JAERI-Conf 95-021

PB54
Status of the Emittance Upgrade Programat the Photon Factory Storage Ring
Masahiro. KA TOH and Yoichiro. HORI
Photon Factory
National Laboratory for High Energy Physics!KEK
1-1 Oho, Tsukuba, 305 JAPANABSTRACTAn emitttance upgrade program of the Photon
Factory (PF) storage ring is in progress. The beamemittance will be reduced to 27 nm-rad by doubling thenumber of the quadrupoles and sextupoles in the normal
cells. This will result in typically ten times higher
brilliance of SR. Designs and developments of theaccelerator components were finished and the fabrications
are in progress. The reconstruction work of the ring will
be started in Jan. '97 and will be finished in Sept ..

1. INTRODUCTION
The performance of the Photon Factory (PF) storage
ring has been steadily improved since the start of its
operation in 1982 [1]. Now the ring stores 300 rnA
positron beam on average with a lifetime of more than
60 hours. The beam energy is normally 2.5 GeV and canbe ramped up to 3 GeV.
The beam emittance, which had been 460 nm-rad in
the early stage of the operation, was reduced to 130 nmrad by changing the quadrupole strengths in 1986 [2].
However, the emittance is still larger than those of thethird generation synchrotron light sources by one order ofmagnitude [3] and the brilliance of the SR beam from
insertion devices is smaller by one or two orders ofmagnitude.
To compete with the new generation machines in thenext decade, a high brilliance ( low emittance ) lattice
was designed [4]. Designs and developments of theaccelerator components for the new configuration werefinished and their fabrications are in progress. The presentstatus of the emittance upgrade program is described.

quadrupoles and the sextupoles are doubled in number andarc reinforced in field strength. No change is required forthe bendings. The optics of the whole ring was designed
for three cases of the horizontal betatron phase advance,
90, 105 and 135 degree per unit cell. The emittance is44, 33 and 27 nm-rad, respectively. The natural beam
sizes for the present optics and for the high brillianceoptics (135 degree lattice) are shown in Figure 2. The
smaller beam size of the new optics will results in higher
brilliance of SR at all existing beam lines by factor of 5to 10.
Because the sextupole fields become stronger for thelower emittance optics, the dynamic aperture becomes
smaller and this may be a serious problem [5]. The
commissioning of the new lattice will be started with the90 degree optics which has relatively larger dynamic
aperture. The lower emittance will be challenged step bystep.

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2. LATTICE
The present FODO type normal cells which occupy
one third of the ring will be modified for the highbrilliance configuration, as shown in Figure 1. The-401-Figure I. The present (upper) and the new (lower)
configurations of the accelerator components in thenormal cell section.

JAERI-Conf 95-021

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By turning off some of the magnets and changing thepolarities of some of others in the normal cells, an optics
almost same as the present one can be reproduced [4].
This enables us to restart the operation quickly just afterthe reconstruction work with our familiar optics.

3. DEVELOPMENTS OF ACCELERATOR.

COMPONENTS

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2,Hill';~a:,Figure 2. The natural rms beam sizes of the presentlattice (upper) and new one {lower) with 135 degree
cells. One half of the ring is shown.

3-1. Magnets
All the present quadrupoles and sextupoles in thenormal cells will be replaced with the new ones of higher
field gradients. All of them are Collins type, not todisturb the synchrotron radiation extraction to theexisting beam lines. Since the spaces are very limited,
they have relatively short lengths and small bore
diameters. The sextupoles have auxiliary windings forvertical steering. The fabrication of all the magnets werefinished and the field measurements are under way [6].
3-2. Injection
The injection kickers will be reinforced to becompatible with the optical functions around theinjection point of the new lattice. A traveling-wave typekickers are developed and under fabrication[?], whose
short pulse length enables a single-tum injection scheme.
No change will be made for the septum magnets..

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OF.pFigure 3. New configuration of the PF storage ring for higher brilliance. Mainly the normal cell sections will.bereconstructed. There are also minor changes in the insertion sections.

