HF HV Decision path Y.Onel

HV Micro PRR August 3, 2012 Follow up of August 3 rd Meeting At the meeting the HCAL HF group presented the HV PSU options for the HF PMT replacement project. The HF group described the experiences and tests with both CAEN and Bulgarian power supplies. The prototype Bulgarian power supply was used at 904 PMT test station. Although it meets with all the specs, Bulgarian power supply produced several problems (e.g. baseboard failure) due to firmware issues. During the tests the firmware was upgraded three times, with waiting time for upgrade. The HCAL HF group expressed that CAEN solution is preferred over Bulgarian solution due to i) long term hardware and firmware maintenance, ii) unified HV and LV system throughout HCAL and with most of the CMS. The HCAL group asked a decision based on the evaluation of the power supply solution by using point evaluation criteria given above, and then the HCAL will inform the PRR committee to obtain final recommendation. Please respond by August 14 th, Comments from the Committee The committee likes the idea to unify the HF HV system with the HCAL Low voltage system and most other high voltage systems in CMS and select a system supplied by CAEN. In addition, the long-term maintenance is dealt with centrally and CERN PH/ESE supports the contract. A study of potential baseboard vulnerability associated with the ramping or tripping of the power supplies should be attached to the final proposal. The project must have a solution to any problems arising from unusual states of the power supply. If there are no problems, the project should say so. Before endorsing a proposed solution the committee must know that the system is robust with respect to the disappearance of any power supply channel from any initial configuration. 2

The Cost Estimate For the CAEN solution there is a need to develop an interlock, patch panel, LED system. We are also considering using CAEN interlock cards but the CERN CAEN members have left for the vacation, and they will not be here for about a month (project deadline for decision is August 15 th, 2012). The attached spreadsheet (for both CAEN and Bulgarian options) considers these components (only for CAEN) to be custom made and therefore their cost are also included. Also, according to latest information from CAEN, they will not charge us to modify modules to meet 10mA value for HF (estimated to be 6000 Euros for both CAEN options). Nevertheless we keep this charge in the cost estimate until we get official information We got the votes from 7 committee members-- The total vote is 58,700 /70,000 for CAEN and 48,300/70,000 for the Bulgarian system. So the CAEN is a clear winner- Once I get your PRR committee recommendations to the HF Upgrade Project I will ask S.Lusin, G.Martinez and A.Mestvirisvili to get ready for the purchase. We have asked the US Project office to pencil in our request and prepare the PO that we can move the money from Iowa to CERN. 3

Magnus Micro PRR Report Follow-up A follow-up review was called by the upgrade project manager with the charge to review the system options for the HF high voltage power system. The CMS committee specifically selected for this review was: Wolfram Zeuner, CERN Magnus Hansen, CERN Ken Bell, STFC/RAL Sergei Lusin, UW/CERN Frank Glege, CERN Two systems are being considered: the first is built by a very capable group at the University of Sofia, Bulgaria, and on the second by CAEN Spa, Italy. Comments CMS HCAL is using and will for years to come be using a CAEN built low voltage power system. The Bulgarian supplies are good hardware wise but serious issues with firmware have been experienced during testing. A CAEN system is installed for component testing and is working flawlessly even though the supplies used are not fulfilling all requirements about e.g. maximal current. CAEN is developing a new high voltage power supply module suitable for e.g. the new HF PMT effectively removing the issue with limited maximal current. The long term maintenance of the CAEN system is dealt with centrally and a support contract is supported by CERN PH/ESE. The long term maintenance situation for the Bulgarian system is less clear and must be considered a weak point. Recommendations A study of potential base board and PMT vulnerability associated with the ramping or tripping of the power supplies should be attached to the final HF high voltage power system proposal. Conclusion The committee likes the idea to unify the HF HV system with the HCAL Low voltage system and most other high voltage systems in CMS. The committee strongly supports selecting the system supplied by CAEN subject to the recommendation about potential base board and PMT vulnerability above. 4

