Bunch length measurement at a bunch-by-bunch rate
based on time-frequency domain joint analysis techniques
and its application
Hongshuang Wang12, Xing Yang12, Yongbin Leng14, Yimei Zhou3, and Jigang Wang4
1. Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China;
2. University of Chinese Academy of Sciences, Beijing 100049, China;
3. Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201204, China;
4. National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230026, China

Introduction

Uncertainty Evaluation

Streak cameras cannot simultaneously achieve high time
resolution and large dynamic range in beam length
measurement[1].
Traditional dual-frequency systems have narrowmeasurement bandwidths and can only provide averagebunch length measurements for multiple bunches overmultiple turns.

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Bunch by bunch
Bunch length
Time-frequency domain
Transfer impedanceAlgorithm•••(a) Uncertainty assessment of the beam length
measurements for different charge values in the singlebunch mode at the HLS.
(b) In the multi-bunch operation mode at the SSRF,with different charges for each bunch, the total charge
for all bunches are calculated, and the beam length
uncertainty is assessed for each individual bunch.
In both experiments, it is observed that the bunch
length measurement uncertainty is approximately
inversely proportional to the bunch charges.

Experimental results• V(f) is the frequency-domain distribution of thedetected signal.
• I(f) is the frequency-domain distribution of the beam
signal (Gaussian distribution).
• R_Button (f) is the frequency-domain transfer
impedance to be calibrated• By measuring V(f), I(f) can be obtained, and then thebunch length can be obtainedExperimental system(a) In the single-bunch experiment at the HLS, inconjunction with a streak camera, the distribution of
the bunch length with respect to the beam charge wasmeasured. The results obtained through the timefrequency joint analysis method showed excellent
agreement with the streak camera results.
(b) Under different charges, the beam length exhibits
noticeable oscillations when the charge exceeds acertain threshold.

Conclusion••

The four-electrode signals from the BPM probes are
acquired using a high-sampling-rate and high-bandwidth
digital oscilloscope. These signals are then imported
into Python scripts for further analysis.
Adding a new bunch length calculation module to theexisting HOTCAP bunch-by-bunch measurement
system• The existing parameters of wideband, high-speed
oscilloscope technology have met the requirements forbunch-by-bunch and turn-by-turn bunch length
measurements.
• The phase measurement uncertainty is more than 0.2 ps,
the bunch length measurement uncertainty is more than 1
ps, and the dynamic range exceeds 10 ms.
• This technique can be integrated as an additional modulein the existing 3D bunch position measurement system,HOTCAP[2], thereby forming a comprehensive multiparameter bunch-by-bunch measurement system that
includes the position, bunch length, and charge.

References[1] Iriso U, and Fernández F. Streak Camera Measurements at ALBA: Bunch Length and Energy Matching, IBIC2012,
Tsukuba, TUPA46 (2012): 458.
[2] Xu X Y, Leng Y B, Gao B, et al. HOTCAP: a new software package for high-speed oscilloscope-based threedimensional bunch charge and position measurement[J]. Nuclear Science and Techniques, 2021, 32: 1-11.

Contact Email: lengyb@ustc.edu.cn