A twelve-dynode photomultiplier

PHYSICS · Multi-part · Fermi University Physics · Electronics, Instrumentation & Communication · Semiconductor devices and analogue circuits · Sensors, detectors and experimental instrumentation

Inside the Instrument, Ch References, regulators and switching converters

Problem

A twelve-dynode photomultiplier, with gain law exponent k=0.75k = 0.75, is to run at 1800 V1800\,\mathrm{V} and draws 150 μA150\,\mu\mathrm{A} through its divider chain. It is fed from a Cockcroft-Walton ladder driven at f=100 kHzf = 100\,\mathrm{kHz} by a transformer secondary of 150 V150\,\mathrm{V} peak. The tube's gain must hold steady to 0.05 %0.05\,\%. ((a)) How many stages does the ladder need? ((b)) Find the largest ripple the supply may carry and the smallest stage capacitance that achieves it. ((c)) Choose the next value above that from the series 220220, 330330, 470 nF470\,\mathrm{nF}, and find the resulting ripple and gain modulation. ((d)) Find the droop with that capacitance, and the steady fractional shift in gain it would cause if the drive were not raised to make it up.

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