High Voltage Cooling system for High Dissipation Power GaN Transistors

The beam deflector is among the key components of the Medium Energy Beam Transport (MEBT) of the Proton Improvement Plan-II (PIP-II). It will be driven by a high voltage (HV) switch currently under development at Fermilab. It is based on an array of field-effect switching transistors (FETs) operating at kV floating potentials and at as high as 30 MHz frequency. The transistors dissipate ~200 W/cm2 power and need to be electrically insulated while the FET operating temperature is kept below 60C. In this project, RadiaBeam Systems will develop an effective cooling system without distortion of the nanosecond waveform that can be affected by presence of the HV cooling structure. The cooling system robustness and efficiency is enabled by a number of innovations: a) all- diamond heat spreader structure with vacuum-brazed fins; b) mini-channels enhancing heat transfer coefficient; b) expansion-matched holder for the spreader; c) low parasitic capacitance (<1pF) enabled by combination of the large area diamond spreader, small brazed area, and low permittivity of the fluorocarbon cooling fluid; d) ultrasound-enhanced heat transfer due to low acoustic impedance of the fluid, streaming, and cavitation; and e) low-melting-temperature alloy used as the interface between the FET and polycrystalline diamond surface. In Phase I we will analyze and compare different approaches for cooling enabling the HV, low- capacitance performance; select and optimize the most promising configuration with electrical and thermal simulations; compare and choose the most suitable materials, which are critical for the performance and design/engineer the cooling assembly; develop the experimental setup and mockup equivalent for a single-FET; and perform a feasibility demonstration.Commercial Applications and Other Benefits: The initial target segment for this technology is accelerator facilities. Other future applications include civil and military electronic components including radars and power conversion devices, frontier lasers and high power electro-optics, ozonators, ground penetrating radars, pulsed radiolysis.