INJECTION CONTROL SYSTEM FOR THE SuperKEKB PHASE-2
OPERATION
H. Kaji∗ , H. Sugimura, KEK, Ibaraki, Japan
Y. Iitsuka, East Japan Institute of Technology Co., Ltd., Ibaraki, JapanT. Kudou, Mitsubishi Electric System & Service Co., Ltd., Ibaraki, Japan
Abstract
The SuperKEKB is an electron-positron collider whichaims the world’s largest luminosity of 8 × 1035 cm−2 s−1 . Its
injection control system is upgraded for the phase-2 operation. Both the Event Timing System and Bucket Selection are improved to realize the positrons injection with the
newly constructed damping ring. The injection control system works excellently during the entire run period of phase2. The simultaneous injections to electrons and positrons
rings are carried out with the injection rates of 6.25 Hz and12.5 Hz, respectively. The several filling patterns at mainrings which are required from a variety of beam studies are
realized by the Bucket Selection. The further upgrade of
injection control system is planned for the phase-3 operation.

INTRODUCTION
The SuperKEKB accelerator [1, 2] is an electron-positron
collider with the center-of-mass energy of 10.58 GeV. It
consists of High Energy Ring (HER) and Low Energy Ring
(LER) for electrons and positrons, respectively. The target
luminosity of this project is to be 8 × 1035 cm−2 s−1 . It will
be realized with the large beam currents of 3.6 A (HER) and2.6 A (LER).
The phase-2 operation is carried out from March to Julyin this year. The first collision is observed on April 26th.
Then, after iteration of several beam commissionings, weachieved the peak luminosity of 5.55 × 1033 cm−2 s−1 .
One of the most important upgrades in phase-2 is theDamping Ring (DR). The positrons are once stored into DR
for suppressing the beam emittance. Then they are injected
into LER. Note, the electrons are directly delivered from theinjector linac (LINAC).
The injection control is implemented with the Event Timing System. It is upgraded to satisfy the requirements inphase-2 and to operate the DR for the positron injection.
The upgrade is limited only on the software since the hardware has already been developed to realize the DR operation [3]. The robustness and long term stability of hardware
are demonstrated with the successful phase-1 operation in2016 [4].
The Bucket Selection system is upgraded. It selects theoperation RF-bucket at DR (DR-bucket) together with theinjection RF-bucket at LER (LER-bucket) in the positrons
injection. The standalone operation of DR is supported.
In this report, we discuss the above mentioned upgrades
and report some performance in the phase-2 operation. Be∗ hiroshi.kaji@kek.jp

Figure 1: Trigger scheme for the injection and extraction at
DR: the left figure shows the configuration of Event modules. The EVGs form two layers. Two lower-layer EVGs are
triggered by the signal from the upper-layer EVG. The rightfigure is the time chart of module operation. The upper-layer
EVG is triggered by the divided SuperKEKB revolution andprovides the 50 Hz triggers. The time relation of different
lower-layer EVG triggers can be perfectly controlled by thesequence of the upper-layer EVG. Therefore we can manage
the injection and extraction triggers at DR.

sides, the necessary upgrade for the phase-3 operation is
introduced.

DR OPERATION
Figure 1 explains how the Event Generator (EVG) module
manages the DR operation. The injection and extraction of
positrons at DR must be performed in the different LINAC
pulses since the minimum storage time at DR is 40 ms. The
minimum storage time is defined to secure the enough radiation damping time in terms of emittance suppression.
The upper-layer EVG provides the 50 Hz triggers. This
process is triggered by the main ring (MR) revolution so that
all output triggers can be utilized for the Bucket Selection.
The lower-layer EVGs control the 50 Hz LINAC operation.
They can control the injection and extraction of positrons
at DR with their triggers. The time relation of individual
LINAC pulses can be controlled perfectly. It is guaranteed
since the processes of lower-layer EVGs are triggered by the
50 Hz from the upper-layer EVG.

