JAERI-Conf 95-021

2p1-3
DEVELOPMENT OF RIKEN 180HZ ECRISTakahide NAKAGAWA, Yoshitoshi MIY AZAWA, Masatake HEMMI, Toshiya CHIBA, Naohito IN ABE,Masayuki KASE, Tadashi KAGEY AMA, Osamu KAMIGAITO, Eiji IKEZAW A, Akira GOTO, and Yao;;ushige Y ANO
The Institute of Physical and Chemical Research (RIKEN), Hirosawa 2-1, W ako, Saitama 351-01, JapanAbstract
We constructed a new ECRIS which has an
operating frequency of 18 GHz. The intense beams ofmulti-charged ions are successfully produced. We observedthat the beam intensities of highly charged and heavier
ions are strongly enhanced using an afterglow mode.
This ion source is connected to a new variable-frequency
RFQ and used as a new injector of the RILAC(Rikenheavy ion Linear ACcelerator)-Ring cyclotron complex.

In this paper, we present the description and theperfonnance for producing multi-charged ions fromgaseous elements in the 18GHz RIKEN ECRIS.
2. Description of RIKEN 18 GHz ECRIS

Figure 1 illustrates the design of RIKEN 18 GHzECRIS. A single 18 GHz, 1.5 kW klystron supplies RFpower to the source. The axial confinement of plasma is
obtained by two solenoid coils which provide magneticmirror. The source is completely enclosed by an iron .
yoke in order to reduce the current of solenoid coil. The
1. Introduction
maximum power consumption is 140 kW. The mirror
ratio has a nominal value of 3.0. as shown in fig.1 (BmaxElectron Cyclotron Resonance Ion Source-1.4 T, Bmin - 0.47 T). To optimize the radial(ECRIS) technology has developed rapidly since theoriginal pioneering work of the Grenoble group. Theseconfinement of the plasma,used a hexapole magnet
ion sources are capable of producing intense beams ofwhich consists of 36 segments made of Nd-Fe-B
highly charged ions. 1l These are used as an extemal ion
permanent magnets. 5l The outer diameter (OD) and innersource of cyclotrons and linacs, and also for atomic
diameter (ID) are 180 and 80 mm, respectively. The field
physics experiments. Recently, intense beams of medium
strength at the surface of magnets is about 1.4 T. To
mass heavy ions, mainly metallic ions, becomes one ofprotect the hexapole magnet from demagnetization by
the major requests in RIKEN Accelerator Researchhigh temperature, a water-cooled plasma-chamber ( ID=Facility. For satisfying such request, a new ECRIS is74 mm, OD= 80 mm) has been constructed. The water
demanded as an extemal ion source of the RILAC 2>-Ringcooled hexapole housing also protect the permanent
cyclotron accelerator complex. According to tl1e scaling
magnet from the high temperature caused by the solenoid
low proposed by R. Geller, the beam intensity increases
coil.
with increasing micro wave frequency and magnetic field
The high vacuum of the plasma chamber is very
strength.ll Therefore, the micro wave frequency of 18
important to produce the intense beam of highly charged
GHz has been chosen for tl1e RIKEN new ECRIS. It isions .6l This may be due to the effect of recombination ofconnected to a new RFQ and used as a new injector as
the ions. To minimize such effect, the plasma chamber is
described in refs 3 and 4 .
evacuated with 500 and 150 l/s turbo-molecular pumps.
The ultimate vacuum pressures of the plasma chamber""'·«iJ•u.-. Magnetand extraction stage are the middle of 10·8 Torrs.
Soler,oid coil
Iron yoke

weTMP 150l/s

TMP 500 l/s
Fig. 1. Cross sectional view of RIKEN 18 GHz ECRIS-224-JAERI-Conf 95-021

3. Performance of 18 GHz ECRIS

3.1.CW mode operation.
Figure 2 shows the beam intensities of highly
charged ions produced from gaseous element. Theseresults were obtained by using the gas mixing method. 1l
The typical gas pressures of plasma chamber andextraction stage were l.Ox10· 6 ,and 9x10· 7 Torrs,
respectively. The extraction voltage was 15 kV. For
example, beam intensities of Ar 11 + and 0 7+ were 160 and
130 eJ..LA, respectively. Figure 3 shows the beam
intensities of Ar 11 + as a function of the extraction
voltage. As shown in fig.3, the beam intensity is
proportional to yu below 10kV, which follows theChild-Langmuir law, where V is the extraction voltage.
Above 10 kV, it is deviated fonn it ru1d increases linearlywith increasing the extraction voltage.
The distru1ce between the orifice(<!>= 10 mm) andthe extraction electrode (<!>= 13 mm) is also one of theimportant parameters to optimize the performance ofECRIS. It strongly depend on the condition of plasma,
shape of extraction electrode, and charge state of extracted
ions. 7J For RIKEN 18 GHz ECRIS, the best results of
medium charge states of heavy ions (i.e., Q5+,6+, Ar 8+-ll+) could be obtained at the distance of about 30 mm
Figure 4 shows the berun intensities of Ar 11 +i<;>ns for 18 GHz ECRIS, CAPRICE (14.5 and 10 GHz)
developed in Grenoble 8 J and ECRIS 4 (GANIL)9J as afunction of RF power. At the srune RF power, the beam
intensity increases with increasing the frequency of micro
wave and magnetic field strength. In the figure the Bmax
indicates the maximum field strength of the mirror
magnetic field.

