Abstract
In this paper, we present the design and realization of high bandwidth pickup electrodes with a cutoff frequency above 40 GHz. The proposed cone-shaped pickups are part of a bunch arrival-time monitor (BAM) designed for high (> 500 pC) and low (20 pC) bunch charge operation mode providing for a time resolution of less than 10 fs for both operation modes. The proposed design has a fast voltage response, low ringing, and a resonance-free spectrum. For assessing the influence of manufacturing tolerances on the performance of the pickups, an extensive tolerance study has been performed via numerical simulations. A non-hermetic model of the pickups was built for measurement and validation purposes. The measurement and simulation results are in good agreement and demonstrate the capability of the proposed pickup system to meet the given specifications.
Highlights
High gain free-electron lasers (FELs) are able of generating ultrashort x-ray pulses with a duration in the femtosecond range [1]
The proposed cone-shaped pickups are part of a bunch arrival-time monitor designed for high ( > 500 pC) and low (20 pC) bunch charge operation mode providing for a time resolution of less than 10 fs for both operation modes
In order to provide an optimal operation of the FEL for pump-probe experiments or for seeding using external laser systems, the arrival time of the bunches has to be synchronized with femtosecond precision
Summary
High gain free-electron lasers (FELs) are able of generating ultrashort x-ray pulses with a duration in the femtosecond range [1]. An arrival-time monitor using a cavity as a beam pickup and a radio frequency (rf) based phase detection is described in [2] Such a detection scheme is realized at the Linac Coherent Light Source freeelectron laser at Stanford Linear Accelerator Center. At the free-electron laser at DESY, Hamburg (FLASH), the installed BAMs have an intrinsic time resolution better than 10 fs for bunch charges above 500 pC [9] These arrival-time monitors combine a transient beam induced pickup signal with an electro-optical signal detection scheme as proposed in [10]. The arrival time of the bunches is determined by comparing the sampling pulse energy with the laser pulses from the train [9] In this scheme the achievable time resolution is proportional to the steepness of the pickup voltage signal at the first zero crossing.
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