UPGRADE OF INJECTION CONTROL
After successful operation in phase-1 [4], the softwareof Event Timing System is upgraded for realizing the more
complicated injection control in phase-2. Some operation
parameters, like “DR storage time”, are decided. The several

new functions are applied for the injection control. We
introduce them in this section.

DR Storage Time
There are new important parameters for the injection control in phase-2. They are the DR storage time, TDR , and its
MAX . We decide them following way.
maximum value, TDR
The TDR is determined as the interval of two LER injections. Therefore the TDR in 5 Hz (25 Hz) is 200 ms (40 ms).
This determination is derived from one pulse DR operation
which is carried out in the phase-2 operation.
We schedule the LER injection at even intervals so that
we keep the constant TDR . The TDR is changed only when wechange the injection frequency. It is necessary to simplify
the Bucket Selection algorithm.
There is the concern with TDR to make the LINAC operation unstable. The LINAC hardware must be operated
with the same phase of AC power 50 Hz (AC50) to keep
their stable conditions. However, with the following reason,
this AC50 phase becomes unstable when the TDR becomeslarger.
The extraction timing must be determined TDR before
the operation since the Bucket Selection determines it together with the injection timing. Of course, it refers theAC50 phase. However the AC phase is unstable and always
drifted. Therefore the operation timing for the DR extraction
becomes different AC phase when the TDR is large.
Figure 2 shows the time difference between the DR extraction trigger and AC50 in the several TDR cases. The time difference becomes larger when the TDR becomes larger. With
MAX to be 200 ms.
these measurements, we decided the TDR
There is the other unavoidable limit on our Event Timing
System. The sequence length of upper-layer EVG must be
equal to or longer than TDR . Otherwise we cannot guarantee
the time relation between the injection and extraction triggers
at DR.
The sequence length of upper-layer EVG is lengthened
MAX = 200 ms.
to be 16 or 18 injections for satisfying the TDR
Note, they are 8 or 9 injections in the phase-1 operation [4].

Figure 2: Time difference between the DR extraction trigger
and AC50: the histograms in four DR storage time cases areshown.

electron gun and some MR components like injection kicker
and septum magnets. Besides, we must synchronize also the
DR components since phase-2.
The distributed bus bit (Dbus) function of Event Timing
System is activated and utilized to deliver control signalsof individual injection hardware. The synchronization ofindividual control signals are guaranteed with the precisely
controlled Event interruption. The details of entire system
is described in Ref [5]. The control of DR hardware with
Beam Gate information is separately reported in Ref [6].

Time Synchronization
The CPU time for all IOCs of both Event Timing System and Abort Trigger System [7] are synchronized. The
accuracy of synchronization is ∼100 ns. Therefore, we caninvestigate the causality between injections and aborts withthis time information. The details are described in Ref [8].

Beam Mode information
We deliver the beam mode information via the data buffer
of Event Timing System. It is one of software upgrades andis utilized for more complicated pulse-to-pulse modulation inphase-2. LINAC installs lots of pulsed components for phase2. For example, the pulse quadrupole magnets are installedin the downstream section of LINAC and they utilize thisbeam mode information.
We deliver three kinds of beam mode on the data buffer
waveform. They are the beam mode of current, next, andnext-to-next injections. So individual hardware can utilize
the prefer element of this waveform with respect to theirlatencies and control procedures.

Beam Gate Control
The upgrade of Beam Gate control is required to improve
the synchronization of enable/disable controls between the

UPGRADE OF BUCKET SELECTION
Bucket Selection plays many important roles in the injection control. Its general specifications are described somewhere in Ref [9, 10].
The upgrades of Bucket Selection system are required forthe phase-2 operation. They are mostly related with the DR
operation. We describe the new features of Bucket Selectionin this section.

Subroutine to Decide Injection Timing
Bucket Selection has several subroutines to decide injection RF-bucket (HER-bucket, LER-bucket) and to determine
the LINAC operation timing. We prepare new subroutines
for the LER injection since the algorithm to determine theoperation timing is quite different in phase-2.

