Beam Diagnostics of the SPring-8 Storage Ring

Characteristics of synchrotron radiation (SR) are closely related to those of the source electron beam. For
example, pulsed nature of SR is originated from bunched structure of the electron beam. Brilliance of SR isdominated by transverse size and angular divergence of the electron beam. This laboratory course is practice at
the SPring-8 diagnostics beamline I (BL38B2).

1) Accelerator diagnostics beamline I (BL38B2).
BL38B2 has a bending magnet light source, and wide band spectral availability from visible light to X-rays
has been achieved. The schematic layout of the beamline is shown in Fig.1. The visible synchrotron light istransported to two dark rooms on the experiment hall. Single bunch purity is measured by gated photon counting
method in the dark room 2 and bunch length is measured by a streak camera in the dark room 1. X-rays are usedin the optics hutch to measure profiles of the electron beam (X-ray beam imager).

Accelerator TunneleBending M agnet

Front EndMirror(U)V isib le /UV4-JawSlit

X-raylight

MovableMetal FilterDouble Crystal
Monochromator
FZP

Mirror(L)edi eldShX-raye
PipVis iblTran e Ligh ts port L ine

Wh it

Tra n e X -r aysport Line

X-ray Zooming TubeOptics Hutch

Streak Camera

Dark Room 1

Dark Room 2
Bunch Purity
MonitorExperiment HallFig.1 Layout of the accelerator diagnostics beamline I. Components of the beam diagnostics systems are shown.

2) Practice2-1) Photon counting
When the photon beam is attenuated by slits and filters, we can count photons form each electron bunch one
by one (Fig. 2). The counting rate of photons is in proportion to the number of electrons in each bunch. Thus thetime spectra of detected photons give us the information on the filling pattern of the storage ring. The block
diagram of the photon counting system prepared for the BL practice is shown in Fig. 3.

Storage Ring

SRSlitND filter
PhotonDetector

Fig. 2 Concept of photon counting method.

Cable for HVshutter
MCPPMT

SR

Cablefor Signal

Discri.

att.

ND slitfiltert
209kHzDivider
508MHz1/2436

Variable
Delaystart

HVTAC

MCAstopVV∝ tFig.3 Block diagram of the photon counting system for the BL practice.

2-2) Streak Camera
A streak camera is a fast device to detect short light pulses. The length of SR pulses gives information of thelength of electron bunch. The principle of operation of a streak camera is illustrated in Figs. 4 and 5. At theSPring-8, we use the streak camera Hamamatsu C5680 with time resolution of 2 ps. The timing signal system for
operating the streak camera is shown in Fig. 6.

Circuit for Vertical Sweep

TriggerStreak Imageon the Screen

Sweep Electrode(Vertical)SlitPhotocathode(Photon→Electron)

Accelerating
Electrode

MCP(Intensifies
Electron Beam)

Phosphor Screen(Electron→Photon)

Projected Time Profile

Fig.4 Principle of operation of a streak camera (single sweep mode).

TriggerTrigger

Slit

Circuit for Vertical Sweep

Circuit for Horizontal Sweep

Sweep Electrode(Vertical)

MCP(Intensifies
Electron Beam)Streak Imageon the Screen

Photocathode(Photon→Electron)
Accelerating
Electrode

Sweep Electrode(Horizontal)

Phosphor Screen(Electron→Photon)

Fig.5 Principle of operation of a streak camera (dual sweep mode).

Projected Time ProfileTrigger Unit
C4547
～10 HzDivider
1/2436508MHzStreak Camera
C5680-01
Hori. Scan Unit

BPF
Divider
1/7508MHz

Vert.
ScanUnit

BPF

508MHz508MHzVariableDelay
72.65MHz72.65MHz

Delay Unit
C6878
Ref. inCamera Cont.
C4742-95

Fig.6 Timing signal system for operating the streak camera.

Power
Supply