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JAERI-Conf 95-021

3-3. Vacuum
About a half of vacuum chambers will be replacedwith new ones, which arc now under fabrication, to becompatible with new configuration of the magnets. The
straight sections of the chambers are newly constructed.
The bending sections are remained because there is no. change on the bendings. A design consideration is taken
to install all the components, such as pumping port,
bellows and flange, in the narrow space limited by the
doubled magnets. The smaller emittance and the shorterbunch length in the new lattice are expected to result in ashorter Touscheck lifetime and a higher sensitivity toirregularities of inner wall of the vacuum chambers. To
guarantee a long beam lifetime, the new chambers arerequired to have effective pumping speeds equal to or
higher than those of present chambers. The bellows andflanges are equipped with a shielding contact to cure theirregularities.
3-4. RFFor a low emittance beam, Landau damping producedby the octupoles cannot be effective to suppress the beam
instabilities. The existing four RF Cavities will bereplaced with damped cavities, in which dangerous higherorder modes giving rise to beam instabilities are damped.
A high power model is now under testing [8].
3-5. Beam Channels
The front-ends of the existing SR beam channels in
the normal cells will be modified to fit with the new
configuration of the magnets and vacuum components
and also to cope with the increased power density of SR[9]. The reconstruction of the beam lines has already been
started in advance to that of the storage ring. All thework will be finished in 1996.
3-6. Beam Monitors and Handlings
The present beam position monitors in the normalcells, each of which consists of six electrodes, arereplaced with new ones with four electrodes to fit with
the new vacuum chambers. The signal processing will be
improved to achieve an accuracy as good as a few
micron, a speed of data taking as fast as 2 kHz. A turnby-turn beam position measurement scheme is underdeveloping [10], which will be useful for commissioningof the new lattice.
For the orbit stabilization, which will be more
important for a lower emittance light source, a fast andprecise feedback system for fluctuations lower than 50 Hz
is now under developing [11], which utilizes the new fastand precise BPM system mentioned above.

A transverse feedback system to suppress the beam
instabilities is under developing, which consists of one
deflector and two BPM's[12]. This will be a effective tool
to suppress the beam instabilities due to the RF cavities,
beam-ion interactions or beam-electron interactions;3-7. Control
The control system will be replaced with a new one
which consists of UNIX work stations and VME
systems[13]. Since the control of the magnets and thebeam monitors are more important in the commissioningof the new lattice, their control system will be replaced,first during the shutdown in 1997.

4. SUMMARY
The developments and fabrications of the accelerator
components for the emittance upgrade are in progress.
All the preparations will be finished until the end of
1996. From Jan. to Sept. in 1997, the ring will be shut
down. All the reconstruction work will be completed
within this period. The operation of the ring will berestarted in Oct. 1997 with the present emittance optics,
as mentioned in section 2. Commissioning of the newhigh brilliance optics will be tried in the machine study
time, typically one day a week. The new optics will be
introduced to users times as soon as possible.

REFERENCES[I] e.g. Photon Factory Activity Report 1982 - 1993

121 Y. Kamiya et al., Proc. of the IEEE Particle Accel. Conf.,(1986)[3] e.g. V. P. Suller, Proc. of European Particle Accel. Conf
(1992)[4] M. Katoh andY. Hori (ed.), KEK Report 92-20 (inJapanese ), (1993)[5 j M. Katoh et al., Proc of European Particle Accel. Conf
(1994)[6] Y. Kobayashi et al., in these proceedings
17] T. Mitsuhashi et al., in these proceedings[8] T. Koseki et al., in these proceedings
19] l/. Maezawa et al., in ref.[4], p.147
I /0] T. Honda et al., in these proceedings
I 11] N. Nakamura et al., in these proceedings[12] T. Kasuga et al., private communication[13] C. 0. Pak et al., in ref[4], p.167

ACKNOWLEDGM ENT
It is a pleasure to acknowledge all the contributionsof the other Light Source Division staff of the Photon
Factory.

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