Reconstruction of the time profile of 20.35 GeV, subpicosecond long electron bunches by means of coherent Smith-Purcell radiation

Abstract

We have used coherent Smith-Purcell radiation (cSPr) in order to determine the temporal profile of sub-ps long electron bunches at the Facility for Advanced Accelerator Experimental Tests, at SLAC. The measurements reported here were carried out in June 2012 and April 2013. The rms values for the bunch length varied between 356 to 604 fs, depending on the accelerator settings. The resolution of the system was limited by the range of detectable wavelengths which was, in turn, determined by the choice of the grating periods used in these experiments and the achievable beam-grating separation. The paper gives the details of the various steps in the reconstruction of the time profile and discusses possible improvements to the resolution. We also present initial measurements of the polarization properties of cSPr and of the background radiation.

Electron bunch profile reconstruction based on phase-constrained iterative algorithm

“…Alternatively, iterative methods [13][14][15] have been used for the determination of the missing phase; these can give stable solutions for the 2D and 3D cases [16] but it is known [13][14][15][16] that the problem remains unresolved in the 1D case, such as the determination of the time profile of ultrashort bunches of charged particles. This is of particular interest to us because of its importance in relativistic beam diagnostics and free electron lasers [1][2][3][4][5][6][7]. Present and future particle accelerators will produce fs-long bunches whose shape is unlikely to be a simple Gaussian [17][18][19][20] and, given the importance of the temporal profile of the bunch for the understanding of beam-beam interactions and in FEL lasing, any advance in the phase retrieval problem would be highly desirable.…”

“…The problem of retrieving the phase of a signal from a measurement of its power spectrum alone is well known and has been under investigation for a few decades [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Measurements in the frequency domain (power spectrum) are necessary in cases where a direct measurement in the time domain is not possible, for instance because of the limited response time of the available detectors.…”

“…The nondestructive techniques which are used to determine a bunch profile are based on the analysis of the amplitude of the coherent radiation spectrum generated by the bunch and the application of a phase recovery technique [1,5,6]. Some information about the missing phase can be obtained from the so-called "minimal" phase [θ m ðωÞ].…”

Bunch Length Measurement Employing Cherenkov Radiation from a Thin Silica Aerogel

“…In particular, coherent SPR is considered especially useful as a monitor that can measure the beam non-destructively like DR. The FACET facility reported measurement results of a bunch length of 350 fs using SPR [8]. When measuring the bunch length with coherent radiation, it is important to obtain the radiation spectrum accurately over the necessary wavelength range.…”

Millimeter-wave periodic surface lattices for mode control in vacuum electronic sources

“…To advance the performance parameters and extend the frequency range of vacuum electronic devices, electromagnetic structures that can enhance and control the mode selection process in the beam wave interaction region are being investigated. Various structures and materials such as diffractive surfaces [1], metamaterials [2], photonic structures [3], metadielectrics and periodic surface lattices [4] are being studied in different regimes of operation. The use of such diverse structures enables the wave dispersion to be engineered within its own discrete parameter space with often shared theoretical principles, and similar numerical modelling methods being used.…”