A tuning method based on the coupled mode frequencies in biperiodic coupled-cavity linear accelerator

Area of Science:

• Particle Accelerators
• Radio Frequency Engineering
• Electromagnetics

Background:

• Coupled-cavity linacs (CCLs) are essential in various scientific fields, with radio frequency (RF) design being a critical aspect.
• Biperiodic structures, particularly side-coupled CCLs, exhibit different frequency drops in accelerating cavities (ACs) and coupled cavities (CCs) due to coupling slots, complicating precise frequency control.
• Accurate prediction of normal mode frequencies is crucial for effective CCL design and tuning.

Purpose of the Study:

• To develop a simplified method for designing and tuning triplet CCLs.
• To introduce a new parameter, frequency gap difference (ΔF), for predicting and controlling cavity frequencies.
• To reduce the complexity and time required for CCL tuning processes.

Main Methods:

• A lumped resonant circuit model was employed to accurately predict normal mode frequencies.
• Equivalent circuit equations were solved to derive the frequency gap difference (ΔF) parameter.
• The proposed method was validated through application in the Nanjing University CCL Project.

Main Results:

• The frequency gap difference (ΔF) parameter was found to be directly proportional to the frequency difference (df) between ACs and CCs, with a one-to-one ratio near resonance.
• A simplified tuning method was proposed, requiring only the measurement of coupled normal mode frequencies, eliminating the need for individual cell tuning.
• Analysis of frequency drops with varying coupling coefficients was performed by comparing cavities with and without coupling slots.

Conclusions:

• The proposed frequency gap difference (ΔF) parameter provides an effective means to manage frequency discrepancies in CCLs.
• The simplified design and tuning methodology significantly streamlines the CCL fabrication process, reducing turnaround time.
• The successful application at Nanjing University validates the practicality and efficiency of the developed method for RF design in CCLs.