Leakage Current Summary Cosimo Cantini, Kevin Fusshoeller, Laura - - PowerPoint PPT Presentation

Leakage Current – Summary Cosimo Cantini, Kevin Fusshoeller, Laura Molina Bueno

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Reminder

• When the CAEN boards for the LEM were installed, the group from Kiev tested them and observed a non-

zero current in several LEMs: LEM 3 down, LEM 4 down, LEM 6 down, LEM 8 up, LEM 12 down.

• During the HV tests in June and July this current was again observed, both during ongoing tests and when

everything was disconnected. More LEMs showed a non-zero current compared to the tests by Kiev group.

• For periods with no tests, the current was identified as a non-constant offset of the CAEN power supply.

CAEN power supply: From left to right: Board 0, Board 1, Board 2 The LEM are ordered in logical

• rder: first LEM 1 Up, then LEM

1 down, LEM 2 up, LEM 2 down etc. Board 0: LEM 1 up, … , LEM 4 down Board 1: LEM 4 up, … , LEM 8 down Board 2: LEM 9 up, … , LEM 12 down

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Motivation

• To investigate the source of this current, it was monitored over time with and without HV to

understand if there is an intrinsic effect of the power supply or it is related to the HV system.

• We would also like to understand if the HV tests have had an impact on the evolution of these

currents over time.

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Current in periods of no HV test: Offset Current

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Observations

1) The current is (anti-)correlated to the hall temperature. (plot for the period of 07.07.2017 – 09.07.2017) Affected LEMs: LEM 1,3, 7,8,12 up and down LEM 2, 4, 6 down

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Observations

2) The current is higher on some LEM (see table) and the current drops from Board 0 to Board 2.

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Fan providing a uniform air flow

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Observations

LEM 1 up LEM 1 down LEM 2 up LEM 2 down LEM 3 up LEM 3 down LEM 4 up LEM 4 down

• Max. Current

0.3 nA 4.8 nA 0 nA 0.4 nA 1.4 nA 0.4 nA 0 nA 10.9 nA

Rate of change

0.50 nA/K 2.15 nA/K / 0.5 nA/K 0.50 nA/K

• 0.47 nA/K

/

• 1.10 nA/K

LEM 5 up LEM 5 down LEM 6 up LEM 6 down LEM 7 up LEM 7 down LEM 8 up LEM 8 down

• Max. Current

0 nA 0 nA 0 nA (0.3 nA) 0.1 nA 0.3 nA 4.6 nA 3 nA Rate of change / / / / (< 0.2 nA/K) 0.50 nA/K

• 0.50 nA/K

1.25 nA/K LEM 9 up LEM 9 down LEM 10 up LEM 10 down LEM 11 up LEM 11 down LEM 12 up LEM 12 down

• Max. Current

0 nA 0 nA 0 nA 0 nA 0 nA 0 nA 0.6 nA 2.8 nA

Rate of change

/ / / / / / 0.24 nA/K 0.18 nA/K

Board 0 Board 1 Board 2

 Since the board on the corner of the CAEN power supply is affected the most, this strongly suggests that the forced air flow is not homogeneous in the crate where the CAEN boards are placed.  CAEN people assured us that variations of up to 100 ppm/K are still considered to be good values.

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Observations

3) There is a shift of 1-3h in the (anti)correlation. We don‘t think this is a timestamp problem. More investigations are being performed. One idea is that the hall temperature is not the same as the local temperature at the boards. (plot for the period of 20.07.2017 – 23.07.2017)

Affected LEMs: LEM 1,3, 7,8,12 up and down LEM 2, 4, 6 down

Max current Min temp. Max current Min temp. Max current Min temp.

The current seems to predict the change in temperature.

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Observations

Comment: because of the time shift, the current oscillates by up to 1.5 nA for the same temperature and depends

• n whether the temperature is rising or falling.

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Current during HV test:

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Observations

1) The slope of the current oscillations does not seems to be affected by the HV. However for some LEM the absolute value of the leakage current can change. For example we start seeing a current on LEM 6, which we were not seeing before. This current is anti-correlated to the temperature and behaves like the other leakage currents.

