04/22/23 Report on Casaccia test 11-01-2006 1

Report on radiation test done in Casaccia on

January 11, 2006

M. Beretta INFN Frascati

C. Landi CAEN

A. Lanza INFN Pavia

G. Passuello CAEN

A. Pezzini CAEN

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The ENEA Casaccia sourceIt is a 60CO source, called “Calliope” , available to external users in the ENEA-Casaccia research center, 30 km from Roma.

The source is shaped as a cylindrical rack, with radioisotope pencils placed externally to the rack surface. It is immersed in a pool 8 m deep, from where can be extracted by means of a motorized rail system.

The present activity is 6.72 x 1014 Bq.

The Calliope source in its pool (to the left) and in operational position (to the right)

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The dose rate profiles were simulated (in collaboration with CERN), by using the FLUKA code, taking in account all three interactions, photoelectric, Compton and (even if negligible at 1.25 MeV) pair production. The horizontal profile inside the irradiation room is shown to the left (scale in Gy/h) and the vertical one to the right. The comparison between simulated and measured values in two different positions has shown an agreement better than 20%.

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The distributors under test

Four devices were irradiated:-1 A3540, 12 channels 4kV 1mA, all channels loaded on 5M and monitored by means of 10k resistors;

- 1 A3025, 4 channels 8V 25A, with two channels open (ch 2 and ch 3) and two connected to active loads (ch 0 and ch 1). Ch 1 was independently monitored by the datalogger with 1:1 ratio;- 1 A3016, 6 channels 8V 16A, with two channels open (ch 4 and ch 5) and four connected to active loads. No channels were monitored by the datalogger;

- 1 A3535 single DC/DC channel, 3.2kV 0.5mA, not on-board, loaded on 10M and only monitored by the datalogger with a ratio of 1:1000.

All distributors were placed in an EASY3000 crate, and supplied with an AC/DC generator A3484. The A3535 single DC/DC channel was placed over the crate and supplied by means of a generic power supply.

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The test setupThe EASY3000 crate was positioned with the front at 180 cm from the source, were the measured dose is 50 GY/h. The attenuation due to the distributor aluminum front panels is of the order of 4%.

The distributors are 40 cm long, so the dose on the back of them is considerably smaller (~ 33 GY/h, not considering the masking effect of components). In order to compensate for this, the run was divided in two equal parts, and the crate was flipped at the end of the first period, so to place the rear of the distributors at the same 180 cm from the source.

The picture to the left shows the crate position with respect to the source pool, while the picture to the right illustrates the distributor connections.

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Another view of the irradiation room (top left), with in foreground the Atlas Pixel PP2 board, tested in parallel.

The A3535 channel (top right) on the top of the crate.

The A3540 passive loads (bottom left), connected to the data logger.

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The control room (top left) during the preparation of the setup.

The power supplies and the SY2527 controlling and monitoring the distributors (top right).

The EASY3000 and the source photographed through the lead window in control room during the second part of the run, after the crate was flipped.

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The runAll parameters of the three distributors (22 channels) were monitored by the SY2527 mainframe, and saved in an ASCII log file.

Moreover, the screen view of the mainframe and the comment voices were recorded by a PC during all the run period. An example of such audio-video files is shown below.

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All A3540 channels, one of the A3025 channels and the A3535 single channel were monitored with an Agilent 34970A 20-channel data logger, together with the 48V Power and the 48V Service supplied by the A3484. The acquisition rate was 12 seconds.

The run was divided in two periods: the first lasted 120 minutes, the second started after 50 minutes, but was stopped after 6 minutes for communications problems with the Pixel PP2 board. Then, after an access, the second period was restarted and lasted 130 minutes. Total irradiation time was 256 minutes, and the average accumulated dose was 175 Gy (167 Gy taking in account the aluminum attenuation).

Monitored Service and Power currents overall the irradiation period

0,00

1,00

2,00

3,00

4,00

5,00

6,00

7,00

8,00

0 1 2 3 4 5 6

Time (h)

Cur

rent

(A)

48V Service current48V Power current

End first period

End second period

Start second period and stop after 6 minutes for problems to PP2 board

Second period final start

Post-irradiaton tests

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ResultsA3016:This distributors was only monitored through the SY2527.

After 95 minutes (78 Gy on DC/DC channels, 52 Gy on the controller daughter board) one channel (ch 3) went undervoltage, quickly followed by a second channel (ch 4) that gave an Vmax alarm.

After other 3 minutes, also the A3540 started giving many undervoltage alarms (see picture below), but no change was seen on the data logger, indicating that only the controller was affected.

After 114 minutes other A3016 channels showed the same problem, and the board was switched off. At the start of the second period the board was switched on again, but after few minutes it went undervoltage again.

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A3025:

This distributor worked well for 205 minutes (136 Gy on the controller), after that started showing undervoltages on all channels. Still the channel monitored with the data logger continued to work until the board was switched off, after 218 minutes (see the picture below).

A3025 ch 1

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1,00

2,00

3,00

4,00

5,00

0 1 2 3 4 5 6

Time (h)

Volta

ge (V

)

A3025 ch 1

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A3535:Because it was a single channel without any motherboard, it was only monitored with the data logger. It switched off after 88 minutes (73 Gy), with no recovery. It was switched on again during the time in between the two periods, and showed a partial recovery (instead of 3kV went to 1.8kV). At the beginning of the second period it was left on at 1.8kV, and lasted at this voltage up to the end of the test.

A3535 single channel voltage

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0,50

1,00

1,50

2,00

2,50

3,00

3,50

4,00

0 1 2 3 4 5 6

Time (h)

VOlta

ge (k

V)

A3535 singlechannel voltage

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A3540:As already reported, it suffered of many undervoltages after 98 minutes (54 GY), but without any inconvenient to the outputs. During the interval between the two periods, the controller board was replaced with a new one, but again after 73 minutes (60 Gy) from the beginning of the second period it started showing undervoltages.

Before, after 184 minutes (134 Gy), one channel (ch 6 in the below picture) started oscillating and in few minutes died, followed by other channels. The last channel to die was ch 1, which lasted 239 minutes (165 Gy).

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0,10

0,20

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0 1 2 3 4 5 6

Time (h)

Cur

rent

(mA

)

A3540 ch 1A3540 ch 2A3540 ch 6A3540 ch 10

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ConclusionsAll three distributors had shown failures on their controllers. Three of them, including the spare one used on the A3540 during the second irradiation period, survived around 50 Gy, while one, belonging to the A3025 distributor, reached 2.5 times more.

The problem was traced by Caen to the EEPROM, a Xicor “old” type. After some days from the irradiation all EEPROM were able to recover, but there is no certainty that they can perform well again under radiation.

The test also showed some other bugs, quickly traced by Caen:-the A3535 DC/DC channel suffered for a wrong polarization of the VMOS regulator;- the A3540 DC/DC channels had a diode placed in a wrong position.

Caen is writing a detailed report on what was discovered during the analysis of the four irradiated devices, complementing the present report.

Some corrections were already implemented on the A3535 and the A3540 before delivering those distributors to Uppsala, so the test at TSL will tell us whether they have solved the problems.