JAERI-Conf

95-021

2a1-2
Present Status ofPNC High Power CW Electron LINAC
T. Emoto, A. Ohomura, Y. Yamazaki, H. Takei, K. Hirano,
M. Nomura, S. Toyama,Y. L. Wang
Power Reactor and Nuclear Fuel Development Corporation (PNC)
4002 Narita, Oarai-machi,lbaraki-ken, 311-13 Japan
I. Sato, J. Kobayashi, A. Enomoto
KEK, National Laboratory for High Energy Physics (KEK)
1-1 Oho-cho, Tsukuba-shi, lbaraki-ken, 305 Japan
Abstract
Pre-commissioning of the PNC high power electron accelerator,
a 10 MeV CW(Continuous Wave) TWRR(Traveling Wave ResonantRing) electron linac, has been started. All the major components ofthe injector are installed and aligned. After pre-commissioning, therest of six accelerating TWRR tubes will be installed by the end of the1996 fiscal year. Commissioning of the entire machine will begin inApril1997.
1. Introduction
Design and construction of a high power CW electron linac tostudy feasibility of nuclear waste transmutation [1] was started in
1989atPNC.
A high power L-band klystron and a prototype high power TWRR
accelerating tube were built and successfully validated many ofdesign concepts by the end of 1992 at KEK facility. The injector,
first accelerating tube and utility equipments were installed. Theseportion is ready to accelerate beam by winter 1995 at beam energyof 3 MeV. The whole facility will be completed in March 1997 atenergy of 10 MeV.
The accelerator facility building has been completed in August,1991. The facility has three floors, where there are the accelerator
in the basement, klystrons and their power supply in the first floor.
The accelerator room is surrounded with 2.3 m concrete shielding on
its roof and wall. The utility facility such as a gas processing
equipment and a cooling-water system are in the basement and firstfloor, respectively. A schematic isometric view of the building isshown in Fig. 1A.
PNC linac is a 10MeV, 20mA (average current, 20%duty) CW
accelerator with eight normal conducting TWRR disk loaded
accelerating tubes[2]. The linac uses 1249.135 MHz constantgradient of 1.2 MeV/manda Q.ofabout 5800 (with beam loading).
The L-band as accelerating frequency was chosen to be suppressed
the regenerative beam break up. In order to achieve the highaccelerating efficiency, the TWRR (or Feedback of rf power) isadopted. In this manner, the rf power entering the accelerator can beincreased to the value above that available from the rf source.
The injector consists of a 200kV DC gun with thermionic cathode,a rf chopper, a prebuncher, and a buncher. Solenoid coils cover theseelements from the gun exit to the first accelerating tube except the rfchopper and chopper slits. A beam dump is located in the end ofaccelerator. The high power low energy (200kW of 1OMeV electron)
beam dump poses some challenging problems because of very shortelectron range in a beam dump target.

2. Present status of the PNC facility
Fig. 1(A) to 1(H) show recent pictures of major components ofeach system with a schematic isometric view of the whole facility.
As of October, 1995, all construction works of the building andutility facility has been completed. The injector, the first accelerating
tube, and a beam dump are installed in the accelerating room.

The cooling-water system for the accelerating tubes and theklystrons has been optimizing for the injector test.
The new klystron designed specifically for this project and the rf
power supply, 90kV 4 msec 50Hz, can be produced the power of200kW. The klystron development includes much effort to make a
L-band 1MW CW klystron with one pill-box type rf window. Theklystron is able to handle continuous power of about 1MW at factory
test. Fig. 1(8) shows picture of the klystron and the power supply inthe klystron gallery.
Fig. 1(G) shows the electron gun and power supply. At present,
the electron gun is under the conditioning up to 200kV. The injector
is shown in Fig. 1(E) and 1(F) with view of solenoid coils andTWRR. To reduce the transverse momentum to the part of beam, therf chopper cavity is driven at fundamental frequency with TM210 modeand second harmonic with T~ 10 mode, and DC magnetic bias.
Adjusting rf field amplitude and phase, a superposed magnetic field
can be equal to nearly zero on the beam center line in 120 degree
phase length[3]. The aluminum mock up cavity has shown goodresults but the feeding rf power and tuning the cavity with different
frequency very critical. A copper made cavity was fabricated with theresults of prototype. The beam dump core and cooling plumbing isshown in Fig.1 (D) without a vacuum jacket.
The beam line components such as profile monitors, position
monitors, and current monitors were installed and have been adjusted.
The injector beam acceleration test (as pre-commissioning)will bestarted with short pulse (-1 OOj.lsec) and few repetition rate (-1Hz) to
avoid the temperature changes of accelerating tubes by feeding highpowerrf.
3.SummaryAll components for the injector has been adjusted and tested at thePNC site to confirm the performance toward injector test.
Presently the PNC accelerator facility is coming to the injector
commissioning. This partial operation is necessary for verification ofa few new ideas such as two frequency driven rf chopper and thestudies of the accelerator that has no existence in the past.
After commissioning of the injector, the rest of six accelerating
TWRR tubes are going to be installed by the end of the 1996 fiscal
year.
References[1] S.Toyama et. al., "Transmutation oflong-lived Fission Product(137Cs, 9<Sr) by a Reactor-Accelerator System" , Proceeding of
the 2nd International Symposium on Advanced Nuclear Energy
Research ( 1990)[2] Y.L.Wang et.al.,"Design of High Power Electron Linac at
PNC", Journal of Nuclear Science and Technology, 30 [12] 1261
(1993).
[3]Y.L.Wang et.al., "A Novel Chopper System for High Power CW
Linac", Proceedingofthe 1994 International Linac Conference,
205 (1994)- 177-

JAERI-Conf 95-021(E) Injector(Q-magnet, solenoid coils)

Fig. 1 Schematic isometric viewand recent pictures of PNC facility.

(F) Injector (1WRR, rf-feeding)-178-(H) Gas processing equipment (partial)