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Thermal Analysis of a Stationary Target of X-Ray Sources Operating in Pulse Mode

P Kandlakunta

P Kandlakunta*, R Pham , W Rao , R Khan , T Zhang , Washington University School of Medicine, St Louis, MO


SU-K-702-2 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: 702

Purpose: To evaluate the maximum power limitation of multi-pixel x-ray sources with a stationary x-ray target.

Methods: The maximum power of an x-ray tube is limited by the heat load of the target focal spot. A Monte Carlo model was built in Geant4 to simulate the penetration and energy deposition of an electron beam in a tungsten target. A transient thermal model of the target was built in LISA finite element analysis software. The focal spot is modeled as multi-layer heating elements with powers as a function of depth given by the Monte Carlo calculation. The resulting transient temperatures of the X-ray focal spot for different pulse durations and repetition rates were studied. The maximum allowed tube power is determined to keep target temperature spikes under 2000 °C for a given pulse duration. The model is experimentally validated with multi-pixel thermionic emission x-ray source at selected pulse durations.

Results: From the Monte Carlo simulations, the energy deposition of 100 keV electrons as a function of depth in the target was determined. Transient thermal simulations showed the focal spot temperature rose rapidly and cooled within 1 ms. The maximum source power as a function of pulse duration was determined. The experimental study validated the model prediction for 400 μs pulse width.

Conclusion: The peak power of multi-pixel x-ray source with a stationary target is determined primarily by pulse width. The focal spot temperatures for various pulse widths and repetition rates were predicted using the finite element model. The relationship between the pulse width and maximum tube power was obtained.

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