupled motion the covariance matrix of reconstruction errors can be calculated "by hand", the usage of the obtained solution, as a tool for designing of a "good measurement system", is not straightforward. A better understanding of this problem is still desirable. We make a step in this direction by introducing dynamics into this problem, which seems to be static. We consider a virtual beam obtained as a result of the application of a reconstruction procedure to ‘‘all possible values'' of BPM reading errors. This beam propagates along the beam line according to the same rules as any real beam and has all beam dynamical characteristics, such as emittances, dispersions, betatron functions, and all these values describe the properties of the BPM measurement system. As an application we formulate requirements for the BPM measurement system of high-energy intra-bunch-train feedback system of the European XFEL Facility in terms of the introduced concepts of error emittance and error Twiss parameters.

 
MOPE064 The European XFEL Beam Position Monitor System 1125
 
  • B. Keil, R. Baldinger, R. Ditter, R. Kramert, G. Marinkovic, P. Pollet, M. Roggli, M. Rohrer, V. Schlott, M. Stadler, D.M. Treyer
    PSI, Villigen
  • W. Decking, D. Lipka, D. Nölle, M. Siemens, T. Traber, S. Vilcins
    DESY, Hamburg
  • O. Napoly, C.S. Simon
    CEA, Gif-sur-Yvette
  • J.-P. Prestel, N. Rouvière
    IPN, Orsay
 
 

The European XFEL is an X-ray free electron laser user facility that is currently being built in Hamburg by an international consortium. The electron BPM system of the XFEL is developed by a collaboration of PSI, DESY, and CEA/Saclay/Irfu. Cavity BPMs will be used in all parts of the E-XFEL where highest resolution and lowest drift is required, e.g. in the undulators and some locations in the beam transfer lines. In the cryostats of the superconducting 17.5GeV main linac, 2/3rds of the BPMs will be buttons, while 1/3rd will be re-entrant cavities that promise higher resolution than buttons at low bunch charges. The transfer lines will also be equipped with cost-efficient button BPMs. The BPM electronics is based on a modular system concept, with a common FPGA-based digital back-end design for all BPMs and pickup-specific analog RF front-ends. This paper introduces the design concepts and reports on the project status and measurement results of BPM pickup and electronics prototypes.

 
TUPE002 Low charge electron beam SASE parameter study for European XFEL 2144
 
  • V. Sahakyan, A. Tarloyan
    CANDLE, Yerevan
  • W. Decking
    DESY, Hamburg
 
 

The options for an extremely low bunch charge regime (20 pC) of the European XFEL project are studied. The parameter study (saturation length and power) is performed for a wide range of the beam normalized emittance, bunch length and energy spread. The study is based both on analytical scaling of the SASE FEL performance and numerical simulations.

 
TUPE005 FLASH II: a Seeded Future at FLASH 2152
 
  • B. Faatz, N. Baboi, V. Balandin, W. Decking, S. Düsterer, J. Feldhaus, N. Golubeva, T. Laarmann, T. Limberg, D. Nölle, E. Plönjes, H. Schlarb, S. Schreiber, F. Tavella, K.I. Tiedtke, R. Treusch
    DESY, Hamburg
  • J. Bahrdt, R. Follath, M. Gensch, K. Holldack, A. Meseck, R. Mitzner
    Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Elektronen-Speicherring BESSY II, Berlin
  • M. Drescher, V. Miltchev, J. Roßbach
    Uni HH, Hamburg
 
 

FLASH has been a user facility since 2005, delivering radiation in the wavelength range between 7 and 47 nm using the SASE principle. In order to increase user beam time and improve the radiation properties delivered to users, a major extension of the user facility called FLASH II has been proposed by DESY in collaboration with the HZB, which is a seeded FEL over the parameter range of FLASH. As logical continuation, the HHG development program started with sFLASH, will result in direct seeding. Because in the foreseeable future there will probably not be HHG seed lasers available at high repetition rates down to wavelengths of 4 nm, a cascaded HGHG scheme will be used to produce short wavelengths. After a first design report, the project now enters its preparation phase until the decision for funding will be taken. During this time, the FLASH beam parameters after the present upgrade 2009/2010 will be characterized and the present design will be re-evaluated and adjusted. In addition, complete start-to-end simulations will complete the simulations which have been performed so far, including a complete design of the extraction area.

