1-3

PRESENT STATUS OF JAERI LINAC

A.AsamiК.Mashiko

N.Akiyama

M.Kitajima

Y .Nobusaka

Physics Division/ Japan Atomic Energy Research InstituteAbstract
Major modifications to the linac axe sunmarized which have been made since thecompletion of the accelerator in 1972.

Systems and parts modified are , ( 1 ) theelectron gun pulser, prebuncher, and beam transport of the injector,
waveguides including a buncher,(2) accelerating(3) RF circuits for the first few accelerator sectionsand (4) beam transport and vacuum systems.

1 . Ins tгоduc t ion
It is six years since the completion of the 120 MeV JAERI linac in 1972.

Variousmodifications to the linac have been made during this period, only part of which were1)2)3.)
previously reported.
report.

Its major modifications so far made are described in thisExpreriments which are made with the linac will be first briefed.

Two kinds of research were mainly performed so far, one being neutron physics, withTOF (time of flight) method various neutron cross sections have been measured in theneutron energy region of a few volts to about five hundred kilovolts using the linac asa pulsed neutron source.

Inspectroscopy nuclear structures of radioisotopes producedwith the linac have been studied by measuring 3,
studies made are ( 1 ) neutron diffraction study,

丫 raysand conversion electrons.

Other(2) reactor physics and (3) radioisotope

production•
Table 12.

Major modifications of J A E R I linac
Modified parts

Major Modifictions

SystemThe systems and parts

Injector

Gun pulser, Prebuncher, Beam transport

Accelerating
waveguides

Buncher, 1st Accelerator,
2nd Accelerator (in plan)

Beam transport,
Vacuum.

That for buncher, Achromatic TransportThat for waveguides

Modulator,
ConlrolThat for buncher, PFN Switch,
Timming ccircuits

modifed are sumarized inTable 1 . Details of thesemodifications are presented
ih other papers.

So, they

will be described only
briefly here.

Waveguide2.1-Э20 主5

Injector
Arrangement of themodified injector is shownin Fig.l.

70 ^220•100GunBeammonitor—

ISO-S3A

Pre buncher

Main parts
Gatevalvechanged concern theelectron gun and theprebuncher.

Purpose ofСthe modification is toZOO

BuncherП

120

obtain higher currentseI

particularly at short pulsewidths.

It is advantageous

for the gun to be near theaccelerator and the drift

400

distance of the prebuncher
to be short, using theexisting gun.

I.pFig.1

Arragemcnt of the present injector

Higher RF power is then required for the prebuncher, so that a prebuncher

was newly designed, parameters of which are shown in Table 2.
2.2

Accelerating Waveguides
The first few accelerator sections are shown in Fig.2 together with the RF waveguides

RF window

The most important modification of the accelerator system is the installation of an
independent buncher section, which is already reported in r e f s . 1 and 3.

The first

accelerating waveguide was replaced last year
Table 2

Specifications of prebuncher

by a new one/ the characteristics of which are
shown in Table 3.

In the waveguide , holediameter 2a of the discs changes in four steps

1 • Frequency
22856.75 + 10 MHz. Max RF power
peaksmaller toward the waveguide end, leading tomore efficient use of the RF power and higher
current by lessening the beam blow up problem.
The accelerating waveguide is cooled
efficiently with a water jacket for the50 KW

Auerage

60 W

3. Q-Value

500

4. Cooling

Water •

5. Temperature

40 °C

6 . Total Length

150 ramwaveguide and the input and output couplers
also cooled.
An accelerating waveguide of the same specifications as in Table 3 is being
construced which will replace the existing second accelerating waveguide made in trial
because of its inadequate cooling.
2.3

RF system
Corresponding to the new arrangement of the first few accelerator sections andprebuncher, the high power RF waveguides were largely modifed as shown in Fig.2.

AnRF system with the maximum power of 10 MW was newly made, from which an RF power withthe maximum of 40 KW is divided to feed the prebuncher.
The waveguide windows were repositioned from just above the input couplers of theaccelerating waveguides to theTable 3

Specifieations of accelerating waveguide. TypeApproximate constant gradient(four steps). Number of cavities

61 cavities + 2 couglers

3. Mode

2tt/3

4. Frequency

2856.75 土 0.05 MHz (40°C/ Vac)

5. Phase variation+ 3°

6. VSWR< 1.05 (at 2856.75 MHz)2

く 1.1(+1.2 MHz)> 13000

8 . RF power

22 MW (peak). Total length

couplers.

The output waveguide

windows were also repositioned

couplers.
The RF oscillator currently
used is a solid-state oscillator2)

as already reported.
2.4

Beam transport andvacuum systems

25 kW (average)10

be directly seen from thefurther away from the output

7. Qvalue

9. Disc hole (2a)place where the windows cannot

26.8, 26.2, 25.4, 24.6 іпшфBesides the solensid coils
required for the buncher, a2300 ш-13-doublet of quadrupole magnets and a pair of beam steering coils are inslalled between thebuncher and the first accelerating waveguide.
At the end of an electron beam line for the neutron experiments a deflection magnet
is installed to bend the beam to a neutron producing target.
suffers from instability
time measurements.

This arrangement, however,of the beam current due to the variation of beam energy in long

To reduce the instablity, an achromatic beam transport system with two

deflection magnets is under construction.

References
1 . A.Asami et: al., Proceedings of the 1976 Linac Conference at Tohoku Univ. p.3
2. K.Mashiko et al., Preceedings of the 1976 Linac Conference at Tohoku Univ. p.6
3. K.Mashiko et al., Preceedings of the 1977 Lianc Conference at KEK.