Heavy Ion Linear Accelerator in the NUMATRON Project
T. Katayama, S. Arai, T. Hattori, T. Hori, T. Nakanishi,
A. Noda, E. Tojo, N. Tokuda, N. Ueda, S. Yamada and K. Yoshida
Institute for Nuclear Study, University of Tokyo

1.

General Description

NUMATRON is a high-energy heavy-ion accelerator which accelerates theheavy ion such as uranium up to an energy around 1 'V 2 GeV/nucleon [1]. It
was proposed in 1977 as a future project at INS and since then the preparatory studies have been performed on the many accelerator subjects. The
main purpose of the project is a high energy nuclear physics but researchers
in various scientific fields will be involved in the project. The design
objectives for the injector linac of the main accelerator, which consistsof cascade synchrotrons, specify the beam energy of 10 MeV/u and the kindsof aceelerated particle of a to uranium with an enough intensity not only
to fulfil the synchrotron but also to provide the beam to the relatedscientific studies such as atomic physics, solid state physics, irradiation
experiments and so on. The operation mode of the linac would be a repetition rate of 40 Hz and the pulse width of 300 ]JS as a synchrotron injector.
However, the linac should provide a beam also to the other various facilities and the duty factor of the operation is designed to be 25 % for theheaviest ion such as uranium and cw (continuous wave) for the light heavyions.
The linac is exclusively an integrated complex because the injectionenergy to the linac is around 15 Kev (S ; 0.57 %) due to the small charge
to mass ratio of the extraeted beam from the PIG type ion source. Herethe terminal voltage of the Cockcroft-Walton pre-accelerator is designed
at 500 KV. The low velocity section of the linac should be envisaged
carefully and studied experimentally for the good beam aeceleration.
Another reason for the complexity of the heavy ion linae is the neeess4ty
of charge stripping between the linac tanks for the effieient acceleration.
In the present design three stripper sections are provided at each specificenergies of 300 Kev/u, 1.6 Mev/u and 10 Mev/u. In the paper, results ofdesign and experiments of the low velocity linac are described.
2.

Wideroe Type Structure

In the first stage of design, the low velocity linac.was assumed asa Wideroe type of whieh the parameters were decided based upon the experimental data at GSI [2] and at our institute [3]. It consists of two TI-37T
mode tanks and one TI-TI mode tank which accelerates the uranium ion in theenergy range of 15 'V 146 Kev, 146 'V 305 Kev and 305"' 1102 Kev, respectively.
In Fig.l, the drawing of first TI-37T mode 1inac is given and the basic
characteristics of the tanks are given in Table 1. It was found that the-235-----~--·~-------~~-----------

effective shunt impedance, of -the Wideroe type structure were around 50_ "-' 60
Kl/m in the specific energy region.. In this· structu.re, the power loss ismainly occurred at the drift tubes and stub lines and the loss at the stubline amounted to nearly the half of the total power loss.
In Table 2 the 'power loss at' each part in the 'Wideroe type structure
are given. This large power loss is inevitable due to the large current
in the stub lines of wl:i.ith the short positions are adjusted to give anadequate gap voltage distributions in the array of drift tubes. It is truethat the large diameter of the stub line can reduce the power loss in it,
but it results in the more complicated structure and it would not bedesirable.
Then ·we have studied other ·two types of lowyelocity structure, namely
iriterdigital H structure and RF-Quadrupole linac, both of which are excited
in TE mode.
3.

