The' 11th Symposium on Accelerator Science and Technology, Harim<J Science Garden City, 1997

Experimen ts of Synchrotro n Injection Using the Direct Fast Chopped H- Beam
Extracted from Surface-Pla sma-Type Negative Hydrogen Ion Source
Katsuhiro SHINTO, Akira TAKAGI, Shinji MACHIDA, Yoshiharu MORI,
Masahito YOSHII, Masashi SHIRAKATA and Kiyomi KOBA
Accelerator Laboratory, High Energy Accelarator Research Organization,
1-1 Oho, Tsukuba, lbaraki, 305 JAPAN
AbstractBeam.Extrac:tiou(ro Main Ring)

An experiment of synchrotron injection using the· direct fast chopped H- beam extracted from asurface-plasma -type H- ion source has been successfully
achieved. The injection phase of the fast chopped beamfrom linac into the booster synchrtron is adjustableagainst the center of rf bucket by using this beam. It
was obtained that the longitudinal emittance was controlled at the extraction of the booster synchrotron, andthat the beam loss during the injection into main ring of
the KEK-PS was reduced by this fast chopped beam.
OscilaiOr(201 ~Hz)

1 Introduction
Recently, high energy and high intensity beam acceleration programs are proposed and developed. For example, JHF project shows the beam intensity of 2 x 10 14
particles per pulse at the 50 GeV proton synchrotron.(!]One of the difficulties to realize such a high intensity
project is the beam loss due to the beam divergence by
the space charge effect of the beam itself. To reduce theeffect, some methods are examined.
The beam in the synchrotron is bunched andcaptured to the rf bucket. The space charge effect canbe reduced by making the line density of the bunchedbeam small. Generally, the lina.c beam is continuousand this beam injects into the synchrotron. After theinjection, the particles are captured by the rf bucket adiabatically and the beam acceleration is started. But inthis method, the line density of the beam in the rf bucket
cannot be controlled.
To control the line density of the beam, theinjected beam from the linac has to be bunched beforehead to the same frequency of the rf bucket of the synchrotron. And the injection phase of the beam is shiftedto the center of the rf bucket. Using this method, thebeam can be spread into the rf bucket by the broadeningof the synchrotron frequency. There are some methods
to make the injection beam chopping.(2][3][4] One of themethods is tl1e beam chopping directly at beam production in the ion source. At KEK, a surface-plasma -type
H- ion sourec is used to produce the n- beam. The
method to produce the chopped beam extrcacted fromthis ion source was reported previously.(5]In this paper, the results of the experiment of theinjection into KEK 12 GeV synchrotron using the direct
fast chopped H- beam extracted from the ion source isreported.
2 Experimenta l Apparatus and Control System

In KEK-PS, a surface-plasma -type negative hy-7SOI<V DCConvener DC Power SupplyFig .. 1 Control system for the longitudunal emittancein the booster.

drogen ion source is developped and used. The H- ions
are mainly produced by the sputtering process on themetal surface, called converter, which is negatively biased to the pla1;ma. As the H- ion beam current extracted from ion source depends on the converter bias
voltage, the direct fast chopped u- beam extracted fromion source is produced by modulating this bias voltage.
The results of this chopped H- beam experiment is reported at the previous symposium.(5]By mismatching the phase of the injected beam to
the rf b_ucket of the booster synchrotron at injecting thechopped H- beam from the ion source into the booster
synchrotron, the particles spread into the bucket becauseof the broadening of the synchrotron frequency. And
then, the longitudinal emittance of the beam extracted
from the booster synchrotron can be controlled. The
scheme of the longitudinal emittance control! system of
the fast chopped H- beam extracted from the ion sourceis shown in Fig. l. The signal of the frequency generator
ofthe rf cavity i1i. the booster is triggered to the highvoltage pulser biassing the converter in the ion source.
The delay circuit is set between the frequency generator
and the pulser to control the injection phase to the rfbucket. The acceleration frequency of the rf cavity at thebeam injection is about 2.25 1\'iHz, equal to about 444 ns
period, and the injection phase control can be changed
to 1 ns (about 0.81 radian). The rfpattern ofthe booster
synchrotron is not that using for the adiabatic capture
but that of high voltage beforehead at beam injection.

