Beam Instrumentations
Makoto Tobiyama
for SuperKEKB Beam Instrumentation Group1

SuperKEKB Beam Instrmentation

COD monitor‒ Change of measured beam position with beam current

X-ray beam size monitor
Visual synchrotron radiation monitor‒ Replacement of first mirror‒ Coronagraph‒ Injection beam monitor

Bunch feedback system‒ FIR filter effect‒ Broadband noise in the front-end circuit

Tunnel environment monitors2SuperKEKB Beam Instrmentation

HER beam position change with beam current
QD3E.26 ATT. 切替による Beam 位置跳ね 2022/06/13

0.35

-0.40

0.30-0.45

0.25
19:20:00-0.35

19:20:00

0.40

19:15:00-0.30

19:15:00

0.45

19:10:00-0.25

19:05:00

0.50

Y 位置（㎜）

y(mm)

-0.20

19:00:00

X 位置（㎜）x(mm)Similar behavior of four BPMs in thesame narrowband detector(D6 QF2E32 QD3E26 QF4E26
QD1E16) have been observed.
Suspected to be caused by the HP
1GHz narrowband detectorʼscharacteristics.

時刻

QD3E.26 ATT. 設定値 2022/06/13
if att(dB)

19:10:00

19:05:00

6055
50
45
40
3530
25
2015
10
50
19:00:00

ATT. （ dB ）rf att(dB)

時刻

3

SuperKEKB Beam Instrmentation

HER 1GHz BPM detector
HP4391A Det. Module

HP4392A Mux. Module

入力側
20dB
ATT.

20dB
ATT.

10dB
ATT.

5dB
ATT.

4

SuperKEKB Beam Instrmentation

Suspected source: Impedance mismatch
w/o 1GHz isolator

with isolator
1GHz 狭帯域検波器 Beam 位置跳ね測定 Isolator 有り 3dB ATT. 無し 2022/07/01
x(mm)

y(mm)

-0.75
09:55:00

16:20:00

時刻

ATT. 設定値 2022/06/30
if att(dB)

5050

40

403030

時刻

時刻

CW measurement at the bench did not show large position jump
510:30:00

10:25:00

10:20:00

10:15:00

16:20:00

16:15:00

16:10:00

16:05:00

16:00:00

15:55:00

015:50:00

100
15:45:00

10
15:40:00

if att(dB)

20

10:10:00

20

10:05:00

ATT.(dB)60

15:35:00

ATT. 設定値 2022/07/01

rf att(dB)

60

10:00:00

rf att(dB)

1GHz 狭帯域検波器

09:55:00

1GHz 狭帯域検波器

10:40:00-0.2

10:40:00-0.75

10:35:00-0.2

10:35:00-0.74

10:30:00-0.19

10:25:00-0.74

10:20:00-0.19

10:15:00-0.73

10:10:00-0.18

10:05:00-0.73

10:00:00-0.18

X 位置（㎜）-0.72

Y 位置（㎜）-0.17

16:15:00-0.72

16:10:00-0.17

16:05:00-0.71

16:00:00-0.16

15:55:00-0.71

15:50:00-0.16

15:45:00-0.7

15:40:00

-0.15

時刻

ATT.(dB)

y(mm)

-0.7

15:35:00

X 位置（㎜）

x(mm)
-0.15

Y 位置（㎜）

1GHz 狭帯域検波器 Beam 位置跳ね測定 Isolator,3dB ATT 無し 2022/06/30

SuperKEKB Beam Instrmentation

Burst signal response
Original detector

Spare detector

1GHz Det. 位置跳ね測定 (Burst 信号 ) Isolator, ATT. 無し QD3E.26 2022/09/02

New 1GHz Det. 位置跳ね測定 (Burst 信号 ) Isolator, ATT. 無し QD3E.26 2022/08/31
x(mm)-0.69

-0.2

-0.7

-0.2

-0.7
15:10:00

10:45:00

時刻

時刻

ATT. 設定値 QD3E.26 2022/09/02

New 1GHz Det.(Burst 信号 )if att(dB)

50

50

40

4030

30

時刻

時刻

6

15:50:00

15:45:00

15:40:00

15:35:00

15:30:00

15:25:00

10:45:00

10:40:00

10:35:00

10:30:00

10:25:00

10:20:00

0

10:15:00

10

0
10:10:00

if att(dB)20

10

15:20:00

20

15:15:00

ATT.(dB)60

10:05:00

ATT. 設定値 QD3E.26 2022/08/31

rf att(dB)

