Enhancing particle bunch-length measurements based on Radio Frequency Deflector by the use of focusing elements

Abstract

A method to monitor the length of a particle bunch, based on the combination of a Radio frequency Deflector (RFD) with magnetic focusing elements, is presented. With respect to state-of-the-art bunch length measurement, the additional focusing element allows to measure also the correlations between the longitudinal and transverse planes in terms of both position and divergence. furthermore, the quadrupole-based focusing increases the input dynamic range of the measurement system (i.e. allows for a larger range of beam Twiss parameters at the entrance of the RFD). Thus, measurement resolution and precision are enhanced, by simultaneously preserving the accuracy. In this paper, the method is first introduced analytically, and then validated in simulation, by the reference tool eLectron Generation And tracking, eLeGAnt. finally, a preliminary experimental validation at CLEAR (CERN Linear Electron Accelerator for Research) is reported.

Focused VHEE (very high energy electron) beams and dose delivery for radiotherapy applications

“…As in the literature 33 , the matrix element for a focusing quadrupole M QF of length L Q and focusing strength K is given by similarly where = √ |K|L Q . The matrix element for a defocusing quadrupole, M QD of length L Q and strength −K is similarly given by Note that the magnetic field gradient, g (T/m) of a quadrupole magnet can be found from the focusing strength, K (m −2 ), via where E is the beam energy (MeV).…”

VHEE beam dosimetry at CERN Linear Electron Accelerator for Research under ultra-high dose rate conditions

“…The beam is generated using a photocathode in Cs2Te then thanks to three accelerating stage, powered by two RF sources, it is possible to reach the top energy of 200 MeV. The accelerator line continues with a diagnostic section, where different setups allow a precise bunch length measurement and beam energy measurement (Arpaia et al 2020). Following, two irradiation areas are located, the first is VESPER, a test stand for irradiation installed on a spectrometer line, and the second is the so called 'in air' TeraHertz (THz) test-stand (Lagzda et al 2020, McManus et al 2020.…”

A Measurement Method Based on RF Deflector for Particle Bunch Longitudinal Parameters in Linear Accelerators

“…The uncertainty on K cal as well as the measured energy chirp and bunch length is only due to the linear fit. The approximation of a constant calibration factor in the RFD phase range leads to a relative error less than 1.5% and thus negligible with respect to the theoretical calibration factor (10).…”

“…In the actual prototypes of those machines, ultrashort (tens of femtoseconds) bunches are affected by huge energy spread and chirps, nowadays limiting their performances, and they need to be carefully measured. Since RFDs are very common in high-brightness LINACs [8]- [10] due to their very high resolutions, as state-of-the-art methods [11], however, an extended metrological theory behind this measurement method, capable of highlighting all the terms affecting the bunch length measurement, is still missing. The standard technique is based on the assumptions of negligible energy spread and/or correlation between particle longitudinal positions and energies (namely, energy chirp) and/or correlations between particle positions, divergence, and energies at the RFD location.…”