Upgrade of Event Timing Systemat SuperKEKB
H. Kaji, K. Furukawa, M. Iwasaki, E. Kikutani, T. Kobayashi,
F. Miyahara, T.T. Nakamura, M. Suetake, M. Tobiyama(KEK, Japan)

T. Okazaki(East Japan Institute of Technology Co., Ltd, Japan)

T. Kudo, S. Kusano(Mitsubishi Electric System & Service Co., Ltd, Japan)

2SuperKEKBSuperKEKB at KEK- an electron-positron collider- center of mass energy: 10.58GeV, Υ(4S) resonance- upgrade of KEKB
- will start commissioning in early 2015.

Belle-IIMain Ring

Designed luminosity: 8x1035 cm–2s–1- 40 times larger luminosity than the KEKB achievement(Note, KEKB achieved the world’s largest lunimosity for colliders.)- Enhancement strategy consists of
2 times larger storage beam current
20 times smaller vertical beta function at interaction point
Requirements to Injector Linac- storage beam current at Main Ring (MRs):- Low emittance beam:Damping
Ring (New)doubledNeed Damping Ring (DR) for positrons

Electron beam

Positron beam

KEKBSuperKEKBKEKBSuperKEKB

Energy

8 GeV

7 GeV

3.5 GeV

4 GeV

Beam current

1.64 A

3.6 A1.19 A

2.6 Ax2

Injector
Linacx2More sophisticatedinjection control is needed.

3Requirements to Injection Control
Injector Linac provides beams into 4 rings.

Injection control needs to bemore efficient and complicated at SuperKEKB.

Top-up injection more complicated- change rate of Linac parameters: typically 50Hz.
- number of top-up rings: 3 rings ⇒ 4 rings

Storage beam current at MRs more efficient- doubled from KEKB
- beam lifetime: a few tens of min ⇒ 5min
DR for positrons more complicated- makes injection scheme complicated- affects Ring Selection and Bucket Selection(they are described more detailed in the later slides.)4Ring Selection
Linacarbitrates requests from individual rings and schedules the injection process.
performs injections by changing the injection ring in 50Hz.
They are needed for the top-up injection into more than one ring.

The Event Timing System is used to change more than 150 of Linac parameters in 50Hz.

Following new functions are neededfor the Event Timing System at SuperKEKB.
The sequence must be longer than 20ms, one
injection period in 50Hz since injection process of
positrons extend 20ms.
Positrons are stored at DR for at least 40ms.
The programming of sequence needs to know
long-term schedule since DR storage time depends
on injection rate of positrons.
Two sequence can be run in parallel since morethan one injection processes are implemented inparallel.
- Electrons are injected during positron damping.
- The 1st and 2nd halves of Linac work separately.

5Bucket Selection
The injection RF-bucket of ring is selected by using the delay time.
- In each 20ms period, injection process is synchronized with the reference signal.
- Individual rings have the reference signal which is made from the revolution.
- In case of MRs, we controlled this delay time to select the targeting RF-bucket.
- The delay time of 0 – 493ms in the unit of 96.3ns.
MR（5120 bucket）

508.9MHz

Linac/BT
RF:2856MHz

Injection timing of MR
decides injection RF-bucket.

6Bucket Selection at SuperKEKB
The injection RF-bucket of ring is selected by using the delay time.
- In each 20ms period, injection process is synchronized with the reference signal.
- Individual rings have the reference signal which is made from the revolution.
- In case of MRs, we controlled this delay time to select the targeting RF-bucket.
- The delay time of 0 – 493ms in the unit of 96.3ns.
Extraction timing of DR and injection timing of MR
must be synchronized.
⇒ Bucket Selection for DR also needed.

MR（5120 bucket）

508.9MHzDR（230 bucket）
508.9 MHz
Extraction timing
Linac/BT
RF:2856MHz

We choose harmonic number of
230 so that 23 kinds of combination
between DR and MR are made.

