National Centre for Nuclear Research
Astrophysics Division
Cosmic Ray Laboratory

90-558 Łódź
ul. 28 Pułku Strzelców Kaniowskich 69
tel./fax (+48 +42) 6786431
tel./fax (+48 +42) 6783223

High Voltage Power Supply for POLAR –
Space Based GRB Polarisation Detector

POLAR on the orbit

The Tiangong-2 orbital module with detector POLAR on board has been launched from the Jiuquan Satellite Launch Center on 15 September 2016 at 14:04 UTC (16:04 polish time). POLAR will measure polarisation of photons from Gamma Ray Bursts.

X-ray polarisation measurements of Gamma Ray Bursts may provide important information about the emission processes. These very energetic astrophysical events are also candidates for ultra high energy cosmic ray sources.

POLAR is a Swiss project of a satellite detector for 50-500 keV photon polarisation measurements using Compton scattering. 1600 low-Z scintillation bars are viewed by 25 multianode photomultipliers (MAPMTs) (Hamamatsu 8500 series – 64 anodes). Simultaneous measurements of signals from two bars would indicate Compton scattering.

In the middle of 2011 we were asked to design, develop and produce a functional model of a high voltage power supply for 25 MAPMTs. The goal was to provide individually adjustable high voltage to every MAPMT, retain the redundancy required in space experiments, make power efficient device, provide the opportunity to measure some actual performance and finally fit the allocated space and weight. From the 3 different solutions we proposed one was selected for development.

The basic idea was to generate one high voltage (-700V – -1100V) below any required level by MAPMTs, and reduce it for each MAPMT to an individual level. Each MAPMT has a resistance divider to distribute voltages to cathode, dynodes and grid. We propose to use current sources to reduce the current individually on each divider, and this way to provide a cathode voltage equal to the product of this current and the divider resistance.

At the beginning of 2012 we provided a HVPS engineering model, a simple controller and HV-board for tests of HVPS performance to the University of Geneva, the leading institution of the POLAR experiment.