SYNCHRONIZED TIMING AND CONTROL SYSTEM CONSTRUCTION
OF SUPERKEKB POSITRON DAMPING RING
H. Sugimura∗ , K. Furukawa, H. Kaji, Y. Ohnishi, M. Satoh, F. Miyahara, S. Sasaki, T. Nakamura
KEK, Tsukuba, Japan
Table 1: Parameters of the Damping RingAbstract
A KEK electron/positron injector linac delivers beams forparticle physics and photon science experiments. A damping ring has been constructed at the middle of the linac togenerate a positron beam with sufficiently low emittance andto support 40 times higher luminosity in the SuperKEKBasymmetric collider than the previous project of KEKB. A
timing and control system at the damping ring has been
constructed to enable the timing synchronization and beam
bucket selection among the linac, the positron damping ringand the SuperKEKB main ring. It should manage precise
timing down to several picoseconds for the beam energy andbunch compression systems. Besides precise timing controls to inject and extract positron beams, it has to meet local
analysis requirements owing to measure beam properties
with changing RF frequency. The timing control system isconstructed with MRF modules.

Parameters

Value

Unit

EnergyRepetition frequency
LengthRF frequency
Harmonic Number
Number of bunches
Bunch spacing

1.150
135.5
508.9
230
296GeVHzmMHz

time of Kicker magnets. Ideal bunch position is shown inFig.2.
96ns>100nsINTRODUCTION
SuperKEKB, electron/positron assynmetric collider, isbeing constructed for flavour physics experiment of elementary particles. It aims at a luminosity of 8×1035 cm−2 s−1 , 40
times higher than that of previous KEKB project by squeezing the beams at the collision point. To achive this luminosity, a Damping Ring(DR) was constructed for making lower
emmitance positron beams. It is located at the middle of theinjector Linac as shown in Fig.1. The main beam parameters
are listed in Table1.

ns>100ns
96ns

Figure 2: The storage configuration of 2-bunch, 2-pulse atDamping Ring

EVENT TIMING CONTROL SYSTEM
Overview

Figure 1: SuperKEKB Accelerator

The emmittance of positron beam is gone down to 92 µm
at DR in the case of strage time of 40 ms. The DR canaccumlate 2-pulses × 2-bunches, and need to keep morethan 100 ns between pulses because of rising and falling∗ hitoshi.sugimura@kek.jp

The control system of injector linac is required very complex system to operate such a several rings (SuperKEKB
electron/positron ring and two light source rings) with several parameters. One of the important technologies is Pulseto-Pulse Modulation (PPM). The PPM enables to inject simultaneously the top-up filling operation to four rings. To
identify which ring will be injected, Event Timing Control
system is introduced. This system delivers not only timing
signal but also PPM information as an "Event" to beam linedevices. We introduced event timing system produced by
MRF [1] company to satisfy our requirement. MRF’s event
timing system consists of an “Event Generator (VME-EVG230)” and an “Event Receiver (VME-EVR-230RF)”. The
protocol is based on 8B10B encoded characters. 2 byte ofcharacters are transmitted to EVR on event clock cycle. Theevent clock cycle is used with 114.24 MHz RF frequency.
The first encoded byte is an event code and the second encoded byte is shared by the distributed bus and synchronousdata buffer. The system is worked on EPICS [2] IOC in
the version of 3.14.12, and operated with the device/driver
version of mrfioc2.
The event distribution system was constructed at Main
Timing Station, Linac. It is a master brain of event andtiming generation, and manages injection pattern and bucket
selection system. A schematic diagram at Main Timing
Station is shown in Fig.3.

measure beam properties with changing RF frequency. The
schematic diagram is shown in Fig.4.
erpre-trigg

SeptumEVR

monitor
DelayLogic

DR RF

monitorer
pre-trigg

114 MHz RFPF
PF-ARDR Injection Timing

EVGEVGKicker

DR Extraction Timing
SeptumEVR

114 MHz RFrev/49/23

Kicker

DR Injection Timingmonitor(DR toLinac)

EVR
114 MHz RFPF-ARPF

DR Extraction Timing

EVG

Figure 4: Event Timing System at DR

Figure 3: Event Timing System at Main Timing Station

Event timing system at Main Timing Station is configured with two-layer delivery. Upper EVG-EVR couples arefunctioned with the division of MR revolution which indicates original starting point of bucket number of DR andMR. Lower EVGs generate timings with bucket selection
delay by using base timing information received from upper
EVR. The EVGs generate it for injection or extraction timingfor DR, respectively. In addition to DR timing, the EVGs
manage the timing for two light sources, PF and PF-AR by
putting into extra input. These timings are selected in an
IOC according to injection pattern and send to each rings.

