SuperKEKB Linac RF Distribution System Upgrades Overview

The SuperKEKB Linac RF Distribution System underwent various upgrades and installations to enhance performance and functionality. These included improvements to the Injector Master Oscillator Phase Shifter, S-band Phase Shifter for DR Downstream, LLRF Control Unit, RF Monitoring systems, and more. Additionally, replacements and enhancements were made to the Solid State Amplifiers, Pulse Modulators, and RF Reference Signal Transfer Lines. The upgrades aimed to optimize RF distribution and control for the KEKB Accelerator system.

• SuperKEKB
• RF Distribution System
• Upgrades
• Linac
• LLRF

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1. Injector RF and LLRF Takako Miura for the Linac RF Group The 23rd KEKB Accelerator Review Committee, July 8-10, 2019 1

2. List of Installation and Replacement New Installations for SuperKEKB Injector Master Oscillator Phase Shifter (HER/LER Injection Phase Control) S-band Phase Shifter for DR Downstream (for Bucket Selection) Phase Drift Compensation System between Linac MO and Ring MO LLRF Control Unit (Amplitude/Phase Control, EVR, VSWR Meter) RF monitor (AMP/Phase Detection, EVR) & Applications Beam Induced RF Monitor Klystron KL_DN/KL_DS Units High Precision Pulse Modulator (installed in KL_A1A) Replacement SHB1 (114MHz) / SHB2 (571MHz) Solid State Amplifier(SSA) replacement to new one RF Reference Signal Transfer Line : Coaxial Cable -> Phase Stabilized Optical Fiber to each sector Seven pulse modulators were replaced to small inverter-type for making space 2

3. List of Installation and Replacement New Installations for SuperKEKB Linac Reference RF Distribution System Injector Master Oscillator Phase Shifter (HER/LER Injection Phase Control) S-band Phase Shifter for DR Downstream (for Bucket Selection) Phase Drift Compensation System between Linac MO and Ring MO LLRF Control Unit (Amplitude/Phase Control, EVR, VSWR Meter) RF monitor (AMP/Phase Detection, EVR) & Applications Beam Induced RF Monitor Klystron KL_DN/KL_DS Units RF Monitor System High Precision Pulse Modulator (installed in KL_A1A) Replacement SHB1 (114MHz) / SHB2 (571MHz) Solid State Amplifier(SSA) replacement to new one RF Reference Signal Transfer Line : Coaxial Cable -> Phase Stabilized Optical Fiber to each sector Seven pulse modulators were replaced to small inverter-type for making space 3

4. Linac Reference RF Distribution System SuperKEKB Control Room LINAC Main Station LINAC-MO Main MO MR-MO Sync Sync 10MHz 1/51 1/51 10MHz 571.2 MHz 510MHz 508.9MHz MO Phase Shifter Injection phase controller until Phase-I f1 qHER Main Ring Freq Multi/Div LER: :qLER -qHER HER: 0 Linac reference RF phase is changed to HER/LER injection phases depending on the beam mode. Laser system cannot accept such a high speed phase change. f2 10.384 MHz 2856MHz f1+ f2 Master Oscillator Phase Shifter (MOPS) has been installed. RF phase for laser system is kept qHER. Linac RF phase is switched qHER /qLER Freq Multi/Div Event System Phase Shifter for DR 114MHz 2856 MHz E/O Sector5 Sector4 Sector3 571 MHz O/E Sector A/B/C/1/2/3 O/E O/E EVR LLRF Cont Unit 571 MHz to RF Monitors to RF Monitors TD4V SHB1 SHB2 Grid Pulser Thermionic Gun KLY KLY DR LINAC Laser System RF Gun 4 Sampling freq. for LLRF Control Unit, RF Monitor

