Beam Abort Diagnosis
H.Ikeda2022/10/31 BPAC

1

Contents
How can we protect the hardware components of the detector and theaccelerator from the damage caused at high beam currents ?

↓1.

Abort the beam as soon as possible when the abnormal situation happen.
2.

Improve Abort System

Investigate the cause of abnormalities in the beam and deal with them.


Abort diagnosis especially for Sudden Beam Loss2

1. Abort System
 In order to protect the hardware components against the high beam currents, weinstalled the controlled abort system.

 The beam is kicked by an abort kicker, taken out of the vacuum chamber through an

abort window made of Ti, and throwed into a beam dump.

 Dumped beam length : one revolution time (10 μs).
 Build-up time of the abort kicker magnet : 200 ns (empty bucket space).
 Synchronization of the kicker timing and the abort gap is required for theprotection of hardware.

3

Dump

Loss Monitor System
•
•

•
•

Measure the beam loss
Used for• triggering the beam abort kicker• tuning and analysis of the beam
operation
No. of Sensors : 200
Ion Chamber: Cover a wide range inspace.
•••

IP(Belle)

Trigger generation time for beamabort in integrator : <2μs

Optical Fiber ←New!

e+

Overview of SuperKEKB LM

Oh
o

Nik
o

PIN photo diode: Fast response andidentify the ring in which the beamloss occurred.
••

Put to cable lack of all over the tunnel
to cover a wide range in space.
Free Air Ion Chamber (20D co-axial
cable )

e-Sensor: IC, PIN
Monitor: ADC, data logger: Experimental Hall

CCR

eFuj
i

e+
4

: Local Control Room
: Data Logger: RF
Station: Collimator: Ion Chamber: Loss Monitor Signal: Abort Request Signal

Abort Trigger Delays

We minimized abort trigger time to protect the hardware damage.

Beam Abort
requesta failure is detected…

Devicerequests
Abort

Beam Interlock system
Processt1

Depends on the optical cable
length from the local control
room to CCR.

All bunches
are aborted
max 10μs

3μs～8μst2

To summarize the abort
request on the beam abortsystem.

Kicker fired

Beam Dumping
System waiting
for beam abort gap

2 ~10 μs

> ~2μsHardware dependent

earliest abort
request arrival to
CCR

t3

t4

Synchronization of the abort request signal withrevolution/2 in FPGA.:Max delay=5μs
Delay to synchronize to the abort gap(fixed delay) : ～0μs
Delay from CCR to kicker (400m) : 2μs
Thyratron ON :1μs
5
Rise time for the kicker : 200ns

Minimum Abort Delay = 17～30μs

Minimize “Abort Trigger Delays”
Introduced the injection veto system to PIN beam loss monitor for collimator to set
lower threshold and the abort trigger can be issued quickly.

Changed the signal route of the loss monitor installed at the downstream of one
collimator that frequently issues abort triggers.→the abort trigger can be sent out
earlier.



Introduced new loss monitor near the abort kicker.

minimized delay to synchronize to the abort gap.
 removed unnecessary fixed delays
 increased the abort gap in the beam train from one to two.

6

New sensor : Optical fiber The cause of the beam loss is unknown, but when
the loss occurs, abort requested from the LM ofdownstream of collimator, Belle diamond, CLAWS,
and also RF arc sensor.
 Since the loss monitor signal is sent to five LCRs
around the ring, the cable length is not the shortest.
 In order to send abort signals at the minimum
distance, a optical fiber was laid from the D6 power
supply building to D6V2. After that, a single opticalfiber is connected and extended upstream anddownstream.
 The cable is input to PMT module and converted toelectrical signals.
 Capture/save waveform data Trigger output by event detection (abort
trigger)
Beam Dump
BOR/BCM
LiberaD1

TL

筑波 TR D2

12C
D01H5
D02H4 (TR14)D02H2 (TR120)(TL18)
D02H3 (TR67)D02H1 (TR142)
D01H4 (TL34) D02V1 (TR80)
D03V1 (TR300)
D01H3 (TL47)
D03H1 (OL352)
D01V1 (TL60)

D12V4(NR354)

D11
NR

D12H4
(NR307)
D12V3 (NR285)
D12H3 (NR274)
D12H2 (NR236)
D12V2 (NR209)
D12H1 (NR199)
D12V1 (NR134)

3C

D4 D4RF
H
G
大穂 F
OL
赤:LER
青:HER

日光

D5RF
A
B
D5 C
D
E
F

NL

OR

D10

9C

D09V4 (NL156)
D09H4 (NL203)
D09V3 (NL232)
D09H3 (NL236)
D09H2
D09H1 (NL307)(NL279)D09V2 (FR354)

D06V2(OR271)

QF4P21 D06V1 (FL362)

D09V1 (FR209)

D8

FR

D06H3 (FL276)
D06H1 (FL200)
7

富士 FL

6C

D7

QF4E21

10μs
Threshold=1000



ADC1 wid=3us



ADC2 wid=5us
Fiber1Fiber4

Fiber3Fiber5

D6V2

D6V1

Fiber2The time to issue the abort trigger has become several μs faster.
After installing the fiber loss monitor, this abort trigger was mainly the first to
fire.