Pre-Trigger Algorithm
The kicker magnet is the most important devices to inject and extract positron beam among linac and rings. it
is required to generate “charging start timing” 15 ms before injection or extraction timing (main trigger). We arecalling “pre-trigger“ as chaging start timing. Since it is difficult to generate pre-trigger timing from EVG due to outof generation sequence of 50 Hz repetition, the pre-trigger
is originally made by EVRs at DR. The detailed pre-trigger
generation logic is shown in Fig.5.

Bucket selection system

Dmain [n-2]D pr eDmain [n-1]D pr epretriggate

Shot#nD pr e

EVR

20ms

Shot#n − 1

Pre2The event signal which is generated at Main Timing Station is delivered to Linac devices and sub Timing Station at
DR and MR. The event timing system at sub Timing Stationat MR is already reported [4] The sub Timing Station at
DR is newly constructed to distribute timing signal to somedevices in DR. The two event timings for injection and extraction are received at sub timing station at DR. One of theimportant timing is discharged trigger for extraction kicker
magnets. It is sensitive to increase beam jitter. Therefore,
it is required to jitter less than nanosecond. Besides precise timing, it has to meet local analysis requiments due to20ms

Shot#n − 2EVG

D pr eSub Timing Station at DR

Figure 5: Pre-trigger generation logic

Pre2

The bucket selection makes it possible to put the beamin which the RF buckets in the ring, that is different RF frequency between Linac (2856 MHz) and DR (508.9 MHz).
The chance of injection or extraction timing turns up in
10.38 MHz (96 ns, 49 buckets duration) which value iscalculated by common frequency between 2856 MHz and508.9 MHz. The number of injection timing is 230 whichis harmonic number of the Damping Ring. Furthermore, it
becomes 5120 × 23 pattern timing including the harmonic
number of the Main Ring. The bucket selection delay is calculated on IOC at Main Timing Station and is set on lower
EVGs each 96 ns steps [3].

tt

15ms
Dmain [n]pre-trigger

main-trigger

At first, the EVG generates “pre” and “pre-pre” timing toinform which event code will be send in the next and nextnext sequence, respectively. The EVR makes pre-trigger
generation gate with this “pre-pre” timing. When the EVR
receives “pre-pre” timing for positron beam, it opens software gate for pre-trigger generation. Then, the gate closes at“pre-pre” timing for non-positron beam. This algorithm isable to avoid blank firing in the Kicker magnets. Next, theEVG sends data buffer including shotID, bucket selection
delay, RF phase and so on. The EVR makes pre-trigger timing with data buffer information. If shot#n will be generate
positron main timing, EVR has to receive the information of
pre-trigger generation timing at shot#n-2. If we would liketo make pre-trigger 15 ms before at shot#n, the generation

timing (D pr e ) could calculate in following formula:
D pr e = Dmain[n] − Dmain[n−1] + 5 ms(1)where Dmain[n] is the bucket selection delay value scheduledon the EVG. The value of D pr e is calculated on the EVG
and send with data buffer. The EVR receive the delay andset it at shot#n-2 sequence. The pre-trigger generates atshot#n-1 sequence with the delay of D pr e . In this algorithm,
we succeeded to make precise pre-trigger timing in EVR.
We also checked trigger jitter in timing system. According
to MRF’s original specification [1], timing jitter is 15 ps.
However, the real operation includes RF jitter, cable jitterand so on. Therefore, we tested jitter including these devices.
Figure 6 shows timing jitter of output trigger.

The output trigger is synchronized with RF clock at DR.
The jitter value was measured to be about 30 ps. The result
was sufficiently small value and doesn’t influence on beamjitter at Kicker magnet.

REFERENCES[1] MRF website:
http://www.mrf.fi/index.php/vme-products[2] EPICS website:
http://www.aps.anl.gov/epics[3] H. Kaji et al., Bucket selection system for SuperKEKB, Proceedings of 12th Annual Meeting of PASJ, THP100.
[4] H. Kaji et al., Injection control system for the SuperKEKB
Phase-I operation, Proceedings of 13th Annual Meeting ofPASJ, TUP092.

Figure 6: Timing precision of output trigger from EVR