Answers to the Comments-I By design the baseboard with divider is safe for any combination of legal voltages at the photo-cathode, and the last two dynodes (D9 and D10). The divider provides Hamamatsu recommended voltages for photo-cathode -Dy1-...-Dy8, and separate booster voltages at Dy9 and Dy10. V(Dy8) = 0.24*V(photo-cthode) Maximum actual operating voltage for HF PMTs will be 700V, and V(Dy8) - 175Vmax. Since V(Dy9) = 0-112V, V(Dy10)=0-56V, the mostly stressed components would be the bypass capacitors between Dy8 and Dy9. Voltage across C8_9 could be up to 56V in normal operating conditions; 112V if V(Dy9) is maxed at 112V, and V(photo-cathode) = 0-175V if V(photo-cathode) is maxed, and V(Dy9)=0. Bypass capacitors between Dy9 and Dy10 can be subjected maximum to 112V when V(Dy9)=max, and V(Dy10)=0. Bypass capacitors used in the design are Kemet C0603C103K2RACTU, rated at 200V, and having maximum withstanding voltage of 500V. An additional requirement for the maximum withstanding voltage testing is that charging current does not exceed 50mA, and this requirement leads to a ramp-up speed limit of 20MV/s, which is beyond technical abilities of both CAEN, and Bulgarian PSs. It is worth note that internally Bulgarian power supplies are made of independent power supplies, not synchronized during ramp-up or ramp-down, so the above considerations valid for both HV systems under consideration 5

Answers to the Comments-II We plan to use the External trip lines provided by CAEN to interlock the channels. This should provide a normal trip protection, in which if for ay reason a dynode or cathode channel trips, the associated dynodes/cathode would trip also. This probably does not provide a protection for the case for example that a channel or a whole module "dies" without asserting an external trip line. It will not prevent either from mistakes on the settings (for example one could set the voltage of a dynode to 0 (or a very low value) or operators mistakes in which a dynode/cathode channel is turned but not its partners. It is essentially impossible to make a foolproof system; the most that it can be made is a DCS watchdog (as we already have for other DCS parameters) that monitors the channels and sends SMSs and/or takes automatic actions like turning off the affected channels if something is wrong. On the other hand, we wanted to investigate that, if the situation of having power on a cathode, without power on the dynodes, or vice-verse can make any damaging stress at all on the PMTs. We performed some tests with the CAEN power supplies at 904 by using 8 new PMTs (single anode readout) with production baseboards. First a reference data with LED light (which is distributed to individual PMTs) was taken with all voltages on (black line). Then we switched off the cathode voltage and kept PMT's for about 10 minutes with only two last dynodes on. After that we switched back the cathode voltage and took the data again (red line). The plots below show that in both cases the digitized pulse shapes from LED light are indistinguishable. With this test we demonstrated that it is safe for PMTs to be (accidentally) operated with only two last dynode voltage about 10 minutes, which is more than enough to implement a software mechanism to shut down the dynode voltages, if for some reason cathode voltage trips. 6

ItemDescriptionQuantityUnit Price (Euro)Total Amount (Euro) 6New HV System (CAEN Solution, Option-2) 6.1Purchase of A1538D PSU3€ 3,181.00€ 9,543.00$11, Purchase of A1511B Module4€ 4,777.00€ 19,108.00$23, Rework Price**7€ 1,000.00€ 6,000.00$7, HF Integration of CAEN PS Modules 6.4.aSHV Cables36$80.00$2, bSHV patch-panel connectors40$50.00$2, cDB37 cables, and patch-pane connectorsl6$50.00$ dCircular HV connectors (to existing cables going to the detector)15$200.00$3, ePrinted circuit boards (including prototypes)5$400.00$2, fMechanics (3 production + 2 prototypes)5$600.00$3, gComponents for the boards5$400.00$2, hMisc. connectors5$200.00$1, iEngineering Time (between 3months and 6months)3$8,000.00$24, jEngineer Travel to CERN2$3,000.00$6, Total$88, The Cost Estimate including the HF Integration cost for the CAEN Module

CAEN SYSTEM 8