Then, the timing of 1st LINAC, TEVG1 is determined to
inject positrons into NDR :
Ttotal1 · 49
NDR = MOD, 230 ,
(4)
96.3
TEVG1 = Ttotal1 − Npulse1 · 20000000,(5)Figure 3: The schematic view of timing determination for
the LER injection: it explains in the case injecting positrons
into DR at pulse #1 and extracting them at pusle #3. Two
black dashed lines show the operation timings of injectionand extraction. The Ttotal1 and Ttotal2 are determined as theinterval from the input trigger of upper-layer EVG while
the TEVG1 and TEVG2 are determined as the interval from theindividual output triggers of upper-layer EVG.
For HER, the algorithm is same as that of the phase-1 and
KEKB operations which are described in Ref [9, 10].
The new subroutines for the LER injection take care of DR
operations. Its specific features are: the 1st and 2nd halvesof LINAC (1st LINAC, 2nd LINAC) work with the different
timings. The 1st LINAC works for injecting the positron
beam into DR while the 2nd LINAC works for extracting
the positron beam from DR and delivering toward LER.
Figure 3 explains the procedure of timing determination
for the LER injection. This example shows when we inject
positrons into DR at pulse #1 and extract them at pulse #3.
Therefore, Npulse1 and Npulse2 are 1 and 3, respectively, inthe following discussion.
The injection and extraction timings of positrons must
be determined before the DR injection. After deciding theLER-bucket, NLER , we determine the timing of 2nd LINAC
operation, TEVG2 , as follows:
Ttotal2 · 49
, 5120 ,(1)
NLER = MOD
96.3
TEVG2 = Ttotal2 − Npulse2 · 20000000,(2)
where Ttotal2 is the timing to decide the LER-bucket which
is illustrated in Fig. 3. The Ttotal2 and TEVG2 are shown inunit of ns. The denominator, 5120, of Eq (1) is the harmonic
number of MR. Note, the Ttotal2 has the periodic solutions.
Therefore we choose one which is nearest to the AC50 phase.
The next step is the determination of DR-bucket, NDR :
Ttotal2 · 49
NDR = MOD, 230 ,
(3)
96.3
The denominator is changed to be 230, which is the harmonic
number of DR.

where Ttotal1 is the timing to decide the DR-bucket which isillustrated in Fig. 3. The Ttotal1 and TEVG1 are shown in unitof ns.
Note TEVG2 is buffered until the extraction pulse of LINAC
while TEVG1 is immediately set on EVG for the DR injection.
Also the subroutines for the DR standalone operation aredeveloped. They are utilized for the DR commissioning
which is carried out just before phase-2.

Information for Injection Control
Here we summarized the operation parameters which aredecided by Bucket Selection and are provided to the Event
Timing System. The parameters related with DR are addedsince phase-2.
RF-bucket numbers at DR and MRs
The HER-bucket and LER-bucket are informed with their
number. They are delivered via the data buffer of Event
Timing System.
The information is utilized at the Belle-II detector to veto
the DAQ at the timing of injected bunches. Besides, someaccelerator components at MR utilize to monitor those condition [11].
Besides, the DR-bucket is delivered since phase-2.
Timing of Main- and pre-triggers (1st LINAC)
The operation timing of 1st LINAC is determined. Thistiming coincides with the injection DR-bucket for the LER
injection while it coincides with the HER-bucket for HER.
In addition to the main-trigger timing, we determine thepre-trigger timing. The pre-trigger timing is determined asfollowing formula:0
Tpre1 = TEVG1 − TEVG1+ 5000000,(6)0where the TEVG1
is the operation timing of 1st LINAC in the
one pulse before (previous injection period). The TEVG1 and0
TEVG1are defined with unit in ns.
After providing to the Event Timing System, the TEVG1 is
set on the delay of Event delivery while the Tpre1 is delivered
via the data buffer.