60

15:10:00

rf att(dB)

15:50:00-0.19

15:45:00-0.69

15:40:00-0.1915:35:00-0.68

15:30:00-0.18

15:25:00-0.68

15:20:00-0.18

15:15:00-0.67

X 位置（㎜）-0.17

Y 位置（㎜）-0.67

10:40:00-0.17

10:35:00-0.66

10:30:00-0.16

10:25:00-0.66

10:20:00-0.16

10:15:00-0.65

10:10:00-0.15

1GHz Det.(Burst 信号 )ATT.(dB)

y(mm)

-0.65

Y 位置（㎜）

y(mm)

-0.15

10:05:00

X 位置（㎜）x(mm)SuperKEKB Beam Instrmentation

We will try to insert 1GHz isolators between the MUXs
and the detectors at the “important” BPMs.
‒ 30 isolators have been ordered. Waiting for delivery.

Another way might be to use 500MHz detectors (newlydeveloped for SuperKEKB) used for LER BPMs.
‒ 6 spares are available now.

7

Turn-by-Turn BPMs
Building
LC5
D07LC4
D7BPM
QD3E18
QEAP25QD3E23
QM2E

Date
2022/1/4
2022/3/23
2022/3/23
2022/5/3

BrokenPSPS
LAN
Gated sw.

Repaired date Repaired parts
2022/1/4
PS replacement
2022/3/23
PS replacement
2022/3/23
Power on/off & IOC reboot
2022/5/11
Under investigation• The power supplies have been malfunctioning for the recent two years;

3 BPMs in 2021abc and 2 BPMs in 2022ab. Broken PSs were replaced every
time by us (not in a beautiful way).

• PSs of 55 BPMs in total (1/3 of all turn-by-turn BPMs) were replaced by acircuit maker.
The rest of the replacements are planned for the next FY.
8

X-ray beam size monitors
X-ray irradiation inside the detector box was so severe at ~1 A.

• Malfunctioning of the CMOS cameras became frequent, and we replaced thecameras two times in HER and once in LER in 2022ab.

• The new “big” detector box makes enough room for the Pb shielding.

• Scintillation efficiency of the YAG:Ce scintillator in HER decreased above 0.9 A.
A visible check on maintenance day found no significant damage on thescintillator and the CMOS camera.

• Quick solution: we added the Cu filter upstream from the scintillator, and it
looked OK.

• A diamond scintillator would be a good alternative.
The copper filter reduced X-ray
intensity by 30%, which wasconsistent with the calculation
overall.

Why two peaks?
Reasonable single peak

Two weeks later…

9A large leak in the HER X-ray line

1.

Two (middle #2 and downstream #3) out of the three ion pumps
didn’t turn on at the beginning of August after the power
maintenance.

2.

We suspected the humid atmosphere in the OHO straight section,
where ceiling repair work has been ongoing, caused an electricalleakage around the HV connector.

3.

We tried to turn on the ion pump #2 and #3 several times, and finally,
the ion pump #2 started though the ion pump #3 still stopped.

4.

Shortly later, we replaced the detector box as scheduled and found asignificant leak in the downstream Be window.

5.

Once we stopped all the ion pumps and replaced the leaked
downstream Be window with a new one. At the same time, wereplaced the upstream Be window (confirmed to be healthy) for sure.
In this work, we found that the ion pumps #2 and #3 were failing.

6.

After replacing the ion pump #2 and #3, we believed everything was
OK and tried to turn on all the pumps. But the upstream ion pump #1
didn’t wake up and turned out to be broken.

7.

Consequently, we replaced two Be windows and three ion pumps #1#3.

IP #2

IP #1
10

Though the pressure wasgood, there should havebeen a small leak in 2020b.

This trial was a problematic
action to make the ion pump
#2 and #3 broken.
Did something make a bighole, or did a small holewidens gradually?

It seems natural to think thepressure inside the X-ray line
has been at the atmosphericlevel since 3.

IP #3

Detector box
LER
Ion pump #3

HER

X-rayline

Ion pump #2

11

Ion pump#1

Be window (upstream)

New detectorbox12Be window (downstream)A large leak in the HER X-ray line•

We don’t yet clearly understand when and why a large leak occurred.

