JAERI-Conf95-021

2a2-2
CONSTRUCTION OF A NEW PRE-INJECTOR SYSTEM FOR THE RILAC
Akira GOTO, Yoshitoshi MIY A.ZAWA, Masatake HEMMI, Osamu KAMIGAITO,Takahide NAKAGAWA, Masayuki KASE, Toshiya CHIBA, Naohito IN ABE,Shigeo KOHARA, Tadashi KAGEY AMA, Yuri BATYGIN and Yasushige Y ANO
The Institute of Physical and Chemical Research (RIKEN)
Wako-shi, Saitarna 351-01, JapanAbstract
A new pre-injector system for the RIKEN heavy-ion 1inac(RILAC), which is used as an injector of the RIKEN Ring
Cyclotron (RRC), has been completed in order to increase beam
intensities of heavy ions by one or two orders of magnitude. Thesystem consists of an ECR ion source, a variable-frequency RFQ
linac and a beam transport line between them. The performance
tests of the whole system including beam acceleration test are
being made successfully. It is planned to be installed on site next.
year.

resonator tanks, each being of the Widoroe type and frequency
tunable. The existing pre-injector system consists of an 8 GHz
NEOMAFIOS and a 450 kV Cockcroft-Walton terminal. In thenew pre-injector system is used a high-field, 18 GHz ECR ion
source that is expected to have significantly high performancecompared to the present 8 GHz NEOMAFIOS. A variablefrequency RFQ linac is adopted as an equivalent to the existing
Cockcroft-Walton terminal, which is unable to accomodate suchan 18 GHz ECR ion source that requires high electric power.
In this paper we describe the characteristics of the new preinjector system and the status of its construction.

1. Introduction

2. Description of the New System

Recently we have started to do R&D's for the Rl-beamfactory.project, 1) which aims to increa~e beam energies up to 400
MeV/u for light heavy-ions and 150 MeV/u for very heavy ionsusing a superconducting ring cyclotron as a booster of the RIKEN
Ring Cyclotron (RRC). One of the main purposes of the project isto produce radioactive-isotope beams and/or new isotopes in thewhole range of nuclear masses up to uranium. In order to achieve
the goal, it is indispensable to provide the RIKEN heavy-ion linac(RILAC),2) the injector of the RRC, with much higher-intensityof heavy ions.
To meet the above demand, we have developped a new preinjector system for the RILAC. The RILAC consists of sixFigure. 1 shows a planned layout of the new pre-injector
system toghether with the beam transport line from the existingone. The existing beam transport line is slightly modified fromthe present for installation of the new system.
2.1 18 GHz ECR Ion Source
The ECR ion source3) is of a single-stage type and operates
at 18 GHz. The axial mirror field has peaks of 1.4 T (mirror ratiois 3.0) and the radial hexapole field is 1.4 Tat the pole surfaces of80 mm in diameter, both of which are high enough for the doublefrequency operation. The axial mirror field is produced

FromNEOMAFIOS
on theCockcroftWalton
PMDQ : quadrupole doublet
TQ : quadrupole triplet
ATT : attenuator
PM : profile monitor
SL: slit
FC : Faraday cup
EM : emittance monitor

18 GHzECRIS

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Fig. 1 Planned layout of the new pre-injector system for the RILAC together with the beamransport line from the existing one.

