Precision high voltage sources for nuclear radiation detectors

Publications, 19 September 2022

Employees of the Flerov Laboratory of Nuclear Reactions and the Dzhelepov Laboratory of Nuclear Problems have developed precision high voltage sources for nuclear radiation detectors (semiconductor detectors, based on photomultipliers (PMTs), etc.). Instead of a specialised high-voltage source, researchers have used a standard industrial transformer switched on in the opposite direction with a voltage multiplier. This is a novelty of the development. Such sources are used in a number of experiments and industrial installations providing quality, reliability, temperature range, and necessary functionality.

High voltage sources (HV) are key elements of measuring setups in experimental nuclear physics. As a rule, they are used to power a variety of nuclear radiation detectors (semiconductor detectors, based on PMTs, etc.) In experiments, depending on the task being solved, the number of detectors can vary considerably (from several units to several thousand). There are a number of requirements for such sources: a wide range of output voltage with different polarity (from tens of volts to kilovolts), minimal noise and ripples (units of millivolts), stability, power up to 10 W, compactness, reliability, and maintainability. Different types of detectors can be used in each setup.

Thus, there are also special requirements for power sources such as low output voltage ripples, minimal electromagnetic interference , the possibility of a smooth rise and fall of voltage for semiconductor detectors, for example. As for detectors based on PMTs, they are high stability of the output voltage (0.004%/◦C) and efficiency of the source.

HV sources are created in analogy with DC-DC converters consisted of a power node that forms HV, a smoothing filter for ripples and noise, a control system with a PWM controller, as a rule.

All this ensures high efficiency of the equipment and its technical characteristics. Thanks to the fact that the transformer operates at lower output voltage, the transformation coefficient is small, that is why the total scattering capacitance and inductance of the transformer are several times smaller, whilst the operating frequency is much higher with the same conversion losses. This allows obtaining high technical characteristics of the equipment while reducing the size of the magnetic circuit and filter. Although the requirements for the transformer are less strict than for the designed HV transformer, nevertheless the main consumer characteristics of the power source will depend on accurate calculation and its quality. For this reason, it is preferable to use a ready-made transformer of industrial assembly.

High voltage units: a – PMT power supply unit (BVN-2kV) in the control basket of the PAC setup; b – stand-alone high voltage unit (BPF-2kV); c – silicon semiconductor detector power supply unit (BPD-500V)

Based on available electronic components, specialists have developed precision high voltage sources for PMTs and semiconductor nuclear radiation detectors. Units have the form of reverse DC-DC converters. The key element of the circuit is a power node based on the available and affordable POL-12012 transformer with a capacitive diode voltage multiplier. The frequency of the converter is 80-150 kHz. Such circuit has made it possible to obtain output voltage up to 2,500 V with low ripples and noise and high equipment efficiency up to 77%. Designed high voltage units are successfully used in spectrometers of perturbed angular correlations (PAC), for the detecting system of the COMBAS fragment separator (FLNR JINR), in setups for detecting (dangerous) explosives based on the tagged neutron method.

An article on the performed work was sent to the journal “Instruments and Experimental Techniques”.