Interdigital H Structure

The low velocity linac which is excited in TE11n mode
Interdigital
H structure have been studied by H. Morinaga, M. Brez et al, and J. potter[4,· 5, 6] and it has been demonstrated that the structure has a large shunt.
··impedance with a small diameter of the tank and a relative low RF frequency.
At Munchen University, the IH structure linac was constructed as a post accelerator of the Tandem Van de.Graaff. They obtained a high shunt impedanceof 120 ~ 200 Mn/m in the velocity region of S = 5 "-' 10 %, but the drift
tubes did not contain the focusing quadrupole magnet because it was served
as a post accelerator with a relative large velocity. In order to study
the -feasibility of this structure in the low.energy region, one-eighth
scale model resonator is constructed (Fig.2) which is a TI-TI mode with aconstant velocity ancl has a tank length of 1215 mm, a tank diameter of150 mm and cell length of 22.5 mm (corresponding to 8 = 3.0 %). Two kindsof drift tubes are alternfjtively aligned in the tank axis, one is assumed
to have a quadrupole magnet in it and has a cliameter of 25 mm, and theother has a diameter of 14 mm without Q magnet. The resonator length canbe varied by moving the· _short plate at the ·tank end. The n-th resonant
frequency of TE1 in mode are plotted against n/9.. where 9.. is .a resonator
length (Fig. 3). I t is clearly seen that the resonant frequency is dependent
upon the value n/9.. (not on the absolute. value of 9..) with a constant dimension of ridge. _These behaviours are well analyzed with a transmission-type equivalentcircuit-analysis which also well explains the field distribution in thegaps. On the basis of the above analysis, the effective shunt impedances
Zeff of IH structures are calculated. The results show that Zeff is 54.
"-' 197 Mn/m in the velocity region of S = 0.5 'V·l.4% with. a TI-3TI mode _and
it is around 150 Mn/m in the region 8 = 1.4 "-' 4 % in the TI-TI mode. They
are two or three time's larger than the measured values at the Wideroelinac.
Considering the simplicity of structure and the high shunt impedance,
IH structure wouid be superior to the Wideroe structure. In the low-236-

energy region such as 15 Kev, however, Zeff decreases to 'V 50 Mnf.m which
i13,nearly equal to the value· obtained in the Wideroe structure •. 4.

R.F-Q Linac

It was proposed by Kapchinskii and Teplyakev [?J that the four'chamberresonator excited with TE21n mode, has a action of acceleration and f~cusing
by a quadrupole R,F electric field and the structure is' expected to exhibit
very high capture efficiency (greater than 95 %) because it captures thebeam adiabatically before the beam experiences ,much acceleration; It canaccept the DC beam from the ,electrostatic accelerator and can make abunched beam suitable for .the following linear accelerator without any beamloss. Then it is a good interface between the DC accelerator and theusual drift tube type RF linac.
A one-eighth model cavity was made with a tank length of 1.0 m and adi;1meter of 18.8 em. It has four vanes and interstitial· vane· at both endsof the tank. (Fig.4) The TE 21n and TElln modes interfere with each otherat the large depth of vane (Fig.5-a) but the TE11n mode can. be completely
suppressed by interstitial vane (Fig.5-b). The measurement of electricfield shows the usefulness of RF Q type linac. The beam dynamics in the.
RF-Q structure is studied by computer~simulation and a typical result isgiven in Fig.6 where the ion is assumed as 238 u 7 + and the injection energy
is 15 Kev/u. The R,F frequency is 50 MHz. The vane modulation is varied
from 1. 0 to 2. 2 linearly along the cell number and the equilibrium phase isalso varied linearly from~ 90° to- 30°. It is shown that the u 7+ can beaccelerated froin 15 Kev t.o 125 Kev with a tank length of 2.62 m and a vanepotential of 300 KV. The bore diameter is 2.0 em and the gap capacitanceis experimentally measured at 40 pF/m. The shunt impedance is calculated
at 60 Mn/m whe.re we must note that the definition of !;!hunt impedance isdifferent fr,om the effective shunt impedance at IH or Wideroe structures
because the equilibrium phase is varied in this structure.
Considering the quite simple structure of the resonator and hightrapping efficiency of the be.am, it can be concluded that the RF-Q
structure is suitable for the initial part of the linac. ·References[ 1] "Nl!MATRON" INS-NUMA-5 (1977)[ 2] K.- Kaspar, GSI, 73-10 (translated in English, UCRL-Trans~l522)[ 3] s. Yamada et al. "Model Measurements· of Wideroe Linac"
INS-NUMA-11 (1979)[4] H. Morinaga, Japan. Phys. Soc. Meeting. Osaka (1949)[5] M. Bres et al. Particle Accelerators, 1971, Vol. 2[ 6] J. Pottier, Revue de Physique Appliquee, Tome 12 (1977)[ 7] I. M. Kapchinskii and V. A. Teplyakev, .Prib. Tekh. Eksp. No. 2 (1970)-237'--Table 1

