INJECTION CONTROL SYSTEM FOR THE SuperKEKB PHASE-I
OPERATION
H. Kaji∗ , K. Furukawa, F. Miyahara, T.T. Nakamura, M. Satoh, KEK, Ibaraki, Japan
Y. Iitsuka, N. Yoshifuji, East Japan Institute of Technology Co., Ltd., Ibaraki, JapanT. Kudou, S. Kusano, Mitsubishi Electric System & Service Co.,Ltd., Ibaraki, Japan
M. Hirose, Kanto Information Service Co.,Ltd., Ibaraki, Japan
Abstract
Injection control of the SuperKEKB accelerator is managed with Bucket Selection and the Event Timing System.
Both systems have their own optical network and functions torobustly communicate among distant EPICS I/O controllers.
The entire control system is ranged into both the injector
linac and main rings. Bucket Selection selects the RF-bucketof main ring to be injected the next beam-pulse and calculates the operation timing of injector fitting with selectedRF-bucket. The Event Timing System has been developed
to provide triggers to hardware on the injector beamline.
We configure Sub-timing Station to provide triggers also tomain ring hardware. Both Bucket Selection and the EventTiming System are operated certainly and stably during thephase-I operation of SuperKEKB. Besides, they show thegood capabilities for the the phase-II operation.

INTRODUCTION
SuperKEKB [1, 2] is the electron-positron collider whichis constructed at KEK. The beam-energies are 7.0 GeV forelectrons and 4.0 GeV for positrons, respectively. The target
luminosity is 8 × 1035 cm−2 s−1 which is realized with beamcurrents of 2.6 A for electrons and 3.6 A for positrons.
The phase-I operation of SuperKEKB has been successfully carried out from February 2016 to June 2016 [3–5]. We
performed vacuum scribing operation for main rings (MRs)of SuperKEKB. The commissionings for both machine andbeams are performed continuously. The beam-currents aregradually increased and achieved to be 870 mA (electronMR, HER) and 1010 mA (positron MR, LER). The integrated beam-currents at the end of phase-I operation are
662 Ah (HER) and 776 Ah (LER).
The injection control system is one of the most successful
system during the phase-I operation. We choose EPICS [6]as the software of control system. EPICS is well designed
for controlling the system with separated multi CPUs andsuitable as the software for operating accelerators. The important hardware for the injection control system are Bucket
Selection [7] and the Event Timing System [8–10]. They
have fast and robust communication schemes with dedicatedoptical networks for distant EPICS I/O controllers (IOCs).
The injector linac (LINAC) [11] performs beam-injection
into one of four rings (HER, LER, and two light sources [12,13]) in 50 Hz. Therefore above systems transfer necessary
information in every 20 ms.
∗ hiroshi.kaji@kek.jp

Figure 1: Schematic view of Bucket Selection: threenodes with a distributed shared memory configure the looptopology optical network. The nodes at Central Control
Building and D7 sub-control hall are placed in the MR side.
The remaining one node is placed at Main Timing Stationof LINAC.

In this report, we describe the specification of Bucket
Selection and the Event Timing System and introduce theirperformance in the phase-I operation.

BUCKET SELECTION
Hardware Overview
Bucket Selection is described in ref [7]. The system consists of three EPICS IOC nodes with a distributed sharedmemory [14]. Figure 1 is the schematic view of the Bucket
Selection nodes. Two IOC nodes are placed in the MR sideand the remaining one is placed at LINAC. Three nodes configure the loop-topology network with the dedicated opticalcables.
The RF-bucket of MR to be injected beam-pulse in thenext LINAC operation is selected by the node at Central
Control Building (CCB) in the MR side. The CCB nodecalculates the LINAC timing to fit with the selected RFbucket. The timing-information is transfered via the distributed shared memory and the LINAC node implements
the timing control for injection. This process is implemented
in every 20 ms.

