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7835 Lifetime Analysis

7835 Lifetime Analysis. Elliott McCrory December 15, 2004. Basic Information. 5 MW, 201.25 MHz Power Amplifier, Model 7835 Matched 1 MW driver, model 4616 Original model 4617 Difference: Thoriated filament Burle Industries, Lancaster, PA Spun off from RCA in 1987

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7835 Lifetime Analysis

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  1. 7835 Lifetime Analysis Elliott McCrory December 15, 2004

  2. Basic Information • 5 MW, 201.25 MHz Power Amplifier, Model 7835 • Matched 1 MW driver, model 4616 • Original model 4617 • Difference: Thoriated filament • Burle Industries, Lancaster, PA • Spun off from RCA in 1987 • Remember: An average year is 8766 hours

  3. The 7835: Sliced! Ion Pump would go here Anode Getter Cathode/Filament Pinch-off

  4. Current users of 7835 • Fermilab • 5 sockets; 8000 hours/year • Brookhaven Lab • 9 sockets; ~4000 hours/year • Argonne • 1 socket; <1000 hours/year • Los Alamos • 5 sockets; ?? • Quadulan Islands (DOD) • 4 sockets; 8000 hours/year?? • 4617 model tube

  5. Costs/Failures • Costs • New: $150,000 • Rebuild: $50k to $120k • Num rebuilds: Have seen R9 • Rebuild as good as new • ~1/5 attempts to rebuild fail • More or less independent of rebuild number • Failures • Half fail due to emission limit • Half fail for other reasons • Water leaks • Irreparable sparks • We can repair some sparks locally • Vacuum failure

  6. Date Received vs. Hours to EOL Reached End Of Life In Service Burle RCA 11/1968 11/1972 11/2000 11/2004 Date Tube Received by Fermilab

  7. Tube Lifetime Histogram

  8. Number Tubes Received Per year Average: ~6/year

  9. Date Received vs. Hours to EOL Median life: 11791 hrs; RMS = 8000 hrs, Standard Error = 8000/sqrt(n) = 1153 hrs

  10. Brookhaven’s Data (Thru 4/03) • Average Tube Lifetime at Brookhaven • 12203 hours

  11. What Has Happened?? • RCA became Burle in 1987 • Some expertise retired • This tube is half engineering and half artwork (it seems) • Many (most?) of the original experts/artisans have now retired • Some (most?) apprentices were properly trained, but some not! • Example: Anode temperature • Example: Getter decision

  12. How Many Burned Up Per Year? • Assuming • Median life of 11800 hours (~25000 T1) •  1.48 (3.0 @T1) years of tube life • 1 year = 8000 hours • Or ~4.5 weeks off per year • Then we need • N = ΣS [ 1 / LSi ] • S is the number of sockets • L is the median lifetime of the tube in a socket • (4 tubes/1.48 yrs) + (1 tube/3 yrs, T1) • 3.04 tubes/year • Assuming EOL at 5500 hours (0.69 years): • 6.13 tubes/year

  13. Number Tubes Needed vs. Lifetime But Might Be Here We Are Here Burle Average Flux

  14. Stable Operation Today? • 2001: • March • 5 spares and 2 deliveries imminent—Wow! • Division Management pleads to reduce expenses • Decision by Webber and me (~march 01) not to order rebuilds • Oops! • June 22 through October 1, 2001 • Replaced 6 tubes, leaving 1 spare • Were forced to borrow tubes from Argonne and from Brookhaven • Moral: We want ~6 good spares at all times • Required flux: At least 6/year.

  15. Conclusions • Historical median lifetime • About 11000 hours (1.4 years) • Need at least 6 good spares for stable operation • Longevity of 7835 power tubes has decreased since 1990 • Some indication (hope?) this has turned around • Must get at least ~6 tubes/yr from Burle • If lifetime is under 8000 hours? • Then Burle needs to improve flux

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