Injection timing of MR
decides injection RF-bucket.

The delay time of 0 – 11.34ms (=493ms×23)
is needed when we control both DR-bucket
and MR-bucket with the same method.

7

New requirements to Event Timing System
Mostly for positrons injection via DR

Top-up injection into 4 rings⇒ Small change of trigger configuration, skip today

The sequence becomes longer than one injection period.
The programming of sequence needs to know long-term schedule.
⇒ or long-term sequence should be programmed in advance.
Two sequence can be run in parallel.
Bucket Selection for positrons needs the 11.34ms cycle ofreference signal and the delay time, 0 – 11.34ms.
⇒ Difficulty is in the synchronization
between master 50Hz trigger and the reference signal.

The new configuration of Event Timing System is developed.

8Event Timing System at SuperKEKB
AC 50Hz
coincidence TTL(<50Hz)11.34ms cycle

EVG

DR・MR
Lower-layer EVGs

Event in 50Hz

Upper-layer EVG- receives coincidence trigger ofmaster 50Hz and 11.34ms cycle.
every a few second.
- generates “Event” in 50Hz.
- Event becomes injection trigger.

EVR

PF-ARPF- deliver “Event” to local devices- add the delay time for Bucket
Selection.
- Relation between individualtriggers and 11.34ms cycle isprecisely controlled by upper-EVG.

PF-AR
PF

EVG

EVG

SH_A1
KL_B5/B6

SB_B

Injection

SB_A

e− GunARC

Cont-ABC
SB_C

KL_51/52

SB_1

SB_2

SB_3

SB_4

SB_5

e– BT (PF: 2.5GeV, 0.2nC)

e– BT (PF-AR: 6.5GeV, 5nC)
e+ BT (SuperKEKB: 4GeV, 4nC)

e+ Targete– BT (SuperKEKB: 7GeV, 5nC)
Cont-1

Cont-2

Cont-3Cont-4

EVRs

Cont-5

9Feasibility study
Followings are key elements for our new configuration:
Two-layers of EVGs configuration
operation with long term, a few seconds, sequence
Their feasibilities are studied. The accuracy of output should be O(100)ps.

Two layers EVGs are configured for feasibility
test.
EVGs are synchronized with 114.24MHz clock.
Timing of output TTL is tested as a referenceof 114.24MHz clock.
Oscilloscope with equivalent time sampling isused for measurement accuracy < 1ps.

After collecting 1000 samples,timing and its jitter is determined fromcenter value and standard deviation ofdistribution.

10Sequence length
Upper-layer EVG is operated with long-term sequence and send an Event at theend of sequence.
The output of lower-layer EVG is tested.

The jitter is always to be ~10ps.
There is no significant difference in the length of sequence.

11Long term stability
The test setup is operated for 5 days continuously.
The timing and jitter are determined in every one-minute.

Timing of output TTL is clearlycorrelated with room temperature.

Magnitude of timing
drift is determined fromslope to be 18.00±0.16ps.

We found out there is correlation between timing and room temperature.

However It is no problem when we can control room temperature
within 1 degree by using air conditioning.

12Conclusion
The injection control becomes complicated at SuperKEKB.
- Number of top-up injection ring: 3 ⇒ 4.
- More than one process are implemented in parallel.
- 1st and 2nd halves of Linac are operated separately in case of positrons.
The Event Timing System is upgraded.
- Two-layers of EVGs are configured at Main Trigger Station.
- Upper-layer EVG generates 50Hz injection trigger.
- Lower-layer EVG add the delay time for Bucket Selection.

The feasibility study for new configuration is carried out.
- The timing accuracy of output trigger is to be ~10ps.
Long-term stability is tested.
- The timing drift of 18ps/degree is observed.
- It is no problem when we can control room temperature within 1 degree.
Above results satisfies the required accuracy of O(100)ps.
We conclude the new configuration is no problem for SuperKEKB.