Bunch Current Equalizing
Bucket Selection has the Bunch Current Equalizing (BCE)
mode. The bunch-currents become different since the beam
lifetime depends on the position of stored RF-bucket. In theBCE mode, we automatically select the RF-bucket with thelowest bunch-current for the next injection.
The decision on the next RF-bucket is made by two nodes
in the MR side. The node at D7 sub-control hall measuresindividual bunch-currents for the RF-buckets and put themthe beam gate1 . Therefore we developed two kinds of quick
close signals in the Bucket Selection network.
One is the beam-current limitation. The injection is immediately stopped by closing the beam gate when the current isexceeded the threshold. We set the threshold to both the total
beam-current and individual bunch-currents. The thresholdis necessary to protect the MR hardware.
We integrated quick close signal from the MR nodes to theLINAC node. It is processed when the bunch-current or total
current measured with the D7 node exceed the threshold.
The other is the BCE limit, which is implemented onlyin the BCE mode. We set the threshold in the number of
injections to individual RF-buckets and do not select one
exceeding the threshold even though it is with the lowest
bunch-current. This function is integrated to avoid the misoperation when the bunch current monitor cannot measurecorrect beam-current.
The BCE limit is useful also to know an imbalance in thelifetime among RF-buckets since BCE performs to inject theRF-bucket with short lifetime, more frequently. The alarm
message is popped up on the operation console when one of
RF-buckets achieves the threshold.
Two beam gate functions are quickly integrated during
the operation period. They can be carried out with the only
software upgrade since the complicated functions of Bucket
Selection are programmed in C language on the multifunctional hardware. The flexibility and expandability of Bucket
Selection are shown in these upgrades. They will be anadvantage in the phase-II operation.

EVENT TIMING SYSTEM
Hardware Overview

Figure 2: Performance of BCE: the bunch-current for the RFbucket at LER is shown before and after the BCE operation in(a) and (b), respectively. They are shown also as histogramsin (c) and (d). The r.m.s. of bunch-currents is 0.019 mA(before BCE) and 0.009 mA (after BCE).

into the distributed shared memory. Then the CCB node
selects the RF-bucket with the lowest bunch-current.
The performance of BCE is demonstrated in Figure 2. The
bunch-currents of LER around 11pm of March 1st, 2016 areshown. Even though we injected beam-pulses into individual
RF-buckets in the same number of times, the bunch-currents
became different as shown in Figures 2 (a) and (c). Then,
13 minutes after turning “ON” BCE, the bunch-currents
became equal as shown in Figures 2 (b) and (d).

Beam Gate Control
Two months after starting the phase-I operation, we received the requests to integrate the functions to quickly close

The configuration of Event Timing System for theSuperKEKB accelerators is described elsewhere [8–10].
The star-topology optical network is configured with EventGenerators (EVGs) and Event Receivers (EVRs). We normally utilize the MRF products, VME-EVG-230 and VMEEVR-230RF [15] for the EVG and EVR modules.
We build MR Sub-timing Station at CCB. It is configured
at one edge of Event network and manages the complicatedtiming-triggers for the MR components which are operated
on the injection timing.

MR Sub-timing StationFigure 3 is schematic view of MR Sub-timing Station. Weinstall the EVG and EVR modules produced by Shanghai
Institute of Applied Physics (SINAP). The SINAP-EVG canreceive upstream-Event directly and launch sequence-Events.
The set of SINAP-EVG and SINAP-EVR modules produces
15 kinds of outputs, in 50 Hz, with only one upstream-Eventfrom LINAC.
The SINAP-EVG eliminates the large timing-jitter of upstream events. This timing-jitter is produced through thelong distant (approximately 1 km) transportation of Event
1 This system controls the enable/disable of injection from the MR side.

Figure 3: Schematic view of MR Sub-timing Station: thegreen arrows indicate Event network. The Event from
LINAC Main Timing Station is divided and delivered to
EVG (SINAP) and EVR (MRF). Note, the EVG (SINAP)
can receive upstream-Event directly and launch sequenceEvents. EVRs (SINAP) are connected on the downstreamof EVG (SINAP).

between LINAC and MR. The MR’s RF clock is put into theSINAP-EVG so that events delivered from SINAP-EVG aresynchronized with it precisely. Therefore all outputs fromSINAP-EVR are synchronized with this RF clock and its
precision is to be ∼10 ps. Figure 4 shows the timing-jitterof output triggers from MR Sub-timing Station. Note, thisprecision is same level as both that measured at the test studyfor SINAP modules [16] and that of MRF Event modules.
Of course, the output triggers from SINAP-EVR are synchronized also with the injection-timing to which Bucket
Selection is considered.
VME-EVR-230RF is installed for receiving data buffer
and for the time synchronization with LINAC in the futureoperation.