Timing of Main- and pre-triggers (2nd LINAC)
The main- and pre-triggers of 2nd LINAC are provided.
The pre-trigger timing is determined in the same way withEq (6).
The timings of 2nd LINAC are treated on the 2nd
lower-layer EVG while those of 1st LINAC are treated on
the 1st lower-layer EVG.
Number of bunches per injection pulse

Figure 4: MR beam currents during the luminosity run: thebeam current is shown for both HER and LER. They aremeasured with the DCCT from 1am to 9 am of the June 7th,2018.

Control flags of extraction septum and kicker (DR)The control flags for extraction septum and kicker magnets are provided. Their specifications are same as those of
injection kicker and septum magnets. However the control
flags are treated on the 2nd lower-layer EVG.
The control flags for injection and extraction components
realize a variety of DR operations. They are utilized for the
DR commissioning. For example, we can store positronsand perform the beam study at DR. It can be realized byenabling the injection components and disabling the extraction components. After this beam study, we can throw thepositrons with the opposite condition.
When the LER injection rate is less than 5 Hz, the interval
MAX . In thisof two LER injection pulses is longer than the TDR
case, two different LER injection modes are scheduled to
MAX . The positrons injection (extraction) is
realize TDR = TDR
carried out by operating only the 1st LINAC (2nd LINAC).
The control flags are utilized also in a such kind of case.

PERFORMANCE ON PHASE-2
Figure 5: Demonstration of auto injection: the beam currents
during the auto injection is shown. The Beam Gate is opened
when the beam current is decreased 5 %. Partially, it isoperated with the 0.5 % loss.

LINAC can generate and operate one or two bunches inevery pulse. Bucket Selection decides also the number of
injection bunches. For example, we cannot implement twobunches injection at the tail of bunch train at MR.
Bucket Selection can switch one bunch and two bunches
injections in pulse-by-pulse. Besides, the zero bunch
injection is possible. It is implemented when the timing
system has something abnormal. The beam operation of
LINAC can be stopped immediately with the zero bunch
injection mode.
Control flags of injection septum and kicker (DR)
Bucket Selection provides control flags which enable ordisable the operation of injection septum and kicker magnets.
Even though the LINAC pulse mode is the LER injection,
the trigger delivery to those hardware is stopped with thedisable condition.
We make the “AND” logic between these flags and Beam
Gate signal on the Event IOC. The 1st lower-layer EVG
delivers the results via the Dbus. Then the Event Receiver(EVR) controls the trigger channels of septum and kicker
with the received information.
We do not lay any new optical fibers for the delivery ofthese control signals since the Dbus shares the optical linewith the Event delivery. Another advantage is the Dbus
can deliver 8 different signals in parallel so that the kicker
and septum magnets are controlled separately with theindividual control flags. Therefore, the abnormal operations
for the hardware studies can be realized with this function.

Figure 4 is an example of MR operation in phase-2. We
carried out simultaneous injections for both LER and HER
with the large injection rates. Typically we perform theinjections with the rate of 6.25 Hz (HER) and 12.5 Hz (LER).
We take the only ∼10 minutes to stack beam currents fromzero to those for luminosity run, 285 mA (HER) and 340 mA(LER). The re-filling after beam decays with their lifetime
is quite fast. We suppress the down time of luminosity run
with the intelligent injection control.
The upgraded Beam Gate system is operated excellently.
The system becomes fast and robust even though the control
becomes complicated.
The auto injection system is implemented correctly during
the vacuum scrubbing operation. Figure 5 demonstrates its
performance. Typically we open the Beam Gate and re-fillthe beams when the current loss becomes 5%. The auto
injection with the 0.5% loss is tested and succeeded.
Bucket Selection realizes the several filling patterns. Figure 6 shows the bunch current distribution at LER. Typically,
the 789 bunches operation is performed in the luminosity
run. The number of bunches is increased to 1576 in case of
vacuum scrubbing since it needs large beam currents.

