1. Belle-II bKLM RPC Readout Power & Ground Discussion 12 th Belle II General Meeting Gerard Visser Indiana University CEEM 7/24/2012

2. bKLM RPC overview and grounding philosophy Signals are handled — insofar as practical — in a balanced, differential manner Allow ground loops AC ground reference is the detector (RPC boxes / magnet steel). Unshielded cables, re-used from Belle Cables carry only small signals – no EMI risk to other subsystems Z 0 = 50 Ω microstrip Z 0 = 113 Ω twisted pair Length 5.1 – 6.1 m 50 Ω RPC FEE Prototype (4x 1/2x FEE board)

3. bKLM RPC signal schematic magnet structure GND 7mm FOAM 3mm GLASS AT +HV 3mm GLASS AT -HV 2mm GAS GAP Signal induction strips (parallel microstrip over a solid ground plane) Ground planes are capacitively coupled to the aluminum case (and hence to each other). Signal current flows through this. Twisted pair 113Ω (24 pairs per cable), length ≈6m RPC module aluminum case strips plane strips Signal current flow IDENTICAL AS BELOW analog test pulse to TDC FPGA FEE crate GND Strips and planes are (DC) isolated from module case and from glass/HV DC ground potential reference through readout crate (a legacy of old system, will not be changed)

4. as far as any signals (intentional or EMI) are concerned, HV circuit is all high impedance and no ground loops introduced positive HV has 8 units fed from one HV channel negative HV has individual RPC per HV channel leakage currents drawn from HV (through RPC glass & spacers) is of order 10 μA magnet structure GND 7mm FOAM 3mm GLASS AT +HV 3mm GLASS AT -HV 2mm GAS GAP RPC module aluminum case HV input cable grounds are NO CONNECT at RPC module HVPS electronics hut safety GND 6 more bKLM RPC HV schematic

5. No changes from Belle system 8 readout crates (6U “VME”) on each end of detector, in the indicated racks. bKLM RPC FEE crate/rack locations

6. Cables are re-used from Belle. Routes are same as before. The signal cables are unshielded twist-n-flat. However they carry only millivolts signals and no risk of being an EMI source. Also they are effectively shielded overall by the magnet steel. Since the signals are received at FEE balanced/differentially (an improvement from old system), good rejection of EMI is expected No changes from Belle system bKLM RPC signal cables

7. We plan to re-use the crates (6U “VME” from ELMA) from Belle system, at most to replace the backplane and/or power supplies. Tests are planned soon to evaluate low latency data transfer over backplane (13 →1 concentration). Assuming this works out, we re-use the backplanes. Supply voltages and currents will be quite different for new design, TBD at present. It may lead to replacing the supplies. This may also be motivated by an overall power reduction goal. Old system used linear supplies, but if replaced would (likely) use some switching PS. Will evaluate noise carefully, of course... Conclusions bKLM RPC should be reasonably immune to EMI from differential signal path design for the same reason, and due to small signal size on cables, bKLM RPC should generate no EMI to other subsystems we are taking this all into account in design and look forward to further discussion and review THANK YOU bKLM RPC FEE crate / power