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with a pair of solenoids enclosed with an iron yoke that are
excited by two power supplies of 800 A. The power consumptionof the solenoids is 140 kW and the required electric power for thepower supplies is 210 kV A. The outer dimension of the yoke isabout 700 mm in diameter and 550 mm in length. The radial field
is produced with 36 segments of permanent magnets made of NdFe-B, each segment 224 mm in length. The permanent magnet isprotected from plasma heat by a plasma-chamber that is cooled bywater of 20'C. The chamber is made of two copper cylindricaltubes that are welded to each other after the surface of the innertube is carved to make conduits for coolant water. The thicknessof the chamber is 3 mm. The temperature of the chamber is
expected to rise up to 26'C at the maximum. The magnet is also
protected from the heat of the solenoid coils by a similar copper
cylindrical tube. RF of 18 GHz is fed by a Thomson TH 2463
klystron with a maximum output power of 1.5 kW. This RF
power source is designed to operate in both cw and pulse modes.
A rod of metal can be inserted axially for producing metallic ions.
The plasma cathode method can be applied. The inside of theplasma chamber is evacuated with 500 and 150 1/s turbomolecular pumps. Ions are extracted from an orifice of 10 mm indiameter with a maximum voltage of about 10 kV. The orifice ispositioned at the end of the permanent magnet.
2.2 FC-RFQ Linac
The RFQ linac4,5) is required to have the same function asthat of the existing 450 kV Cockcroft-Walton terminal. It is
designed to accelerate ions with a range of m/q = 6-27 up to 450
ke V/q in the cw mode. The operational frequency should bevaried between 18 MHz to around 40 MHz, which is one of themost important problems to be solved in the design of the RFQ
linac. We have adopted a "folded coaxial" RFQ (FC-RFQ)
structure. This structure allows the cavity to be tunable in a wide
range of frequencies and to be compact even in the low frcquncy
region below 20 MHz. The FC-RFQ structure can also enable theintervane voltage to be flat enough to obtain high beamtransmission efficiency. The length of the vanes is 1420 mm andthe inner volume of the resonator is about 1700 mm (length) x700 mm (width) x 1000 mm (height). The stroke of the shorting
plate for coarse tuning is 790 mm. For the details of the structure,
see ref. 4. The required maximum intcrvane voltage is 33.6 kV.
RF power is fed by an oscillator with an Eimac 4CW50000E witha maximum output power of 40 kW between 16.9 MHz to 40
MHz. The total water now for cooling is about 200 1/min of 7 atm
and the temperature of water is 30 'C. The temperature of thevanes is expected to rise up to about 40 'C at the maximum. The
resonator is evacuated with two turbo-molecular pumps of 1500
1/s.

maximum is required to be applied to the lens. The bending
magnet has a curvature radius of 500 mm and a gap of 80 mm.
The maximum magnetic field is 0.16 T. The angle of the slant
edge is 28.7' at both the entrance and the exit. The solenoid
magnet consists of coils and an iron yoke enclosing them. The
inner diameter, outer diameter and length of the magnet are 90mm, 610 mm and 310 mm, respectively. The maximum magnetic
field is 0.63 T. Beam diagnostic devices such as a profile monitor,
a Faraday cup and a pair of slits arc set in the beam diagnostic
chamber located between the bending magnet and the solenoid
magnet. A beam emittance monitor can also be set in thischamber. The beam transport line is evacuated with two turbomolecular pumps of 350 1/s.
3. Fabrication and Test
Fablication of the whole system was completed in the springof 1995. Performance test of the characteristics of the 18 GHz
ECR ion source and the FC-RFQ linac as well as beamacceleration test in the system have been made. Details of theresults arc reported in refs. 3 and 5.
Figure 2 shows a photograph of the 18 GHz ECR ion
source. Ion beam intensities were measured for gaseous elements
such as oxygen, argon and klypton with an extraction voltage ofup to 15 kV (though a required maximum voltage is about 10 kV
for delivering a beam to the FC-RFQ). Obtained beam intensities
of Ar11+ and o7+ ions, for example, were 160 and 130 CIJ.A,
respectively, with an RF power of about 600 W and an extraction
voltage of 15 kV. Typical gas pressures of the plasma chamber

2.3 Beam Transport LineFig. 2 Photograph of the 18 GHz ECR ion source.

The beam transport line6) between the ECR ion source andthe FC-RFQ linac consists mainly of (from tupstream) an Einzcl
lens, a 90' bending magnet, a beam diagnostic chamber and asolenoid magnet. In the design an ion beam is at first focused with
the Einzel lens onto a spot of 10 mm in diameter at the symmetricposition of the extraction orifice with respect to the lens. Thebeam is then analysed with the 90' bending magnet having slant
edges and doubly focused at a point between the bending magnet
and the solenoid magnet. The dispersion and magnification in thehorizontal direction at this point arc 2.2 em/% and -0.98,
respectively. From the values of dispersion and magnification,
mass resolution m/t.m is about 200. The beam is finally matchedto the FC-RFQ linac with the solenoid magnet.
The Einzel lens is of three-electrode type with different
diameters: the diameter of the center electrode is 100 mm and thatof the end electrodes is 74 mm. A voltage of about 15 kV at theand the extraction stage were 1.0x10-:6 and 9x1o-7 Torr,
respectively. Figure 3 shows the comparison between beam
intensities from the 18 GHz ECR ion source and those fromNEOMAFlOS 8 GHz. It can be seen that the beam intensities
from the 18 GHz ECR ion soucc arc higher than those from
NEOMAFIOS 8 GHz by one or two orders of magnitude. It isalso noted that the beam intensity of, for example Ar11 + ions,from the 18 GHz ECR ion source was twice higher thanCAPRICE 14.5 GHz. Pulse mode operation was also tested andsignificant afterglow effect was seen particularly for heavy ionslike klypton and high charge states: the ratio was 4 for Kr20+ions. A rod for metallic ions and a plasma cathode have not yet
been tested.

