JAERI-Conf 95-021

2p2-5
Conceptua l Design of Compact HIF Driverby RF Linac with High Accelerati on Rate
T. Hattori, K. Sasa, M. Okamura, T. Ito, H. Tomizawa, T.Katayose,
N. Hayashizaki, T. Yoshida, K. Isokawa, M.Aoki, N. Fujita, and M. Okada**
Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology
Ohokayama, Meguro-ku, Tokyo 152, Japan.
** Institute for Nuclear Study, University of Tokyo,Midori-cho, Tanashi-shi, Tokyo, 188, Japan.
keep the acceleration rate to 10 MV/m inenergy region of about 50 MeV/amu by using
high shunt impedance. From consequence ofit we chose the IH type to main linac 9f HIF
driver, We found that the length would be 1~2km. As we designed the conceptual design ofcompact driver for HIF, the following is thereport.

Abstract
The Interdigital-H(IH) type linac isfor its high shunt impedance atknown
wellparticle velocity. Therefore
mediumlow andis possible highstructure
typethe IH
The IH linac
power.
samebyacceleration rate
( effectiveMV/m
10cavity is able to generatebyparticle
acceleration voltage ) with focusing
thesuper conducting solenoid. We designed
compact HIF driver by the IH linac with highacceleration rate. The IH linacs can accelerateparticles with a charge to mass ratio (q/A)
greater than 1!250 from 0.3 MeV/amu up to 50
MeV/amu; The total effective length of the IH
linac cavities is about 1250 m.

2. High Shunt Impedance of IH Linac
2.1 IH type Linear Accelerator

1. Introduction
Until now for the electric power plantof 1 GW, Heavy Ion Inertial Fusion (HIF)
driver system was needed to the length ofseveral km, even if it were RF linacs[1-3] orInduction linacs. In the case of Induction
linac, we could not make the acceleration rate
up because of the voltage limit of ferrite. Andin the case of RF linac because of beam focus
and wall loss of Alvarez type cavity, we could
not make acceleration rate over about 2 MV/m.
So that driver system of HIF is necessary thelength of several km.
The LBL and LLNL group[4] in USA
presented the plan of compact HIF driver in1991. It was the type of Induction linac, theaim was to be compact of driver bycombination of Induction linac and circularnng.
On the other hand, the progress of RFlinac was shown in 1980's and 1990's.
Especially the study of the IH linac wasremarkable. In the IH type structure, it wasproved that the shunt impedance was high in
low and medium energy region, comparing toother linac structure. So it was possible toIn 1956, an interdigital H (IH) typelinear accelerator was first proposed by
As one of the various
J.P.Blewett[5].
candidates for an injector of BNL proton
synchrotron, AGS. In the survey of the BNL
injector, Blewett indicated that the shunt
impedance of the IH type structure is high at
low and medium particle velocity. At higher
200 r----.---.----.- -.-.--.....-..-.- --....,.---,
TIT-IH (48MHz)

150
IH-structure
65-85MHz100

TIT-IH (96MHz)

80

E.......

a~

2

4

6810

f3 (%)
Fig.1 Effective Shunt Impedance of IH andother type.

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15

JAERI-Conf 95-021

energies, however, its shunt impedance falls
rapidly. The further development of thisstructure has been abandoned in USA for along time. The RF characteristics of an IH
resonator,
instead, have been extensively
studied by Russian[6,7] and French [8,9].
According to their experimental results, the HI
structure has the substantial advantages ofsmall transverse dimensions and high shunt
impedance especially at low velocity region

double ridged circular wave guide resonator.
As suggested by J.Pottier[20] and othergroups[10,21], the shunt impedance of theridge wave guide is estimated as.
Zs = C' ·a · (3- 2 · d ·l 5.
Where the symbols are Zs: shunt impedance, f:
operation frequency, D: diameter of cavity, ~:synchronous particle velocity divided by light
velocity c and a: correction factor du to thesurface roughness.
The effective shunt impedance is given
as follows.
zeit = C' . a . T2. (3-2 . D3 . ps(~~0.1).

The small tank diameter gives relatively
low Q-values of the resonator, and therefore,
the RF excitation is very easy to handle. A
simple mechanical structure of linac cavity isalso one of the most attractive points of the IH
resonator.
This accelerating structure,therefore, is suitable for heavy ion accelerator.
The high shunt impedance has beenrealized in a post accelerator of the large
Tandem Van de Graff accelerator inMunich[10-13]. The beam energy boosters
for tandem accelerators have a relativ:ely smallenergy gain in comparison with incident beamenergy.
r=C. (3-2 . D3 . !3.5
where T: transit time factor, C(H): coefficientof effective shunt impedance for IH structure
linac. C(H) is displayedc = zeff. (32. n-3. f-3.5.
Figure 2 shows comparison ofcoefficient of effective shunt impedance ( C )and particle velocity.
The empiricalcoefficients are near the straight line as log-log
plots as shown in Fig.2. If diametor ofresonator cavity is estimated, the effective
shunt impedance is expected various energy
region by using the empirical line.