8

2. Sudden Beam LossThe biggest goal of SuperKEKB is to increase luminosity, but one of the obstacles issudden beam loss.

The cause of the sudden large beam loss is unclear.

→ Causes collimator (and other component)damage, QCS quench, Large B.G. to Belle-II.
→ Cannot storage a large current since it causes beam abort.
↓Start the international task force to investigate and resolve the cause of the “sudden
beam loss”.
9Observations : LM
When we looked at the loss monitor when
the abort occurred, which was thought tobe caused by beam loss, beam loss looks
started within one turn at the whole ring
collimator part and Belle-II detector.

10μs

2min.

10

Observation : Belle dose

50μs

11

Observations : Bunch Current Monitor

In order to investigate where in the train the beam loss started at the moment ofbeam loss, we recorded the bunch current 4096 turns before the abort trigger using
feedback processors .

Beam loss has been measured by bunch current monitor (BCM) to occur suddenly on acertain turn.

10μs

Abort

12



Beam loss occurs inboth HER and LER,
but the damage tothe hardware isparticularly large
when loss occurs inLER.

We don't know if itwill happen evenwith a single beam
operation, lowcurrent beam
because we haven't
operated for a long
time.

13

Observations : Beam Loss TimingIn order to find out where in the ring the beam loss first started, we installed a loss
monitor specialized for timing measurement inside the ring.



Beam loss occurs in collimator & IR, and where it occurs first depends on collimator tuning .

14(Y.Liu)Observations : Bunch Oscillation Recorder (BOR)

The Bunch oscillation is measured 4096 turns before the abort trigger using feedback
processors and the orbit is calculated from the data.
 The orbit changed small ～1mm@FB position
17/MAY QCS quench , D6V1

03/JUN QCS quench, D2V1

14/JUN QCS quench, D2V1

Ibunch[ｍA]
H [mm]
V [mm]

0.2mm

0.5mm

0.4mm

1.5mm

0.2mm
0.2mm

L [a.u.]15(H.Fukuma)

Observations : Bunch Current of Operation

It is likely to occur when a certain bunch current is exceeded.

16(K.Matsuoka)

Observations


There are no signs before beam loss starting.
 No small beam loss (beam loss monitor, BCM)
 No oscillation (Bunch Oscillation Recorder (BOR) ) No beam size change (X-ray monitor (XRM))
 It is not clear if the orbit changed significantly.(Libera)

17

Observations : VacuumPressure bursts have been observed here and there, and it rarely occurs in the sameplace except in the collimator section. It may be the result, not the reason.

18(Y.Suetsugu)

Observations : Acoustic waves
Acoustic waves were detected at the same time with collimator beam loss.
 We measure a few event before shutdown

19(T.Abe)Candidate of the beam loss reason
Damage of vacuum component : measured @ KEKB & PEP-II phase changes (beam energy losses) had been observed ms ～ hundreds of μs before aborts.

→ not observed in SBL abnormal temperature risings at bellows chambers had been observed and the catastrophic

damages in the RF-finger had been confirmed.


Dust:Early stage @ SuperKEKB
 Beam aborts accompanied by local pressure bursts. →not observed the burst that causes it

in SBL Beam loss lasted a few ms before the beam abort. → time scale is different Cleanor hit the vacuum chamber to remove as much dust as possible and fixed the problem.

 When the energy of the particles deviates greatly, the loss occurs in the horizontal collimator,

so it may be possible to find out something by examining the conditions that the loss occurs in20
the vertical collimator in more detail.
Fireball:Measured @ RF cavity

21(T. Abe)Candidate of the beam loss reason
Vertical abort kicker misfire
 We are using the same thyratron for horizontal kicker.

Electron cloud effect in collimator In this case, SBL should be measured at LER only, but

HER beam also lost.

 Simulation of EC growth will be done.
FB kicker trouble or lack of power : measured @ BEPC II
 Sinch the growth time of coupled bunch instability might be O(～several 10turns), our sbl was not caused by FB system problem.
Equilibrium of tuners, piezo's parameter, LLRF, noise from transmitter, 50Hz
filter of RF system could cause sudden beam loss. : measured @ BEPC II, DAFNE

RF system are monitored at each abort, and were not seen abnormal signal.
22

Future plansAdd new loss monitor for timing analysis and abort trigger

Add BOR for another place on ring

Setup acoustic sensors

Check the temperature of vacuum component

So far, there is no reliable way to investigate the cause of sudden beam loss

23

SummaryIn order to protect the hardware from dangerous beam loss, we are trying to speed up
the abort trigger.
 Increased the number of abort gap.
 Introduce injection veto for LM.
 Change the cable route and introduce new LM.