The injector llnac sped.ficntlon.

Wide rOe

OperAtion HodeTT-)TT,Synchrotron Phase (de g.)

38 gaps

WlderOe 211-)TT 1-30.0

Wide rOe

20 gnpsll-lT'Al v;:~ rez

36 gaps

-30.0

-30.0

Alverez

1,6 ft<lpR

2TI 1-25. 8~- ]. 60j

2TT, 108

T/A (lleV/u)

0.015 -

0.1~6

0.146- 0.305

0. 305 - 1.102

1.102v/c (%)

0.562 - 1. 768

1. 768 - 2.557

2.557- 4.861/1.861- 5.859

0.029~

0.029'• (Ul+)

0.0672 cul6+J

0.0672 (lll6+)

5 ·''
1.00

8.0

7.5

J2 .1

1.119

0. 988

l. 36

cu7+J

L (m)

5.5

6T/(L·£) (NeV/m)

0. 85

Zeff (ll!l/m)

67 .a

36.0

47.6

41.8- 43.~

Power Loss (In<)

0. 076

0. 215

0. 494

0. 206Q-magne t Sequence
G (kG/em)
COS\JAperture(mm~)

Admittance (mm mrad)

Table 2g~ps-25.84
1. 600 - 10.023- J ~. 553
0. 193 (Ut.6+)

5. 85~

43.3

-31.6

1. 903

FDFD

FDFD

FFDD

FFIJO

FFDD

10.0 - 3.18

3.18 - 2. 20

3. 50 - 1. 83

lL00 - 3. 30

3.30- 1.33

o. 849o. at.. g

0. 5720. 906

0. 90620, 25' 30
114 ••

30

35t,o

88.7

12 7

"248"

40"

Tne power dissipation of each Wideroe tank*.
Tank lTank 2All drift tube and stems

13.6 kW

20.7

Drift tube line

7.8

11.9

Tank wall

1.0

1.6

9.0

Stub line inner conductor

23.8

90.9

124.5

Stub line shorting plungers

4.6

11.6

28.1

Stub line outer conductor

7.4

28.4

34.2

Total power dissipation

58.2

165.2

380.2

Including joint losses

75.6

214.7

494.3

kW

Tank 3116.6 kW
67.8* Duty factor 100 %Orlft Tubes

Fig. 1 n-3n mode Wideroe linac-238-203

11Fig. 2

1/8 scale model of IH structureFig.

~j:/:7

Without Interscitia11000

TEu

800/.1·J 700"500#c:~;~~=~stiti;·,. 800g/TEzl~ 700/"
/.

'-'

TEu

A.

~ 900;;;:

t 600t·~·oOOL/k;With

RF-Q structure

11ane.

900~~1000~~ 500 _ _ / ·"400"'"'"'

400

0:012

Harmonic No.

Harmonic No.

Fig. 5 Dispersion curves of RF-Q mo.del linac withand without interstitial var

15023au•+
To=15 kttV/utl. = -90- -30•
m= 1-2.2
I: 50 MHZ
V=300 kV
L~ 262 em

.

>
....

-100"'f'•c•

65-;
c50

...

3=...
uc•ll lttngth

2klntttlc •n•rgy
0

102030~.r.
4 c~:;;'E40
50&0c•ll numllttr

708090100

Fig. 6 Beam dynamics in the RF-Q structure-239-