•Eca~ 50

1510Extraction Voltage (kV)520Fig.3. The beam intensity of Ar 11 + as a function ofextraction voltage

AIKEN 18 GHz ECRIS(Bmax-1.35 T}

150~

CAPRICE 14.5 GHz(Bmox -1.3 T}........................... ..
.

;::==:~100/-·~:~;~·:CRIS~~.CAPRICE 10.0
(Bmu-1.2T)

Em 50ID<HzCAPRICE 10.0 GHz(Bm,.-0.8 T)//::i4 14.5 GHz/ . (Bm,.-1.1 T)

~100~
(/)

RF power (watts)

c:

JB
c:

Fig.4. Berun intensity of Ar 11 + for various ion sources asa function of RF power. The extraction volt:'lge ofRIKEN ECRIS is 13 kV. The extraction voltageof the other sources is 20 kV.

E 10CISC1)

m3.2.Pulsed mode operation
1020Charge State

Fig.2. Charge state distributions of 0, Ar ru1d Kr ions

It is well known that at the tumoff of U1e RFpower of an ECRIS, the extracted current for highly
charged heavy ions drrunatically increases. As described inRef. 10. if the central plasma shows a depressed negative
potential ~<!>. the ratio between the berun currents of asteady sate and the afterglow cru1 be written as follows,(1)-225-JAERI-Conf 95-021

where q, d$ and Ti are the charge state of ions,depressed negative potential, and ion temperature,respectively. Figure 5 shows the typical result ofIarterglowllsteacty as a function of charge state in the caseof Kr and 0 ions. In this figure, we observe theexponential dependence of this ratio as described in eq.
(1).

~Ar:::i.

Cl)

Kr~·-100IA!torglowr-----------------,

01:

I StoadyCl)

1:

E

asCl)
m10

1020
Charge State

10Charge State (q+)

20Fig.6. Charge state distributions of Ar and Kr ions.
Open and closed circles are the results of CW andpulsed mode operation, respectively
References

Fig. 5. Ianergiowiisteacty for Kr and 0 ions
The maximum current can be produced only if
the duration of the RF pulse is long enough to achieve
the maximum ionization of the considered ions. In ourcase the duration was fixed to 15 ms to produce the Kr,and Ar ions. Figure 6 shows the comparison between thebest results of CW mode operation (open circles) andafterglow mode (closed circles) at the extraction voltage of
10 kV. The RF power was kept at the same value forboth operations. It is clearly seen that the beam
intensity of highly charged and heavier ions strongly
enhanced by pulsed mode operation.
4. Conclusion
The RIKEN 18 GHz ECRIS has been
constructed and tested in cw and pulsed mode operation.
The intense beam of multi-charged ions can be produced
at the relatively lower micro wave power ( for example,160 ef.!A of Ar11 +, 130 ef.!A of 0 7+ at 600 W). In the caseof pulsed mode operation, we observed that the beam
intensities of highly charged and heavier ions werestrongly enhanced. In the next step, we will try toproduce the highly charged ions from solid materials.

1) R. Geller," ECRIS :The Electron Cyclotron
Resonance Ion Source", Anno. Rev. Noel. Sci.
40(1990)15 and references therein2) M. Odera et al., "Variable Frequency Heavy-Ion Linac,
RILAC", Noel. lustrum. and methods, 227(1984)187
3) A. Goto et al., in this proceedings
4) 0. Kamigaito et al., in this proceedings
5) P. Schiemenz et al., " High field permanent sextupole
magnets for Stern Gerlach separation in atomic beamsources", Noel. Instrum. and Methods, A305(1991)15
6) T. Nakagawa et al., "Upgrade of RIKEN 10 GHz
Electron Cyclotron Resonance Ion Source using
Plasma Cathode Method", J. J. A. P. 32 (1993)
Ll3357) R. Leroy et. al., " ECRIS Optimization for on lineproduction", Proceedings of 12th Int. workshop onECR Ion Source and their Application, April, 1995,Saitama, in press
8) D. Hiz et al., "The new 1.2 T CAPRICE source:
Presentation and Results", Proceedings of 12th Int.
Workshop of ECR Ion Sources and their Application,
April1995, Saitama, Japan, in press
9) P. Sortais et al, "Results of the new "ECRIS4" 14.5
GHz ECRIS at GANIL", Proceedings of lOth Inl.
Workshop on ECR Ion Sources, January 1991,Knoxville, USA, p3510)P. Sortais, " Pulsed ECR ion source using U1eafterglow mode", Rev. Sci. lustrum. 63(1992)2801-226-