Single Bunch Storage in UVSOR Storage Ring
T.Kasuga, T.Kinoshita, M.Hasumoto and H.Yonehara
Institute for Molecular Science
Myodaiji-cho , Okazaki,444 Japan
Abstract

A pulse shape monitored at the pulse divider ofthe output circuit of the pulser is shown in Fig. 2.
Pulse width is slightly longer than the designed
Though the pulse length of the beam of thevalue.
linac ought to have been measured, it was difficult tomeasure because of the poor frequency response of theFor that reason wecurrent transformer in the linac.
observed adjacent buckets to the aimed bucket of theThe result issynchrotron and the storage ring.
discussed in the following section.

is a 600 MeV electron storage ring
UVSOR
dedicated to ultraviolet synchrotron orbital radiation
research in molecular science and related fields. The
injector is a 600 MeV electron synchrotron with a 15
The radio frequency of the storage ring
MeV linac.
( Harmonic numbers ofand the sychrotron is 90 MHz.
Therefore, thethem are 16 and 8 respectively . )period of the pulsed light is about 11 nsec, when allSomeof the storage ring are filled.
bucketsSingle
experiments require the longer pulse period.
bunch can be injected into the storage ring for thatIn this case the pulse period is elongatedpurpose.
to 180 nsec which is the revolution period of thestorage ring.
Introduction
Two methods to store a singel bunch in the storage
First, "nano-second grid pulser"
ring were tried.
The grid of the electron gun ofmethod was tested.
the linac is excited by a short pulse which issynchronized to a certain bucket of the synchrotron,and only this bucket can be filled with electrons.
Another method is an RF knockout method. All bunches
except two bunches in the synchrotron are destroyed bya deflector which excites a betatron side band, andone of two survivors is transfered to the storage
As the radio frequency systems o:C the tworing.
rings are synchronized , it is easy to transfer thebunch from the bucket of the synchrotron to the bucket
As the ratio of the harmonicof the storage ring.
numbers of the two rings is 2, two buckets of thestorage ring are synchronized to a bucket of theTherefore the transfer timing must be
synchrotron.
synchronized to either of the two buckets. These two
methods can be used together to improve the purity
which is the ratio of beam current in the single bunch
to total current.

Fig. 2 Output Pulseof Pulser (5 ns/div)
RF Knockout Method
An RF Knockout system in the synchrotron whichbetatronofto measure numbers
installedwasoscillations (tunes) is diverted to the single bunch
forming system. The knockout signal must be modified,
as all bunches are destroyed without the modification.
A blockdiagram of a circuit which generates theknockout signal is shown in Fig. 3 , TvJO sinusoidal(revolution frequency
wav3s whose frequencies are fin the synchrotron) and qf rer q is the fractionala signal proportionalpart of tune ) are generateae~to the product of them is formed by means of a double
balanced mixer (DBM), the signal is amplified andsupplied to the deflector of the knockout system. Twobunches which correspond to 11 and 211 phases of therevolution frequency survive as the knockout signal
vanishes at these phases, and all bunches except them·are killed. One of two survivors must be selected a.ndinjected into the storage ring. As a rise time of thefast kicker magnet of the extraction system is about
60 nsec and an interval between two bunches is 44
nsec, only one of two survivors can be extracted.

Nano-second Grid Pulser
As the bucket width of the synchrotron is about
10 nsec, a short beam must be injected into the bucket
We decided
or the adjacent buckets are also filled.
the pulse length of 5 nsec ( FWHM ) taking jitters ofThe grid circuit
the grid pulse into consideration .
i.e.
of the electron gun was slightly changed,
the termination resistor was attached because it had
no matching network for the old micro-second pulser.
The nano-second grid pluser was installed on the topof the pulse transformer tank of the electron gun.The channels of the nano-second pulser and the microswitches.
second pulser are switched by coaxial
The blockdiagram of the nano~second pulser is shown
A pulse forming circuit consists ofin Fig.1.
avalanche transistors and a coaxial cable which forms
isThe formed pulse
a pulse forming network.
amplified by a three stage vacuum tube amplifier andfed to the grid of the gun.

