End of phase A meeting CNES (Toulouse) 2/02/2012 Ph. Gorodetzky APC - Paris Diderot 1

High Voltage power suppliesHV Switches

Design:J. Szabelski, J. Karcmarczyk, Lodz, Poland

Tests: P. Gorodetzky, C. Blaskley, S. Selmane, APC, Paris

For the JEM-EUSO collaboration

End of phase A meeting CNES (Toulouse) 2/02/2012 Ph. Gorodetzky APC - Paris Diderot 2

MAPMT polarization

Current flowing in PMT loads the voltage divider. For Jem-Euso, and balloon, with this design, we have 0.1 W / EC (4 PMTs) and for 1233 ECs, we have 123 W. Too much. Also, impedance to the different dynodes is given by the voltage divider resistors: impedance is high, then dynamics are low.

Solution: Cockroft-Walton (CW): a succession of voltage multipliers.Works because most voltages between adjacent dynodes are equal (60 - 65 V for Hamamatsu M64)Also, impedances are low at the first dynode, raising when going towards K.

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Cockroft-Walton

Remote commands: - total ON-OFF- variation of the "60 V", to adjust the gains between 1 and 5 106

Tests at APC

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Cockroft-Walton tests on one PMT

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1 nW on sphere NIST = 3000 ph / sec (1000 pe / s) per pixel

Total power for 137 PDM (Jem-Euso) if one CW per PDM = 6 W. It is 50 W if one CW per EC. Safety factors for Jem-Euso are 1/137 or 1/1233. For the balloon, they are 1/1 or 1/9. So it is here mandatory to have one HV per EC.

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HV SwitchesLIGHTNINGS AND EXTREMELY BRIGHT SIGNALS

A system of HV switches is foreseen in JEM-EUSO to reduce the PMT current when the PMTs are subject to very bright signals. A lightning is more than 106 times more brilliant than the UV background.

An example is described in the following.

The balloon could give us the opportunity to check the functioning of this switch system. In principle the current level to apply the switch can be arbitrary decided so that it could be tested even in presence of city lights, if the balloon will not be exposed to lightning.

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Original idea by M. Sato

-860 V -640 V

-900 V-640 V

Switch organigram

End of phase A meeting CNES (Toulouse) 2/02/2012 Ph. Gorodetzky APC - Paris Diderot 8

The light amount is measured by the KI: charge integrators located in the LAL ASIC digitizing the charge of 8 anodes every GTU (2.5 µs). This is counted in the FPGA of the PDM board, in which this organigram is written. The dynamics of the KI are a factor of 100, from 2.5 pC to 250 pC. So, 4 switches are enough to go from a gain of 106 to a gain of 100.However, changing the voltage of the cathode only can change the gain such asillustrated in the adjacentswitch logic.

The PDM board cannot give more than 4 lines of signals to the switches. We decided that the full PDM would switch gain at the same time. Then 4 lines (one per gain) are enough.

The Lodz switches

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Power measured at APC was about 6 W. However, most of it was for the GTU generator which will be the PDM board in the final version. So, the power due to the switches only, and not their command, is virtually 0.

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Switching in one PMT

Going from HIGH to LOW

(one square is 4 µs)

Going from LOW to HIGH

One square is 100 µsThe overshoot (not dangerous in that direction) has since been corrected.

Only of two days ago do we have at APC 4 M64 MAPMTs to make an EC, and the corresponding CW and switches (the prototype at the right size). Tests will be done immediately after this meeting.

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Simulations of strong light problems(M. Bertaina)

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Development plan

Many prototypes have been realized in Lodz, and their tests at APC showed they worked perfectly. We are building actually a qualify model with the right technology and dimensions to be tested in February 2012 at APC. Then we start to make a flight model.The difference between them is that the FM will be potted.

It will require optimization in the cabling in order to ensure that all remnants of high frequency are eliminated. The FM will be tested at APC at 3 mbar in a 1 m3 vessel in order to mitigate the risk of Corona discharge at PMT-HV with damage to FEE.

The HV cabling is the object of a special study which is now finished and needs to be tested with the flight model (it cannot be made with the prototypes because they are independent of the EC-boards) Once the design is completed, and the prototypes OK, the Flight Model will be produced (by the industry, in Poland) => assembly and potting.

These FM elements will be delivered to APC for the acceptance and validation tests which will include tests in an opaque vessel set at 3 mbar with every component (a mock-up of an EC, that is 4 PMTs, the HV cables and the HV box) potted inside, and everything working. There will be at least 2 tests at 3 mbar: one for the HV box to deliver something that does not spark and one for the EC-boards with the MAPMT soldered and powered. Here, we are dealing only with the test related to the HV box.Integration inside the PDM will follow. Then the PDM could require a test at 3 mbar, however, each component apt to spark will have been previously tested.

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Risk analysis