 
THPD083 Apochromatic Beam Transport in Drift-Quadrupole Systems 4476
 
  • V. Balandin, R. Brinkmann, W. Decking, N. Golubeva
    DESY, Hamburg
 
 

A straight drift-quadrupole system, though not being an achromat, can transport certain incoming beam ellipses without introducing first-order chromatic distortions. Several examples of such apochromatic beam transport are available in the literature. In this paper we show that the possibility of apochromatic focusing is a general property: For every drift-quadrupole system there exist an unique set of Twiss parameters (apochromatic Twiss parameters), which will be transported through that system without first order chromatic distortions. Moreover, we prove that at the same time the apochromatic Twiss parameters bring the second order effect of the betatron oscillations on the shift of the average bunch path length to the minimal possible value and also minimize the effect of betatron oscillations on bunch lengthening for Gaussian beam. As an example we consider the application of the apochromatic focusing concept to the design of matching sections and phase shifter of the post-linac collimation section of the European XFEL Facility.

 
THPD084 Two Cell Repetitive Achromats and Four Cell Achromats Based on Mirror Symmetry 4479
 
  • V. Balandin, R. Brinkmann, W. Decking, N. Golubeva
    DESY, Hamburg
 
 

An achromat is a focusing system, in which as large a number of higher order aberrations as possible is canceled by symmetries of the linear optics and the rest is corrected by the usage of third and higher order multipoles. The first achromats ever considered were repetitive achromats, in which the cancellation of higher order aberrations relies on appropriate selection of cell tunes. Later on achromats, employing mirror symmetry, were also developed. In this paper we remove one superfluous constraint on the linear optics in the theory of four cell mirror symmetric achromats, make an accurate consideration of two cell repetitive achromats, and compare the number of multipoles required for each of those achromats. Moreover, we contribute a point of view, from which both approaches to the achromat design become identical. As a practical application we consider the design of the arcs of the post-linac collimation section of the European XFEL Facility.

 
THPD086 Measurement and Correction of Transverse Dispersion in PETRA III 4485
 
  • G.K. Sahoo, K. Balewski, W. Decking, J. Keil
    DESY, Hamburg
 
 

PETRA III is a 6GeV positron light source with a design horizontal beam emittance of 1nm.rad and 1% emittance coupling. This low emittance is achieved with proper correction of horizontal dispersion to its theoretical values in the arcs as well as dispersion free sections. The spurious vertical dispersion, arising due to misalignment and rotational errors of the magnets is also duly corrected as this contributes to the vertical beam size of the photon beam. Here we discuss the method taken to correct the horizontal dispersion using a combined orbit and dispersion correction scheme. In the vertical plane the same procedure can be used as that of horizontal plane or only the dispersion can be corrected using dedicated skew quadrupoles to millimeter level after orbit correction has been done. In this paper we present the methods used and results obtained in correction of dispersions in transverse planes.

 
THPE062 Tilted Sextupoles for Correction of Chromatic Aberrations in Beam Lines with Horizontal and Vertical Dispersions 4656
 
  • N. Golubeva, V. Balandin, W. Decking
    DESY, Hamburg
 
 

We consider a beam line, in which pure betatron oscillations are transversely uncoupled, but which has nonzero horizontal and vertical dispersions simultaneously. We show that transverse oscillations in such a beam line could be chromatically coupled if the horizontal dispersion is nonzero in the vertical bending magnets and vice versa. We also show that the ability of sextupoles to generate chromatic coupling terms depends on the relation between sextupole tilt angles and the direction of the dispersion vector at the sextupole locations. We discuss different approaches to the setup of sextupole tilt angles depending on chromatic aberrations taken for correction. As a practical application we consider the usage of tilted sextupoles in the design of the beam switchyard at the European XFEL Facility.