MAINTENANCE ISSUES ON THE ANU 14UD ACCELERATOR TANK OPENINGS #117 through #122 Alistair Muirhead ATF2014 20-23 rd May 2014
2 The 14UD Van De-Graff accelerator National Electrostatics Corporation 15MV terminal potential 3 Charging chains ~25 m height x 6m dia vessel Tandem, electron stripping at mid length using carbon foils or gas
Systems within the 14UD Shaft drive motor Shaft driven alternator, powering terminal systems (obscured) Terminal Gas stripper Carbon stripper Charging chain x 3 Chain x 3, drive motors Shaft drive motor Shaft driven alternator, powering terminal systems (obscured) 3
4 Some simpler issues easy fixes Snail trails on perspex drive shafts 10-11 2012 Broken chain 65k hours TO118 10-11 2012 Tube resistor failure TO 121 10-11 2012 Charging system failures TO 121
5 Chain charging system failures Spark damaged Standoffs Leaking HV co-ax (external @ supply) HV feedthrough - Silicon grease to eliminate air spaces, raise permittivity. Experiment not a success
6 More significant issues 2-years saga: introducing SF6 to gas stripper Motivation for introduction was from positive ANSTO experience fixing gas stripper leak Ceramic insulators- column and tube vital statistics in-situ diagnostics of ceramic and resistors service platform upgrade investing in stock of posts and tubes: $$$
14UD Gas Stripper 7
8 Post Opening Performance Dates TO# Faulty components Leak fixed by Leak is back at GS pressure with tank pressure, PSIA turbos off, mtorr 5Jul-24 Aug 2012 117A Added SF6 gas 22 Aug 2012 117B O2, SF6 bottles, solenoid valve to O2 bottle 25Oct-23Nov 2012 13Feb-1Mar 2013 1Jul-19Jul 2013 6Jan-26Feb 2014 3Mar-5Mar 2014 6Mar-12Mar 3 2014 Crucial observations Solenoid valve replaced with Tube, back to single gas 103 0.2-0.52 118 Four 4BK swagelock valves Tightened gasket 103 0.14 initially rose to 0.5-1.5 in two sudden jumps in Nov 2013 119 120 Going OK. (U13 sparking/ Leaking tube ceramic) 121 4BK valves (screwed assembly) Replaced with welded 4BK Valves, bake out traps 122A GS turbo O-ring suspected No fix, GS valve closed to separate it in 2 parts for test, gas up and check 65 6.5@80 PSI 43 Raised to >1000 because of no pumping 122B Swagelock elbow Tightening of nut on elbow 103 0.4
9 Crucial observations Post Opening Performance Dates TO# Faulty components Leak fixed by Leak is back at GS pressure with tank pressure, PSIA turbos off, mtorr 5Jul-24 Aug 2012 117A Added SF6 S gas 22 Aug 2012 117B O2, SF6 bottles, solenoid valve to O2 bottle 25Oct-23Nov 2012 13Feb-1Mar 2013 1Jul-19Jul 2013 6Jan-26Feb 2014 3Mar-5Mar 2014 6Mar-12Mar 3 2014 Solenoid valve replaced with Tube, back to single gas 103 0.2-0.52 118 Four 4BK swagelock valves Tightened gasket 103 0.14 initially rose to 0.5-1.5 in two sudden jumps in Nov 2013 119 120 Going OK. (U13 sparking/ Leaking tube ceramic) 121 4BK valves (screwed assembly) Replaced with welded 4BK Valves, bake out traps 122A GS turbo O-ring suspected No fix, GS valve closed to separate it in 2 parts for test, gas up and check 65 6.5@80 PSI 43 Raised to >1000 because of no pumping 122B Swagelock elbow Tightening of nut on elbow 103 0.4
10 Crucial observations Post Opening Performance Dates TO# Faulty components Leak fixed by Leak is back at GS pressure with tank pressure, PSIA turbos off, mtorr 5Jul-24 Aug 2012 117A Added SF6 S gas 22 Aug 2012 117B O2, SF6 bottles, solenoid valve to O2 bottle 25Oct-23Nov 2012 13Feb-1Mar 2013 1Jul-19Jul 2013 6Jan-26Feb 2014 3Mar-5Mar 2014 6Mar-12Mar 3 2014 Solenoid valve replaced with Tube, back to single gas 103 0.2-0.52 118 Four 4BK swagelock valves Tightened gasket 103 0.14 initially rose to 0.5-1.5 in two sudden jumps in Nov 2013 119 120 Going OK. (U13 sparking/ Leaking tube ceramic) 121 4BK valves (screwed assembly) Replaced with welded 4BK Valves, bake out traps 122A GS turbo O-ring suspected No fix, GS valve closed to separate it in 2 parts for test, gas up and check 65 6.5@80 PSI 43 Raised to >1000 because of no pumping 122B Swagelock elbow Tightening of nut on elbow 103 0.4 Comprehensive bake-out of turbo backing traps, outside and in-situ.