•We got where the leak occurred on the Be window: brazing between the Cu holder and the Be window.

••

Did severe copper oxide make the Be window peel off?

•

A Be-window maker investigates a reason for leakage in detail.

What we must do in LS1:•

Production of spare Be windows•

CCG-based interlock systems to protect the ion pumps

13

SRM
2022/12/13 SuperKEKB Review14

SRM 1: Diamond Mirror• Developed a single crystal diamond mirror and made efforts tosuppress the current dependence of thermal deformation, butthe mirror had not only the current dependence of thedeformation at high currents, but also some deformations madeduring manufacturing at beginning of SuperKEKB.

• Made a new thick polycrystalline diamond mirror that is noteasily deformed by heat and installed it in 2020.

• Resistance to thermal deformation is similar to single crystal.
• Reflectance is high because the coating is changed from gold toplatinum.

⇒ obtain a sufficient amount of light for beam profile measurement
for each bunch, and it became possible to measure the beam halo andinjection beam for each turn.

• Measured surface flattens of the new diamond mirrors have been
confirmed less than λ/5 with beam current larger than 1A, thatenabling to create diffraction-limited image at the optics station.

• Imaging using fast gated camera, streak camera measurements,
coronagraph... etc.

15

SRM 2: Coronagraph Beam halo may cause unexpected beam loss or long-term irradiation leading to luminosity
degradation and damage to accelerator components.
 Introduced Coronagraph to SRM.
 Sensitivity of the measurement : Ratio of beam halo/Core ~ 2e-3 x 2e-3 ~ O(1e-6)

1st stage:Objective lens system
To eliminate a chromatic aberration, the 1stsystem adopts a reflective mirror system rather
than a refractive lens system.

2nd stage:
Re-diffraction system

3rd stage: Relay lensInput opaque disk to hide beamcore.

blocked by the Lyot stop

16

HER 0.57mA

LER 0.61mA

Results for the observation of beam halo in HER and LER. The beamcore image and shadow of opaque mask are superimposed in the halo
image.
17

Gate width=100ns,Log, mask=1mm×2mm
Delay changed (position @ train)

1874

1974

2074

2274

2974

3574

4074

5274

SRM 3 : Injection beam measurement• It is important to observe how the injection

beam turn in the ring usually and prepare forthe measurement of difference with worth
efficiency injection beam.

• Since it became possible to measure thebeam for bunch by bunch, we tried to see
the state of the injection beam.

• Object system which designed forcoronagraph is used to measure the injection
beam.

• Single-turn injection was applied on the HER
beam. (Each injection bunch kicks out theprevious injected bunch. Then the ringalways has only one bunch).

19

Injection Beam Measurement
Result : HER injection beam
• The beam just after
the injection
repeatedly oscillation.
• Since SuperKEKB
operating tune is close
to a half-integer, it canbe seen that the bunch
moves left and right atevery turn.
• The beam size does
not shrink
monotonically, butshrinks while repeating
oscillation.

• Gate width : one turn (10μs).
• Trigger was applied at the injection
timing20

Injection Beam Measurement
Result : HER injection beam
• Horizontal beam size for each turn of the injection beam after calibration.
•The injection beam repeatedly expands and contracts and damped after 10,000 turns (10 ms).

•

The beam size is including the diffraction effect.

• The injection beam oscillation•

it can be seen that the amplitude becomes stable while oscillate with a width of about ± 4.5 mm at the maximum.

previously injection beam andcorresponds after a complete
dump for comparison
21

Injection Beam Measurement
Result: LER injection with stored beam•

We also observed the injection
beam when stacking normal
collision beams.

•In order to see the injection beamduring the collision, we put a maskin front of the camera to hide thestored beam.
Some measurement is possible.

•22

LER23

SuperKEKB Beam Instrmentation

Bunch FB system (HER)
With increasing number of bunches‒ Feedback gain drops‒ Total beam current increase (growth rate of the instability might
be increased)
Found vertically unstable behavior: tried to increase vertical FB
gain step by step (around 0.5dB step)Finally, we have increased the FB gain of upstream loop
around 6dB.
‒ Checked the luminosity behavior before and after change of thegain‒ no significant change have been observed.
‒ Checked the grow-damp behavior during collision.

