The 9th Symposium on Accelerator &ience and Technology, Tsukuba, Japan 1993

Beam Tests of a cw 4-rod RFQ
Hiroshi Fujisawa, Masayuki Tamada, Talcao Matsumoto,
Yoshihisa I washita*, Akira Noda*, and Makoto Inoue*
R&D Division, Nissin Electric Co., Ltd. 575 Kuze Tonoshiro-cho, Minami-ku,Kyoto-shi, Kyoto-fu 601 Japan*Accelerator Lab., ICR, Kyoto University, Uji-shi,Kyoto-fu 611 Japan
Abstract

B. Faraday

The results of a series of the initial beam tests of the 4rod RFQ are presented. The measurements include determining
an ion beam transmission, surveying the beam emittances
both at the input and output of the linac, and obtaining themomentum spectrum of the input and output beam. Inaddition a SIMS (secondary ion mass spectroscopy) analysis
was performed for an ion implanted silicon wafer to get thedefinitive information on the energies and identification of an
RFQ output beam.

There are five Faraday cups in total to measure theintensity of the ion beam. Fl is retractable and practicallyworks as a beam stopper as well as a pseudo-Faraday . F2 andF3 are retractable, too and true Faradays. F2 and F3 are used tomeasure the intensity of a beam at the upstream anddownstream of the RFQ, respectively. F4 and F5 are both demountable true Faraday systems and are similar to F2 and F3in construction.

C. Emittance monitor

I. INTRODUCTION
The emittance monitors EMI and EM2 are of "a slit
A cw RFQ linac system of "modified" 4-rod type has and multi-wires" type, both exactly identical in construction.
been constructed. The cross-section of the RFQ electrodes are In the emittance monitor, there are only 10 detector wires. The
not circular as usually proposed in literature but rectangular construction is simple and the total costs is relatively low inand the electrode poles are three-dimensionally machined. We such configuration however, the angular separation of thepropose that this design makes the handling and maintenance detector wires is such that only a rough measurement isof the RFQ electrodes particularly easier [1,2].
possible in the present design. This is preferred anyway for
An ion injector to the RFQ comprises of a Freeman the very first study of the beam emittances. The performancetype ion source, a 90 degree analyzing magnet, magnetic of the emittance monitor will be upgraded to better angularquadrupole lenses, and a HV (high voltage) rack where a mass resolution in an appropriate timing in the course of our future
flow controller and electrical power supplies are all installed. development.
The vacuum system comprises of a 550 liter/sec. turbo
molecular pump and a 350 liter/min. oil rotary pump. All
those beam optical, electrical, and vacuum components areIII. EXPERIMENT DATA
arranged and installed in a X-ray shielded cabinet. Details ofthe ion injector is found in ref. [3].
A. Transmission
Beam tests have been in progress since the first beam
acceleration experiment in late December 1992. The ionFig. 2 is a plot of He+ and N2+ ion beam transmission
beams used so far for the acceleration tests of the 4-rod RFQ of the RFQ as a function of rf power. Please notethat theare He+, N+, and c+.
value of ion current obtained at F3 represent a total unanalyzed beam current. The beam transmission of He+
approaches 90 % and those of N2+ and c+ ion beam areII. EXPERIMENT SETUP
approximately 80 %. The typical beam currents obtained at theRFQ
output .are 32, 13, and 220 pJ.lA for He+, N2+, and c+
A. Setupions, respectively.
Fig. I is a schematic drawing of the beam experiment
setup of the RFQ linac. The purpose of this experiment is to B. Emittancedraw as much information as possible of both the input andFig. 3 typifies the results of beam emittance
output beam of the RFQ. The input and output beam current
are measured with Faradays cups. The emittance and measurements for a He+ ion beam. The measurements wereorientation in the trace-space of the beam are surveyed using done at the probe position of 233 mm upstream of and 388
an emittance monitor. The energy of the input beam can be mm downstream of the RFQ electrode boundaries. In those
known accurately (better than ±0.5 %) by measuring a figures, the trace-space ellipses obtained by the calculations
terminal voltage of the ion extraction high voltage power using PARMTEQ and TRACE-3D are superposed on thesupply using an appropriate resistor divider. The output beam raster image of the measured emittance data. Although crudeenergy of the RFQ can be estimated by taking a momentum the experimental data are, it is adequate for making
comparison.
spectrum of a beam with a 15 degree bending magnet system.

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Descriptions of icons[Fixed Faraday.

lRetractable Fa<aday.

I

Gate valve.

Beam defining slit.

