Fabrication and implementation of compact, low-power, three-dimensional, Cockcroft-Walton photomultiplier tube power supplies

Abstract

A photomultiplier tube high-voltage power supply was constructed using a ”Free-Form” method of fabrication. The main goal of this project was to benchmark the performance of an experimental additive manufactured high-voltage power supply that is currently being investigated at Kansas State University. This is achieved through the comparison of non-traditional methods and material to traditional materials of the same circuit in a similar oriented geometry. A printed circuit board layout was considered to be insufficient for comparison due to the large differences in geometry compared to the 3-dimensional additive circuit. The method used to provide high-voltage and proper dynode stage biasing was a half-wave Cockcroft-Walton voltage multiplier. The 3-dimensional orientation was achieved through the Free-Form process with surface mount devices connected end-to-end or stacked together to form 3-dimensional shapes using temporary scaffolding and supports. This construction method used a low component-count design that was developed in an earlier phase of the project. The Free-Form method along with the previously designed circuit helped achieve a minimal package footprint while offering reliable biasing to the dynode stages. This work includes an in-depth description of the Free-Form construction methods used to produce the 3-dimensional circuit along with electrical characteristic testing, and spectral analysis results. A comparison for size and weight was made between the prototypes and the commercially available E11807-01 resistive divider base. A performance comparison was made using an external +5V supply for the prototypes and an external NHQ 103M highvoltage power supply for the E11807-01. The electrical characteristic measurements included dynode stage voltages, photocathode regulation, photocathode voltage stability, and power consumption. Spectral analysis was conducted using the following check sources, 137Cs, 60Co, and 22Na. The prototypes and the E11807-01 were tested using a CsI(Na) crystal attached to an R11265U series photomultiplier tube. A total of two prototypes were produced using the Free-Form fabrication method. The final bulk dimensions for prototype A are 2.99 x 2.78 x 0.75 cm with a weight of 7.73g. Prototype B’s final bulk dimensions are 2.98 x 2.77 x 0.87 cm with a weight of 8.7g. The final dimensions of the additive manufactured printed experimental power supply that is being benchmarked are 2.99 x 2.77 x 0.65 cm with a weight of 8.36g. A 38.8% reduction in volume and a 34.7% reduction in weight was achieved through the Free-Form fabrication method when compared to the E11807-01 resistive divider. The photocathode voltage regulation values about its set point achieved for each prototype were +0.36% -0.60% for prototype A, +0.35% -0.83% for prototype B, and ±0.68% for the printed prototype. The maximum power consumption of each prototype while driving the photomultiplier tube were 53.41 mW for both prototype A and B and 69.53 mW for the printed prototype. The energy resolution’s measured for the full Cs-137 energy peak using a CsI(Na) crystal were 6.949% for prototype A, 7.851% for prototype B, 6.93% for the printed prototype, and 6.855% for the E11807-01.