INJECTION AND EXTRACTION TIMING CONTROLSAT SuperKEKB 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
SuperKEKB project aims at the world highest luminosity
to 8 × 1035 cm−2 s−1 . To achieve the luminosity, a lot ofequipment was newly constructed or upgraded. Especially, aDamping Ring (DR) was newly constructed at the middle ofthe injector linac for making lower positron emittance. TheDR timing control system was also fabricated as a branchof the main SuperKEKB timing system. The synchronizedtiming is generated at the main timing system. It is received
at DR sub-timing station and is distributed to the end ofsome equipment, Kicker, Septum, and monitoring devices.
We succeeded to generate not only synchronized timing
but also beam control information such as beam gate for trigger inhibit signal and injection and extraction timing "value"
via data buffer delivery. By using this method, accelerator
operation became more convenient system.

state is needed to occupy different bucket, different timing information is needed. Therefore, damping ring timing system
has two timing receiver for injection control and extraction
control.

TIMING CONTROLAT THE DAMPING RING
Overview
The timing signal is generated and controlled at SuperKEKB main timing station at injector linac [2, 3]. The
timing is distributed to all over the SuperKEKB accelerator
timing receiver with the fiber-optic cables. The DR timing
system is its branch of the main timing system. Figure 1
is the picture of DR timing system. It is fabricated in one

INTRODUCTION
SuperKEKB accelerator is electron-positron collider for
high-energy physics experiment [1]. Electron and positron
are stored in High Energy Ring (HER) and Low Energy
Ring (LER) at the energy of 7 GeV and 4 GeV, respectively.
To overcome the luminosity of previous KEKB project, aDamping Ring (DR) has constructed to provide low emittance positron to LER. The specification of DR is listed inthe Table 1.
Table 1: Key Parameters of Damping Ring
Parameters

ValueUnitEnergy
Repetition frequency
Circumference
RF frequency
Harmonic Number
No. of bunch trains
No. of bunches / train

1.150
135.5
508.9
23022GeVHzmMHz

The positron beam is accelerated to 1.1 GeV in the injector linac, and delivered to the DR through beam transportline. The DR stores the positron beam during 40 ms which
is an essential damping time to make low-emittance. On theother hand, since the maximum injection repetition is 50 Hz,
it is necessary to simultaneously control three kinds of statesof injection, extraction, and storage. However, since each∗ hitoshi.sugimura@kek.jp

Figure 1: The picture of Damping Ring Timing System.
VME crate, and consists of a controller, a device monitor(RAS), two timing receivers and a time to digital converter(TDC). We use MVME5500 on-board CPU controller andVxWorks-6.8.3 is working on the board. The RAS monitors
power voltage and temperature, and is controlled by serial
port connection. As the timing receiver, we use Event Receiver (VME-EVR-230RF) developed by Micro Research
Finland [4]. The TDC is originally developed to monitor thetiming whether it is generating at an appropriate timing [5].

All the generated timings are distributed to TDC and eachdevice.
The timing system receives timing as a digitized 8-bit"event code" with fiber-optic cable, then generate the trigger
when suitable event code is received. So, we call the system"event timing system". Application software is developed
as EPICS device support [6].

Beam Gate Control
We integrated Beam Gate control system to event timing
system by using "distributed bus bit" [7]. The distributed
bus bit is one of the function of MRF event timing moduleand it can be transferred 8 types of bit information simultaneously. By using this function, we can change beam gate
status faster than EPICS process and control each device
independently. When the beam gate status is changed, thesignal is input to Event Generator (EVG). The EVG sends
it to EVRs at different timing for each device. EVR change
trigger enable or disable status according to distributed bus
bit status. This method made it possible to control injection
only or extraction only mode. The greatest benefit was thatthe hardware can be done with no changes.

Pre-Trigger Generation
The kicker magnet of DR is needed to supply not only discharged trigger but also charged trigger, and charging timemust be kept at 12 ms. In the operation of 2017, charged trigger for kicker magnet (we call it "pre-trigger") was not able
to generate at EVG. Therefore, DR timing system is uniquely
set delay timing by receiving appropriate pre-trigger timing
as a "delay value" via data buffer. The data buffer function isalready equipped in the MRF timing system. It is also used
to send bucket number and shot number information and soon. The delay value for pre-trigger is sent before two shotof discharged trigger then set the value. This method could
be kept fixed charged time in spite of fluctuated timing ofbucket selection. The detail algorithm is described in [8].

Manual Extraction System
In the normal operation mode controlled by bucket selection algorithm, the extraction timing at DR is already calculated before its positron’s injection timing. However, after
unforeseen abort in the Main Ring happen, extraction cannot
be controlled by the bucket selection algorithm. Same situation also happens after dispersion measurement there. To
solve this situation, we developed manual extraction system.
Bucket No.
DR RFDR Revolution

ManualExtraction
SystemSeptumcharge
discharge

KickerFigure 2: Schematic view of the manual extraction system.
Figure 2 shows schematic view of the manual extraction
system. The system counts RF clock of the DR. The fre-quency is 508.89 MHz which is the same frequency of theMain Ring. Furthermore, the system has input of revolutionof the DR. It is the starting point of the bucket number-0. If
the charging time is set, the pre-trigger is first issued. Then,after waiting charging time, the main trigger is generated.
Since the main trigger timing has to depend on the storedpositron bucket number, the system gives delay according tothe number. When the extraction bucket number-N is set via
epics process, the system counts N clocks from revolution
timing, then generate trigger.

SYSTEM OPERATION IN
SuperKEKB PHASE-2
SuperKEKB Phase-2 project was started operation fromMarch 2018 and finished July 2018. Before the project, DR
standalone operation has been done for a month. We tried
to operate beam handling with this timing system. There
was no major problem throughout. But to say a little bit, atthe beginning of the operation, the charged trigger duration
for kicker magnet was fluctuated and sometimes the magnet
generates alarm information. This was because the timing
calculation is initialized when the operation setting changed.
At that time, wrong value of the delay timing was set atEVRs. To solve this problem, we changed output generation
to disable mode during operation setting change.

SUMMARY AND OUTLOOKWe developed timing control system at Damping Ring.
There are three characteristic control components, the first is
we integrated beam gate control to event timing system withdistributed bus bit. It became useful function by separating
injection and extraction control. Since it became unnecessary additional cable connection, the hardware component
became simple structure. Furthermore, beam gate control isable to operate more quickly than EPICS process.
The second is we constructed pre-trigger generation algorithm in the EVRs by using data buffer function of event
timing system. The kicker magnet is need 12 ms to charge
condenser with precise timing. So, pre-trigger is additionally generated at EVRs. The pre-trigger setting value is sentfrom EVG, and set delay in previous shot. The system could
be kept fixed charging time for Kicker magnet.
The last is we developed manual extraction system. Extraction would be done in the bucket selection calculationin the normal. However, after some optics measurements oroccurred irregular abort in Main Ring, manual extraction
system manages trigger signal to deliver to each device bysetting stored beam bucket number.
The DR operation was successfully finished with no serious event timing problems. Phase-3 project is scheduled tostart in spring 2019 to attempt to update the world highest
luminosity record and obtain new particle physics eventsby Belle2 experiment [9]. We will prepare to ensure morestable operation than phase-2 operation.

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