Development of CMR Manganite Sensors for Energy Measurement of the Linear Coherent Light Source Free Electron Laser Xray
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0928-GG05-05
Development of CMR Manganite Sensors for Energy Measurement of the Linear Coherent Light Source Free Electron Laser Xray Pulses Grace J. Yong1, Rajeswari M. Kolagani1, David E. Cox1, Rajeh Mundle1, Anthony L. Davidson III1, Stephan Friedrich2, Zaheer A. Ali2, Owen B. Drury2, Lisa G. Li2, Linda L. Ott2, and Yong Liang3 1 Physics, Astronomy, and Geosciences, Towson U., 8000 York Rd., Towson, MD, 21252 2 Advanced Detector Group, Lawrence Livermore National Lab, 7000 East Ave. L-270, Livermore, CA, 94550 3 Physical Science Research Labs, Motorola Labs, 7700 S. River Parkway, Tempe, AZ, 85284 ABSTRACT We are developing Colossal Magnetoresistive (CMR) manganite thin film bolometric sensors to be employed as total energy detectors for beam diagnostics of the Linear Coherent Light Source (LCLS) Free Electron Laser (FEL) (at the Stanford Linear Accelerator). LCLS is an ultra bright, ultra short coherent x-ray source whose peak brightness will exceed that of third generation x-ray sources by about ten orders of magnitude and average brightness by three orders of magnitudes. It is expected to produce 1012 x-rays per 200 fs pulse with a repeat frequency of 120 Hz through self-amplified stimulated emission. In characterizing the beam, it will be necessary to measure the total energy of the FEL pulse. The Advanced Detector Group at Lawrence Livermore Laboratory has developed a scheme for FEL total energy measurements based on bolometric detection and are collaborating with Towson University to implement such a detector using CMR manganite thin films. Here we discuss the basic scheme, results of simulations of the thermal response and the materials development efforts towards fabricating the thin film detectors. DESIGN CONSIDERATIONS The total energy detector consists of an array of CMR manganite bolometers fabricated on a substrate capable of withstanding the FEL pulses without melting and without thermal expansion exceeding the material yield strength. The FEL pulse is incident at the back of the substrate, resulting in a temporal evolution of the temperature profile within the substrate leading to a temperature transient in the sensor array. The substrate thermal conductance and thermal mass dominate the dynamics of the temperature evolution and are chosen such that the response time of the detector is faster than the FEL pulse repetition rate. Under such conditions, the peak temperature rise in the sensor array can be used as measure of the FEL pulse energy. In the bolometric detection scheme, this peak temperature rise is accompanied by a change in resistance (∆R) of the detector element; ∆R may be measured either in a voltage biased or in a current biased mode. The requirement that the substrate must be stable under bombardment by FEL pulses necessitates that the substrate is composed of low Z elements. High Z elements, due to the large number of electrons will absorb the x-ray pulse (in the energy range between 800 to 8000 eV) over too short a distance leading to overheating and melting or fracture of the subs
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