5. MO Phase Shifter (MOPS) 571.2 MHz Specification of Phase Shifter Phase Range -450.00 deg ~ + 450.00 deg Resolution 0.01 deg Speed 1 deg/ms ~ 1000 deg/ms Linearity < 0.1 deg Mode High: LER / Low: HER to Laser ?2= 0 (HER, PF, PFAR) ?2= ???? ????(LER) ?1= ???? Phase change: 400deg 0 deg @ 500 deg/ms to Linac ?1+ ?2 ?1 0.8 ms In the operation of SuperKEKB, phase change speed : PS1 = 1 deg/ms PS2 = 100 deg/ms 5

6. Linac Reference RF Distribution System SuperKEKB Control Room LINAC Main Station LINAC-MO Main MO MR-MO Sync Sync 10MHz 1/51 1/51 10MHz 571.2 MHz 510MHz 508.9MHz MO Phase Shifter f1 qHER Main Ring S-band phase shifter Freq Multi/Div LER: :qLER -qHER HER: 0 f2 10.384 MHz 2856MHz RF phase downstream of DR will be changed for higher synchronization rate against MR bucket selection. (Phase will be controlled by "bucket selection" and set by "EVG" for each pulse ) f1+ f2 Freq Multi/Div Event System Phase Shifter for DR 114MHz 2856 MHz E/O Sector5 Sector4 Sector3 571 MHz O/E Sector A/B/C/1/2/3 O/E O/E EVR LLRF Cont Unit 571 MHz to RF Monitors to RF Monitors TD4V SHB1 SHB2 Grid Pulser Thermionic Gun KLY KLY DR LINAC Laser System RF Gun 6 Sampling freq. for LLRF Control Unit, RF Monitor

7. Test of S-band Phase Shifter KBP phase was set by embedded-EVR via data-buffer of event record. Phase was changed every 10 degree. Phase Range : 0 - 400 Resolution : 0.015 380 0 200 RF test REF@sector3 Monitored phase (deg) LO REF@sector2 KBE RF monitor can detect phase difference of Ref(LO) & RF. RF is generated by using Reference signal. => we cannot detect reference phase change. KBP 390 By using upstream REF signal, ref phase rotation can be detected. 7

8. Reference RF Control Station Thermostatic chamber : 28 0.05 C Reference Signal Generator (Frequency Multiplier/Divider) Freq Mult/Div (#0) MO Phase Shifter Freq Mult/Div (#1) Amplifiers S-band Phase shifter (for sect.3- sect.5) 571.2 MHz 1/5 114.2 MHz 571 MHz phase det. 571.2 MHz P/D 1/5 1/11 10.38 MHz 2856 MHz VCO 2856 MHz 197 MHz 83 MHz 3053 MHz VCO 1/8 1/6 508.8 MHz 10.38 MHz phase det. P/D Linac Master Oscillator 571.2 MHz Sampling oscilloscope for phase monitoring of the reference signals 8

9. Block Diagram of MO Synchronization System linac gallery KEKB control room MMO 510 MHz PLL 510 MHz 1/51 1/51 PS 10 MHz linac MO 571.2 MHz 10 MHz New MR MO 508.9 MHz DR MO 508.9 MHz PS1 MOPS Phase Drift Compensation System PS PS2 RF-Dist.&PLL RF-Dist.&PLL O/E REFSG1 REFSG2 372 m PSOF DR control room PS PS Laser System Gun Trigger System PS DR RF Gun HER LER Injector linac BCS ECS Thermionic Gun MR MO and DR MO phases have been locked by PLL. Linac MO phase had not been locked to Ring MO phase. Phase monitor system for Linac MO (571.2 MHz) and Ring MO(508.9 MHz) was installed at Linac side. The phase drift compensation system was also installed. 9

10. Phase Drift between Linac MO & Ring MO Linac MO & Ring MO phases are monitored with the clock based on Linac MO This phase drift has strong correlation with Ring MO room temperature (by T. Kobayashi) Large phase drift between Linac MO and Ring MO Making BCS@RTL tuning difficult BCS RF : 2856 MHz (Linac MO x 5) Drift of MR injection phase @571.2 MHz 10

