Author: Kelez, N.M.
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WEBA02
 Minimization of Mechanical Constraint Effects of Eutectic GaIn as Thermal Interface  
 
  • L. Zhang, D. Cocco, J.H. James, N.M. Kelez, D.S. Morton
    SLAC, Menlo Park, California, USA
  
  Eutectic Gallium-Indium (eGaIn: 75% Gallium + 25 Indium) is widely used as the thermal interface in water-cooled X-ray optics. The thermal contact resistance of the eGaIn can be smaller than 0.1 mm2. K/W. The LCLS-II KB mirrors will be water cooled, and mostly dynamically bendable. The requirement on the bending accuracy can be expressed as residual slope error after the subtraction of the ideal ellipsoidal shape. This residual slope error should be smaller than 0.1rad, which is at least 4 orders of magnitude smaller than the mirror bent slope. Therefore, the mechanical constraint force from the eGaIn interface should be at least 4, and mostly 5 orders of magnitude smaller than the bending forces with the bending arm length comparable to the mirror length. But what is the mechanical constraint force of the eGaIn interface? What are the mechanical properties of the eGaIn in terms of Youngs or shear modulus. How should this eGaIn interface optimized, for instance the thickness of this interface? In this paper, we will present experimental studies conducted at SLAC to answer these questions, and propose a solution to minimize the constraint forces of the eGaIn.  
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WEPE20
 KB Mirror Design for the LCLS-II SXR Beam Line  
 
  • D.S. Morton, D. Cocco, N.M. Kelez, L. Zhang
    SLAC, Menlo Park, California, USA
  
  Funding: Work supported by Department of Energy contract DE-AC02-76SF00515.
One of the key components of the beam transport, in the SXR beam-line is the bendable focusing mirror system, operated in a Kirkpatrick-Baez Configuration. For the first time in the Synchrotron or FEL world, the large bending needed to focus the beam will be coupled with a cooling system, since the full FEL power is delivered through all of the optics to the sample. In this paper we will discuss the key design elements of the KB mirror system. We will cover the flexure hinge based bender mechanism which provides a well-defined axis of rotation. The flexure based twist and height correction mechanisms which allow correction for manufacturing and assembly tolerances. The parallel leaf spring lever arms which allow the use of relatively low bending forces with high resolution and do so while maintaining a constant direction of force application. The epoxy joint which was designed to minimize the tensile loading of the epoxy to increase its performance. We will then go on to discuss the cooling scheme which allows us to mechanically decouple the cooling system from the mirror. 		 
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FRAA02
 Optimizing X-Ray Mirror Thermal Performance Using Variable-Length Cooling for High-Repetition-Rate FELs  
 
  • C.L. Hardin, L. Amores, D. Cocco, N.M. Kelez, D.S. Morton, V.N. Srinivasan, L. Zhang
    SLAC, Menlo Park, California, USA
  • M. Carlucci-Dayton
    BNL, Upton, Long Island, New York, USA
  
  Funding: DOE
SLAC National Accelerator Laboratory is developing LCLS-II, a superconducting linear accelerator based free electron laser capable of a repetition rate up to 1 MHz. To deliver the FEL beam with minimal power loss and wavefront distortion, we need grazing-incidence plane mirrors with height errors below 1nm rms, under operational conditions. We also need to mitigate thermal effects of a complex photon energy-dependent thermal profile. We discuss a mirror cradle that minimizes figure error using variable length water cooling through a gallium-indium eutectic bath, and curve correction with an off-axis bender. We present thermal and mechanical analysis, design and prototyping results of figure sensitivity under bender corrections. 		 
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FRBA04
 LCLS-II KB Mirror Systems: Technical Challenges and Solutions  
 
  • L. Zhang, D. Cocco, N.M. Kelez, D.S. Morton
    SLAC, Menlo Park, California, USA
  
  Based on the success of the Linac Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory, the Department of Energy has funded the LCLS-II - a billion-dollar project. In addition to the existing LCLS copper linac that delivers FEL pulses at 120 Hz, the LCLS-II project will provide a 4 GeV superconducting (SC) linear accelerator to deliver high-repetition-rate FEL pulses, up to 1 MHz. The average power of the FEL beam from the SC linac will range from 20 to 200 W, and potentially to 600 W. The FEL beam has ultra-short pulse length (down to a few fs), narrow energy band width (down to less than 10-4, thanks to self-seeding technology), and is fully coherent beam. The preservation of the wavefront is essential to maintain the outstanding FEL beam properties. In this paper, we will describe the technical challenge of the optics design to preserve the FEL beam wavefront. We will focus on the KB mirror system for LCLS-II instruments. We will especially discuss the aspects of cooling technology to minimize the thermal deformation and the management and minimization of the mechanical coupling between the mirror bending and the cooling.  
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