SIGNAL GENERA TOR

qf rev-BEAM~DEFLECTOR
Fig. 3 Blockdiagram of Knockout System
Timing Circuits
A TR

AVALANCHE TRANSISTOR

V T

VACUUMTUBE

The short electron beam must be injected into a
specially fixed bucket of the synchrotron, extracted
from the bucket and injected into one of two bucketsof the storage ring which are synchronized to thebefore.
of the synchrotron as describedbucketPULSERAMPLIFIER

Fig. 1 Blockdiagram of Nano-second Pulser
295

Trigger pulses of the injection into the synchrotron
and the extraction from it ( or the injection into thestorage ring ) are controlled by a main timing system
which consists of a master pulse generator and digitaldelay circuits.
The master pulse generator triggers
power supplies for synchrotron magnets. When magneti,cfield of the magnets reaches previously fixed values,
theinjection
and the extraction
systems
aretriggered.
Though we have a magnetic field monitor
system ( B-clock system ), we use digital delay
circuits which generate trigger pulses equivalent toones generated by the B-clock system, as the stabilityof the magnetic field is sufficient after about one
hour warm-up.
These trigger pulses are not sychronized to theRF buckets.
The sychronization is done by a single
bunch control module of which blockdiagram is shownin Fig. 4 • Main circuits of the module are octal andbinary counters and fast D-type flip-flop circuits.
The counters count the radio-frequency from a master
oscillator for the acceleration system.
The octal
counter marks a certain bucket in eight buckets of thesynchrotron and the binary counter marks one of two
buckets of the storage ring which are synchronized to
the fixed bucket of the synchrotron.
The trigger
pulses from the main timing system are synchronized tothe marked bucket by means of the D-type flip-flop
circuit.
A variable delay line between the master
oscillator and the single bunch control module is used
to compensate a signal delay in cables andtransittime of the beam in a beam transport system.

RFFig. 5in Storage Ring
(20 ns/div)

horizontal one. When energy of electrons was about 90
MeV, the knockout voltage was supplied, as the changeof tune was small at this energy level.
The single
bunch formed by the knockout method is shown in Fig.5.
Upper- and lower traces of Fig. 5 show the cavity
voltage and the signal from a button monitor.
Only
one bucket in sixt·een buckets is occupied,andbackground current is too small to measure.
Discussions
The single bunch was stored successfully. Single
bunch purity required by users is better than99%(This figure depends on experiments.) i.e. backgroundcurrent must be less than 1%.
In the case of thenano-second pulser, the purity is determined by fieldemissions from the electron gun and the accelerating
structure of the linac. The background current due tothe field emissions is estimated at about 1%.
As anobservation of the short beam from the linac isdifficult as mentioned before, this figure is notconfirmed yet.
In the case of the RF knockout method, factors
which determine the background current are the tune
spread of low energy electron beam in the synchrotron,phase jitters of the knockout voltage, unstable tunedue
to flickering of the power supply for thesynchrotron magnets and so on.
We have no way except
oscillograms of the single bunch to measure the low
current
precisely forthepresent.
backgroundThe background current measured by the oscillograms isless than few percents.
If the better purity isrequired, the nano-second pulse and the RF knockout
method can be used together.

l\l\l\l\1\l\1\l\l\l\l\l\l\l\l\l\f\~;''.

t~ll\J V V4J V VVV\JVV vVVSingle Bunch_ll_f'l_fl_[l_pv·':r~I

1/16-1'---------.J,,'-------+-----

Acknowledgement
We would like to thank K. Yoshida of INS andK. Takami of KURRI for their suggestions in several
discussions, and also our many colleagues in the UVSOR
group who contributed to this work.

INJECTION COMMAND

GRID

PUL&S"'E"'R-------------1~--'EXTRACTION COMMAND____]:
I

I
I_____/1__

KICKER PULSER

Fig. 4

Timing System·

Experimental Results
The single btinch was stored successfully using
the nano-second grid pulser in March.
The beamcurrent in the single bunch was too weak to measure.
The beam current was not improved because of a bad
condition of a tuner of the storage ring RF cavity.
The RF phase between the synchrotron and storage ring
jumped suddenly, and some buckets adjacent to the
fixed bucket were also filled.
The second try of thesingle bunch storage using the nano-second pulser is
not done yet, and it must be done as soon as possible.
The RF knockout method was also tried in August.
The vertical deflector was used, because the required
voltage for the vertical knockout is smaller than the296