REAL cooled mirror for FEL application: FEA modelling and wavefront propagation simulation (Conference Presentation)

Abstract

To preserve the full coherence of the FEL, the acceptance of the optics should be at least 2*FWHM of the X-ray beam. The LCLS-II soft X-ray experiments cover a photon energy range from 250 eV to 1300 eV. The photon beam footprint on the flat and KB mirrors varies from 150 mm to 1000 mm. The length of the mirror is chosen as 1 meter. Resistive Element Adjustable Length (REAL) cooling technique has been proposed to minimize the thermal deformation [1] for LCLS-II mirrors when the power FEL is above 200 W. The water cooling of the mirror is applied on the top-up-side [2]. The additional electric heater is adjustable both in length and power density to cope with the variable X-ray beam footprint length. A R&D project including the prototype of this REAL cooling technique is funded by DoE for FY2017 & FY2018. In this paper, we will present the modeling results of this REAL cooled prototype mirror. The two parameters of the electric heater (length and power density) are optimized for the thermal deformation minimization of the mirror Finite Element Analysis (FEA) with ANSYS. This optimization of two parameters within ANSYS is not straight forward and necessity large number of FEA calculations. SRW software is used for the wavefront propagation simulation to compare the performance of REAL cooled mirror with other frequently used cooling techniques. 1. Zhang L., Cocco D., Kelez N., Morton D.S., Srinivasan V. and Stefan P.M. - Optimizing X-ray mirror thermal performance using matched profile cooling, J. Synchrotron Rad. (2015). 22,1170–1181, doi: 10.1107/S1600577515013090 2. Zhang L. , Barrett R. , Friedrich K. , Glatzel P. , Mairs T. , Marion P. , Monaco G. , Morawe C. , Weng T. - Thermal distortion minimization by geometry optimization for water-cooled white beam mirror or multilayer optics, Journal of Physics : Conference Series 425, 052029-1-052029-4 (2013)