MODEL TEST OF 1/5 SCALE MOVABLE BOX TYPE RF RESONATOR FOR THE RIKEN SSC
K. Ogiwara, T. Fujisawa, and Yo Oikawa
The Institute of Physical and Chemical Research
Abstract
A resonator ~ltese resonant frequency is varied from 17 to 45 MHz by
the movable box in the resonator is designed for the RIKEN SSC, The transBased on themission line approximation is used :in the calculation.
calcul~tions. the 1/5 model resonator was constructed and the resonant
frequencies, Q-value·s and radial distributions of RF electric field at theaccelerating gap were measured.

~1) Introduction
A new method to vary the resonant frequency is investigated, In Fig. 1,
the new type resonator is shown. The resonant frequency is varied from 17 MHz
to 45 MHz by moving the "movable box". The box does not make contact with thestem but contact only with the outer wall. The gap between the stem and box
is 4 em. This resonator has following merits:
1) The height is less than 3 m.
2) The distance which the box is moved is short (0.6 m).
3) The contact fingers are not at the location where the current density ismaximum.
calculated by theFigure 2 shows resonant frequencies and Q-values
transmission line approximation.
2) The 1/5 scale model resonator
To .investigate the RF characteristics of this resonator, the 1/5 scalemodel resonator was constructed, The resonant frequency, Q-values and theradial distribution of RF electric field were measured, The resonant
frequencies and Q-values measured are shown in Fig. 2 with the calculatedvalues. · The resonant frequencies measured are fairly well reproduced by
the calculations. However, the Q-values measured are about 0.4 times of thecalculated values. The poor agreement between the measured and calculated
be due to poor contact between the movable box and theQ-values mayouter wa:ll,and the complex structure of this resonator,
Relative distributions of RF electric field along the dee edge of themodel resonator were measured by perturbation method.l) The distributions
measured are shown in Fig. 3 , ·Wbien ~ne normalized at injection radius.
The strength of the field at middle radius is 75 % of that at the injection
radius for 45.9 MHz. This is not desirable for beam acceleration. In orderto improve the distributions, the stems were reconstructed as shown in Fig. 1(hatched). The electric field distributions after the reconstruction are
The distributions are improved.
shown in Fig. 3.
Conclusion
The dee voltages required for beam acceleration were calculated forseveral particles. The dee voltage as a function of RF f~:equency is shownin Fig. 4. The maximum output power of the amplifier for the resonator is tobe 300 kW. The dee voltages generated by the amplifier are estimated using
the Q-values measured and calculated. The results are shown in Fig. 4.
The dee voltages estimated are sufficient for the beam acceleration.
3)Reference1) L.C. Maier, Jr. and J.C. Slater: J. Appl. Phys., ~. 68 (1952)

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Distance from end of resonatorto movable box ( m )Fig. 2. Resonant frequenc ies (f)and Q-values measured and calculat edby the transmis sion line approxim ation.

Q' ' ' ' 1 ' ' '1Qbo. 8-8 Cross section
Fig. 1.

f

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911Position along accelerati ng gap

15202530 35 40 45
Frequency ( M!-lz )Fig.4. Dee voltage required for beam
accelera tion.

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Fig.3. Relative distribu tion of RF
electric field along the accelerating gap for the 1/5 model resonator. Solid lines show after thereconstr uction.