Pre-trigger for Septum Magnets
One of the most important roles of MR Sub-timing Station is the production of the pre-triggers for the septummagnets. The pre-trigger is launched different way fromother injection-triggers. For the operation of septum magnets, the pre-trigger must be delivered on 18 ms earlier fromthe main injection-trigger. As we has already described, MR
Sub-timing Station is operated by the upstream-Event in
50 Hz. So the pre-trigger is produced in one pulse previous
operation with one pulse previous upstream-Event.
Figure 5 is the schematic view to explain the timing relation between the pre-trigger and main injection-triggerof septum magnet. For compensate the difference in thetiming for Bucket Selection, we set the delay, Dpre , on thepre-trigger output of SINAP-EVR. It is calculated with following formula:
Dpre = Dmain1 − Dmain0 + 2 ms

(1)

where Dmain0 (Dmain1 ) is the delay scheduled on the EVG at
LINAC Main Timing Station when we launch pre-trigger

Figure 4: Timing precision of output trigger from SINAPEVR: the result of only one channel are shown here as a
example. The jitter of all output triggers from SINAP-EVR
are around 10 ps. The output triggers are synchronized withboth the injection-timing and the MR’s RF clock.

(main injection-trigger). They are determined to fit injectiontiming with the RF-bucket selected by Bucket Selection on
the individual injection-pulses. The timings of upstreamEvents have already included these delays.
The Dpre is calculated and deliver from the EVG at LINAC
Main Timing Station. The MR Sub-timing Station receives
it with the VME-EVR-230RF module via the data buffertransportation.
The successful production of pre-triggers during thephase-I operation shows the good feasibility of upgrades
which we plan for more complicated injection control in
the phase-II operation. There are two thing to note in theproduction of pre-trigger.
One is the timing relation between the pre-trigger andmain injection-trigger. They are produced in the different
upstream pulses with different delays for Bucket Selection.
However we produce the precise time interval of 18 ms
thanks to the new Event Timing System of SuperKEKB[8–10]. We developed the new LINAC EVG IOC to schedule delays for coming several injections and it will be neededfor damping ring operation.
The other is the data buffer transportation of Event Timing System. This brand-new technology will be utilized inthe future operation at LINAC. We will control the individual phases of RF cavities in 50 Hz with the data buffertransportation.

CONCLUSION
The injection control system is successfully operated during the phase-I of SuperKEKB. Bucket Selection and theEvent Timing System are the key hardware for the injection
control. They have their own network to robustly communicate among the distant EPICS IOCs.
The Bucket Selection system well manage the MR RFbucket to be injected the LINAC beam-pulse. The individual

REFERENCES[1] Y. Ohnishi, et al., “Accelerator design at SuperKEKB”,
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Figure 5: Schematic view of relation between the pre-trigger
and main injection-trigger of septum magnet: for example,“P1” and “M1” indicate the timing of pre-trigger and main
injection-trigger which are a pair for one injection. The pretrigger is launched on one pulse before with an additional
delay, Dpre .
bunch-currents of RF-buckets are properly equalized in theBCE mode. The flexibility and expandability of Bucket
Selection are well shown through the quick upgrades during
the operation period.
The timing control at LINAC is implemented by the EventTiming System. The main Event IOC at LINAC Main Timing Station receives timing information via Bucket Selection
and set it into EVGs. MR Sub-timing Station is configured
on one downstream edge of Event network in the MR side.
The 15 kinds of triggers including the pre-triggers for theseptum magnets are produced with only one upstream-Event
from LINAC. The pre-triggers are successfully deliveredon 18 ms earlier from the main injection-triggers. The data
buffer transportation of Event Timing System is performed
from EVG at LINAC to EVR at MR Sub-timing Station.
Above mentioned systems work certainly and stably during the phase-I operation. We finally deliver integrated
beam-currents of 662 Ah and 776 Ah to HER and LER, respectively. Also they show their capabilities become goodadvantages for the phase-II operation.

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