24SuperKEKB Beam Instrmentation25SuperKEKB Beam Instrmentation

Found 1 failed HER Final amplifier after 2022b run.
26

SuperKEKB Beam Instrmentation

LER




Changed the FIR filter from 10 Tap FIR to 4 Tap FIR(upstream), 8 Tap FIR to 6 Tap FIR (downstream) on11/Mar.
Tuned the FB phase and tool several GD data on
28/Mar with LER single beam.

27

SuperKEKB Beam Instrmentation

FB off at few bunch, high bunch current operation

betatron +fs (like) line

28

normal betatron freq.

SuperKEKB Beam Instrmentation

FB filter (Uppersterem V)

29SuperKEKB Beam Instrmentation

FB filter (Downstrem V)

30

SuperKEKB Beam Instrmentation

4 Tap filter

31SuperKEKB Beam Instrmentation

32

SuperKEKB Beam Instrmentation

Mode -1 faster than e-cloud related mode

33

SuperKEKB Beam Instrmentation

34

SuperKEKB Beam Instrmentation

During LS1Planned to reduce broadband noise in the FB front-end
circuit by changing the first 2GHz BPF.
‒ Replace 2GHz-3tap comb filter with 2tap cable-type comb filter.
‒ Similar gain at the front-end‒ Expected to have ½ of broadband noise‒ Much severe timing margin‒ need much longer tuning time after
restart of the beam operation.

35

SuperKEKB Beam Instrmentation-22+11+25+11=+25dB

36

SuperKEKB Beam Instrmentation-4+25=+21dB

RMS counts at iGp12s: 14 counts -> 6.5 counts

37SuperKEKB Beam Instrmentation

New cable BPF

38

SuperKEKB Beam Instrmentation

2 tap 2GHz BPF (up to 20GHz)

39

SuperKEKB Beam Instrmentation

Original 3 tap stripline-coupled comb BPF

40

SuperKEKB Beam Instrmentation

Environment monitor

Raspberry Pi + home made USB sensor (temperatureand humidity)
LC1-LC8, Nikko, Fuji (planned OHO and Tsukuba)
Easily hanged-up during beam operation (LC6 and LC7),
even with thick Lead radiation shield.

41SuperKEKB Beam Instrmentation

42SuperKEKB Beam Instrmentation

SummaryBeam instrumentation of SuperKEKB rings are almost working, without
severe failures.
HER COD measurement systems (original KEKB circuits) will be needed tobe improved.
‒ SWR effects with change of internal attenuators.
‒ Day-night effects (cable temperature).
‒ Will try to install isolators on several important BPMs.



Re-built HER X-ray monitor box
Replaced first optical mirrors (polycrystal diamond, HER and LER).
‒ Much better image, much higher photon intensity.
‒ Injection bunch measurement‒ CoronagraphEffect of bunch feedback side-effects‒ Lower number of FIR taps in the digital filter‒ Much better NF with cable BPF

Environment monitors are working.
43SuperKEKB Beam Instrmentation

backup44

SuperKEKB Beam Instrmentation

Beam image and diffraction fringe (l=500nm)
To eliminate a chromaticaberration, the 1st system
adopts a reflective mirror systemrather than a refractive lenssystem.

1st stage:
Objective lens system

Clearly observed ~18th order fringes

45

2nd stage:
Re-diffraction
system

3rd stage:
Relay lensSuperKEKB Beam Instrmentation

Diffraction image on the Lyot stop

Geometrical imageof the aperture ofobjective lens

1st stage:
Objective lens system

2nd stage:
Re-diffraction
system

3rd stage:
Relay lens

blocked by the Lyot stop

10mm• Input opaque disk to hide
beam core.
• Diffraction fringes ofobjective lens aperture isshown.

Observed image

46

SuperKEKB Beam Instrmentation

Observation of beam halo

1st stage:
Objective lens system
Beam core

2nd stage:
Re-diffraction
systemCore blocked by a Φ3mm disk

47

3rd stage:
Relay lensRe-diffraction fringes blocked by
the Lyot stop

Observation : Bunch-current dependence in HER
0.15 mA/bunch

0.055
mA/bunch

Due to beam orbit changes

0.28 mA/bunch

Diffraction fringes made by
the latter optics than the Lyot
stop
Leakage of diffraction
fringes by the diamondmirror

48

0.55 mA/bunch

Comparison of halos between HER and LER
Gate width 10msec

HER 0.57mA

LER 0.61mA49