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Calculating the availability of KEKB Power Supplies

Calculating the availability of KEKB Power Supplies. Cherrill Spencer, ILC 28 th April 2006. Current General Layout of a 500Gev ILC Schematic borrowed from Fred Asiri of Conventional Facilities & new labels added. 31 km overall. superconducting linac.

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Calculating the availability of KEKB Power Supplies

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  1. Calculating the availability of KEKB Power Supplies Cherrill Spencer, ILC 28th April 2006

  2. Current General Layout ofa 500Gev ILC Schematic borrowed from Fred Asiri of Conventional Facilities & new labels added. 31 km overall superconducting linac Part of e+ source, e+ booster & auxiliary source Beam Deliveries + 2 Interaction Regions e- Damping Ring TWO e+ Damping Rings Cherrill’s rough count totals 12,000 conventional magnets Plus about 6,000 power supplies. All these components must be very reliable. Cherrill Spencer,SLAC KEKB PS Availability

  3. MOST CHALLENGING ASPECT OF ILC CONVENTIONAL MAGNETS and Power supplies: MAKING THEM RELIABLE ENOUGH • Consider the availability requirements of the ILC as set out in the BCD • A good idea for each engineer to read Chapter 10 of the BCD • Go to this URL and download the Operations and Reliability chapter: • http://www.linearcollider.org/wiki/doku.php?id=bcd:bcd_home • Describes a simulation of the whole ILC that has been developed and the model’s output tells you how long the ILC will be down if its components have certain mean time between failures (MTBF) and certain times to repair (Mean Time to Repair, MTTR). • OVERALL ILC UPTIME GOAL IS 85% during the official runs of 9 months per year Cherrill Spencer,SLAC KEKB PS Availability

  4. Availability DEFINITIONS Availability: Average ratio of the time that the system or component is usable to the total amount of time that is needed. MTBF (Mean Time Between Failure): MTBF is a basic measure of reliability for repairable items. It can be described as the number of hours that pass before a component, assembly, or system fails. Failure rate = MTBF-1 =l MTTR (Mean Time To Repair): MTTR is the average time required to perform corrective repair on the removable items in a product or system. Availability of N magnets = (Availability of one magnet) N Expected Downtime in hours = (1-Availability) x Operation hour/year Cherrill Spencer,SLAC KEKB PS Availability

  5. How total allowed downtime of 17% is distributed among tech systems (assuming 17% = 15%) Power Supplies + controllers allowed 17% of 17% = 2.9% Magnets allowed 5% of 17%=>0.8% In certain scenario each magnet’s MTBF has to be 20 million hours All ~12600 magnets allowed to be down 0.8% of ILC running time. Same as need to be up 99.2% of time! Cherrill Spencer,SLAC KEKB PS Availability

  6. MTBF,MTTR, Availability for several KEKB PS families, Aug04-June 05 Cherrill Spencer,SLAC KEKB PS Availability

  7. Summary of SLAC magnet & PS failure data “solid “= magnets with solid wire coils; “water” = magnets with water cooled coils; small PS <12A, <50V; large PS >12A,>50V. “Time to repair” is the total hours the beam was down for the stated failures, so MTTR = Time to repair/No. of failures. Cherrill Spencer,SLAC KEKB PS Availability

  8. How the MTBF value can vary depending on time period studied, choice of magnets • From SLAC 1997-2001 data: water cooled electromagnet’s average MTBF was 1,150,000 hours, i.e. about 1/20th of what the ILC needs! • But– look at a different period and eliminate the worst offenders: • * This 2002 dataset does not include any magnets in the 2 SLC damping rings, which have notoriously failure-prone magnets—by removing them from the dataset one can make the average MTBF vastly longer: 12,000,000 hours,. We understand why the DR magnets fail more frequently and would avoid making the same design mistakes in ILC magnets. • IN ANY EVENT, FOR THE ILC, WE CANNOT DESIGN AND FABRICATE MAGNETS LIKE WE HAVE BEEN DOING FOR THE PAST ~40 YEARS AT SLAC. • We have to carry out a detailed Failure Modes and Effects Analysis (FMEA) to learn how to revise our magnet designs and fabrication techniques to make more reliable magnets Cherrill Spencer,SLAC KEKB PS Availability

  9. When we really get to design the ILC magnets we will have to do FMEAs on basic magnet styles • Failure Mode and Effects Analysis (FMEA) process considers each mode of failure of every component of the system, identifies their causes and ascertains the effects of each failure mode on system operation (ALL ILC components should have FMEA done on them). • As we cost estimate the ILC magnets we will have to account for the cost of doing FMEAs and paying for some higher quality materials and more expensive processes. • The causes of the most severe and likely to occur failures of a standard SLAC water- cooled electromagnet were identified as (a) water leaks and corrosion (b) various assembly errors. • Design changes were made in the conductor, terminals, core & numbers of items. Cherrill Spencer,SLAC KEKB PS Availability

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