Thermal behavior of the optical transition radiation screens for the ELI-NP Compton Gamma source

A high brightness electron Linac is being built in the Compton Gamma Source at the ELI Nuclear Physics facility in Romania. To achieve the design luminosity, a train of 32, 16 ns spaced, bunches with a nominal charge of 250 pC will collide with the laser beam in the interaction point. Electron beam spot size is measured with optical transition radiation profile monitors. In order to measure the beam properties along the train, the screens must sustain the thermal stress due to the energy deposited by the bunches; moreover, the optical radiation detecting system must have the necessary accuracy and resolution. This paper deals with the analytical studies as well as numerical simulations to investigate the thermal behavior of the screens impinged by the nominal bunch; the design and the performance of the optical detection line is discussed as well. In particular with the numerical simulations the behavior of the aluminum and silicon under thermal stress can be studied. The simulations allow us to see how the heat spreads on the OTR screen and frame, and what are their deformations during the heating.