NEW STREAK-CAMERA SYSTEM FOR THE KEKB LINAC
Y. Ogawa, K. Furukawa, T. Kamitani, S. Ohsawa and A. Enomoto,KEK, 1-1 Oho, Tsukuba-shi, Ibaraki-ken, 305, Japan
T. Suzuki, S. Abe and K. Iwazaki,
Hamamatsu Photonics K. K., 812 Joko-cho, Hamamatsu-shi, Shizuoka-ken, 431-31, Japan
Abstract

section. The system configuration and functions aredescribed together with the first results of a beam test.

A new streak-camera system optimized for beamdiagnostics of a linac has been developed. It is an all-inone system such as oscilloscopes, involving not only thestreak camera itself, but also a delay unit synchronized toa linac beam trigger and an rf, and a control system for
input optical systems. Two such systems have been
installed for the KEKB linac as bunch-length monitors
utilizing optical transition radiation (OTR) at the end of
the bunching section as well as at the exit of the J-arc
section. The first beam test was successfully completed;the operation as well as the set-up of the system becomesquite simple, which enables the linac beam diagnostics to
be much easier than before.
1 INTRODUCTION
Prompt beam diagnosis plays an essential role for stable
operation of accelerators, like the KEKB linac[1], inwhich frequent injection into the ring is absolutely
necessary; whenever the beam is down, it must be
recovered as soon as possible while diagnosing the beamstate. Various kinds of beam instrumentation[2, 3] havebeen employed at the KEKB linac for this purpose; wallcurrent monitors, position monitors, screen monitors andwire-scanner monitors have been installed. Although it
has been recognized that bunch monitors[4] are also
indispensable for precise beam tuning and diagnosis, they
have been used not as easy tools that anybody could use,
but as special ones that only experts could handle.
One of the reasons is that the pulse width of thebeam is very short (10 ps) in the case of an S-band linac,such as the KEKB linac. Therefore, streak-cameras[5]had usually been used to see a bunch structure byobserving a light pulse (e.g. OTR) emitted through theinteraction between charged particles and matter inserted
into the beam line. The system, however, was neither
easy to cope with nor optimized for beam diagnosis oflinacs; control of the optical beam transport from thebeam line to the streak camera, which is usually quite long,
and a streak triggering is one example of the maindifficulties of easy handling. In this connection, a new
streak-camera system optimized for the KEKB linac has
been developed and tested at two positions of the linac:
the end of the bunching section and the exit of the J-arc

2 SYSTEM SPECIFICATIONS
2.1 System Configuration
The hardware of the new streak-camera system comprises
three parts: an input-optical system, a streak camera witha trigger-delay unit synchronized to the rf of the linac anda data-analyzing computer. The key feature of the design
was an integration of controls; it is an all-in-one system,
such as oscilloscopes.
Cabling to the system is also quite simplified; only
two inputs (a beam trigger and an rf signal) and twooutputs (a steak video signal and its trigger) are required
apart from connections of GP/IB controls. Figure 1 shows
the system configuration.
Streak Camera

OTR

Trigger INRef (RF Signal) IN
Video OUT
GP/IBFigure 1: System configuration of the new streak camera.
2.2 Input Optical System
The input optical system is divided into two parts: thetunnel optics for extracting and transporting OTR from thebeam line to the klystron gallery, and the gallery optics forthe input of the streak camera (Fig. 2). It was usuallycontrolled with another software separated from the mainstreak-camera control, which made the set-up of theoptical system quite tiresome. The new integrated
software allows the set-up to be very easy.

Figure 2: Input optical system controlled by integrated
software.

The streak sweep timing (trigger) used to be adjusted tothat of the input light by comparing a beam trigger with awall-current monitor signal near to the bunch monitor
using an oscilloscope. This procedure took a long time
and was one of the main difficulties to use a streakcamera system. The function of an automatic peak search,
in which a signal is searched automatically by changing
the trigger delay, is thus introduced; it turns out that it
worked quite well, provided that the input light had acertain amplitude level.
(3) Real-time gravity integration of a single shot
For observations with a time resolution of the streak
camera (better than 2 ps), a single-shot measurement mustbe performed. The single-shot signal, however, is usually
not so large as to accomplish this resolution. Moreover,
the timing jitter of triggers dose not allow an average
process (integration) for an improvement of the S/N ratio;
as a result, off-line gravity integration must be performed.
The new system automates this function as a real-timeprocess, which enables a measurement with a good S/Nratio, as long as the input signal has no fast time variations.

