Accelerating cavity

Four points were optimized for the cavity design;

• acceleration efficiency
• 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.

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
 

modes	frequency (MHz)	unloaded Q	half power band width (kHz)	shunt impedance (MW or MW/m)	threshold current (mA)
TM010	508	44100	11.5	6.7
TE111	712	56000	12.7	4.1	555
TM110	763	52800	14.5	10.7	188
TM011	905	43500	20.8	2.8	208
TM111	1077	44000	24.5	13.7	166

 
 
 

coupling of the input coupler

The coupling constant of the input coupler is adjusted to 2.