Author: Nuhn, H.-D.
Paper Title Page
MOP045 Phase Shifter Design for iSASE 123
  • S.D. Chen, K. Fang, H.-D. Nuhn, C. Pellegrini, J. Wu, L. Zhu
    SLAC, Menlo Park, California, USA
  • S.D. Chen, C.-S. Hwang
    NCTU, Hsinchu, Taiwan
  • K. Fang
    Indiana University, Bloomington, Indiana, USA
  • C.-S. Hwang
    NSRRC, Hsinchu, Taiwan
  A phase shifter to generate an additional phase advance of the spontaneous light versus the electron beam was de- signed for the iSASE scheme. The iSASE mechanism is for reducing the bandwidth further from SASE FEL process. A large phase advance about 1600*2Pi as the FEL operating at wavelength 0.8 nm was needed according to the simulation of iSASE process. Since the iSASE is thought to implement into LCLS II project, the space limitation causing by LCLS II should be considered when designing the phase shifter. An optimized three-pole electric phase shifter with 7.3 mm gap has the center field of 1.8 T . The vanadium steel was considered as pole material and the magnet physical length is 260 mm, meanwhile the water-cooling type copper coil was adopted. The temperature increment, force analysis, low field operation mode concept, and preliminary tolerance study were discussed.  
MOP046 Undulator Radiation Damage Experience at LCLS 127
  • H.-D. Nuhn, R.C. Field, Yu.I. Levashov, X.S. Mao, M. Santana-Leitner, J.J. Welch, Z.R. Wolf
    SLAC, Menlo Park, California, USA
  Funding: Work supported by U.S. Department of Energy contract DE-AC02-76SF00515
The SLAC National Accelerator Laboratory has been running the Linac Coherent Light Source (LCLS), the first x-ray Free Electron Laser since 2009. Undulator magnet damage from radiation, produced by the electron beam traveling through the 133-m long straight vacuum tube, has been and is a concern. A damage measurement experiment has been performed in 2007 in order to obtain dose versus damage calibrations. Radiation reduction and detection devices have been integrated into the LCLS undulator system. The accumulated radiation dose rate was continuously monitored and recorded. In addition, undulator segments have been routinely removed from the beamline to be checked for magnetic (50 ppm, rms) and mechanic (about 0.25 μm, rms) changes. A reduction in strength of the undulator segments is being observed, at a level, which is now clearly above the noise. Recently, potential sources for the observed integrated radiation levels have been investigated. The paper discusses the results of these investigation as well as comparison between observed damage and measured dose accumulations and discusses, briefly, strategies for the new LCLS-II upgrade, which will be operating at more than 300 times larger beam rate.
TUB03 FEL Overcompression in the LCLS 337
  • J.L. Turner, F.-J. Decker, Y. Ding, Z. Huang, R.H. Iverson, J. Krzywinski, H. Loos, A. Marinelli, T.J. Maxwell, H.-D. Nuhn, D.F. Ratner, T.J. Smith, J.J. Welch, F. Zhou
    SLAC, Menlo Park, California, USA
  Funding: This work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515
Overcompression of the Linac Coherent Light Source (LCLS) x-ray Free Electron Laser (FEL) at the SLAC National Accelerator Center is studied. The studies and operational implications are summarized in this talk.
slides icon Slides TUB03 [4.493 MB]  
TUP035 Investigation of Reverse Taper to Optimize the Degree of Polarization for the Delta Undulator at the LCLS 465
  • J.P. MacArthur
    Stanford University, Stanford, California, USA
  • Z. Huang, A. Lutmann, A. Marinelli, T.J. Maxwell, H.-D. Nuhn, D.F. Ratner
    SLAC, Menlo Park, California, USA
  Funding: U.S. Department of Energy under contract No. DE-AC02-76SF00515
A 3.2 m adjustable phase Delta undulator* will soon be installed on the last girder of the LCLS undulator line. The Delta undulator will act as an afterburner terminating the 33 undulator line, providing arbitrary polarization control to users. Two important figures of merit for users will be the degree of polarization and the x-ray yield. In anticipation of this installation, machine development time at the LCLS was devoted to maximizing the final undulator x-ray contrast and yield with a standard canted pole undulator acting as a stand in for the Delta undulator. Following the recent suggestion** that a reverse taper (dK/dz > 0) in the main undulator line could suppress linearly polarized light generated before an afterburner while still producing the requisite microbunching, we report on a reverse taper study at the LCLS wherein a yield contrast of 15 was measured along the afterburner. We also present 1D simulations comparing the reverse taper technique to other schemes.
