Observation of Crab
Crossing with StreakCamera
2007/3/19
KEKB Review
H. Ikeda

Contentsz Introductionz Calibrationz Measurementz SummaryIntroductionz We use streak cameras to observe CrabCrossing.
z For this purpose, a streak camera is
installed in synchrotron radiation monitor(SRM) hut of each ring.

Introduction : KEKB SRM
We use the synchrotron
radiation from the individual
beam bunches produced in a
weak bending magnet tomeasure the beam size.
z High and low energy rings(HER, LER) have independentSRMs.
z The light path from weakbending magnet to cameras
are 35m and 38m for HER andLER, respectively.
zIntroduction : Streak Camerazz

The streak camera (Hamamatsu C5680) is used to measure
the bunch length and bunch-by-bunch beam size.
Beam profile (Longitudinal vs Horizontal) is measured tocheck the crabbing angle.

(Copyright 2002 Hamamatsu Photonics K.K.)

Calibrationzz

Longitudinal scale (time) iscalibrated by Hamamatsu.
Parallel bump (±2mm) is set forhorizontal size calibration.

Calibrationz Calibration constant is calculated by fitting ofbump height vs streak camera pixels.

Measurement : 2007/2/19 Crab ONzz

1mA/single bunch was injected into both rings after Crab ON tocheck the crabbing.
The opposite direction tilt was also checked by changing the crab
phase 180°.

Crab OFF

Crab ON
0°＋180°

Crab ON
0°＋180°

HER(1.43MV)

LER(0.9MV)

HER

LER

CrabOFF

CrabON(1.43MV)(1.09MV)Measurement :Crabbing Direction CheckIP
tailhead－+
Longitudinal

headtailHER

LER

Horizontal

HER－+－LER

Longitudinal direction and tilt direction were checked.
Both beam are tilted to the inside of the ring at the SRemission point.

Measurement :Crabbing angle @ SRM
HERLER

φSRM
β SRM cos(πν − ψ crab −ψ SRM )νH
νHβHβH=φIP
β IP cos(πν − ψ crab −ψ IP ) Crab 199.977 11.2498 74.0000 10.2500
φIP = 11mrad ,SRM 25.8768 35.3627 24.1507 21.3615
φSRM ( HER ) = 39.1mrad ,44.5114 0.59
45.5098
0.8IP
φIP ( LER ) = 43.7 mrad

Sign does not change between IP and SRM.

(2/21 optics)

Measurement :Accuracy of measurementzzzzσ H = 0.022 ×L

Bunch is divided into several pieces (10)and each center of gravity is calculated.
The centers of gravity are fitted with alinear function, H = a + b×L .
“b” corresponds to the tilt of the bunch.
The width of the “b” distribution with CrabOFF beam is 0.022.

512 / 180[ch / mm]
16.413 ± 2.75[ch / mm]= (3.8 ± 0.657) × 10 −3 [rad ]Accuracy of the measurement～10%

Measurement : Fitting examplezResult of calculated tilt is similar whether using 10
pieces case or all longitudinal pixels.

Measurement : tilt
zzz

HER

The results of the tilt calculations are shown below.
The two peaks correspond to the two sweep phase of the streakcamera.
LER values are consistent with the expected value, but HER values
are off by a factor of 2.

LERMeasurement : tiltz

Sweep frequency of streak camera is ¼ of KEKB RF and theimage appears as bellows.

Summaryz Crabbing is observed with the streak cameras.
z Crabbing angle is measured quantitatively, andthe LER angle is consistent with the expectedangle from optics calculation.
z Inconsistency of the HER crabbing angle withthe expected value will be studied.

Measurement : HER tiltz I checked about the HER inconsistency.

• The fitting result of the tilt are constant when
the number of dividing peaces.
• The calibration bump shape is changed for
the SR to hit against the same place of
extraction mirror, and the result dose notchange.
• Longitudinal beam size are 6.4mm andconsistent with expected value but thecalibration constant should be checked.