Cryostat Instrumentation Cabling Grounding and Shielding Eric Hazen Boston University 12/15/08 1
Electromagnetic Compatibility We need to classify our instrumentation in terms of Emission and Susceptibility (quantitatively), to sensibly answer the following questions: What emission level is permissible inside cryostat? What measures are required to meet this level? Shielding some/all wires inside cryostat Replacing switching supplies with linear supplies or even batteries Other measures... 12/15/08 2
Instrumentation Principles Ground each circuit at one point only Electrostatic shield (Faraday cage) should surround all circuits connected to interior of cryostat Individually shield each circuit where practical Isolate all connections through shield Optical fiber for all signals Shielded transformer, motor-generator or batteries for power 12/15/08 3
Noise sources inside Faraday cage Power supplies in slow control instruments Should not be a problem for quality instruments (linear PS?) HV Supplies for PMTs Typically switching type... can use linear ones? VME crates only 1 for PMT digitizers Avoid switching supplies... current requirements relatively low for 16 channels of WFD CAEN WFDs do not require a VME controller Optical fiber interface directly to modules 12/15/08 4
Ideal Layout No DC connections to Cryostat instrumentation circuits terminate inside top-hat. Nice idea, but can we afford it? Probably not :( Instrumentation With fiber optic interfaces Top-Hat Cryostat Battery Power Fiber Optics Electronics Racks 12/15/08 5
Currently Proposed Layout (to the best of my knowledge!) Shielded House DAQ / Slow Controls Grounded only to Cryostat Cryostat SQUID Front-Ends Fiber Optics Computers DAQ / Slow Controls Fiber Optics SQUID Racks 12/15/08 6
Zoom In... All interfaces by fiber optics Isolated Power Electronics House Instruments Power supplies WFDs, HV RF Shielded Cable Tray SQUID Front-Ends SQUID readout by fiber optics Shielded pair Instrument cables Magnet leads HV wires Cryostat ground 12/15/08 7
Faraday Cage surrounds all circuits All interfaces by fiber optics Not ideal due to extended geometry, limited magnetic shielding, and internal noise sources. Isolated Power SQUID readout by fiber optics Cryostat ground 12/15/08 8
All seams in Faraday cage must be shielded with solder, RF gaskets, etc Ground Rules Pipes, etc all need electrical isolation Isolated Power Any other equipment connected to cryostat must be included in Faraday Cage Only one ground point Cryostat ground 12/15/08 9
Cabling Inside Faraday Cage Patch Panel / Box Fanout signals to individual instruments Vacuum Feed-Thru (CF Flanges) Shielded T.P. Cable (relatively standard) Cryogenic Cable 0.1mm Twisted Pair Connector (standard type) Connector (vacuum type) Sensors (or other devices) Instruments / Controllers Instrument House Shielded Cable Tray Cryostat Interior 12/15/08 10
Feed-Thru Details Build tree from off-theshelf components as much as possible Purchase flanges from vendor with feed-thrus installed Use double-ended feedthrus with vacuum side disconnect Maximize number of signals per flange 12/15/08 11
Feed-Thru Further Details There are many COTS options... Twisted Pairs (SQUIDS, sensors) 300 pairs in 6 CF flange (ISI) PMTs 7 pin HV connectors (ISI) Coax connectors (BNC or SMA) Magnet leads DB-25, circular or similar Can easily get vendor quotes once the design converges 12/15/08 12
Latest Layout as of Friday Experimental Setup Electronics Racks Shielded Instrument House Shielded Cable Tray 4 12/15/08 13
Action Items Complete inventory of cryo instruments Still need additional input from some subsystems! Perform compatibility testing with SQUIDs Need test bed with candidate SQUID electronics Test each instrument type and powering options Extrapolate noise levels for full complement of instruments Proceed with design and costing 12/15/08 14
Backup Slides Optical Links in Instrumentation 12/15/08 15
Fiber Optic Interfaces for Instrumentation Many commercial and laboratory-developed links exist. This is a nice example of an analog link pointed out by Mohammed (thanks!) 12/15/08 16
Analog Links Typical analog links have dynamic range of ~ 10-12 bits but are difficult to use for DC. The instrumentation electronics is still required to extract a DC signal from the sensor. If we could find an existing solution to multiplex many sensors on a single fiber at low power/cost/noise it would be very interesting. Sensor Instrumentation Amplifier Shielded Region ADC Module Optical Tx Optical Rx Excitation source Power 12/15/08 17
Digital Links Majority of optical links are digital One can easily purchase GPIB / RS-232 multiplexers which combine ~ 8 links on a single fiber These seem ideal for most of our instruments 12/15/08 18