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T2K Horn Operational Experience

T2K Horn Operational Experience. Tetsuro Sekiguchi (KEK) for T2K Beamline Group 2012/11/8. Just for Reminder. Specification Three horns Aluminum alloy A6061-T6 320kA (rated)  250kA (200kA) operation Water cooling Operated in He atmosphere History Installed in 2008- 2009

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T2K Horn Operational Experience

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  1. T2K Horn Operational Experience Tetsuro Sekiguchi (KEK) for T2K Beamline Group 2012/11/8 8th International Workshop on Neutrino Beams and Instrumentation

  2. Just for Reminder • Specification • Three horns • Aluminum alloy A6061-T6 • 320kA (rated)  250kA (200kA) operation • Water cooling • Operated in He atmosphere • History • Installed in 2008- 2009 • Operation for physics from Jan. 2010. • 8 million pulses operated. 8th International Workshop on Neutrino Beams and Instrumentation

  3. What We struggle with High Power Beam • Design beam power = 750kW. • 200kW = 1x1014 protons per pulse at this moment. • Radioactivity: Be7 and Tritium in horn cooling water. => Oyama’s talk • Hydrogen production by water radiolysis. => This talk • Horns are operated in Helium atmosphere to reduce production of Tritium and NOx. • Air contamination problems sometimes happened. => This talk • In order to achieve 750kW beam, accelerator cycle will decrease to 1.28sec. • Input load to power supply should be low. => Striplines modification. • Power supplies for high rep. rate operation. => This talk 8th International Workshop on Neutrino Beams and Instrumentation

  4. Hydrogen Production He supply Exhaust He gas line Water supply Water return Buffer tank • Horn inner volume filled with He gas. • Hydrogen gas produced by water radiolysis. • Estimated production rate at 750kW = 40L/day(0.7%/day). • Explosion limit in air = 4% • What for He atmosphere? => Try to keep below 1%. • Countermeasures for H2 removal • He flushing once a week at early stage ( < 50kW ). 8th International Workshop on Neutrino Beams and Instrumentation

  5. Hydrogen Recombination Catalyst canister (Catalyst = Aluminapellet with 0.5%Pd ) Cover gas (Helium) Cooling water Buffer tank for horn cooling water Circulation pump • For beam power > 50kW, weekly flushing was not sufficient. • Hydrogen recombination system • He gas circulated through catalyst during beam : ~50L/min • At every maintenance day, He gas sampled and H2 contamination measured by gas chromatography. 8th International Workshop on Neutrino Beams and Instrumentation

  6. Problem in Current System He supply Exhaust H2recomb. diffusion He gas line Water supply diffusion diffusion diffusion Water return Buffer tank • Small flow rate (~50L/min) • At beam power > 150kW, H2 density gradually increased to 5000ppm. • Another pump and catalyst added => kept around 2000ppm. • H2 diffusion from horns to buffer tank is unknown. • H2 density in horns may be higher than buffer tank. • Frequent He flushing was needed, but prohibited during beam. 8th International Workshop on Neutrino Beams and Instrumentation

  7. Upgrade for High Power Beam He supply Exhaust He gas line Water supply diffusion diffusion diffusion Water return Buffer tank 6m3 He buffer tank • He buffer tank (~6m3) • Exhaust gas stored for several hours for short-lifetime radioactivity to decay. • He flushing during beam is allowed. => Everyday flushing 8th International Workshop on Neutrino Beams and Instrumentation

  8. Upgrade for High Power Beam • He buffer tank (~6m3) • Exhaust gas stored for several hours for short-lifetime radioactivity to decay. • He flushing during beam is allowed. => Everyday flushing • Forced circulation • He gas plumbing outside He vessel was modified to allow forced He circulation. (800L/min flow rate) He supply H2recomb. Exhaust Blower He gas line Water supply diffusion diffusion diffusion Water return Buffer tank 6m3 He buffer tank 8th International Workshop on Neutrino Beams and Instrumentation

