2015 IMP & HIRFL Annual Report · 305 ·

The charging and discharging trigger signals for kick power supplies are sent when the kicker control system receives

the event code for beam extraction and the RF signal. The waveform of discharge for extraction captured by an

oscilloscope is shown in Fig. 2. All delay times can be adjusted individually, and the digital delayer achieved a

precision of 2.5 ns. A pre-trigger signal is provided to synchronize by the controller for the beam diagnostic system

and physics experiments. Experimental results indicate that the phenomena of “missed kick” and “inefficient kick”

were not observed, and the beam transport efficiency was improved compared to the original system.

The Chinese “12th five-year plan” major project projects( The major of China’s 12th five year plan)– HIAF(High

Intensity Heavy-ion Accelerator Facility) will use Barrier Bucket longitudinal stacking to achieve high gain stacked

high current heavy ion beam. For the HIAF pre-research project, a new controller is designed by our research group

and the test experiment using the new controller is completed successfully to capture the two beam phases. We

plan to have an experiment in-beam based on the new designed controller under the Barrier Bucket dual-ring mode

and two-RF mode at the HIRFL in 2016.

References

[1] Wenxiong Zhou, Yanyu Wang, Detai Zhou, et al., Nuclear Instruments and Methods in Physics Research A, 728(2013)112.

[2] Yanyu Wang, Wenxiong Zhou, Jinfu Luo, et al., Nuclear Instruments and Methods in Physics Research A, 738(2013)50.

[3] D. T. Zhou, Y. Wang, Y. Li, et al., Nuclear Physics Review, 31(2014)48. (in chinese)

6 - 30 Design of the Tuning Capacitor with the DTL2 RF Cavity

Tian Ruixia, Jin Peng and Fu Xin

SSC-LINAC is as a linear injector for the cyclotron accelerator SSC. DTL2 RF cavity is designed to install

in SSC-LINAC intermediate energy beam line, whose working frequency is 53.667 MHz and working mode is cw.

DTL2 cavity adopts drift tube structure with IH-mode, which having high shunt impedance, high quality, etc.

Tuning of DTL2 RF cavity is designed based on the perturbation[1] theory, which used to compensate frequency

drift of cavity which caused by machining and manufacturing process, the temperature and other factors. The DTL2

RF cavity is designed with two tuning capacitors, a coarse tuning capacitor and a fine tuning capacitor. The coarse

tuning capacitor is used to compensate the frequency error caused by the production and processing accuracy of the

cavity, which regulating frequency range is 0∼1.0 MHz. The fine tuning capacitor is used for real time frequency

tuning to coordinate Low Level Control System[2] in the actual operation of the cavity, which regulating frequency

range is 0∼0.1MHz. The resonant frequency of the cavity could be adjusted with two tuning capacitor to make the

cavity working on the resonance frequency point stability. This paper mainly elaborate the design of the coarse

tuning capacitor.

Fig. 1 (color online)The position of the coarse tuning capacitor in the cavity.

According to the physical requirements of the cavity, the CST simulation model was established (see Fig. 1) and

the electromagnetic field distribution of the cavity could be obtained through simulating calculating. Depending

on the electromagnetic field intensity of different area, the installation position of the coarse tuning capacitor could

be determined, as shown in Fig. 2.

· 306 · IMP & HIRFL Annual Report 2015

Fig. 2 (color online)The different position distribution of the coarse tuning.

According to the electromagnetic field distribution of the DTL2 RF cavity and considering the installation

position of the coupler on the upper of the cavity, the tuning capacitor could design to install on the lower of the

cavity to avoid the interaction between the coupler and the tuning capacitor. The adjusting range requirement of

the coarse tuning capacitor is 0∼1.0 MHz, design and installation position of which has the following three points.

The calculation results are shown in Table 1.

Table 1 Tuning range of the coarse tuning capacitance with different location.

Position 1 Position 2 Position 3

Longitudinal position /mm 0 -125 -250

Horizontal position/mm 0 0 0

Tuning area /mm2 ϕ200×20 ϕ200×20 ϕ200×20

Tuning bar /mm ϕ40 ϕ40 ϕ40

Tuning trip /mm 80-250 80-250 80-250

Tuning frequency range/MHz 0.831 0.726 1.11

Note: the origin is the center of the cavity.

According to the simulation calculation results, when the coarse tuning capacitor is located in position 3, the

adjusting quantity of the coarse tuning capacitor could reach 1.11 MHz, which meet the design requirements.

Considering the high cavity working voltage, coarse tuning capacitor plate can’t stand too close to the T type plate.

Therefore, if the tuning range needs to expand, the tuning area needs to be increased.

References

[1] Z. J. Zhu, B. F. Jia, Z. X. Luo, et al., High Power Laser and Particle Beams, 20(2008)164.

[2] Linghua Wen, Xianwu Wang, Yuan He, et al., Chinese Physics C, 37(2013)087004.