Four points were optimized for the cavity design;
suppression of Higher Order Modes (HOM) and beam instabilities
reduction of discharge
ease of construction and operation
Detail on suppression of HOMs can be seen in references.
H. Ego, et al., N.I.M.400 (1997) 195-212p
H. Ego, et al., N.I.M.383 (1996) 325-336p
To suppress the coupled-bunch instabilities arising from the coupling
impedance with higher order mode resonances;
Low longitudinal or transverse shunt impedances of the HOMs (bell-shaped).
To distribute the resonant frequency of HOMs (i.e. to avoid coincidence
of HOM frequency of multiple cavities )
A systematic modification of inner structures.
Multiple movable plungers are equipped.
The flow rate of the cooling water for the cavity can be adjusted one by
one to change the cavity temperature.
The direction of RF input coupler is changed alternatively (horizontal
and vertical). See Fig. 2.
To keep the resonant frequency of HOMs stable by keeping the temperature
of cooling water constant.
Figure 1. Cross-sectional view of the cavity.
There are seven ports in the cavity;
Two beam ports. Diameter of 100mm. With RF contact using helicoflex.
One RF input coupler port
Three tuner ports. Two movable tuners and one fixed length tuner.
One pickup port.
calculated RF characteristics of TM010-like mode and of the HOMs
band width (kHz)
(MW or MW/m)
Figure 2. Layout of the cavities at an RF station.
coupling of the input coupler
The coupling constant of the input coupler is adjusted to 2.
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