Proceedings of the 15th Annual Meeting of Particle Accelerator Society of Japan
August 7-10, 2018, Nagaoka, Japan

PASJ2018 THP091

TRIGGER CONTROL SYSTEM WITH BEAM GATE AT SUPERKEKBINJECTOR LINAC AND DAMPING RING
H. Sugimura∗ , H. Kaji, F. Miyahara, S. Sasaki, M. Satoh, KEK, Ibaraki, JapanT. Kudou, S. Kusano, Mitsubishi Electric System & Service Co., Ltd, Ibaraki, Japan
Y. Iitsuka, East Japan Institute of Technology Co., Ltd, Ibaraki, Japan
Abstract
Accelerator control system is indispensable for the beamhandling. Especially, a timing control is much important
tool for SuperKEKB project [1]. In the SuperKEKB project,
the timing control system became more complex than previous KEKB project, because a Damping Ring (DR) wasnewly constructed. The DR is located at the middle of injector Linac. Positron beam is delivered from Linac to DR
at the energy of 1.1 GeV, and is made lower emittance there.
After being stored during 40 ms, the positron beam is returned to Linac. To control the beam injection and extraction at DR, we made two different timing at main timing
system. In the DR, it is necessary to control the timing in
the various situation, storage mode that is only injection,
extraction only mode after optics measurement and so on.
To satisfy this situation, “Beam Gate” handling system wasembedded in the timing system. We also adopted beam gatehandling at injector Linac. This system is very useful not
only machine inhibit control but also identification the beamis transported or not.

INTRODUCTION
The SuperKEKB accelerator which is located in TsukubaCampus, KEK, is aiming at the world highest luminosity to8 × 1035 cm−2 s−1 . The injector Linac supplies electron andpositron beam to SuperKEKB main ring at the energy of7√GeV and 4 GeV, respectively for asymmetric collision ats =10.58 GeV. The Damping Ring (DR) is newly constructed for reducing positron emittance, and is located at
the middle of injector Linac as shown in Fig. 1.

through Flux Concentrator (FC). Bunch charge is going to
be reached up to 4 nC. After accelerated at 1.1 GeV, thepositron beams are delivered to beam transport line, and injected to the DR. The emittance before DR is about 3 mmin normalized emittance. When stored for 40 ms, it will be92 µm in the horizontal direction and 7.3 µm in the vertical direction, respectively. Key parameters are listed in theTable 1.

Table 1: Key parameters of Damping Ring
Parameters

Value

Unit

EnergyRepetition frequency
Circumference
RF frequency
Harmonic Number

1.1
50
135.5
508.9
230

GeV
HzmMHzFour bunches can be stored in DR at maximum when
2-bunch and 2-pulse mode is operated as shown in Fig. 2.
Time difference between two bunches is kept 96.3 ns because injection chance comes up at the rate of 10.38 MHz.
Where, frequency of 10.38 MHz is derived from commonfrequency 508.9 MHz in DR, MR and 2856 MHz in Linac.
In the case of 2-pulse storage mode, first pulse and second
pulse should be kept more than 100 ns because pulses of theKicker magnets are active before and after 100 ns of trigger
timing. Therefore, it is limited to inject second pulse since
first pulse (in 2-bunch) is occupied (100 + 96.3 + 100) ns.
The trigger control system calculates which timing is enabled to inject or not using this occupancy criteria.

96ns>100ns>100ns
96ns

Figure 1: SuperKEKB Accelerator.

The positron beams are generated by irradiating electron beams on a tungsten target. The beams are gathered∗ hitoshi.sugimura@kek.jp- 1078 -Figure 2: 2-bunch and 2-pulse operation mode at DR.

Proceedings of the 15th Annual Meeting of Particle Accelerator Society of Japan
August 7-10, 2018, Nagaoka, Japan

PASJ2018 THP091

EVENT TIMING SYSTEM FOR
ACCELERATOR CONTROL
Overview
The timing system calculates various trigger generation
timing and distributes it to many equipment. There aremany timing parameters in the Linac because it provides
beam for four multi-purpose ring, SuperKEKB two mainring, PF, PF-AR, and also DR with different energy and different particle. Therefore, it is necessary to identify whichshot is for which ring. To satisfy in this requirement, event
timing system is introduced. We chose event timing system produced by MRF’s company [2]. MRF’s event timing
system consists of a pair of "Event Generator (EVG)" and"Event Receiver (EVR)". The EVG sends event informationto EVRs for each devices. Originality of the event timing
system is that the system is able to deliver not only timingsignal but also shot information via optical fiber cable. Thetiming has 8-bit information which is called "event code",and is transferred after 8B10B encoding. 2 bytes of information are transmitted to EVR in synchronization with RF
wave of 114 MHz. The first 1-byte is assigned as event code,and the second 1-byte is shared by the distributed bus bit andsynchronous data buffer alternatively. The distributed busbit has 8-bit and can send 8 kinds of HI or LOW bit state
to EVR. By using this function, we are sending Beam Gateinformation. The detail is described next section. The databuffer is enabled to be included 2 kB information at most.
We are packing shot number, event code information, RFphase etc. in the data buffer.