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Timet (ns)Fig. 2 The waveform of the bunched beam just before the extraction from 500 MeV booster synchrotron.
The experiments are examined using this rf pattern andthe control unit.
3 Experimetal Results and Discussions(b)

The injection phase of the linac beam is changed
using the delay circuit between the frequency generatorof the booster rf cavity and the high voltage pulser tomodulate the converter bias voltage. At the injection
phase of the linac beam matched to the center of the rf
bucket, the longitudinal emittance is minimum. And it
increases at the injection phase of the linac beam whichis shifted until ±goo to the center of the rf bucket.
The waveform of the bunched beam just before the extraction from 500 lVIeV booster synchrotron
is shown in Fig. 2. The beam intensity of these bunchedbeam is same. This figure shows that the line densityof the synchrotron beam can be controlled. The bunching factor of goo shifted injection beam is about 0.34
although that of the center of rf bucket injection beam
is about 0.22.
The waveforms of the beam intensity at themain ring is shown in Fig. 3. The decays of the beam
intensity from the time of the injection into the main
ring to that just before the acceleration is different. The
decay of go"" shifted injection into booster synchrotron
shows more gentle than that of the center of rf bucket
injection. This is because the line density of the beam
is controlled.
To confirm this, the beam size of the beam injected into the main ring is measured. To tneasure it,
the fast wire scanner[6] is used. The beam size increment is shown in Fig. 4. The beam size increment of
the goo shifted to the center of the rf bucket injection
is smaller than that of the center of the rf bucket injection, although the beam intensity of the goo shifted tothe center of the rf bucket injection is higher than thatof the center of the rf bucket injection.
Using this method, the beam intei1sity of theg pulses injection into KEK-PS main ring is measured.

Fig. 3 The waveforms of the beam intensity. (a) goo
shifted. (b) center.

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. . . . . . . . . . t',,,':, . .

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Time arter MR injection t,.,, (ms)Fig. 4 The beam size measured by the fast wire scanner.

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The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 19978x10 121:;......

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Beam intensity at booster I 8 STR (particles/pulse)

Fig. 5 The beam intensity of the 9 pulses injection
into main ring using the fast chopped H- beamand the injection phase control system.
The result is shown in Fig. 5. The beam intensity of
9 pulses injection using the 90° shifted to the centerof the rf bucket injection could be obtained to 7.2x 10 12particles, and this is the new record of the beam intensity
at the KEK-PS main ring injection.
4 SummaryThe experiment of synchrotron injection using thedirect fast chopped H- beam extracted from the surfaceplasma-type H- ion source has been achieved. The bl'ow
up of the transverse beam size due to the space charge
effect by the beam itself could be reduced by the control of the longitudinal emittance from the booster synchrotron. Using this method, the beam intensity of the 9pulses injection into the KEK-PS main ring is obtained
the new record of the beam intensity at the I..:EK-PS
main ring injection.
References[1] KEK-Report 97-3., "Proposal for Japan Hadron Facility".

[2] J. l\'I. Brennan et al., Proc.
1154(1989).

1989 IEEE PAC,

(3] H. V. Smith et al., Pro c. 17th Int 'I Linac Con f.,
393( 1994).
[4] R. L. York et al., Proc. 199:3 IEEE PAC, :3175(199:3).
[5] K. Shinto et a!., Proc.
Techno!., 230(1995).

lOth Symp. Accel.

Sci.

[6] K. Koba et al., Proc. 16th RCNP OSAI\:A Int'l
Symp. on Multi-GeV High-Performance Accelerators and Related Technology, (To be published).

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