Fast mapping of terahertz bursting thresholds and characteristics at synchrotron light sources

Abstract

Dedicated optics with extremely short electron bunches enable synchrotron light sources to generate intense coherent THz radiation. The high degree of spatial compression in this so-called low-αc optics entails a complex longitudinal dynamics of the electron bunches, which can be probed studying the fluctuations in the emitted terahertz radiation caused by the micro-bunching instability ("bursting"). This article presents a "quasi-instantaneous" method for measuring the bursting characteristics by simultaneously collecting and evaluating the information from all bunches in a multi-bunch fill, reducing the measurement time from hours to seconds. This speed-up allows systematic studies of the bursting characteristics for various accelerator settings within a single fill of the machine, enabling a comprehensive comparison of the measured bursting thresholds with theoretical predictions by the bunched-beam theory. This paper introduces the method and presents first results obtained at the ANKA synchrotron radiation facility.

Systematic studies of the microbunching instability at very low bunch charges

“…This linear scaling law fits best for high values of Π (Π > 3), however at lower values the simulated thresholds are significantly higher than the fit. Interestingly, the measured thresholds are described more accurately by the fit (see [10]) than the thresholds obtained by the VFP simulations for these low values of Π. This is the case for the VFP simulations in [3] as well as for the ones presented in the following and can be attributed to the simplicity of the parallel plates model.…”

High throughput data streaming of individual longitudinal electron bunch profiles

“…The experiments, outlined in this section, were performed at the storage ring KARA at KIT. During the measurements, the storage ring was operated at a beam energy of 1.3 GeV, with a radio frequency (RF) voltage of 1500 kV and a bunch current of 0.35 mA stored in a single bunch (for additional parameters see [12]). The storage ring was operated in the so-called low-α c mode [21] compressing the electron bunch length to a few picoseconds.…”

“…Because these microstructures produce strong THz radiation bursts with an intensity more than 5 orders of magnitude higher than incoherent synchrotron radiation [2] potentially leading to e.g. applications in non-linear spectroscopy, this process is subject to intense investigations [3][4][5][6][7][8][9][10][11][12]. Although far-field CSR measurements are a useful approach, additional methods exploring the phase space more directly are desirable in order to tighter connect * stefan.funkner@kit.edu † Present address:PSI, Villigen, Switzerland ‡ Present address:DESY, Hamburg, Germany theory and experiment.…”

Stable coherent terahertz synchrotron radiation from controlled relativistic electron bunches

“…As the main motivation, the patterns which spontaneously appear during an instability increase the terahertz radiation power by factors exceeding 10000 [5,6]. However the irregularity of these patterns [5][6][7][8][9][10][11] largely prevented applications of this powerful source. Here we show how to make the spatiotemporal patterns regular (and thus the emitted THz power) using a point of view borrowed from chaos control theory [12][13][14].…”

“…Such "parameter search" methods succeeded in identifying parameter regions with stable coherent emission. However, this corresponds to special configurations (with short and low charge electron bunches, in the so-called low-alpha operation [5,6,10,11,[18][19][20][21][22][23]) which are not compatible with most of the user experiments. Therefore, this type of THz source is used in relatively few synchrotron radiation facilities (SOLEIL, DIAMOND, BESSY-II), and only during a small part of the year."Parameter search approaches" are however not the only possibilities for avoiding instabilities.…”