Bunch Repetition Frequency Research Articles

Synchrotron X-ray induced acoustic imaging

X-ray induced acoustic imaging (XAI) is an emerging biomedical imaging technique that can visualize X-ray absorption contrast at ultrasound resolution with less ionizing radiation exposure than conventional X-ray computed tomography. So far, medical linear accelerators or industrial portable X-ray tubes have been explored as X-ray excitation sources for XAI. Here, we demonstrate the first feasible synchrotron XAI (sXAI). The synchrotron generates X-rays, with a dominant energy of 4 to 30 keV, a pulse-width of 30 ps, a pulse-repetition period of 2 ns, and a bunch-repetition period of 940 ns. The X-ray induced acoustic (XA) signals are processed in the Fourier domain by matching the signal frequency with the bunch-repetition frequency. We successfully obtained two-dimensional XA images of various lead targets. This novel sXAI tool could complement conventional synchrotron applications.

Stable bunch trains for plasma wakefield acceleration

A train of short charged particle bunches can efficiently drive a strong plasma wakefield over a long propagation distance only if all bunches reside in focusing and decelerating phases of the wakefield. This is shown possible with equidistant bunch trains, but requires the bunch charge to increase along the train and the plasma frequency to be higher than the bunch repetition frequency.

An experimental study of electron acceleration with detuning of the bunch repetition frequency from that of an excited wake field

We have experimentally studied the excitation of wake fields in a dielectric structure by a train of relativistic electron bunches and the acceleration of subsequent bunches of the same train due to detuning of the bunch repetition frequency relative to that of the wake field excited in the dielectric structure at the Cherenkov resonance. Electron bunches of the first (leading) part of the train excite the wake wave, and bunches of the second (trailing) part of this train are shifted to the accelerating phase of the wake wave so as to gain additional energy. The possibility of controlling the number (repetition frequency) of bunches exciting the wake field in the dielectric structure and the number of subsequently accelerated bunches has been investigated by changing the value of detuning.

Mul'tybanchevyy rezhym zbudzhennya kil'vaternoho polya v plazmovo-dielektrychniy strukturi

The main results of theoretical and experimental researches concerning the physical processes in a dielectric wakefield accelerator based on the accelerating wakefield excitation in a dielectric structure with the use of a long sequence of electron bunches are presented. The enhancement of the excited wakefield amplitude is achieved owing to the coherent summation of wakefields generated by separate bunches. The bunches are accelerated in the total wakefield by arbitrarily dividing the bunch sequence into the exciting and accelerated parts, by using the appropriate frequency detuning of the bunch repetition frequency with respect to the frequency of the excited principal transverse mode. The influence of plasma in the transit channel on the amplitude of excited wakefields and the focusing of driving and accelerated bunches is analyzed.

Generation of wakefields in a dielectric structure filled with plasma

The effect of plasma on the amplitude of the wakefield excited in a dielectric structure by a relativistic electron bunch train is studied. The structure under study is a dielectric cylindrical waveguide with an axial drift channel filled with plasma. The dependences of the amplitude of a longitudinal electric field on the plasma density are obtained for the following three cases: the parameters of the dielectric structure and bunches are fixed; the inside or outside radius of the dielectric tube changes according a change in the plasma frequency, and the bunch repetition frequency is adjusted to the plasma frequency and the frequency of the first radial mode of a dielectric wave. It is shown that, when the eigenwave frequencies are adjusted to the bunch repetition frequency via a change in the structure radii, the maximum of the accelerating field is determined by a plasma wave, and there is a plasma density range where a dielectric wave significantly contributes to the total field amplitude. In the case of changing the outside radius, this range is substantially wider.

Investigations of the concept of a multibunch dielectric wakefield accelerator

Theoretical and experimental investigations of the physical principles of multibunch dielectric wakefield accelerator concept based on the wakefield excitation in the dielectric structure by a sequence of relativistic electron bunches are presented. The purpose of the concept is to enhance the wakefield intensity by means of the multibunch coherent excitation and wakefield accumulation in a resonator. The acceleration of bunches is achieved at detuning of bunch repetition frequency relative to the frequency of the excited wakefield. In such a way the sequence of bunches is divided into exciting and accelerated parts due to displacing bunches into accelerating phases of wakefield excited by a previous part of bunches of the same sequence. Besides the change of the permittivity and loss tangent of dielectrics under the irradiation by 100MeV electron beam is studied.