11. Linac MO Phase Feedback For the drift compensation between Linac MO & Ring MO, Linac MO phase is changed to follow Ring MO phase by using MO Phase shifter. Normalized to 571 MHz Phase 5 deg Linac MO Phase Ring MO Phase @BCS arc FB ON Slow drift was disappeared 11

12. List of Installation and Replacement New Installations for SuperKEKB Linac Reference RF Control & Distribution System Injector Master Oscillator Phase Shifter (HER/LER Injection Phase Control) S-band Phase Shifter for DR Downstream (for Bucket Selection) Phase Drift Compensation System between Linac MO and Ring MO LLRF Control Unit (Amplitude/Phase Control, EVR, VSWR Meter) RF monitor (AMP/Phase Detection, EVR) & Applications Beam Induced RF Monitor Klystron KL_DN/KL_DS Units RF Monitor System High Precision Pulse Modulator (installed in KL_A1A) Replacement SHB1 (114MHz) / SHB2 (571MHz) Solid State Amplifier(SSA) replacement to new one RF Reference Signal Transfer Line : Coaxial Cable -> Phase Stabilized Optical Fiber to each sector Seven pulse modulators were replaced to small inverter-type for making space 12

13. RF Monitor RF monitors are installed for all RF sources (60 Klystron units & SHB1/SHB2) Moni: 5 ch Rep. rate: 50 Hz Reference Amplitude KLY Pf SLED Pf KLY Kly Pf Pb SLED Pf Acc out Phase(deg) "EVR" is built-in. Identify the Event code & Shot ID ACC timing Stand-by timing 13 For each pulse, RF & BPM data can be linked by Shot ID

14. Short Term RF Stability Measurement result of short-term KLYPF RF stabilities KLY HV stability 0.3% pk-pk (0.05% rms) Estimation of RF stability from KLY HV Amplitude Amplitude stability A/A(%)= 5/4 V/V(%)= 0.063% rms Phase stability q = 4deg* V/V(%)= 0.2 deg rms (from -4deg/%) A/A= 0.068% rms Consistent Phase (deg) K(Perveance) = I/V3/2 P= IV = KV3/2V = KV5/2. P/P=5/2 V/V. A/A = 5/4 V/V 3 min q= 0.18deg rms 14

15. Application of RF monitor The Last Waveform Saving at Klystron Interlock The cause of interlock is identified from the last RF waveform. Reflection occurred btw KLY & SLED Breakdown? 15

16. Application of RF monitor Klystron Pulse Shortening Detection Klystron pulse-shortening events detected by using RF monitor data KL_54 Normal Short Short Beam might be injected the MR 1-day History of Klystron Pulse Shortening KL_B4 If high voltage is reduced, pulse shortening decrease or disappear. KL_C2 KL_54 16

17. Beam Induced RF Monitor Motivation Monitored RF phase is affected temperature drift of cable and monitor system. By comparing the phase of driving RF and beam induced RF in the accelerating structure, we can expect to get the beam phase against RF without system drift error. Amplitude estimation ACC Grad : 20 MV/m -40.9 dB small Beam Induced: 180 kV/m @ 2nC, 3.3ps Amplitude Beam induced Fast ATT switching module STB Timing ACC Timing 30dB or 40dB HV ATT Fast Switching Beam & HV_off Phase Judged by beam trigger & HV trigger 2018/12/10 17 Installed Unit : A2, B7, C1, 12, 22, 38, 45, 53, 57

18. Measurement of Beam Induced RF Amplitude of Beam Induced RF vs. Bunch charge y = 1.4773E-4 x + 2.9636E-3 KL_45: KBE @KL_45:KBE Amplitude of beam induced RF is proportional to bunch charge. (plotted at the same shot ID) Beam-Induced-RF Phase KL_45: KBE When beam phase changed @2019/6/30 10:18, beam charge increased. Beam-Induced-RF Amplitude 18