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resonator was 1-3xlo-7 Tor. We have encountered a serious
problem on the ceramic pillars that are used to fix the highvoltage part (to which the vertical vanes are attached) on thebottom plate of the resonator. A multipactoring occurred on thepillars at an intervane voltage of below 15 kV, and heating due todielectric losses in a local region of the pillars occurred at anintervane voltage of above 35 kV. To fix this problem, ceramicpillars were redesigned and arc being newly fabricated. Beamacceleration tests have been performed for Ar3+, Ar6+, Arll+and o5+ ions at the frequencies of 17. 7, 26.1, 34.4 and 39.2 MHz.
respectively, at the intervane voltage of about 20 kV. The beam
velocity after acceleration, which was measured by the TOF
technique using three capacitive pickup probes, was in agreementwith the designed value within 1 %. The beam transmission
efficiency of 85 % at the maximum, was obtained. Beamemittance has not yet been measured in the acceleration test.

>-·u;s::Cl).5Em1mNEOMAFIOS 8GHz

10Charge State

4. SummaryFig. 3 Comparison between beam intensities from the18 GHz ECR ion source and those fromNEOMAFIOS 8 GHz.
Figure 4 shows a photograph of the FC-RFQ linac. Thevanes have been three-dimensionally machined and assembled
within an accuracy of± 50 J..Lm, the value meeting the requirement
for good beam transmission. 7) The surface of the vanes were
polished with electrochemical buffing within a flatness of lessthan 1 J..Lm. The resonant frequency was measured to vary from
17.7 MHz to 39.2 MHz. The measured Q-values and shunt
impedances were about 60 % of the MAFIA calculations. Fromthe shunt impredance measurement, the required maximum RFpower was found to be 26 kW (cw). Typical gas pressure of theA new pre-injector system for the RILAC was completed in
the spring of 1995. The performance tests including beam
acceleration test showed that the beam intensity from the RILAC
will increase by one or two orders of magnitude as expected. Thesystem is planned to be installed on site next year. A beam
rebuncher will also be installed at that time between the FC-RFQ
linac and the RILAC.
5. References
[1]
[2]

[3]

[4]

[5]

[6]

[7]

Fig. 4 Photograph of the FC-RFQ linac.

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Y. Yano, "RIKEN RI beam Factory Project," in thisproceedings.
M. Odera, Y. Chiba, T. Tonuma. M. Hemmi, Y.
Miyazawa, Y. Inoue, T. Kambara, M. Kase, T. Kubo andF. Yoshida, "Variable Frequency Heavy-Ion Linac,RILAC," Nucl.lnstrum. and Methods, 227, 187 (1984).
T. Nakagawa, Y. Miyazawa, M. Hcmmi, T. Chiba, N.
lnabc, M. Kasc, T. Kageyama, 0. Kamigaito, A. Goto andY. Yano,"Developmcnt of RIKEN 18 GHz ECRIS," inthis proceedings.
0. Kamigaito, A. Goto, Y. Miyazawa, T. Chiba,M.
Hemmi, M. Kase andY. Yano, "Design of a New Type ofa Variable-Frequency Radio-Frequency Quadrupole Linac
with a Folded-Coaxial Resonator," Jpn. J. Appl. Phys. 33(1994) L537.
0. Kamigaito, A. Goto, Y. Miyazawa, T. Chiba, M.
Hcmmi, S. Kohara, M. Kase, Y. Batygin andY. Yano,"Development of a Variable-Frequency RFQ Linac for theRILAC," in this proceedings.
N. Inabc, M. Kase, 0. Kamigaito, Y. Miyazawa, M.
Hcmmi, T. Chiba, A. Goto, Y. Batygin andY. Yano,"Design of a Beam Transport Line between the 18 GHzECRIS and the RFQ linac," RIKEN Acccl. Progr. Rep. 28(1994) p.l66.
Y. Batygin, A. Goto, 0. Kamigaito andY. Yano, "Effectof Field Variation on Beam Parameters in RIKEN RFQ
Linac," in this proceedings.