Proceedings of PCaPAC2018, Hsinchu, Taiwan- Pre-Release Snapshot 18-Oct-2018 15:00 (CST)TIMING SYSTEM FOR MULTIPLE ACCELERATOR RINGSAT KEK e+/e- INJECTOR LINAC
F. Miyahara†, K. Furukawa, H. Kaji, M. Satoh, H. Sugimura, KEK, Ibaraki, JapanT. Kudou, S. Kusano, Mitsubishi Electric System & Service Co., Ltd, Ibaraki, Japan
H. Saotome, Kanto Information Service, Ibaraki, Japan
Abstract
The KEK e+/e- injector linac is operated in multiple
beam modes that can be switched every 20 ms for e+/ebeam injection to five different circular accelerators,
SuperKEKB High Energy Ring (HER), Photon Factory(PF) ring, PF-AR, positron damping ring (DR) andSuperKEKB Low Energy Ring (LER). Because those
accelerators have different ring energies and radio frequencies, the linac is required to have a timing system
which supports multiple modes and synchronization system to the circular accelerator. Those systems to fulfil
multiple injections to independent circular accelerators
are described in this paper.

phases and the currents pulsed magnets can be changed
every beam pulse by employing the event timing system.

TIMING SYTEM OF THE LINACINJECTOR LINAC

Figure 2: Timing system of the linac.

Copyright © 2018 CC-BY-3.0 and by the respective authors

Figure 1: Schematic view of the e+/e- injector linac andaccelerator rings at the KEK.
The KEK e+/e- injector linac and five different rings
are depicted schematically in Fig. 1. The HER requires
low emittance electron beam, thus the photocathode rfgun [1] is used for HER beam injection. High charge(~10 nC) electron bunches for positron production andelectron beams for PF, PF-AR are given by the thermionicgun. The linac consists of 8 sectors (A-C, 1-5) which have
8 high power RF units except for injector (rf-gun, thermionic gun and bunching section) and positron production
section. The RF unit provides RF power to 4 accelerating
structures. The beam energy at the end of the linac iscontrolled by RF phase of the unit. In order to set optimum beam optics for each the beam mode, 28 pulsed
quadrupoles and 36 steering pulsed magnets were installed in last year [2]. Parameters such as accelerating RF____________________________________________† fusashi.miyahara@kek.jp

Figure 2 shows the linac timing system with the fundamental RF signals. The master frequency of 571.2 MHzis generated with a signal generator which is synchronized with the SuperKEKB oscillator via a 10 MHz reference signal [3]. The 571.2 MHz phase shifter set the linac
whole RF phase according to the beam mode. The phaseof φ1 and φ2 correspond to the HER and the LER injection
phase, respectively. In case of the PF and the PF-AR
injection, the φ2 is set to zero. Because large phase shiftaccompanying beam mode change makes the laser system
for the rf-gun unstable, the laser system always synchronized with the HER.
The trigger signals to various components are distributed by the MRF event system [4] which consists of event
generators (EVG) and event receivers (EVR). The event
timing system has three EVGs [5]. The first EVG-EVR
set makes a trigger timing signal for the HER/LER injection. The trigger timing signal for the PF/PF-AR injection
is sent from a special module to make a synchronizedsignal with the circular accelerator. The EPICS IOC program for the event system selects a corresponding trigger
for 2nd EVGs of the beam mode. Then, the 2nd EVGs
distribute an event code which corresponds to the beam

THP190Hardware Technologies and Custom Hardware, Feedback Control and Tuning, Timing and Synchronization

Proceedings of PCaPAC2018, Hsinchu, Taiwan- Pre-Release Snapshot 18-Oct-2018 15:00 (CST)

mode and a data buffer including some parameters suchas a the HER/HER/PDR injection RF bucket number,setting current of pulsed magnets. Because the external
RF clock used in the event system depends on the beammode, the phase of the event system could be varied everypulse.

BEAM INJECTION TO A CIRCULAR ACCELERATOR WITH DIFERENT RFSynchronization Systemsend a trigger output to the event system and a veto signal
to the thermionic gun. Figure 3 shows the variation of thePF RF and the synchronization failure rate. The annual
variation of the PF RF is about 15 kHz owing to the circumference compensation of the ring. The RFs and variations in a day/year are summarized in Table 1. A very low
synchronization probability region is found around500.093 MHz, but there is no such a region in the operating frequency. We can enlarge the probability of the synchronization by increasing the Γsyc, but it is trade-off forthe beam injection phase jitter.
Table1: RF and Its Variation in a Year/Day
Ring Accelerator
SuperKEKB
PF
PF-ARFrequency
508.88 MHz
500.11 MHz
508.57 MHz