* Nuhn, H.-D., Anderson, S., Bowden, G., Ding, Y., Gassner, G., et al., (2013).
** Schneidmiller, E. A. and Yurkov, M. V., Phys. Rev. ST Accel. Beams 16, 110702 (2013).
Soft X-ray Self-seeding Setup and Results at LCLS  
  • D.F. Ratner, J.W. Amann, D.K. Bohler, M. Boyes, D. Cocco, F.-J. Decker, Y. Ding, D. Fairley, Y. Feng, J.B. Hastings, P.A. Heimann, Z. Huang, J. Krzywinski, H. Loos, A.A. Lutman, G. Marcus, A. Marinelli, T.J. Maxwell, S.P. Moeller, P.A. Montanez, D.S. Morton, H.-D. Nuhn, D.R. Walz, J.J. Welch, J. Wu
    SLAC, Menlo Park, California, USA
  • K. Chow, L.N. Rodes
    LBNL, Berkeley, California, USA
  • U. Flechsig
    PSI, Villigen PSI, Switzerland
  • S. Serkez
    DESY, Hamburg, Germany
  The soft X-ray self seeding program was designed to provide near transform-limited pulses in the range of 500 eV to 1000 eV. The project was a three-way collaboration between SLAC, Lawrence Berkeley National Lab, and the Paul Scherrer Institute in Switzerland. Installation finished in the Fall of 2013, and after the early stages of commissioning we have measured up to 0.5mJ pulse energy and resolving powers of up to 5000 across the design wavelength range, representing a several-fold increase in the brightness compared to the normal LCLS operating mode. Future work will aim to increase the total pulse energy and establish self-seeding as a robust user operation mode.  
slides icon Slides TUC02 [10.464 MB]  
THA03 A Plan for the Development of Superconducting Undulator Prototypes for LCLS-II and Future FELs 649
  • P. Emma, N.R. Holtkamp, H.-D. Nuhn
    SLAC, Menlo Park, California, USA
  • D. Arbelaez, J.N. Corlett, S.A. Myers, S. Prestemon, D. Schlueter
    LBNL, Berkeley, California, USA
  • C.L. Doose, J.D. Fuerst, E. Gluskin, Q.B. Hasse, Y. Ivanyushenkov, M. Kasa, G. Pile, E. Trakhtenberg
    ANL, Argonne, Illinois, USA
  Funding: Work supported by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DE-AC02-76SF00515, DE-AC02-05CH11231, and DE-AC02-06CH11357.
Undulators serve as the primary source of radiation for modern storage rings, and more recently for the advent of Free-Electron Lasers (FELs). The performance of future FELs can be greatly enhanced using the much higher magnetic fields of superconducting undulators (SCU). For example, the LCLS-II hard x-ray undulator can be shortened by up to 70 m using an SCU in place of a PMU (permanent magnet undulator), or its spectral performance can be critically improved when using a similar length. In addition, SCUs are expected to be orders of magnitude less sensitive to radiation dose; a major issue at LCLS-II with its 1-MHz electron bunch rate. We present a funded R&D collaboration between SLAC, ANL, and LBNL, which aims to demonstrate the viability of superconducting undulators for FELs by building, testing, measuring, and tuning two 1.5-m long planar SCU prototypes using two different technologies: NbTi at ANL and Nb3Sn at LBNL. Our goal is to review and reassess the LCLS-II HXR baseline plans (PMU) in July of 2015, after the development and evaluation of both prototypes, possibly in favor of an SCU for LCLS-II.
slides icon Slides THA03 [29.468 MB]