STATUS OF THE PHOTON FACTORY 2.5 GEV LINAC
Jiro Tanaka
Iniector Division, Photon Factory, KEK

The general picture and special feature of the Photon Factory 2.5 GeVinjector electron linac are described. This report also describes the statusof constructio n and the results of the test operation of some components ofthe linac.
1.

Introductio n

The Photon Factory accelerator consists of a 2.5 GeV injector linac anda 2.5 GeV storage ring. The linac will be used not only for the injector ofthe storage ring but also for the electron and positron injector of theTRISTAN and for other purposes; injector for lower energy small storage rings,for example, 400 MeV, 1 GeV, etc. and for undulators. In addition to theordinary pulse width (~ second range) beams, the linac is capable of producing
very short (ps range) single pulses of electrons and light which will be
useful not only for studies of transient phenomena but all:;o for studies ofaccelerator itself and for development of fast detectors.
2.

General description

The linac was designed to accelerate electron beams of 50 mA to energies
of 2.5 GeV with a total rf power of 840 MW and to 3.0 GeV with 1,200 MW.
It consists of an injection system, a main accelerator and an energy
compression system (E.C.S.). The E.C.S. is added down stream of the main
accelerator in order to get stable and narrow energy spread beams. For
single bunch beam acceleratio n, a special injection system and a low jitter
trigger system synchronize d with an rf wave are provided. The main accelerator is composed of five sectors, each of which contains eight acceleratio nunits. One acceleratio n unit consists of four 2 m long accelerator guides
mounted on a 9 m long cylindrical supporting girder, a 30 MW klystron and apulse modulator with controller. ·The power from the klystron is split and fed
into the four accelerator guides. The phase lengths of the four feed lines
are made so precisely
equal that high power
phase shifters in thefeed lines are eliminated.
The results of various
tests on a prototype
acceleratio n unit showedthat the structure wassatisfactory and thephase differences of thefour feed lines werewithin 2.5 degrees. At
the end of June 1980, thefirst acceleratio n unitwas installed in thelinac tunnel as shown inFig. 1.
Fig.l

Accelerator unit.

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3.

Accelerator guide
The accelerator guide is a conventional 2TI/3 mode quasi-constant gradienttype; the disk hole diameter decreases linearly along the length. This
structure makes possible mass production of the accelerator guides in precision, and also makes division of the accelerator guides into five different
types (A ~ E) easy, so as to reduce beam blow up effects. The accelerator
guide are made by means of an electro-plating method. In order to fabricate
many accelerator guides in a limitted period, automation was widely introduced
into the production processes. Due to the method, the phase shift error ofeach cell of the completed guide is less than ±2 degrees without any tuning
process. As the results of high power rf tests, 30 MW was successfully fed
into one of the accelerator guide which is five times as large as the designed
value for 2.5 GeV acceleration at 50 mA loading. 37 accelerator guides werecompleted in the 1979 fiscal year.
4.

RF power source

The rf system is composed of following stages; a 476 MHz master oscillator, a 476 MHz C. W. booster klystron, frequency multipliers, 2856 MHz
booster klystrons (pulsed) and final 30 MW klystrons.
Pulse modulated 476 MHz waves are also suitable as low jitter (<20 ps)
trigger signals which are especially important for single bunch beam acceleration and detection.
High power klystron with focusing permanent magnet was developed. The
performance of the klystron was successful and more than 30 MW of rf power
was obtained at 270 kV and 280 A. The focusing magnet is composed of numerous
Alnico 9 rods packed cylindrically. The charging test was successfully
performed and desired maximum field and field distribution were obtained.
Test operation of the prototype pulse modulator has been continued sinceApril 1979, and the pulse to pulse variation of less than 0.1 % was obtained.
In April 1980, 12 modulators were installed in the klystron gallery.

The injection system has two functions. The first is production andacceleration of ~s range electron beam pulses. After acceleration to anenergy of 30 MeV, the beam is injected into the main accelerator. The second
is to produce intense single bunches isolated from the finestructure of2856 MHz or the satellites. In order to satisfy these requirments, theinjection system has a special composition; an intense and fast (<2 ns)
electron gun, a subharmonic buncher, a prebuncher, a short buncher, two-2m
long accelerator guides, beam focusing system and beam diagnostic system.
6.

Control system

The control system consists of a distributed processor network interconnected in loops by serial communication circuits which are classified into
three ranks: Loop-! (5Mbit/s), Loop-II (500kbit/s) and Loop-III (48kbit/s).
Nodes of Loop-! are seven minicomputer stations. Terminal nodes of Loop-II
and III are various microprocessor-controlled units: Gun and klystron-pulse
modulator controllers (Loop-II), focusing system controllers, vacuum system
controllers, etc. (Loop-III). In order to avoid troubles due to intensenoises, optical fiber is used for the communication loops.
At present, Loop-! with seven minicomputer stations, camac modules
connected to the minicomputers, pulse modulator controllers, etc. are in test
operation.

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