AnnualVariation~300 Hz~15 KHz~1.5 kHz

Variation
in a day~10 Hz~1 kHz~200 Hz

Figure 3: Variation of the PF radio frequency and thesynchronization failure rate. White dots show the PF RFin the past 3 years. The colour band represents the synchronization failure rate at the frequency which was estimated by a simulation in a condition of synchronization
width of 500 ps and 114.237423 MHz of the linac RF.
Since the event system uses the 114.2 MHz clock
which is generated by the linac RF system that uses
common sub-harmonic frequency of the 10.39 MHz, thelinac beam timing synchronized with HER/LER revolution timing periodically. However, the PF and the PF-AR
are not synchronized to the linac because the two accelerators use independent RFs. In that case, to generate theRF for the linac from the RF of the circular accelerator [6]in every pulse is one of the ways. We plan to use the rfgun for the beam injection to the PF/PF-AR. In that case
it is difficult to adopt the way in our system because thelaser system requires stable radio frequencies. Thus, wetake the way to use chance synchronization of the linac
RF and the PF/PF-AR revolution frequency. The triple
sync module shown in the Fig. 2 outputs a signal to theevent system on a timing when the linac RF (114.2 and10.39 MHz) is synchronized with a revolution timing ofthe circular accelerator every 20 ms. The width of synchronization (Γsyc) can be changed. Because the synchronization probability depends on the linac and the circular
accelerator RFs, there could be no chance event in a certain period of time. In order to operate the klystron stably,a regular interval of the trigger (20±2 ms in our case) isrequired. In case of no synchronized event in a waitingtime (~0.9 ms) from the 50 Hz trigger input, the module

Figure 4: Layout of papers.
To keep reproducibility of the current to the pulsed
magnet, the power supply of the magnet requires precise
trigger timing which is 3 ms before the beam arrival time.
Then, the trigger should be the first timing in the timing
system and it is generated by the chance synchronizationin case of PF/PF-AR beam injection. Because the RF usedin the event system is different from the PF/PF-AR one, asimple 3 ms delayed beam trigger leads to injection tooutside the separatrix or an unexpected RF bucket. Thus,
we have developed the way finding a synchronized timing
after arbitrary delay from the first synchronized timing.
Figure 4 shows the relation of trigger signals (the outputof the triple sync module, the pulsed magnet, the beamtiming), the RF of the linac and the revolution signal from
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Hardware Technologies and Custom Hardware, Feedback Control and Tuning, Timing and Synchronization

1Copyright © 2018 CC-BY-3.0 and by the respective authors

Resynchronized Delay

Proceedings of PCaPAC2018, Hsinchu, Taiwan

the circular accelerator. If we can know the resynchronized delay longer than the required interval (3 ms), thebeam timing is synchronized with the revolution timing
and the interval can be fixed. The delay Tbeam which has ajitter less than Δtsync is given by Eq. (1),n f
f Circ ,Re v− int  n Circ ,Re v  < f Circ ,Re v Δt sync , (1)f Linac ,min f Linac ,min Copyright © 2018 CC-BY-3.0 and by the respective authors

where, n is the number of clock cycles, int(x) stands forthe integer part of the x. The flinac,min and the fCirc,Rev are theminimum fundamental frequency used in the linac and therevolution frequency of the circular accelerator. In theoperation, the 114.2 MHz of the linac RF and the500.11 MHz of the PF RF (508.57 MHz of the PF-AR),are monitored by using the same frequency counter withthe resolution of 10 digits per second. The delay and thesynchronization probability are calculated every second tofollow the changing of the RFs. We can easily find the n,
and the timing control is implemented by EPICS. The
maximum injection timing jitter is given by Γsyc+ Δtsync,
and the jitter is less than 0.6 ms for the beam injection to- Pre-Release Snapshot 18-Oct-2018 15:00 (CST)the PF. The system using the way has been working sinceautumn of 2017 without any trouble.

REFERENCES[1] R. Zhang et al., “Yb/Nd Doped Hybrid Solid Laser of RF
Gun and Beam Commissioning for Phase-II of
SuperKEKB”, in Proc. IPAC’18, Vancouver, Canada, Apr,2018, pp.304-306.
[2] Y. Enomoto et al., “Pulse-to-pulse Beam Modulation for 4
Storage Rings with 64 Pulsed Magnets”, presented at LINAC18, Beijing, China, Sep. 2018, paper MOPO007, unpublished.
[3] T. Matsumoto et al., “Low-level RF System for theSuperKEKB injector Linac”, in Proc. IPAC’18, Vancouver,Canada, Apr, 2018, pp.2131-3133.
[4] Micro-Research Finland Oy, http://www.mrf.fi/[5] H. Kaji et al., “Construction and Commissioning of Event
Timing System at SuperKEKB”, in Proc. IPAC’14, Dresden,Germany, June 2014, pp.1829-1832.
[6] Y. Kawashima, T. Asaka and T. Takashima, “New synchronization method of arbitrary different radio frequencies in accelerators”, Phys. Rev. ST Accel. Beams, vol. 4, p. 082001,
Aug. 2001, doi:10.1103/PhysRevSTAB.4.082001

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