JAERI-Conf 95-021

2a2-3
PROGRESS REPORT ON THE CONSTRUCTION OF THE
HEAVY-ION LINACS FOR RADIOACTIVE NUCLEI
M. Tomizawa, S. Arai, Y. Arakaki, Y. Hashimoto, A. Imanishi, T. Katayama, H. Masuda, K. Niki,
M. Okada, Y. Takeda, E. Tojyo, N. Tokuda, C. Velissaris, K. Yoshida, and M. Yoshizawa
Institute for Nuclear Study, University of Tokyo
3-2-1 Midori-cho, Tanashi, Tokyo 188, JapanAbstract
A heavy-ion linac complex for radioactive beams isnow under construction at INS. The linacs are a 25.5MHz split coaxial RFQ and a 51-MHz interdigital-H(IH) linac. Ions with a charge-to-mass ratio (q/A)
greater than 1/30 are accelerated from 2 to 172 keV /uby the RFQ. The beam passes through a carbon-foil,and ions with qfA ~ 1/10 are accelerated further by
the IH linac. The output energy is variable in therange of 0.17 through 1.05 MeV /u. The RFQ has already accelerated stable ions, Ne+ and N+. The IH
linac has undergone low-power tests. Other devices
in the beam transport line between the linacs are under fabrication or tuning. The first beam accelerationthrough the linacs is scheduled for March, 1996.

1. Introduction
A radioactive-beam facility is now under construction at INS. The beam from an isotope separator online (ISOL) will be accelerated by a 25.5-MHz RFQ
and a 51-MHz interdigital-H (IH) linac, and used fornuclear physics experiments.
Figure 1 shows the layout of the linac system.
The RFQ accelerates ions with a charge-to-mass ratio(q/A) greater than 1/30 from 2 to 172 keVju. The
output beam is enhanced in charge state in a carbon-foil stripper (q/A ~ 1/10), and then shaped in thelongitudinal and transverse phase spaces by a 25.5MHz rebuncher and 2 doublets of quadrupole magnets. The IH linac consists of 4 tanks and 3 tripletsof quadrupole magnets between tanks. The tanks are
excited separately by 4 rf power sources, and hence,
it is possible to vary the output beam energy continuously in the range from 0.17 to 1.05 MeV /u byadjusting the rf power levels and phases.
In Fig.1, the ion source, low-energy beam transport,
RFQ, and the first quadrupole doublet came into operation in March, 1995. The RFQ, whose parameters
are given in Table 1, accelerated stable ions Ne+ andN+. The ion source was a 2.45-GHz ECR one locatednear the RFQ. The measured transmission efficiencies
and emittance profiles of the output beam agreed wellwith PARMTEQ predictions.l) The IH tanks have undergone low-power tests: tuning of the resonant frequency, measurement of the Q-values, bead-pull measurement of the field distributions in the accelerating
gaps, and evaluation of the shunt impedances. Similar
low-power tests have been conducted on the rebuncher
cavity, which is a folded coaxial-line resonator with 6gaps. 2 ) The second quadrupole doublet is now beingfabricated.
The linac system will be completed in March, 1996.
Then the first beam acceleration through the linacs
will be conducted.

25.5-MHz SCRFQ

IIII
II

i

51-MHz IH Linac·~II
I

IIIII~ f lr\Sontrol Room
05ISOL

Figure 1: Heavy-ion linac system under construction.

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D D

170~1050 keVju.
10m

JAERI-Conf 95-021

Table 1
Design parameters of the RFQ.
Frequency (f)Charge-to-mass ratio (q/A)
Kinetic energy (1ln -+Tout)
Normalized emittance (en)Vane length (Lv)
Number of cells (Nc)Intervane voltage (Vvv)
Maximum surface field (Es,m<>x)
Mean aperture radius ( ro)Minimum aperture radius ( amin)Max. modulation index (mmax)
Final synchronous phase ( cPf)
Transmission (0 rnA input)

Table 3Main parameters of the IH linac.