septum magnets. So, we decided to transmit beam gate via
event timing system network by using distributed bus bit.
Since the distributed bus bit sends bit information at the frequency of 57 MHz, the response speed is about 17 ns. The
bit status can be monitored with EPICS PV, and each EVRs
can process according the status. The beam gate bits for DR
injection and extraction kicker and septum is assigned in 8bit distributed bus. Totally 4 kinds of bit information areused as shown in Table 2.
Table 2: Assigned Beam Gate Bit in Distributed Bus Bit
Category

Dbus bit

DR Injection Kicker
DR Injection Septum
DR Extraction Kicker
DR Extraction Septum
HER LER Beam Gate OR

Upstream DbusBit4
Downstream DbusBit5
Upstream DbusBit4
Downstream DbusBit5
Both DbusBit6

Event System
Dbus4(t=Ev(40))

Kicker-pre

Ev(1)Dbus4(t=Ev(40))

Kicker-main

Ev(42)
Dbus5(t=Ev(41))

System Setup on EPICS IOCSeptumEv(42)We have developed on EPICS base R3.14.12 for SuperKEKB event timing system [3]. Under this version,
MRF’s device support in the version of mrfioc-2.0.2 or 2.0.3
is embedded [4]. Since the original MRF’s device support
is omitted read out of distributed bus bit, we modified to
be able to read it. Hardware settings are also made at eachlocations. Main timing station of EVG is located at the center of injector Linac [5] and each sub-system is working at
DR [6] and MR [7]. The sub-system is originally made andre-made trigger according to receive it from main timingstation.

BEAM GATE CONTROL AT DAMPING
RING
DR operation started from February 2018. We have constructed sub-timing station at control room at DR. There areseveral operation method in DR, continuous injection mode,
one-shot and storage mode, only extraction mode, and so on.
Considering various operation mode, the control method ofinjection and extraction kicker and septum became difficult.
And also, it is necessary to switch beam gate quickly forincoming and outgoing positron in DR. The beam gate handling method is usually processed via EPICS PV. However,
it is not suitable for pulsed-like control such as kicker andFigure 3: Beam gate logic structure.
The trigger for Kicker and Septum magnet is controlledwith AND circuit in the event timing system as shown inFig. 3. Kicker-pre is the timing for charged trigger, and theoriginal event code is No. 1. This trigger is controlled by
the beam gate of Dbus4. Kicker-main is the timing for discharged trigger, and the original event code is No. 42. It is
controlled by same logic of Kicker-pre. Septum timing is
numbered event No. 42 and controlled by the beam gate ofDbus5, which is different timing with Kicker.
Timing chart of beam gate is shown in Fig. 4. The beamgate via distributed bus is pulse like structure which widthis about 20 ms. Which event code to be transmitted is informed before 2-shots. We numbered event code No. 40,41, 42 on the positron beam. The code of No. 42 indicatesthe delivered positron beam timing, and No. 41 indicates
preparation event timing transmitted before 1-shot (20 ms),and No. 40 indicates also preparation event timing transmitted before 2-shot (40 ms). Each beam gate is output soas to overlap with event timing at No. 40 and 41, respectively. The trigger for Septum magnet is output at the timing of event No. 42. To control this output, beam gate sta-- 1079 -Proceedings of the 15th Annual Meeting of Particle Accelerator Society of Japan
August 7-10, 2018, Nagaoka, JapanPASJ2018 THP091

hand, the KBPd mode means that stored positron beam is extracted, but not injected to DR. These mode of KBP, KBPu,
and KBPd is same event code. The beam gate combination makes these differences. An upper limit is set for storage time, Tmax , so as to prevent the timing from shiftingwith long storage time. If the injection interval is longer
than Tmax by low repetition rate, the beam is extracted after
passing Tmax . At this time, the beam is handled with a pairof KBPu and KBPd mode. Including 1-pulse and 2-pulse
mode, the storage time calculation is described in [8].

20ms
Dbus4
interrupt
Kicker
20ms
Dbus5

BEAM GATE CONTROL AT LINAC

interrupt

Overview
SeptumTime
Ev(40)

Ev(41)

Ev(42)

Figure 4: Timing chart of beam gate at DR.
tus is checked at the timing of event No. 41. The triggersfor Kicker magnet are output at the timing of event No. 42for discharged trigger and the timing of event No. 42 before 12 ms for charged trigger, respectively. To control thisoutput, beam gate status is checked at the timing of event
No. 40.