  9. Upgrade for High Power Beam • He buffer tank (~6m3) • Exhaust gas stored for several hours for short-lifetime radioactivity to decay. • He flushing during beam is allowed. => Everyday flushing • Forced circulation • He gas plumbing outside He vessel was modified to allow forced He circulation. (800L/min flow rate) • New horns have two He gas plumbing to allow forced circulation inside horns. He supply H2recomb. Exhaust Blower He gas line Water supply Water return Buffer tank 6m3 He buffer tank 8th International Workshop on Neutrino Beams and Instrumentation

  10. Air Contamination • Horn inner volume filled with He <= He purge. • He purge is not perfect, so a few % air exists. • NOx produced by beam dissolves in water. • Acidification of water occurs by HNO3. • pH=5 expected with 3 months beam (200kW) and 1% air contamination. • Furthermore, large amount of air have been contaminated twice. • Plumbing and pump itself have broken in both cases. • Cooling (pure) water were getting white. • pH measurement: pH=4.3 • Analysis of components in cooling water • Al : ~51 mg/L • NO3- : ~100 mg/L 8th International Workshop on Neutrino Beams and Instrumentation

  11. Aluminum Corrosion by Acid 2.5 2.0 1.5 Corrosion rate (mm/year) 1.0 0.5 0 2 4 6 8 10 12 14 pH • Aluminum Corrosion • Aluminum corrosion rate gets large w/ pH<4. • Water whitened due to Al2O3 or Al(OH)3 • Amount of corroded aluminum: ~51mg/L => 138 g in 2700L • ~6mm-thick aluminum corroded  3mm total thickness. • Not serious problem at this moment. • Countermeasures • Online He purity monitor • Air contamination is monitored. • Remote pH measurement • pH is frequently measured. • Remote ion-exchange • Done if pH is getting lower. 8th International Workshop on Neutrino Beams and Instrumentation

  12. Horn Power Supply • Motivation • Since K2K power supplies (more than 15years old) were refurbished for T2K from 2006, a new power supply was manufactured in 2010. • New power supply • New power supply drives all three horns connected in series. • Energy recovery (60% energy reused for next pulse). • Symmetric circuit is adopted to reduce earth current. 8th International Workshop on Neutrino Beams and Instrumentation

  13. Horn Power Supply Circuit Charger (10kV, 10A) Capacitor Bank (7.5mF) Polarity control by IGBT SCR Switch Bridge layout Output Earth line Return 40 capacitors (750mF) 2 in series and 20 in parallel. Neutral point is grounded. Bridge layoutfor reversing current direction. 8th International Workshop on Neutrino Beams and Instrumentation

  14. Current Flow (Charging) Charger (10kV, 10A) Capacitor Bank (7.5mF) Polarity control by IGBT SCR Switch + Output Earth line _ Return Two IGBT switches turned on. 8th International Workshop on Neutrino Beams and Instrumentation

  15. Current Flow (Discharging) Charger (10kV, 10A) Capacitor Bank (7.5mF) Polarity control by IGBT SCR Switch + Output Earth line _ Return Two SCR switches turned on. 8th International Workshop on Neutrino Beams and Instrumentation

  16. Current Flow (Reverse Charging) Charger (10kV, 10A) Capacitor Bank (7.5mF) Polarity control by IGBT SCR Switch _ Output Earth line Return + Other two IGBT switches turned on. 8th International Workshop on Neutrino Beams and Instrumentation

  17. Current Flow (Discharging) Charger (10kV, 10A) Capacitor Bank (7.5mF) Polarity control by IGBT SCR Switch Polarity not changed _ Output Earth line Return + Two SCR switches turned on. 8th International Workshop on Neutrino Beams and Instrumentation

  18. Charging Sequence 75% (spec.) of energy recovered.  60% due to uncounted joint resistance => Motivation for low resistance (inductance) striplines 8th International Workshop on Neutrino Beams and Instrumentation

  19. Symmetric Circuit Not symmetric circuit Symmetric circuit Shielded power cables Cancel Stray capacitance Stray capacitance • Earth current flows at discharging timing due to stray capacitance. • The earth current will affect the control circuit through ground line, which will cause a malfunction of power supply. • Grounding neutral point of capacitors. • Earth currents from P-side and N-side flow opposite side and cancel at earth line. 8th International Workshop on Neutrino Beams and Instrumentation