19. Summary Linac reference RF control system are almost established by installing injector MOPS, S-band PS, and MO phase drift compensation system. RF monitors are installed for all RF power sources. Not only stability confirmation, they are utilized the investigation of interlock event and the klystron pulse-shortening detection. Beam induced monitor is currently under development. Beam phase information is so useful to confirm the operating condition. 19

20. Future Work Amplitude & phase controllers with digital mode are required for SHB1/SHB2. Replacement of old coaxial cable in RF distribution line is necessary due to contact failure. Change RF drive line from sub-booster drive to SSA drive (Sect 1: already done) Sub-booster not available Solid state amp. 60 kW klystron LLRF control unit 2856 MHz 2856 MHz 0 dBm 23 dBm Mechanical I A I A I A I A I A I A I A I A I A High power klystron Solid state amp. LLRF control unit 2856 MHz 0 dBm 23 dBm Mechanical I A I A I A I A I A I A I A I A I A Instead of sub-booster, 600W SSA will be installed in each unit. 600W Solid state amp. High power klystron 20

21. Back up 21

22. Diagnostics of RF Stability by RF Monitor Water Temperature vs. RF Phase of ACC Structures 5deg 0.26 C ACC_PHASE@KL_B3 ACC_PHASE@KL_B5 T = 0.26 C q = 5 deg Water Temperature Cooling Water Temperature fluctuation is causing RF phase fluctuation 22

23. Application of Beam Induced RF monitor Beam Phase Confirmation for Energy Spread Tuning Beam Energy Profile Beam tail correction (3A) Buncher +1deg. Beam phase: recovered (2) SHB1(114MHz) +1.5deg Beam phase: -2deg (1) Beam energy is split @screen (SC61H1) Correct procedure (deg) C1: ACC_RF_Phase (3B) All S-band RF -2deg (except for buncher) (1) (2) (3A) (3B) (deg) Crest phase => shift C1:ACC_Beam Induced_Phase 23

24. LLRF Control Unit presented in KEKB Review2014 IPAC2018, WEPAK018 Rear Front LLRF cont. unit LLRF cont. unit 60 kW Sub-booster kly. 600W Amp I A 8 klystrons 40 MW Klystron SLED SLED Driveline by sub-booster klystron(left) and independent driveline (right) < Functions of LLRF control unit > Pulse modulation (AMP & Phase) VSWR meter (Power detection) 1ch RF monitor Event receiver Pulse shortening detection Frequency RF output level Linearity of amp. RF pulse rise time Phase setting-range 2856 MHz +10 dBm (100%) 0.3% rms and max < 0.5% < 35 ns (0 - 90%) 0 400 24

25. Installation of LLRF Control Unit KEKB Review2014 IPAC2018, WEPAK018 BUN, RF-Gun Installed this summer B6, B5 B7 SB_B A4, A3, A2, A1A, A1B 26 (+1) LLRF cont. units in operation RF GUN for low emittance 5nC beam For BCS@J-arc Energy Knob Thermionic GUN for positron generation e- SHB1 114MHz ACC. Guide Buncher 2856MHz Prebuncher 2856MHz SHB2 571MHz Sector A Sector B B-5 B-6 SB-B 10kW Solid State Amplifier RF phase is set in "Digital mode" 40MW Klystron I A High power ATT/phase shifter (I A) I A 600W Solid State Amplifer (SSA) LLRF cont. unit I A I A I A I A I A 60kW Receive digital data directly from EVG via optical fiber Sub-booster (SB) LLRF cont. unit LLRF cont. unit LLRF cont. unit LLRF cont. unit SB-B 90m Low noise & good reproducibility Event & Clock System 114 MHz 571 MHz Coaxial cable line Laser system Thermostatic chamber Optical fiber line Main drive system SB-5 509 MHz E/O MR Cont. Optical link 510 MHz Sector R Frequency Multiplier /divider 2856 MHz Phase shifter O/E 1/51 E/O 6-1 10 MHz Frequency Multiplier /divider LLRF cont. unit LLRF cont. unit 571 MHz Phase shifter Linac MO E/O 571 MHz 2856 MHz 80m LLRF cont. unit LLRF cont. unit 30m LLRF cont. unit SB-2 SB-3 SB-4 SB-1 SB-C 60kWkly. Damping Ring 1.1 GeV For PF 2.5 GeV,0.1nC X 1 I A I A I A I A I A I A I A I A I A For PF-AR,6.5 GeV Energy Compression Bunch Compression e+ capture section For LER 4.0 GeV,4nC X 2 SB-5 5-1 5-2 e- bypass orbit Sector C Sector 1 Sector 3 Sector 2 Sector 4 For HER 7.0 GeV,5nC X 2 25 Sector 5 SB_C SB_1 15,16,17,18 21, SB_2 27, 28 DS, DN SB_3 SB_4 SB_5 51,52 61 E-Knob BCS, ECS E-Knob ECS