IMPROVEMENT FOR THE PHASE-3
We need the upgrade of injection control system. The
phase-3 operation is performed with more larger beam currents. Therefore the high frequency injections are required.
Especially the LER injection with >25 Hz is performed since
the beam lifetime becomes shorter and to be ∼5 minutes.
The two pulse operation at DR is necessary for the LER
injection with >25 Hz. The DR storage time is doubled in
the two pulse operation with the fast-in-fast-out rule. Thisis important to secure the enough damping time. The minimum storage time of 40 ms can be satisfied up to the 50 Hz
injection when we perform the two pulse DR operation.

is performed to activate new functions of Event Timing
System. They are utilized for the Beam Gate system, timesynchronization, and so on.
Also Bucket Selection is upgraded. The new subroutines
to select the DR-bucket together with LER-bucket are developed.
The injection control system works excellently in thephase-2 operation. The simultaneous injections for both
HER and LER are carried out with the injection rate of
6.25 Hz and 12.5 Hz, respectively. The several filling patterns at MR which are required from a variety of beamcommissionings are realized with the Bucket Selection.
The further upgrade is planned for the phase-3 operation.

REFERENCES[1] Y. Ohnishi, et al., “Accelerator Design at SuperKEKB”, Prog.
Theor. Exp. Phys., vol. 2013, no. 3, p. 03A011, 2013.
[2] K. Abe, et al., “Letter of Intent for KEK Super B Factory”,
KEK Report 20014-4.
[3] H. Kaji, et al., “Upgrade of Event Timing System at
SuperKEKB”, in Proc. ICALEPCS’13, San Francisco, USA,2013.
[4] H. Kaji, et al., “Injection Control System for the SuperKEKB
Phase-1 Operation”, in Proc. of 13th Annual Meeting of PASJ,
Fukui, Japan.

Figure 6: Example of LER bunch currents: the bunch currents in typical two filling pattern cases are shown. The upper
figure shows 789 bunches operation which is utilized in theluminosity run while the lower figure shows 1576 bunches
operation which is utilized in the vacuum scrubbing.
There is the concern to degrade Bucket Selection in thetwo pulse DR operation. We modulate the RF phase at 2nd
LINAC in pulse-by-pulse to avoid this deterioration. The
details of its Bucket Selection logic is described in Ref [10].
In addition to the Bucket Selection software, the master IOC
of Event Timing System must be upgraded.

CONCLUSION
The injection control system of the SuperKEKB collider is
upgraded for the phase-2 operation. The new system satisfies
the requirements to operate the DR.
Some operation parameters on the master IOC of Event
Timing System are modified. Besides, the software upgrade[5] H. Kaji, et al., “Beam Gate Control System for SuperKEKB”,
in Proc. IPAC’18, Vancouver, Canada, 2018.
[6] H. Sugimura, et al., “Trigger Control System with Beam Gate
at SuperKEKB Injector Linac and Damping Ring”, in Proc.
of 15th Annual Meeting of PASJ, Nagaoka, Japan.
[7] S. Sasaki, et al., “Upgrade of Abort Trigger System forSuperKEKB”, in Proc. ICALEPCS’15, Melbourne, Australia,
2015.
[8] H. Kaji, et al., “Time Synchronization for Distant IOCs of theSuperKEKB Accelerators”, in Proc. IPAC’17, Copenhagen,Demark, 2017.
[9] H. Kaji, et al., “Bucket Selection System for SuperKEKB”,
in Proc. of 12th Annual Meeting of PASJ, Fukui, Japan.
[10] H. Kaji, “Bucket Selection for the SuperKEKB phase-3 Operation”, in Proc. of 15th Annual Meeting of PASJ, Nagaoka,
Japan.
[11] H. Kaji, et al., “Archive System for Injection Current at
SuperKEKB”, in Proc. of 15th Annual Meeting of PASJ, Nagaoka, Japan.