  20. Series Connection of Horns Stripline configuration at Service Pit Total current 169kA Current at inner striplines Horn1 Horn2 Horn3 ~15% Striplines Current at outer striplines • Horn operation • Until 2010 summer: 1 PS for horn1, 1 PS for horn2&3 (series). • From 2010 fall : 1 PS for 3 horns in series. • Three-horn operation by 1 PS • Simple connection of horn1 and horn2&3 caused 15% current unbalance. • Different inductance for inner and outer striplines? • Modified striplines to reduce current unbalance. => 2% 8th International Workshop on Neutrino Beams and Instrumentation Transformer

  21. Power Supply Failure ON! Broken IGBTs Burned choke coils • New horn power supply was broken just before beam resumed after earthquake recovery (2 days before beam came back). • Two IGBTs turned on during discharging due to malfunction. • ~70kA flowed to IGBTs and burned out. 8th International Workshop on Neutrino Beams and Instrumentation

  22. Refurbish Old Power Supply 260kA 260kA 12.3kV 8.2kV • Old power supply • Moved to J-PARC on Jan. 4, 2012. • 250kA operation on Feb. 9, 2012. • Concerns • First operation with 3 horns by old PS • Charging voltage 6.7kV at 250kA  8.5kV(rated) • Spike voltage 12kV => 8kV by filters. • Large inrush current at SCRs • We started physics run from Mar 2. 8th International Workshop on Neutrino Beams and Instrumentation

  23. SCR Failure 2020A 260kA 260kA 1180A Broken SCRs • SCR failure on Mar. 6 • Switched to a spare SCR (4kVx3) but reduced to 200kA for 2 weeks. • Acc. failure happened and 2 week downtime => investigation work. • Investigation • Modified earth line configuration. • Replaced with higher rated voltage SCRs (7kVx3). • Inrush current finally reduced by half (2020A -> 1180A) • No problem happened during physics run. 8th International Workshop on Neutrino Beams and Instrumentation 4.9ms 3.0ms

  24. Stripline Reconfiguration for Dual PS New configuration Old configuration Horn2 Horn3 Horn1 Horn2 Horn3 Horn1 • After new PS is recovered, dual PS operation is preferable. • Low voltage operation greatly reduces risks of failure. • 4.4kV for horn1, 5.5kV for horn2&3  6.7kV for 3 horns • Stripline reconfiguration for dual PS operation. • Small change => easily go back to 1 PS operation if one PS fails. • Current condition • Unfortunately, new PS not recovered yet. Hopefully recovered by Jan. 2013. • 3 horn operation by old PS until Dec. 2012. => currently working well. • One more new PS will be produced by the end of FY2013 (Mar. 2014). 8th International Workshop on Neutrino Beams and Instrumentation

  25. High Rep. Rate Operation with 320kA • For 320kA operation, we really need to reduce operation voltage. • To achieve 1 Hz operation, dual (or preferably triple) PS operation is necessary. • More than two power supplies to reduce input load for each PS. • One more new power supply • Specification should be optimized for 1 Hz. • New low inductance and low resistance striplines. • Shorter, wider and narrower gap. • Improved stripline cooling also applied to survive >750kW (current limit is 400kW). • Existing horns must be replaced with new horns with new striplines. • 1 Hz operation => 2x107 pulses/year  Designed to survive 108 pulses • Time scale • Production of new horns and new striplines will be completed in 2013. • Replacement of horns will be completed within three years. 8th International Workshop on Neutrino Beams and Instrumentation

  26. Summary • T2K horn operational experiences presented. • Hydrogen recombination applied. • Not efficient to remove H2 inside horns. • Need to replace with upgraded horns in near future. • Air contamination causes acidification and corrosion. • Some countermeasures applied. • Horn power supply and stripline system are being modified. • New horn PS: energy recovery, symmetric circuit. • New PS IGBT failure => Refurbish old PS. • Dual PS operation for safety and redundancy. • 1 Hz operation is discussed. • Production of one more PS and new striplines by 2013. • Replacement of horns and striplines within three years. 8th International Workshop on Neutrino Beams and Instrumentation

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