25.5 MHz
1/30
2-+ 172 keV/u0.0611' cm·mrad
858.5 em
172
108.6 kV
178.2 kV /em(2.49 Kilp.)
0.9846 em
0.5388 em
2.53f (MHz)q/ATout (keV /u)
Ltank (em)Dtank (em)Rbore (em)Dd.tube (em)No. of cells. Eacc (MV /m)

-3o•
91.4%

2. Split Coaxial RFQ
During the beam tests conducted in April, transmission efficiencies were measured for various intervane voltages. 1 ) The ion was N+, and the input beam
current was 0.21 ,...., 0.22 rnA in peak (duty factor was
5% = 0.53 ms x 95Hz). At the nominal voltage (Vvv= 50.68 kV), 90% of the injected ions were accelerated; 91.4% is the PARMTEQ value. Good agreements
between the experimental data and simulation predictions were obtained also at higher intervane voltages;
the maximum was 81 kV. At Vvv = 81 kV, the rfpeak
power (Ppeak) and the averaged one (Pave) were 134
kW and 6.7 kW, respectively. At such a Pave level orlower, the RFQ has a good performance; this is ourconclusion for the beam tests.
We aim at operating the RFQ at higher power levels. The issues are to keep the resonant frequency
under control and to verify that the vanes are wellcooled. If they are distorted by heat, the beam performance obtained at the lower powers would not bepreserved. We have been trying to raise the intervane
voltage to 109 kV (design value for qf A = 1/30 ions),and the duty factor to 30%. As shown in Table 2, theduty factor is still lower, but the intervane voltage has
almost reached the goal.

3. Interdigital-H Linac
Table 3 lists main parameters of the IH linac. Theoutput energy is variable in the range of 0.17 throughTable 2
Progress in feeding high power into the RFQ.
Date
3/22/95
4/13/95
6/20/95
7/12/95
9/05/95
goalVvv(kV)
8191
104107108109

Ppeak
(kW)
134
170
220
242
235
242

Pave
(kW)
26.5
2.6
13.2
6.1
18.8
72.6

duty
(%)
19.8
1.5
6.0
2.5
8.0
30.0

width rep.
(ms) (Hz)0.66 3000.53
290.50 120
0.50
50
2.00
40

Tank 151
2:: 1/10
294
68
149
1.0
3.8
9
2.10

Tank 251
2:: 1/10
475
90
149
1.2
4.4
10
2.15

Tank 351
2:: 1/10
725
116
149
1.4
4.6
11
2.17

Tank 451
2:: 1/10
1053
153
134
1.6
5.2
12
2.14

1.05 MeV ju. Figure 2 shows a simulation result of
the energy spread as a function of the output energy. The levels and phases of the rf powers into thetanks are optimized so that the energy spread might
be minimized. The input beam is a simulated C3 +one that has passed all the elements before the IH
linac (a 10-JJg/cm2 carbon-foil stripper is included).
The input energy is 167 keV /u, and the full widths ofthe phase and energy spreads are 35° and 1 ke V /u.
Resultant energy spreads at the output are ±0.85%
at 0.7 MeV /u, and ±0.45% at 1 MeV ju. Without thestripper the energy spreads are 3/4 of these values.
±1.0........_.....

~±0.8-........•~Q. ±0.6
rn~--(i) ±0.4

*Ic::

Cl>

~±0.2

-r-0 ~~~~~~·~~~·~~~·~~~~
0.7

0. 75

0.8

0.85

0.9

output energy (MeV/u)

0.95

Figure 2: Energy spread vs output energy.
We had fabricated a cold model for each of the4 tanks, and studied the rf characteristics of the IH
cavity.3 •4) The models were scaled up to the present
IH tanks; the scale factors are 20/9 at Tanks 1 ,....,
3, and 2 at Tank 4. Low-power tests of the tanks
have been almost finished. The results are summarized in Table 4. Every tank was matched to a 50-0
signal generator via a loop coupkr. It was attached
to a port placed near a ridge end. Before the tuning,Tanks 1 ,...., 3 had resonant frequencies (/initial in Table4) higher than 51 MHz by 84, 134, and 180kHz, respectively. We decreased the frequencies closer to 51
MHz (/tuned) by using capacitive tuners: every tankhas a C-tuner, which is a movable disk (19 em dia)facing a ridge.