Slope Test 1 Slope Test 2 Slope Test 3 Slope no HV LEM 3 down

• 0.40 nA/K
• 0.45 nA/K
• 0.47 nA/K

0.47 nA/K LEM 4 down

• 1.07 nA/K
• 1.20 nA/K
• 1.35 nA/K
• 1.10 nA/K

LEM 6 down

• 0.14 nA/K
• 0.14 nA/K
• 0.13 nA/K

/ LEM 8 up

• 0.57 nA/K
• 0.39 nA/K
• 0.59 nA/K
• 0.50 nA/K
• Test 1: Cathode: 20 kV, Grid: 1.0 kV, LEM down: 1.0, LEM up: 0 kV
• Test 2: Cathode: 20 kV, Grid: 2.5 kV, LEM down: 3.0 (corner: 2.6 kV), LEM up: 0.2 kV
• Test 3: Cathode: 20 kV, Grid: 0.5 kV, LEM down: 1.0, LEM up: 0 kV

Current Test 1 Current Test 2 Current Test 3 Current no HV LEM 3 down 1.0 nA 0.9 nA 1.0 nA 1.0 nA LEM 4 down 5.25 nA 4.1 nA 5.3 nA 7.0 nA LEM 6 down 0.4 nA 0.3 nA 0.2 nA / LEM 8 up 1.7 nA 1.7 nA 2.45 nA 1.75 nA Current at hall temperature T = 298K No obvious difference. Difference of 0.1 nA. No obvious difference. No obvious difference. Absolute current lower. New current. No obvious difference.

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Observations

2) The offset current changes suddenly when the HV is turned on. For LEM 12 it disappears completely as long as the HV system is on. For the other LEMs the current drops by at least 50% when the system is turned

• n.

No voltages applied No voltages applied

Abrupt change during start and end of HV test.

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Observations

Sudden drop when we turn

• n the HV system.

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Observations

3) The leakage current does not seem to be affected by trips of the grid or of the LEMs.

Leakage current behaves the same before and after trips.

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Short drop of the current when the LEM trips, but then it recovers to the value before the trip and behaves normally.

Observations

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4 trips 8 trips 4 trips 12 trips 4 trips 13 trips 5 trips 20 trips 4 trips 12 trips 4 trips 10 trips 8 trips 19 trips 4 trips 12 trips 5 trips 13 trips 7 trips 23 trips 4 trips 10 trips 4 trips 7 trips CRP2 CRP3 CRP1 CRP5 CRP6 CRP7 CRP8 LEM Up LEM Down

N S

Observations

4) Comparison between number of trips on LEM and which LEM show a leakage current.

• The following LEMs always show leakage current during HV tests:

LEM 3 down, LEM 4 down, LEM 6 down, LEM 8 up.

• The highest leakage current is found on LEM 4 down and LEM 8 up.
• The other LEMs only show a leakage current at high hall temperatures (>29°C).
• Data not conclusive enough to say if LEMs with leakage current trip more often.

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Future plans/tests

• Disconnect the cables and put some voltage on the board to check if the LEMs/cables are causing

problems.

• See if we can improve the forced air flow in the crate.
• Install parallel resistors to each channel to monitor such variations of current.

Conclusion

• There is a non-constant offset of the power supply (anti-)correlated to the hall temperature. This

correlation is there whether the HV system is on or off and stronger on the outside board. This strongly suggests that it is due to a non uniform air flow in the crate. Moreover CAEN people assure us that the variations we see are still considered to be good values.

• Turning on the HV influences the offset of the leakage current. For most of the LEM the current drops by at

least 50%, but can recover later on. For LEM 12 it disappears completely, while for LEM 6 we see a current we did not see before.

• The leakage current behaves the same before and after trips in the grid or the LEMs.

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Backup

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Position of temperature sensors

LEM 12: Current and Temperature

From 03.07.2017 to 17.07.2017 Clear correlation between hall temperature and LEM (offset) current.

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