One of the obstacles for luminosity increasing is sudden beam loss and the cause of thebeam loss is still unclear.
 We have been investigating with Loss Monitor, etc., and have been able to find the point

where the loss started, but no phenomena that clarify the cause have been found.

 Started the international task force to investigate and resolve the cause of the sudden beam

loss.

24

backup25

Abort kicker
Abort Kicker is a complex of several magnets.
Four horizontal magnets : extract the beam fromvacuum chamber.
DC sextupole magnet : make beam size larger by thelarge horizontal beta function due to the quadrupole
component of the off-centered sextupole.
A vertical magnet : sweeps the beam in the window
during one revolution time.
Lambertoson septum magnet : transport the extracted
beam to the beam dump.
Dumped beam length : one revolution time (10 ms).
Build-up time of the abort kicker magnet : 200 ns (empty
bucket space).
Synchronization of the kicker timing and the abort gap isrequired for the protection of hardware.

200nsec
26

kicker magnet power

Abort Trigger
The abort request signals from each hardware component collected in 12 local control rooms. The
request signals from LCRs, software abort request signals, and manual abort request signals arecollected in the central control room and sent to the abort kicker within 20 msec.
12 Local Control Rooms
Central Control
Abort Source (>130)
Interlock Module (OR and Latching Circuit)
Room
RF Cavity voltage, Arc sensor,
Interlock Module
Abort
Cooling water flow and temperature,kickerHe liquid level and tank pressure ,etc.

Transfer Cables(max. 3km long)

Magnet(Comparator current)
Vacuum Pressure,
Cooling water flow and temperature
SR Monitor (Chiller power)
Loss Monitor

ManualBeam Phase

SoftwareBelle (Diamond, CLAWS)

27

Received @D2
Received @CCB

Received@CCB final
abort module

Received @ CCB
1.

Opt.Fiber

2.

PIN from D7 (2.7us after)

3.

PIN from D4

4.

CLAWS

5.

RF 5F

28

• Received @ CCB
1. Opt.Fiber
2. RF D5 (4.4us after)
3. CLAWS
4. PIN from D4
5. PIN from D1
The time to issue the abort trigger has become several
μs faster.

29

Data Analysis : Loss Monitor Abort (Injection)
LM aborts happened at the end or start of injection.
↓
Checked Injection timings were checked.
injection kickers of upstream
injection kickers of downstream
septum magnet↓
The upstream injection kicker did not receive the final
injection trigger.
The stored beam was kicked only by the downstream
kicker⇒the beam was lost at that time.
↓
This problem was caused by injection trigger system
software, and was fixed after understanding the reason.
30

Data Analysis : Loss Monitor Abort (Vacuum)・Beam phase oscillation & beam loss
occurs.
・Vacuum pressure spikes took placesomewhere.
⇒Beam was lost at a narrow apertureof the ring.
↓
Adjustment of collimators to protect
the beam pipes .
⇒PINs located on collimators makeabort requests.
This type abort is expected to be
reduced after further vacuum
scrubbing.
31

Injection related abort : BOR & BCM

32

Loss Monitor Signal Flow
Analog out ADC EPICS
IC
(～ms)

PD

Integrator
Gain(×1/×10/× Analog out
100)
～20μs
I/L signal

Analog out ADC EPICS
Integrator
peak&holdAnalog out
circuitGain(×1/×10/×100)～2μs
I/L signal

kblog

Regularly record
Sampling time: ～1sec

Data
Trigger: beam current down
loggerSampling time:～μs
Interlock
Abort trigger
modulekblog

Regularly record
Sampling time: ～1sec

Data
Trigger: beam current down
loggerSampling time:～μs
33
Interlock
Abort trigger
moduleInjection veto
Use for abortveto signal
PD

Veto
moduleAnalog out ADC EPICS

Integrator
peak&hold circuit Analog out
Gain(×1)
W/O
veto signal
I/L signal～2μs

Analog out ADC EPICS
Integrator
peak&hold circuit Analog out
Gain(×100)～2μs
Use for tuning

kblog

Regularly record
Sampling time: ～1sec

DataloggerInterlock
moduleTrigger: beam current down
Sampling time:～μs

kblog

Regularly record
Sampling time: ～1sec

DataloggerTrigger: beam current down
Sampling time:～μs

Abort trigger

34

35

(Y.Suetsugu)

36(Y.Suetsugu)(Y.Suetsugu)