Selection of operation mode using beam gate
Since the beam gate is assigned individually as shownin Table 2, various operation mode can be supported. Especially, injection and extraction at DR is designed to befired simultaneously by assuming 50 Hz continuous injection with storage time of 40 ms. In addition, storage operation mode and low repetition injection mode are necessaryfor optics study. These operation mode can be categorized
like Table 3.
Table 3: DR operation mode according behavior of beamgate
ModeBeam Gate(inj/ext)

UseKBP/

continuous injection

KBPu/×first-shot after B.G open,
storage mode

KBPd

×/

Trigger from event timing system is generated to be kept
duration within (20 ± 2) ms because the Flux Concentrator(FC) and the Klystron must be maintained in equal spaced
trigger with 20 ms even when beam is stopped. The event
timing system is calculated to generate at around commercial 50 Hz under FC and Klystron criteria. However, thetiming is sometimes generated out of 2 ms due to initialization of timing calculation sequence, then the hardware isinterlocked. To avoid trigger lost in this situation, trigger
switch method is introduced.

Trigger Switch for Flux Concentrator
The concept of trigger switch is shown in Fig. 5. FC input trigger is selected either the trigger from event systemor commercial 50 Hz according switching gate level. Theinterval of commercial 50 Hz trigger hardly change, so that
FC input is sent this trigger during event system initialization.
Timing chart of the trigger switch is shown in Fig. 6. The
switching gate is made from the delayed timing signal of
Event No. 41. The switching gate status is originated frombeam gate (Dbus4) status at the timing of Event No. 40,
namely event system is used for FC input when beam gate
opened, and 50 Hz trigger is used when beam gate closed.
The switching gate timing is adjusted 10 ms before EventNo. 42.
EventFC Input
50Hz

extraction after Tmax ,last-shot before B.G close

Switching gate

We call operation mode of positron beam for SuperKEKB Main Ring as "KBP" mode. The KBP mode
is normally used for continuous injection. We assigned"KBPu" and "KBPd" as additional mode in DR. The KBPu
mode means that positron beam is delivered to DR, but not
extracted the stored beam at the same time. On the otherFigure 5: Trigger switch logic.

Trigger Switch for Klystron
Trigger switch method is also developed for Klystron.
The principle is almost same as FC trigger switch method.

- 1080 -Proceedings of the 15th Annual Meeting of Particle Accelerator Society of Japan
August 7-10, 2018, Nagaoka, JapanPASJ2018 THP091

to compensate for trigger-lost of event timing calculation
method during initialization of event timing system. Thisfunction is adopted to devices required for equal spaced trigger such as the FC and Klystron.
SuperKEKB Phase-2 project started from February 2018,
and finished in July this year. The DR operation was successfully finished with no serious event timing problems.
Phase-3 project is scheduled to start in February 2019 toattempt to update the world highest luminosity record andobtain new particle physics events by Belle2 experiment [9].

50 Hz

Event Timing

Dbus4
interrupt

REFERENCES

Switching gate

[1] Preliminary version of TDR of SuperKEKB, https://kds.
kek.jp/indico/event/15914/.
[2] Micro Research Finland (MRF), http://mrf.fi/.

FC Input[3] EPICS, https://epics.anl.gov/.
Time
Ev(40)

Ev(41)[4] MRFIOC2,
http://epics.sourceforge.net/mrfioc2/.
[5] H. Kaji et al., "Installation and Commissioning of New Event
Timing System for SuperKEKB", in Proc. 12th Annual Meeting of Particle Accelerator Society of Japan (PASJ2015), Tsuruga, Japan, Aug. 2015, paper FROL15, pp. 223–227.

Ev(42)

Figure 6: Timing chart of the trigger switch for FC.
The Klystron is operated with the interval of 25 Hz or 50 Hz.
We improved trigger switch system by incorporating commercial 50 Hz trigger as the "Event code", and also 25 Hz
trigger was made from the 50 Hz trigger by pre-scaling. The
switching gate status is originated from Dbus6 status whichis Beam Gate OR of HER and LER as listed in Table 2.

SUMMARY
We developed injection and extraction control system at
Damping Ring by using beam gate via event timing system.
It became useful function by separating injection and extraction control, with Distributed Bus Bit technology. Thismethod was applied to trigger switch in the event timing system at injector Linac. The trigger switch method was able

[6] H. Sugimura et al., "Synchronized Timing and Control System Construction of SuperKEKB Positron Damping Ring", inProc. 16th Int. Conf. on Accelerator and Large Experimental
Physics Control Systems (ICALEPCS’17), Barcelona, Spain,Oct. 2017, paper TUP094, pp. 229–231.
[7] H. Kaji et al., "Injection Control System for the SuperKEKB
Phase-I Operation", in Proc. 13th Annual Meeting of Particle
Accelerator Society of Japan (PASJ2016), Chiba, Japan, Aug.
2016, paper TUP092, pp. 1146–1149.
[8] H. Kaji et al., "Beam Gate Control System for SuperKEKB",
presented at the 9th Int. Particle Accelerator Conf. (IPAC’18),
Vancouver, Canada, Apr. 2018, paper WEPAK015, unpublished.
[9] Belle2, https://www.belle2.org/.

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