2.3 Streak Camera with a Delay Unit Synchronized to RF

3 EXAMPLES OF LINAC BEAM DIAGNOSISThe streak tube is made by Hamamatsu Photonics K. K.,
and has a time resolution of better than 2 ps in the range of
wavelength from 200 to 850 nm. The driver circuits and atrigger-delay unit synchronized to the rf signal as well as
the streak tube with a fiber-coupled CCD camera areconfigured in the streak camera.
When a long delay is required for adjusting thetiming between the input light and the streak trigger inoperating the streak sweep, it may give rise to a timing
jitter in the fast-sweep range. In the electron linac using
an rf for acceleration, the beam timing is in principle
perfectly synchronized to the rf. Therefore, the triggerdelay timing for the streak sweep is resynchronized to therf in the delay unit of the streak-camera system.

Using the new streak-camera system as a tool for beamdiagnosis, tuning of the bunching section and checking
isochronicity along the J-arc section were performed.

2.4 Software

3.2 Observation at the Exit of the J-Arc Section

The image signal from the CCD camera is taken into avideo frame grabber and processed by the software on aPower Macintosh, which also controls the streak-camera
via GP/IB networks. The new features of the software are
the following:(1) Easy set-up of the input optical system(2) Automatic peak search in the streak mode(3) Real-time gravity integration of a single shot pulse(1) Easy set-up of the input optical system
In the former system, the control system for input optics
was not included in the main streak-camera software, asmentioned in section 2.2. The present software integrates
all functions for controlling the streak-camera system into
single software and makes the adjustment of the input
optics quite easy.
(2) Automatic peak search in the streak mode

The J-arc section is designed as an achromatic andisochronous system. In order to verify the isochronicity,
the relative time delay of the beam in the J-arc section wasmeasured as a function of the input energy into the J-arc
section using the streak-camera system installed at the exitof the J-arc section. Figure 4 shows an example ofobservations for the dependence of the beam time delay
upon the input energy, indicating non-isochronicity. Afterthe observation, an isochronicity correction was tried andan isochronous system was realized.

LINAC KLYSTRON GALLERY
Streak Camera
Gallery Optics

Light Shield

XYZ Controller

LINAC TUNNEL
LINAC OTR Emission Point
Tunnel Optics

3.1 Observation at the End of the Bunching Section
Figure 3 shows an example of the tuning process in thebunching section for a beam with a charge of 2 nC, using
the streak-camera system installed at the end of thebunching section. Two subharmonic bunchers (SHB1:114 MHz, SHB2: 571 MHz) as well as a prebuncher and abuncher (2856 MHz) are used for realizing a singlebunch; a beam with a pulse width of several nanoseconds
is compressed into a single bunch with a width of about 10
ps.

4 CONCLUSIONS
A new streak-camera system optimized for the KEKB
linac has been developed and used as a powerful tool (abunch monitor) for beam diagnosis. The system has
several useful features related to an integration of controls∆E / E = 0 % (1.5 GeV)

SHB1 & 2
Stand-by∆E / E = +1.0 %SHB1Acceleration

Figure 4: Examples of isochronicity measurement.
results are quite satisfactory and another two systems (onenear to the positron production target and the other at theend of the linac) are being prepared for the full-beamcommissioning of the KEKB project scheduled in autumn.
5 ACKNOWLEDGMENTS
SHB1& 2
Acceleration

The authors would like to thank all staff members of theinjector linac group and members of the linac beamcommissioning team for the realization of a stable beam.
6 REFERENCES[1] A. Enomoto et al.: ‘Construction status of the KEKB 8GeV Injector Linac’, in these proceedings.
[2] T. Suwada et al.: ‘New data acquisition system for a beamposition monitor and a wall-current monitor for the KEKB
injector linac’, in these proceedings.
[3] Y. Funakoshi et al.,: ‘Beam tests of a wire scanner for theKEKB injector linac and beam transport line’, in theseproceedings.

SHB1 & 2
Acceleration
Bunch Width (FWHM)
13 ps
2 nC/bunch

Figure 3: Tuning process of the bunching section.
allowing easy operation of the streak-camera system. The
bunch structure at the end of the bunching section as wellas the isochronicity in the J-arc section have beenmeasured using the system for verifying the features. The[4] Y. Ogawa et al.: ‘Beam monitor utilizing transition
radiation’, Proc. of the 1993 Particle Accelerator
Conference, Washington, D.C., USA, May 17-20, 1993,p.2516.
[5] K. Furukawa et al.: ‘Control system for a bunch/profile
monitor at the KEK e+/e-linac’, Proc. of the 1994
International Linac Conference, Tsukuba, Japan, August21-26, 1994, p.819.