Crucial observations Bagged Swagelok elbow fitting. 11
12 Current status of GS Adequate performance for all applications in spite of remaining minor leaks Prepare to upgrade with VCR fittings and welded pipework AMS reported operational experience with SF 6 contaminated O 2 gas: with Cl beam the optimum for pure O 2 was 20 mtorr; for contaminated O 2 it was 10 mtorr
13 Ceramic insulators and their condition Ceramic health of 14UD vital statistics in-situ diagnostics of ceramic and resistors variable speed drive for platform- causing damage? investing in stock of posts and tubes: $$$
14 14UD electrical structure 74 tube resistors R S =22.2 GW across 37 ceramic gaps per unit x 28 units 36 post resistors R S =35.4 GW and 72 ceramic gaps in posts per unit x 28 units
Post reconditioning Old post 1970 s and spark-damaged endcap De-greasing Abrasive blasting Aluminium shim Fitting stainless steel endcaps Machining posts to length Tolerance ± 0.001 inch Clamping end Ti electrodes to new endcaps
Refurbishment and replacement 14UD posts TO#112 November 2009 Protrusion of Al foil from manufacturing Propagates breakdown. 2 nd generation posts installed in 80 th April 2011 Eight posts have been ordered from NEC as EIF upgrade RECEIVED and ALL INSTALLED
Faulty posts removed during TO#121 and #122 Five posts removed during TO#121 Two posts removed during TO#122 Replaced with least worst spares
Faulty posts: Collection is Growing Stocktake, 2014 Jan- Two NEC post assemblies received May- Four NEC post bondments ordered ONLY four used posts suitable for re-furbishing STATUS: work in progress
Post-mortem every thing old is new again Quotes from Post-mortem An autopsy of NEC column posts, 1985 Weisser/Brinkely others. - dangerous and expensive - old age at 15, we are now 40 plus - sparking, post end flanges, cleanliness - less sources of dust now - excessive SF 6 pressure, 110psia
20 Repairs during TO#120: 5 faulty tubes Repairs up & down shorted gap shorted gap (also open circuit resistor) shorted gap shorted gap replaced post (crack in insulator) replaced open circuit post resistor shorted gap repaired electrode
Standard entry and exit 30 kv test crack/current leakage thing is probably not new, just that we ve been a lot more careful in our tests. Our range of acceptance, has narrowed a great deal. - Peter Linardakis
22 Conclusion Faulty posts and tubes or the discovery of them, is growing due to (a) age and (b) diagnostics The electrical industry standard of life span of HV ceramic is <30 years Review historic conclusions!!! Column deflection can be significant Improve the service platform drive - fine control. Review the technique of mounting Al casting covers less push/shove on column
23 14UD team John Bockwinkel Alan Cooper Gareth Crook Caleb Gudu Allan Harding Justin Heighway Peter Linardakis Nikolia Lobanov Lorenso Lariosa Thomas Tunningley