MEASUREMENT OF THE BUNCH LENGTH IN AN ELECTRON STORAGE RINGBY MEANS OF THE SINGLE PHOTON COUNTING METHOD
Goro Isoyama, Hideo Kitamura * , Akira Mikuni and Tatsuya Yamakawa *Synchrotron Radiation Laboratory, the Institute for Solid State Physics, theUniversity of Tokyo* Photon Factory, National Laboratory for High Energy Physics
Abstract
The longitudinal bunch length in SOR-RING was measured as a function of elecContrary to previous measurements,
tron energy, RF voltage and stored current.
current dependence of the bunch length was observed in the multi-bunch operationmode but not in the single bunch operation mode, which suggests the phenomenon iscaused by a bunch-bunch interaction in SOR-RING.
1. Introduction

Synchrotron radiation (SR) from electron storage rings has intrinsic time
structure which facilitates time resolved experiments in the time range from subRecently the single bunchnanosecond to revolution time of electrons in a ring.
operation of SOR-RING, which is a 400 MeV electron storage ring dedicated to 2R
experiments ), has been successfully made by means of the RF-knock out method ),As SOR-RING is suitand time resolved experiments as long as 58 nsec have begun.
able for such experiments in short time region, it is important to measure time
duration of a SR pulse which corresponds to electron density distribution in a bunchin order to know time properties of the light pulse precisely.
The longitudinal bunch length measured so far in electron storage rings showsa functional dependencj_gn stored current and the measured bunch length is longer·)•than calculated values
We measured bunch length in SOR-RING by means of the single photon counting
method and studied a functional dependence on operation parameters of the ring.
2. Experimental Procedure
A bunch length of SOR-RING was measured as a function of electron energy E ,voltage VRF and electron current I both in the multi-bunch and singl~
cavityRFThe visible spectral region of SR, passing
bunch operation modes of the ring.
through a glass window mounted on a vacuum chamber of a bending section in SOR-RING,
was attenuated and focused onto a pin hole of about 0.1 mm in diameter and detectedwith a fast photomultiplier utilizing a chevron multichannel plate (HAMAMATSU TV,TheRl294UX) which has better time resolution than an ordinary photomultiplier.
time resolution of the detection system was less than 250 psec under this experiThe timemental condition and is not subtracted from all the data shown below.
Thestructure of SR is a copy of the electron density distribution in a bunch.
RF cavity readout was calibrated by making use of a functional dependence of synchrotron frequency on RF voltage.
3. Result and Discussion
Fig. 1 shows stored current dependence of the bunch length in the multi-bunch
The upper and lower broken lines are the natural bunch lengths~
operation mode.
which are expected from. the balance of quantum fluctuation and radiation damping),
For stored current less than 0.1 mA, measured
at E =380 and 308 MeV, respectively.
buncH lengths at.E =308 MeV are also in good agreement with the natural bunch
I t is ob~ious from Fig. 2 that there is a critical current, above whichlength.
the bunch length begins to increase as the current increases. 113 The measured current
in that region,
dependence of the bunch length is well approximated by log Ie-161-which is shown in Fig. 1 ~y the solid lines.
This current dependence is similar
to that observed in ADONE ).
It is confirmed that the natural bunch length is ingood agreement with the measured one in the wide-ranging values of RF voltage aslong as stored current is less than the critical value.
Fig. 2 shows dependenceof the bunch length on stored current for the single bunch operation. 9 Electron
number in a bunch at I =10 rnA for the single bunch operation is 3.6xl0 and it isequal to the number ofeelectrons per bunch at I =70 rnA for the multi-bunch .operation
because the harmonic number of SOR-RING is seveff.
Contrary to Fig. 1 the measured
bunch length is independent of the stored current for t~e 4 single bunch operation.
The experimental results observed in ACO and ADONE ' ) show that the bunch
lengthening is a function of current per bunch and no of total current and thissuggests the bunch lengthening is due to a electron-electron interaction within abunch.
Our experimental result, however, contradicts with the above results andit is concluded that the bunch lengthening observed in SOR-RING is caused by abunch-bunch interaction because it is observed for the multi-bunch operation but
not for the single bunch operation.
As a conclusion, the bunch length in SOR-RING for the sing9e bunch operation
is independent of stored current, at least, up to 17 rnA (6.lxl0 electrons/bunch)and the time resolved experiments as short as 650 psec (Ee=380 MeV and VRF=23.8 kV)
are feasible.
Acknowledgment
The authors wish to thank Professor H. Kanzaki for encouragement _throughout
this work and critical reading of the manuscript.
References
1) T. Miyahara et al., Particle Accelerators l(l976)163.
2) H. Kitamura et al., Activity Report of Synchrotron Radiation Laboratory (1979)
ISSP, the University of Tokyo, p. 95.
3) F. Amman, IEEE Trans. Nucl. Sci., NS-16, No. 3(1969)1073.
4) F. Amman et al., Pro.Int.Conf. on Hig~Energy Accelerator, Everan(l969) Vol. 2,p. 9.
5) M.A. Allen et al., SLAC-PUB-1313(A)April(l974) ,6) M. Sands, Physics with Intersecting Storage Rings, ed. by B. Touschek (AcademicPress, New York, 1971) p. 257.

i

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SINGLE BUNCH OPERATION~~c1.5------o-------------------------------- ------

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STOREO CURRENT (mA)

STORED CURRENT (mA)

Fig. 1. Stored current dependence of bunch
length for the multi-bunch operation.

Fig. 2. Stored current dependence of bunch
length for the single bunch operation.

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