High Precision Temperature Control for Injector Components of a Free-Electron Laser

Abstract

High precision temperature control of injector components like the RF GUN is necessary to optimally accelerate thousands of electrons within the injection part of the European X-ray free-electron laser XFEL and the Free Electron Laser FLASH. A difference of the RF GUN temperature from the reference value of only 0.01 K leads to detuning of the cavity and thus limits the performance of the whole facility. Especially in steady-state operation there are some undesired temperature oscillations when using classical standard control techniques like PID control. That is why a model based approach is applied here to design the RF GUN temperature controller for the free-electron lasers. Therefore a nonlinear thermal model of the RF GUN and the cooling facility is derived based on heat balances, considering the heat dissipation of the Low-Level RF power. The derived model is used for a linear model predictive controller design in MATLAB/Simulink. A test of the controller in simulation shows promising results.