Table 1 Measured Effective Shunt Inpedance
and Cavity Parameters of IH Structure
InstituteZcff DfL(M!J/m)(m) (MHz) (m)INS(Jn-n:) (198J)14) 4911
TIT&TUM(I994)2-'> 337
GSI (I'NI)24)
320
TIT-I (1986)16)
179
TIT-1110 (1989)18) 132
TIT -2 (1987)251
130
N131-1 (1990)12)
142
TUM-I (1982)11)150
UT (1984)1.1>
137
Nl'll-2 (1990)12)
105
TUM-2 (1990)12)
150

0.48
O.fi5
O.fi3
1.4
0.54
0.7fi
0.72
1.00.75
0.72
0.5

HKl11!3108
48
102
%
100
78
100
100
157

B~tv

Enu1/Ein Ein·Eo111

C*(MeV/u)10

0.92 0.0121 10.7 0.(115-0.Ifi O.fi52
1.89 0.03(,() 15.5 11.1-1.55
1.43
3.55 11.11401 4.7 0.3-1.4
1.57
7.0 0.0470 10.0 0.24-2.4
1.88
0.92 0.0534 2.50 0.82-2.0
2.23
3.0 0.0784 1.42 2.4-3.4
2.10
3.64 0.0803 1.54 2.4-3.7
2.45
5.0 0.0842 1.79 2.4-4.3
2.54
3.0 [J.CJS8
1.27 3.4-4.3
2.66
3.64 0.0955 1.32 3.7-4.9
2.57
3.0 0.1044 1.4 4.3-6.0
2.71~~ ::~~ ~~~~: ~ :~~~~~~~~~~ ~ ~~ ~~ ~ :~ =J: ~: : : : ~!J:::.::::::::1 Empir!cal Coefficient ofr.- ---·· - --· - · . . . . :. . . . . . . ..

--· ·-·--·1 EffectiVe Shunt Impedance 1--- __ ·-- ·-· -· ~~...... ,,_, -· -- --·-·-----· ____, _,,__ -.~f.:::: . .

_......
!.

An IH structure having large energy

gain as main accelerator was studied in INS
university of Tokyo[14] and RLNR Tokyo
Institute of Technology[15-19]. Figure 1
shows comparison of effective shunt
impedance of the IH structure and of otheracceleration structures. Table 1 shows linac
parameters and measured effective shunt
impedance of IH structure until now.

~.-....-',_.:;

t.. -· _. . . . . . . .

::~~ ~~:~~=~: ~· ~=~~~~~ ~~~= ~~ ~~ :~ : : :~ ~: : ~:~ :::::.::: ·: : ·= ::::=.::::..:. ·::::::::: ==: :~:::::~~ ::: ::: :: : : : : : : : : : :..-.. ·--· .... ·-· ,._,_____..__ .....
'"'_,__...·--·- ·-- ·-- ·- ............. .............
,_,

0.01

0.1
{J

Fig.2 Comparison of Coefficient of Effective
Shunt Impedance and Parrticle Velocity

2.2 Effective Shunt Impedance of IH
Structure
In order to obtain a rough estimation ofa shunt impedance for the IH structure linac,
let 1s consider the simplest case where theacceleration structure is approximated by a~-r~.------r-=~~~=r~cr.c=~

3. Conceptual Design of Compact
Driver by IH type Linac with High
Acceleration Rate
First we examine main parameters
using the empirical coefficient shown in Fig.2.
We can keep cavity diameter large even if-246-

JAERI-Conf 95-021

operation frequency is high, in condition of thedrift tube without installing focusing elements.
Therefor the shunt impedance of cavity is kept
over 100 MQ/m until 50 MeV/amu. Even if
we control the voltage between drift tubes intobelow of twice of Kilpatrick limit, we canenough keep acceleration rate 10 MV/m. From
this rate, the peak wall loss is 1.2 MW/m atnormal temperature, and 120 kW/m at liquid
N 2 temperature. So we can operate this linac
system safely.
For the sake of it we can keep theacceleration rate 10 MV/m and construct theRF linac system of HIF driver in the length of
1 to 2 km. The main parameters of HIF driver
linacs are shown in Table 2. As shown inTable 2, The effective length of the IH linac
cavities is 1245 m and the total length of theRF linacs containing RFQ linacs is 1405 m.
Considering the funneling and jointing
sections, it is sufficient to be with 2 km. If
acceleration rate is high at supper conducting
RFQ linac cavity, the length will be shorter.
Table2 Main Parameters of RF linacs for HIF
NnmcnfUnc1c
Frequency (MHz)Input Energy (MeV/u)
Output Energy (MeV/u)
Total Length (m)Diam. of Qwity (m)Zcff(MQ/m)Peak Wall Loss (MW)Wall Loss Rate (kW/m)

RFQ-1
20O.ot0.18
1002RFQ-2
400.180.3

IH-1
1600.3(.01.(,250.42377
11444250
1080
40

1.8
18200.8
1342.50.4
200.8530
0.540\.210at Li<1. N2Accelemtinn Voltage (MV)
Accclcmtion Rate (MV/m)
Peak Ileum Current (rnA)lkam Power (MW)

1.3

m-2
320
1.3
4.9

9tJ
0.24
325
46511
51
900
10\(,{)

288

IH-3
320

m-4

MO

4.9

10.1
50.1
1000
0.12
1381192
103
1192
792
119
79
1300 10000
1010320 640
41(,
3200

10.1
130
0.26
208

4. Consideri ng Subjects in the Future.
We did not mention about beam
As thefocusing in the above chapters.
cavityofcharacteristic of the IH, the diameter
quadrupole
andgets small. The solenoid lenslens of supper conducting will be possible toset in outside of the cavity. It is efficiently
expected to be focus. When it is constructed,
because of the progress of super-conducting
technology, stronger magnetic-field is possible
to generate. We are planning to start thecorrect Particle analysis.
It is necessary to cool the cavity it self
as the cooling shield of the super conducting
system that is set outside of acceleration
cavity. So it is possible that the wall loss ofcavity decrease until 1/10. In the case ofHIBLIC[2], HIF driver is operated in 10 Hz,
and it will be driven 100 Hz. Ad in the case of
100 Hz operation, the 100 fusion reactors are
possible to make electric power of 10 GW.

We must carry out a farther examination ofthese problems.

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