RHIC A bort Kicker Upgrade for Run 17

1. RHIC Abort Kicker Upgrade for Run 17 Jon Sandberg, H. Hahn, K. Hartman, J-L Mi, Y. Tan, W. Zhang

2. Many Important Contributions Many people have worked on and contributed to understanding the abort kicker prefire problems. The work was carried forward over the last few years by: J. Addessi, M. Chiu,A. Drees,W. Fischer,H.Hahn, K. Hartman, J-L Mi, C. Montag, S. Perlstein, Y. Tan, , R. Zapasek, A. Zelenski, W. Zhang Authors list of some of the BNL Technical Notes and Papers on this subject since 1999: L. Ahrens, C. Biscardi, M.I. Blackler, J.M. Brennan, M. Blaskiewicz, T, Curcio, V. DeMonte, L. Desanto, A. Drees, A. Dunbar, W. Fischer, W. Fu, D. Gasner, H. Hahn, H. Huang, N. Kling, M. Lafky, C.J. Liaw, G. Marr, K. Mernick, J. Mi, M. Minty, C. Montag, S. Nayak, C. Naylor, B. Oerter, C. Pai, S. Perlstein, T. Roser, R. Sanders, J. Sandberg, T. Shrey, Y. Tan, P. Thieberger, J. Tuozzolo, B. van Kuik, D. Warburton, K. Yip, A. Zelenski, W. Zhang

3. Abort Kicker Upgrades • Description of the system and why changes are necessary • Attempts made to reducing the number of prefires with the existing topology • Addition of a Mechanical Switch in series with the Thyratron • Some Test results • New operating Sequence

4. RHIC BEAM ABORT KICKER

5. Thyratron Prefires • The voltage on the abort kickers’ PFNs is ramped up to match the energy of the RHIC beam and is maintained at high voltage (27 kV) during each RHIC store • A prefire is defined as a Thyratron spontaneously discharging a PFN through an abort kicker magnet without an intentional command to do so • The result of a prefire is beam being sprayed around the accelerator with the potential of damaging equipment at a very great programmatic cost. • Given the right conditions even one prefire has the potential to cripple a detector and stop a run. • There are 5 kicker modules in each ring. Over a ten year period there have been an average of 8 prefires per ring each year

6. Trigger

7. Abort Kicker Prefire

8. Prefire History 4 16 14 12 13 07 11 15 09 10 08 In 2016 10 Blue prefires over a four day period caused by a redundant trigger board

9. Thyratron Parameters We Control • Grid Bias • Conditioning

10. Thyratron Parameters We Control • Internal Gas pressure • Reservoir Voltage • Spontaneous Discharge • White Arcing

11. What has been Done • Extensive conversations with the Tube Manufacturer • Experimentally determining the best operating point for reservoir voltage (gas pressure) for every Thyratron. This is a cross between “White Arcing” and “Spontaneous Prefiring” • Conditioning each Thyratron to 40 kV verses 30 kV • Replacing old Thyratrons with new Thyratrons. • Changing the Thyratron from a “Two Gap” configuration to a “Three Gap Configuration” • Tests Pulsing/Grounding the Prime Grid—Rise time trade off

12. Thyratron Prefires While it may be possible to reduce the prefire rate it is not possible to eliminate it with the existing topology The Possibility of a Thyratrons prefiring will always be present in this configuration

13. Thyratron Prefires • A solution to this problem would be to put another switch in series with the Thyratron whose prefiringcharacteristics is decoupled from that of the Thyratron

14. Three Proposed Solutions • Conventional High Voltage Relay • High Speed Vacuum Relay • Solid State Switch + Inexpensive (<$1000), readily available easy to mount, good history in ring - 40 msec to reliably close + 5 msec to reliably close? - Expensive ($17,500 ea), hard to mount, long lead time, radiation resistance of trigger circuit unknown +120 nsec to operate - Expensive ($22,800 ea), hard to mount, long lead time, radiation resistance unknown

15. Ross Relay Mounted in Modulator Relay

16. Ross relay test without any modification Unmodified Ross relay using 115VAC to drive the solenoid

17. Modified Ross Relay Test Relay current Abort current Modified Ross relay using a DC pulse to drive the solenoid

18. Ross Relay firing a PFN into an Abort Magnet *Actual voltage multiply volts by 3 kV Spare PFN test current waveform. The test voltage was varied form 5KV to 30KV

19. Operational Sequence • A separate command must be given to close the mechanical relay • This command must be given ~ 40 msec before the Thyratron can be fired • As is the present case a signal to stop charging the PFN will be given and then a signal to fire the Thyratron, synchronized with an abort gap, may be given • At low energies the relay may be proactively closed to allow the beam to be aborted quickly. As the beam energy increases the relay can be opened • The relay can be kept closed continuously if desired

20. Conclusions • The relay has been successfully tested at full current and full voltage • We have pulsed the Relay the equivalent of one full run with no degradation. • The Thyratron has been fired multiple times with the Relay opened simulating a prefire. The relay has not flashed over or conducted current----hence: • “No Magnet Current”. • Until more relays have been tested a 40 msec delay before firing the Thyratron is prudent. • The Relay can be mounted in a PFN in about two days by one person • The Relay can be run closed continuously if desired • There is no longer a requirement for a redundant trigger • We should inspect the relay contacts on maintenance days

21. Concerns with Series Switch • Protection of the Accelerator • An inevitable delay in the firing time of Kicker: • 40 msec verses 12.7 usec • No longer a Redundant trigger • A switch may fail to close • A switch may fail to open (monitor auxiliary contact) • We should still be able to extract with one bad kicker module

22. Some Key Tech Notes on Thyratron Prefires We have tried to solve this problem since before RHIC began operations RHIC Prefire protection masks……..C-A/AP/533…….….January 2015 RHIC abort kicker Prefire report…….C-A/AP/517….…….July 2014 RHIC abort Thyratrons with new trigger modules……………..C-A/AP/194…….…..March 2005 Operation of the RHIC Beam Dump Thyratron CX157C………….AD/RHIC/RD-127….August 1999

23. Backup Slides

24. Present Kicker Requirements 5 Kickers per Ring Beam Should be aborted if one kicker fails to fire Maximum delay for redundant trigger 0.7 us Typical Voltage ~27 kV Typical Current peak 21 kA Bunch Revolution Time 12.86 us Abort Pulse Length min ~13 u Abort Gap 1us Beam must be aborted within 4 turns, 52 us

25. THYRATRON e2v CX3575C Adjustable Reservoir, Filament & DC Prime Grid Control Grid Peak forward anode voltage . . . . . . 60 kVmax Peak forward anode current: modulator service . . . . . . . . 10 kAmax crowbar service . . . . . . . . . 50 kAmax Peak reverse anode current: modulator service . . . . . . . . . 5 kAmax crowbar service . . . . . . . . . 25 kAmax Average anode current . . . . . . . . 3.0 Amax Rate of rise of current . . . . . . . 100 kA/us

26. Thyratron Prefires Tan & Perlstein % cumulative 44 33% 26 52% 22 69% 42 134 31%

28. Ross Normal High Voltage Relay

29. Vacuum Relay • Concern about survivability of trigger unit in radiation area • Test should be done in building 922 to studied its firing characteristics and its interactions with the Thyratron • Concern about degree of modification to PFN and voltage hold off in tighter package

30. 20 kV Solid State Switch under Test S33A