26. Phase Drift between Linac MO & Ring MO Monitored phase with the clock based on Linac MO Phase drift between Linac MO and Ring MO Making BCS@RTL tuning difficult BCS RF : 2856 MHz (Linac MO x 5) Drift of MR injection phase Strong correlation with Ring MO Room Temp. (by T. Kobayashi) @571.2 MHz 26

27. Under-sampling Technique for Linac MO & Ring MO LMO(571.2 MHz):RMO(508.9 MHz)=55:49 fs=124.63MHz ???? 4 +7 ??= 12 I1 M1=12 N1=7 DDC1 ADC1 LMO: 571.2 MHz ????= tan 1( ?1?1) Q1 I2 ????= tan 1( ?2?2) M2=12 N2=1 DDC2 ADC2 RMO: 508.9 MHz Q2 27

28. Measurement of Beam Induced RF Trend graph of beam induced RF @KL_38:KBE Pulse shortening @KL_B4 Amplitude Normal 2018/12/10 18:36:59 KBE Phase (deg) 5deg Peak amplitude was almost the same, but pulse width became shorter. Amplitude is not so high. Phase jitter (error) is 5 deg pk-pk. For more high precision, parameters of attenuator and amplifier will be revised. 28

29. Linac RF System RF GUN for low emittance 5nC beam Thermionic GUN for positron generation e- SHB1 114MHz ACC. Guide Buncher 2856MHz Prebuncher 2856MHz SHB2 571MHz Sector A Sector B B-5 B-6 SB-B 10kW Solid State Amplifier 40MW Klystron I A High power ATT/phase shifter (I A) I A 600W Solid State Amplifer (SSA) LLRF cont. unit I A I A I A I A I A 60kW Sub-booster (SB) LLRF cont. unit LLRF cont. unit LLRF cont. unit LLRF cont. unit SB-B 90m Event & Clock System 114 MHz 571 MHz Coaxial cable line Laser system Thermostatic chamber Optical fiber line Main drive system SB-5 509 MHz E/O MR Cont. Optical link 510 MHz Sector R Frequency Multiplier /divider 2856 MHz Phase shifter O/E 1/51 E/O 6-1 10 MHz Frequency Multiplier /divider LLRF cont. unit LLRF cont. unit 571 MHz Phase shifter Linac MO E/O 571 MHz 2856 MHz 80m LLRF cont. unit LLRF cont. unit 30m LLRF cont. unit SB-2 SB-3 SB-4 SB-1 SB-C Damping Ring 1.1 GeV For PF 2.5 GeV,0.1nC X 1 I A I A I A I A I A I A I A I A I A For PF-AR,6.5 GeV Energy Compression Bunch Compression e+ capture section For LER 4.0 GeV,4nC X 2 SB-5 5-1 5-2 e- bypass orbit Sector C Sector 1 Sector 3 Sector 2 Sector 4 For HER 7.0 GeV,5nC X 2 Sector 5 29