WEPP24

SuperKEKBにおけるイベントシステム診断
The Fault Analysis of Timing System in SuperKEKBワン

デイ王 迪（総研大 加速器科学），佐藤 政則，古川 和朗，梶 裕志，杉村 仁志（高エネルギー加速器研究機構）

要旨

The high availability of an accelerator timing system is of great significance for the operation of theSuperKEKB electron-positron collider. To distribute the high precision level trigger signals for synchronizing
all the relevant components in the accelerator complex, event based timing system is utilized to control
the injection procedure in SuperKEKB. Another critical challenge of the timing system is to control thebucket selection of both electron and positron beam bunch. The failure in timing system would definitely
affect other systems like pulsed magnet, BPM and so on, and as a consequence leading an unfavorable
impact on the effectiveness of the particles collide. Additionally, a newly built positron damping ringdecrease the positron emittance but meanwhile brings higher complexity of the bucket selection. In thispaper, we will demonstrate the algorithm of the timing system and introduce our fault analysis system
which helps up to analyze the timing error, improve the accelerator operation stability.
PASJ2020 WEPP24, D. Wang – 1/7

Timing System in SuperKEKB
Event Generator(EVG)

Event Receiver

Event Receiver

Event Receiver•••4 (+1) rings
10 beam modes (5 for normal operation 5 for beam study)
Positron has three injection options in one pulse:• to DR only (upstream)• DR to MR only (downstream)• bothEvent Receiver

20 ms 50 Hz

HER 7 GeV e-

PF 2.5 GeV e-

LER 4 GeV e+ upstream

PF-AR 6.5 GeV e-

LER 4 GeV e+ downstream

PASJ2020 WEPP24, D. Wang – 2/7

Two EVGs are needed to distribute eventcodes to the accelerator

Bucket Selection• Beam should be injected into the ring RF bucket make sure that the particle always sees an accelerating voltage at RF cavities.
• Define the bucket number `0` as the first bunch which extracts from DR and injects to the MR.
RF Bucket• i.e. by delaying 96.3 ns, we could inject the bunch into DR bucket 49 and MR bucket 49.

𝐵𝐾𝑇𝐷𝑅 = 𝐼𝑛𝑗𝑡𝑢𝑟𝑛 ∗ 49 % 230
0 = 230 ∗ 49 % 230
Injection
opportunity

DelayDRBucket

MRBucket

00 ns

001

96.3 ns4949

2192.6 ns

98

98

3288.9 ns

147

147

4385.1 ns

196

196

5481.4 ns

15245

…

…

…

…

230

22.1 us

01030

…

…

…

…

5120

492.9 us

180

0

…

…

…

…

20771

1.99 ms

29

4019

20772

2 ms

784068…

…

…

…

117,760

11.34 ms00

𝐵𝐾𝑇𝑀𝑅 = 𝐼𝑛𝑗𝑡𝑢𝑟𝑛 ∗ 49 % 5120
1030 = 230 ∗ 49 % 5120
Bucket Selection

MR RF: 508.9 MHz

96 ns (49 buckets)
DR RF: 508.9 MHz

5120
buckets
230
buckets
LINAC RF: 2856 MHz

Positron

DR + MR : 5120 × 96 x 23 = 11.34 ms

MR only : 5120 × 96
= 493 µs

Bunch needs to circle many turns (40 ~ 200 ms) in the DR!
40 ms is the minimal damping period.

For example:
0 = 117760 ∗ 49 % 230

0 = 117760 ∗ 49 % 5120

PASJ2020 WEPP24, D. Wang – 3/7

Other Restrictions••••

Besides the RF frequency synchronization and bucket
selection, other restriction exists too.
The injection opportunity to the same ring bucket
appears every 493 us, so there are 4 opportunities
during 20 ms.
Owing to the hardware requirement (klystron
modulator), we choose the opportunity which is closest
to the AC Power Line (a.k.a. AC50).
Owing to the requirement of the kicker magnet at DR,
only 2 ms fluctuation is allowed for injection. As aconsequence, not all MR bucket can be selected forpositron. The solution by shifting the LINAC RF
frequency to increase the extraction opportunity iscurrently under experiment.
> 100 ns

Oldbunches
at DRExtraction
kickerSuper-period
trigger Npulse = 0

Npulse = 1

Npulse = 2

Npulse = 3

20 ms

20 ms

20 ms

20 ms

Ttotal2

Ttotal1
edelayDamping
period

TEVG1

TEVG2

Newly injectedbunches
Electroninjection

96 ns

DR Injection
AC power line96 ns••

Injectionkicker•

DR Ejection
AC power line

Using Ttotal2 and Ttotal1 to calculate TEVG2 and TEVG1.
TEVG1 and TEVG2 are calculated at the same time but
TEVG2 value is buffered while TEVG1 is sent out
immediately.
Injection should happen near the AC power line.

Some buckets in DR cannot be injected
PASJ2020 WEPP24, D. Wang – 4/7

Timing System Failure Mode

Injection pattern switch
Bunch is still in the DR

HER 7 GeV e-LER 4 GeV e+ downstream

LER 4 GeV e+ upstream••• At pulse t1, the bunch was lost• At pulse t5, the bunch was not extracted from Damping Ring

Beam Gate which controls the gun should close
during injection pattern switch.
Besides the pattern switch, the drift of AC powerline might also cause error.

PASJ2020 WEPP24, D. Wang – 5/7

Timing System Failure
EVG IOC restarted.
Error: when 2 pulses’interval > 22 ms or < 18ms

Since beam repetition rate is 50Hz, the interval
between two pulse should be within 18 ~ 22ms.
Experiment

From 2020-04-01 to 2020-07-02
For better visualization, some kinds of interval
error are omitted.
Average error times per day: 64.80

AC Power Line always fluctuates and if the fluctuation is
sharply timing system might fail to find the injection point.
Right picture: From 2020-01-17 to 2020-07-06
Only edge AC50 values existing days are listed.
Risk AC50 value happens times per day: 21.92

PASJ2020 WEPP24, D. Wang – 6/7

Timing System Monitoring Plan
Contains 2085 EPICS PVs

Event Timing System
Timing System Monitor

MetricPerformance
Alarm

Error Alarm

iocStats/vxStats

Notification
MethodOperationLog

Mail listHeartbeat

MetricVisualize

LogsCritical Data
Analytics

Dashboard(Kibana/Grafana)
Event
CodeAC50

PASJ2020 WEPP24, D. Wang – 7/7

Documentation

Archiver

Reflective
MemoryCheat sheet

BeamGate

BucketSelection

Data Flow

Memo