Abstract
The temporal profile measurement for ultra-short electron bunches is one of the key issues for accelerator-based coherent light sources. A bunch length measurement system using Cherenkov radiation (CR) is under development at the Research Center for Electron Photon Science, Tohoku University. This system allows for the real-time diagnostics of electron bunches. The system comprises a thin silica aerogel as the Cherenkov radiator, a specially designed optical transport line, and a high-speed streak camera. The electron bunch length can be obtained by measuring the time spread of the CR from the electrons passing through the radiator medium using the streak camera. In this paper, we describe the novel bunch length measurement system using CR, discuss the expected time resolution of the system, and finally present the measurement results.
Highlights
R&D work on a coherent terahertz light source using ultra-short electron bunches has been conducted at the accelerator test facility Test-accelerators as coherent terahertz source program (t-ACTS), Tohoku University [1]
R&D work on a coherent terahertz light source using ultra-short electron bunches has been conducted at the accelerator test facility t-ACTS, Tohoku University [1]
Coherent radiation has been used widely to measure such short electron bunch lengths. Various radiation processes, such as synchrotron radiation (SR), transition radiation (TR), Cherenkov radiation (CR), diffraction radiation (DR), and Smith–Purcell radiation (SPR) from short electron bunches can be utilized as a coherent radiation source for beam diagnosis [4,5,6,7]
Summary
R&D work on a coherent terahertz light source using ultra-short electron bunches has been conducted at the accelerator test facility t-ACTS, Tohoku University [1]. Among currently available streak cameras, Hamamatsu FESCA-100 has the fastest sweep rate (of 10 ps/frame), and its time resolution is approximately 100 fs depending on the wavelength of the incident light [12]. To realize this high resolution, it is necessary to strictly limit the wavelength and bandwidth of the light incident on the streak camera This leads to another problem in that the measurable light quantity becomes quite insufficient. The measured bunch length was rather large—more than 400 fs—and limited by the resolution due to insufficient light quantity Under such circumstances, we have developed a measurement system with a modest time resolution of ~100 fs for ultra-short electron bunches using CR from a thin silica aerogel that is much brighter than OTR.
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