1LHCb CALO commissioning meeting 03.06.08 Anatoli Konoplyannikov /ITEP/
ECAL CW base performance
Outline
• ECAL – HCAL CW base difference;
• CW base study with switching on/off Agilent power supply;
• Current limitation in the MV Agilent power supply;
• Possible improvements of the ECAL HV system.
2LHCb CALO commissioning meeting 03.06.08 Anatoli Konoplyannikov /ITEP/
ECAL CW base performance
ECAL CW base features different from HCAL
1. wrongly soldered electrolytic capacitors -> mainly replaced;
2. unexpected DC current through the Agilent PS when power supply is off (it shows a MV to LV correlation);
3. LV protection fuses blowing up during the unexpected MV switching off (general power cuts, DSS action in case of alarm);
4. CW base pumping frequency impact on the PMT anode (CW noise);
5. Painful recovery from MV over current protection relay trip (needs: set ½ of all HV off, set Agilent off, switch on relays and repeat in back order).
3LHCb CALO commissioning meeting 03.06.08 Anatoli Konoplyannikov /ITEP/
ECAL CW base performance
LV regulators
+- 7 V
+5.8 V
-5.8 VIn
+80 V
+80 V
PMT group
CW
CW
CW
~ 80 m
~ 12 m
~ 4 m
Sketch of the LV and MV distribution of the XCAL HV system
Fuses
1
2
8
Agilent PS
Wiener PS
Current limiting
R = 0 or 100 HV_LED_DAC board
4LHCb CALO commissioning meeting 03.06.08 Anatoli Konoplyannikov /ITEP/
ECAL CW base performance
47 nF47 nF
ECAL CW base circuit diagram.
Test Point
The main difference from HCAL case is the additional filtering and integrating capacitors (in my opinion, it leads to main differences)
5LHCb CALO commissioning meeting 03.06.08 Anatoli Konoplyannikov /ITEP/
ECAL CW base performance
Original ECAL CW base oscillograms in Test Point, when Agilent 40 V goes down
HVout = 100 V, R=0HVout = 400 V, R=0
HVout = 400 V, R=100
6
LHCb CALO commissioning meeting 03.06.08 Anatoli Konoplyannikov /ITEP/
ECAL CW base performance
No C+C ECAL CW base oscillograms in Test Point
HVout = 100 V, R=0 HVout = 400 V, R=0
HVout = 100 V, R=100 HVout = 400 V, R=100
7LHCb CALO commissioning meeting 03.06.08 Anatoli Konoplyannikov /ITEP/
ECAL CW base performance
CW noise impact on a PMT anode, in case of original CW
CW noise impact on a PMT anode, in case of modified CW (without C+C)
There is no change of the CW noise behavior for original and modified base
8LHCb CALO commissioning meeting 03.06.08 Anatoli Konoplyannikov /ITEP/
ECAL CW base performance
Unexpected current from Agilent PS
9LHCb CALO commissioning meeting 03.06.08 Anatoli Konoplyannikov /ITEP/
ECAL CW base performance
Current limitation in the MV Agilent power supply
For improving the recovery procedure from MV current protection trip the current limiting resistors have been added for all HCAL boards.
The R=70 allows:
• limit max current of the protection relay up to 0.8 A;
• decrease the cross talk on neighbor protection circuits and exclude collective effects;
• maintenance the HV in smooth way.
Unfortunately for ECAL HV system the current limiting resistor could increase the CW base instability (as was shown above), but may be it should be verified with more CW bases.
10
LHCb CALO commissioning meeting 03.06.08 Anatoli Konoplyannikov /ITEP/
ECAL CW base performance What to do
Unfortunately not so much !
Modification of 6000 CW bases is not realistic and decreasing a number of power cuts seems not realistic too. In the same time we can:
• Decrease the pumping MV voltage for COSMIC runs as much as possible (for example in five times and set an ECAL trigger threshold five times lower)
• Increase the ramping down time of the Agilent PS, but it will work only for planed operations ;
• Modify one spare HV_LED_DAC board with MV current limiting resistors for performing the PMT noise test;
• In case if the noise does not changed, modify all HV_LED_DAC boards.
Now the max HV is about 1.55 kV and required MV is about 75 V (22 x 75)
In case of Gain 5 times less the HV will be about 250 V less and required MV is about 60 V
We have to be ready for some efforts during the ECAL HV system maintenance
