Q11: Describe how the effects of power supply failures on integrated luminosity will be mitigated. TESLA Response : –Mainly consider two types of magnet power supplies, that is LOW power [upto 1 kW] and HIGH Power [100 – 500 kW] –Claims automatic replacement concept resulting the high availability (modular upto six power units per supply) by replacing failing units by redundant one automatically by 15 minutes (failed units can be replaced on maintenance day) LOW : 2,500 sets with Single unit MTBF 200,000 hrs –Low PS MTBF : 80 hrs and Availability : 99.7% HIGH : 250 sets with Single unit MTBF 26,000 hrs –High PS MTBF : 104 hrs and Availability : 99.8% –Data based on HERA PS experience and concluded that the availability of system is independent from a single or double tunnel layout

Q11: page-2 GLC/NLC Response : –Utilize an availability model developed as part of the US Linear Collider Technology Options Study for three cases such as WARM 2-tunnel, COLD 2-tunnel, and COLD 1-tunnel –Using Monte Carlo based model using MTBF and MTTR and quantities of the components (consider large power supply controller with MTBF 100,000hrs and large power supply with MTBF 200,000hrs using nominal values obtained from downtime statistics at SLAC and FNAL) –Simulation predicted downtimes about 30% (design goal 15%) then increase MTBF to achieve design goal that required 30 times higher MTBF than FNAL main injector power supplies (2,000,000hrs) : Need “Redundant hot swappable PS” –For 1-tunnel case, tunes around failed PS while for 2-tunnel case repairs PS => Tuning time and repair time are similar

Q11: page-3 Comments : –TESLA response seems to me a bit simplistic and optimistic although it was claimed that results are derived from HERA PS experience Need to consider two or more modules failed case and controller failure case in simulated calculation for downtime estimation (this consideration could influence 1-tunnel layout availability) Redundant hot-swappable PS needs to be demonstrated with 15 min switching and tuning time Redundancy could keep availability high but it also raises cost of PS high, so the cost impact should be considered