~x Emittance monito<.
HVrackIon source

15 degree bending
madnetIIBeam monitor

F5RFQ
EM2 F3Einzellens

Q-Lenses

4.5 m

Mass analyzer

Figure 1. Schematic drawing of the experiment setup forthe 4-rod RFQ beam acceleration tests.

C. Momentum spectrum

Fig. 4 exemplifies the momentum spectra of beams
from the ion source operated in various source gases. The
measurements were done by recording an ion current at Fl invarying mass analyzer's current. The extraction was in allcases set at the synchronous energy required for the RFQ
injection.
The expected mass resolution M/11M of the 15 degree
bending magnet is about 50. FS measures the analyzed currentof the beam which is collimated through the slits located bothat the entrance and exit of the 15 degree magnet system. Fig. 5
typifies the momentum spectrum of He+, N+, and c+ beams
accelerated by the RFQ.
The energy of the accelerated beam can be approximatedby extrapolating from the spectrum of a mono-energetic beamfrom the ion source with the 15 degree bending magnet
system. The rf power is put off in this measurement. The
estimated output energies for instance of He+ and c+ beams
are 346 KeV ± 2% and 1071 KeV ± 2%, respectively. Thesevalues are off by+ 2.2 %and+ 5.4 %from the calculation ofHe+ and c+ output synchronous energies, respectively.

implanted ions. This sensitive analysis gives a definitive
information on what is where by how much. Fig. 6 shows therange profile of nitrogen in a silicon wafer measured after theimplantation of N2+ beam at dose of approximately lx 1016
atoms/cm2. The expected energy of the N2+ beam is 1.17
MeV. The peak of the profile corresponds to the depth of 1.6J.lm. This is in good agreement with available range profile
data [4-6].
1000~80c:0"(jj-~60E(/)
c~40E20roQ)

OJ

00

D. SIMS analysis of implanted ions

5101520

RF power ( kW )To confirm the acceleration of a beam by the RFQ, anoutput ion beam was implanted in a silicon wafer and SIMS
analysis was used to get the range distribution of theFigure 2. Beam transmission of He+ and N2+ ion beam as afunction of rf power.

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x' (10nd)

c+y'(mrod)

60

60

4040

....

1.2::l

1 .0c..c:i~x(m10)1015~-40-40·u;-60-60(])

c0.6-~

0.4

E0.2

roInput to the RFQ0.8(])

CD

0.001020

30

4050

Magnet current (A)y' (mrod)x' (mnd)60

Figure 5. Momentum spectra of He+, N+, and c+ accelerated
beams as analyzed with the 15 degree bending magnet system.

60
40to••.-~-----------------,~~~-;E-;,.;,.,._~~x(mm)30
10 20-60~!

Output from the RFQ

so 18zFigure 3. Comparison of He+ beam emittance with the results ofcalculations.

~<~

•uzz

so••0u1017+

N

1 .4 -- 1.2 -0c

1. 0 -.?;-0.8 -coenc2cEcoQ)(])+ N +2

IV. REFERENCES

1-e+:::J.0......

Figure 6. Range profile of nitrogen implanted in a silicon wafer.
c+0.6 -Ar2+2+

N0.2 -~

0.4.l .....

_1_He-Ar

J0.00II

51015III202530Magnet current (A)Figure 4. Momentum spectra of the ion source operated in variousgases.

[1] H. Fujisawa, eta!, "Mechanical Design of 33.3 MHz 4-rod
Heavy Ion RFQ Cavity", Bull. Inst. Chern. Res. Kyoto Univ.
Vol. 70, No. 1, pp. 28-36, 1992.
[2] H. Fujisawa, et al, "RF Characteristics of the 33J MHz4-rod RFQ", 1992 LINAC Conference Proceedings, Ottawa,Canada, August 1992, pp. 766-768.
[3] H. Fujisawa, et al, "An Injector to the 33 MHz 4-rod
RFQ", Bull. Inst. Chern. Res. Kyoto Univ. Vol. 71, No. 1,pp. 1-5, 1993.
[4] J.F. Ziegler, "High Energy Ion Implantation", Nucl. Inst.
and Meth. B6, pp. 270-282, 1985.
[5] H. Wong, E. Deng, N.W. Cheung, P.K.Chu, E.M.
Strathman and M.D. Strathman, "Profile Studies of MeV Ions
Implanted into Si", Nucl. Inst. and Meth., B21, pp. 447-451,
1987.
[6] D.C. Ingram, J.A. Baker, D.A. Walsh and E. Strathman,"Range Distributions of MeV Implants in Slicon 2", Nucl.
Inst. and Meth., B21, pp. 460-465, 1987.

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