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JAERI-Conf 95-021[3] M. Tomizawa et al., "Construction of an Interdigital-H linac at INS", 4th European Part. Ace.
Conf., London, England, June, 1994.
[4] M. Tomizawa et al., "Model Measurement andPresent Status of Interdigital-H Linac at INS",
17th Int. Linac Conf., Tsukuba, Japan, 1994.

Table 4
Summary of low-power tests of the IH tanks.
Tank 151.08451.003
10681
nont
264
247t
10.5
±2.0

!initial (MHz)!tuned (MHz)
QunloadedZ.tr (MO/m)
P (kW)~Ygap (%)

* : preliminary,

Tank 251.13451.00715387
11602t289219t15±2.9

Tank 351.18051.057*15758*
13462t
249*
211t
27*
±4.2*

Tank 451.00351.00018490
14541t218179t39±2.21051.00MHz

Tank-1
8..cit : estimated from cold-model tests.

iii

Figure 3 shows the results of bead-pull measurements. An aluminum sphere (6 mm dia) was moved
along the beam axis. We obtained gap-voltage distributions almost flat except at the tank ends (see also~ Vgap in Table 4) without any particular tuning forthe flatness. From the measured unloaded Q-values
and field distributions in the gaps, we figured out effective shunt impedances (Zetr).
The estimated rf powers (P) required for the acceleration of qf A = 1/10 ions up to 1.05 MeV /u arelower than the capacities of the power sources. Theirnominal maximum powers in cw operation are 12 kW(Tank 1), 22 kW (Tank 2), 30 kW (Tank 3), and 50
kW (Tank 4). The stabilities in power and phase weremeasured. Table 5 lists the results obtained from cw
operations with a dummy load. The measurement
lasted for 1 ,...., 1.5 hours after aging of 4 ,...., 6 hours.

"" "::0 6a;u::.g 4~"}iii 20400

300

200

1000500

A700

600

8:e51.01MHz

Tank-276

n:5- 5~ 4.g 30~

w~

J2.\0 fl400

2000600

BOO

7Table 5
Stabilities of the power sources for the IH tanks.
..ci~Pout/Pout

~¢

(%)

No.1
(for Tank 1)

Pout(W)
12,000120±0.24±0.1(deg)
±0.1
±0.1

No.2
(for Tank 2)

22,000220±0.1±0.2±0.2±0.1

No.3(for Tank 3)

30,000300±0.3±0.4±0.15±0.15No.4(for Tank 4)

50,000500±0.4±0.5±0.1±0.15

SourceTank-3

65iii:§ 4

MII.!!!

~

51.06MHz

3~ 2iii

J00200400

Tank-4.e

600

800

1000

~

1200

51.00MHz

4'" 3
::0a;

4. Acknowledgmentsu::

We express our thanks toT. Nomura for his encouragement. The IH linac was fabricated by Sumitomo
Heavy Industries, Niihama Work, and the IH powersources by IDX Corporation.

.!:!

2w

1jo~~~~~~~~~~~~l~0References[1] S. Arai et at~, "First Beam Tests of the INS Split
Coaxial RFQ for Radioactive Nuclei", 1995 Part.
Ace. Conf. and Int. Conf. on High-Energy Ace.,
Dallas, Texas, U.S.A., May, 1995.
[2] Y. Hashimoto et al., "Cold test of a 25.5 MHz
Double-Coaxial >.j4 Resonator", this symposium.

~ ~-~1~1~1~1-Position (mm)Figure 3: Electric field distributions along the beamaxes of the IH tanks.

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