Resonant excitation of plasma wakefields by a non-resonant train of short electron bunches

For long trains of short electron bunches, a mechanism is found which, at the expense of beam population, enables resonant excitation of the wakefield even if the bunch repetition frequency appreciably differs from the plasma frequency. Frequency synchronization results from defocusing of those bunches which fall into a wrong phase with respect to the plasma-frequency wave.

Transition radiation of surface electromagnetic waves by electron bunches in a cylindrical waveguide

Transition surface electromagnetic radiation from electron bunches that cross a metal-insulator-semiconductor structure in a perfectly conducting semi-infinite cylindrical waveguide is studied. It is shown that, using a periodic sequence (train) of electron bunches, a particular surface waveguide eigenmode can be amplified by bringing its frequency to resonance with the bunch repetition frequency in the train. Those eigenmodes are amplified most efficiently whose frequency falls into the range occupied by the first maximum of the geometric factor of one bunch.

Experimental results on electron beam combination and bunch frequency multiplication

The aim of the CLIC Test Facility CTF3 at CERN is to demonstrate the feasibility of the key points of the two-beam acceleration based compact linear collider study. In particular, it addresses the efficient generation of a drive beam with the appropriate time structure of the electron bunches in order to produce high power rf pulses at a frequency of 30 GHz. This time structure requires a high bunch repetition frequency. It is obtained by successive injections of bunch trains into an isochronous ring using transversely deflecting rf structures. The major goal of the now completed first phase of the CTF3 was to achieve the bunch train combination at low charge. In this paper, we give a description of the project and summarize the experimental results, with a focus on the successful bunch frequency multiplication for various factors up to 5.

The South Hall Ring and the BLAST detector

Although the electron injection system of the infrared free electron laser FELIX permits a high electron bunch repetition frequency of 1 GHz, user experiments often require a lower frequency. At the same time, the pulses from the gun have to be sufficiently short to fit within the longitudinal acceptance of a 1-GHz prebuncher. The generation of 300 ps electron bunches with a 25 MHz repetition rate, produced by pulse modulation of a triode gun, is addressed in this paper. The modulating waveform was generated by superposition of a 1 GHz sinusoidal wave, a 25 MHz train of pulses with a duration of 2 ns and a DC bias voltage. The hardware for the adopted modulation method, which consists of two RF cavities and an adjustable delay line, is described and analysed. Measurements of the electron bunch length are presented.

Sub-nanosecond pulse modulation of a triode electron gun at 25 MHz

Although the electron injection system of the infrared free electron laser FELIX permits a high electron bunch repetition frequency of 1 GHz, user experiments often require a lower frequency. At the same time, the pulses from the gun have to be sufficiently short to fit within the longitudinal acceptance of a 1-GHz prebuncher. The generation of 300 ps electron bunches with a 25 MHz repetition rate, produced by pulse modulation of a triode gun, is addressed in this paper. The modulating waveform was generated by superposition of a 1 GHz sinusoidal wave, a 25 MHz train of pulses with a duration of 2 ns and a DC bias voltage. The hardware for the adopted modulation method, which consists of two RF cavities and an adjustable delay line, is described and analysed. Measurements of the electron bunch length are presented.

Methods for suppressing the longitudinal instability of a bunched beam with the help of landau damping

Two methods which have been proposed for increasing the synchrotron frequency spread and consequently stabilizing the longitudinal instability of a bunched beam in a synchrotron include the reduction of the amplitude of the accelerating field to a level ensuring almost complete filling of the separatrix by the bunch and the insertion of an additional accelerating system operating on the highest harmonic of the fundamental frequency of acceleration. In this paper the efficiencies of these methods are compared for the case when the impedance of the accelerator chamber is determined by a narrow-band resonator whose transmission bandwidth is much smaller than the bunch repetition frequency.

Use of ion-exchange materials for preparing low-activity radiation sources

Although the electron injection system of the infrared free electron laser FELIX permits a high electron bunch repetition frequency of 1 GHz, user experiments often require a lower frequency. At the same time, the pulses from the gun have to be sufficiently short to fit within the longitudinal acceptance of a 1-GHz prebuncher. The generation of 300 ps electron bunches with a 25 MHz repetition rate, produced by pulse modulation of a triode gun, is addressed in this paper. The modulating waveform was generated by superposition of a 1 GHz sinusoidal wave, a 25 MHz train of pulses with a duration of 2 ns and a DC bias voltage. The hardware for the adopted modulation method, which consists of two RF cavities and an adjustable delay line, is described and analysed. Measurements of the electron bunch length are presented.