BEAM TEST OF THE RFQ LINAC ' T ALL1

N. Ueda, A. Mizobuchi, S. Yamada， S. Arai,
T. Fukushima, K. Sawada, and Y. Hirao
Institute for Nuclear Study, University of Tokyo
Tanashi，Tokyo 188, Japan
ABSTRACT
Beam test of the RFQ linac TALL was done by using proton beam.
Transmission exceeding 90% was obtained. Energy and its spread of theouput beam were measured by an analyzer magnet as T = 825 keV andAT/T =1.6% in FWHM. They agree with calculated values.
INTRODUCTION
A heavy ion synchrotron-cooler ring 'TARN-U1 is under construction atINS.
The ring is designed to accelerate protons up to 1.3 GeV and heavy
ions with charge to mass ratio q/A of 1/2 up to 450 Mev/u.1) The RFQ linac’TALL1 was constructed as the first stage of an injector linac system for
the TARN-II. The RFQ linac is best for the stage because it can accept low
velocity beam and has bunching function. The machine
can accept ionswith
q/A of 1〜 1/7， By using an ECR ion source it can accelerate heavy ionssuch as Xe and W 。 Injected ions at 8 keV/u are accelerated up to825 keV/u.
ACCELERATION CAVITY
The acceleration cavity is of four vane structure
driven with aloopcoupler.
Thecavity is 58 cm in diameter and 730 cmin length. Detailed
descriptions of the structure and alignment are given in other papers.2,3>
Two sets of vanes are prepared for the TALL.
One is for low power
operation. It is made of aluminum and has no cooling channel. 丁he otheris made of copper and has cooling channels for high power operation. The
beam test were done with the aluminum vanes.
On the input and output ends, a part of each vane end is removable inorder to vary the inductance of the cavity ends. The end wall has four
movable capacitive end tuners.
Each quadrant has four movable sidetuners - They will compensate the resonant frequency shift due to thermal
elongation. Aluminum cylindrical blocks of 100 mm in diameter and various
thicknesses are inserted through side holes to vary transverse inductance.
The field distribution was tuned roughly by varying the shape.of thevane ends. Then fine tuning was done by using the side inductive and end
capacitive timers. The electric field distribution near the vane tops wasmeasured by use of a dielectric pertubator moving guided by the vanes.
Afield uniformity within a deviation of 土 2% azimuthally and 土 5%
longitudinally was obtained, by using two dozen side tuners of fixed lengthand three end capacitive tuners. The TE210 mode was tuned at 101.3 MHz.
The closest mode is TE1113 which has 0.93 MHz higher resonant frequency.
The separation of 0.93 MHz is satisfactory.
M A M TEST
Ions extracted from a microwave ion source at 8 keV are transported toa magnet with two einzel lenses. Protons are separated form other ionswith the magnet. They are focused into the RFQ entrance with a triplet ofelectric quadrupole lenses and an einzel lens. The output ions are focusedwith a triplet of quadrupole magnets on an object point of an analyzer
magnet.
The energy of the output beam was measured by the magnet as
T = 825 keV/u.
The calculated value is 800 keV/u at 100 MHz. Consideringthat the frequency is tuned at 101.3 MHz, the measured energy
isreasonable.
The energy spread was measured as AT/T =1.6% in FWHM。 Itagrees with a computer simulation by PARMTEQ.
Transmission efficiency was measured for input proton beam of 10 m A.
The emittance and intensity of the input beam were measured just in frontof the entrance or，downstream of the final einzel lens. The intensity ofthe output beam was measured at the object point. Transmission exceeding
90% was obtained (Fig.l).
The beam test was done in pulse operation. The duty factor was 16.7%(2 ms duration/12 ms repetition period). The proton acceleration required
rf power of 4.6 kW (peak). The unloaded quality factor Q0 was measured at
7100, It is about 70% of a caluculated value for the aluminum vanes. With
the loop coupler the cavity was stably operated up to the full power of
25 kW of a power supply now available.
CONCLUSION
Transmission exceeding 90% was obtained. The measured energy and its
spread agree with the calculation. On the basis of the experiment theshape of the end part of the high power vanes were determined. The
aluminum vanes were replaced by them. Field tuning and rf characteristics
study with the new vanes are done.
ACKNOWLEDGMENT
The authors are grateful to the members of the Accelerator ResearchDivision, INS for their discussions and assistance.
The acceleration
cavity of the TALL was manufactured by Sumitomo Heavy Industries, Ltd.
REFERENCES
1 ) T. Katayama et.al., Proc. Int. Symp. Heavy Ion Beam Fusion，May 27-29,
19865 Washington, D.C., USA.
2) N. Ueda et al” IEEE Trans. Nuclear Sci” NS-32, No.4 (1985) 3178.
3) N. Ueda et al.5 Proc• Linear Accelerator Conf,5 June 2-63 1986， SLAC,USA.

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04:246810cavity rf level (arbit.)Fig.l.
Transmission vs, cavity rf level for input proton beam of 10 m A.
Input beam emittance for A and B is given in Fig.2.

x* ( m r a d )Y50

50、、(m rad)y (mm)

15A
一15-15-50x(m rad)Y(m rad)Fig.2. Emittance of the input proton beams of 10 iik measured at 21 cm
upstream the RFQ entrance. Thick and thin bars cover 95% and 100% of thebeam, respectively- The ellipses are ones for RFQ acceptance at the designvoltage.
The area is 145兀 m m • mrad, or 0.6tt m m • mrad normalized, A and B
are for beams limited by apertures of 13
and 8 mm dia” respectively,
inserted between electric quadrupole lenses.