All-optical quasi-monoenergetic GeV positron bunch generation by twisted laser fields

Generation of energetic electron-positron pairs using multi-petawatt (PW) lasers has recently attracted increasing interest. However, some previous laser-driven positron beams have severe limitations in terms of energy spread, beam duration, density, and collimation. Here we propose a scheme for the generation of dense ultra-short quasi-monoenergetic positron bunches by colliding a twisted laser pulse with a Gaussian laser pulse. In this scheme, abundant γ-photons are first generated via nonlinear Compton scattering and positrons are subsequently generated during the head-on collision of γ-photons with the Gaussian laser pulse. Due to the unique structure of the twisted laser pulse, the positrons are confined by the radial electric fields and experience phase-locked-acceleration by the longitudinal electric field. Three-dimensional simulations demonstrate the generation of dense sub-femtosecond quasi-monoenergetic GeV positron bunches with tens of picocoulomb (pC) charge and extremely high brilliance above 1014 s−1 mm−2 mrad−2 eV−1, making them promising for applications in laboratory physics and high energy physics.

PLASMA LENS FOR ELECTRON AND POSITRON BEAMS

Focusing of both electron and positron bunches in electron-positron collider is necessary. When long electron/positron bunch is injected into the plasma, the focusing force is not uniform but oscillated. It is shown that a long positron bunch after focusing is destroyed faster than an electron bunch due to betatron and plasma oscillations.

FOCUSING OF POSITRON BUNCH WHEN MOVING IN ELECTRON BUNCH WAKEFIELD IN THE DIELECTRIC WAVEGUIDE FILLED WITH PLASMA

The results of numerical PIC-simulation of focusing accelerated (test) positron and drive electron bunches in the dielectric waveguide filled with radially heterogeneous plasma with the vacuum channel are given in the paper. The wakefield was excited by electron bunch in quartz dielectric tube, inserted into cylindrical metal waveguide. The internal area of dielectric tube has been filled with plasma different transverse density profiles, heterogeneous on radius, with the vacuum channel along waveguide axis. Plasma density for all studied cases was so low that plasma frequency was less, than the frequency of the main dielectric mode. Results of numerical PIC simulation have shown that possibility of simultaneous acceleration and focusing of the test positron bunch are possible in the wakefield. The best acceleration happens in case of plasma absence, however at that there is no focusing of test positron bunch.

First simultaneous detection of electron and positron bunches at the positron capture section of the SuperKEKB factory

The direct simultaneous detection of electron and positron bunch signals was successfully performed for the first time with wideband pickups and a detection system at the positron capture section of the SuperKEKB factory. The time interval between the electron and positron bunches, their bunch lengths, and bunch intensities depending on the phase of accelerating structures were measured to investigate their capture process and to maximally optimize the positron intensity. The results show that the time intervals were measured in the range of 135–265 ps, and the line-order switch of the electron and positron bunches in the axial direction was clearly observed as a function of the phase. The positron (electron) intensity was maximized at the optimal phase (180$$^{\circ }$$ ∘ shifted from the optimum). These series of measurements have never been experimentally conducted so far. It is demonstrated that the positron intensity can be systematically optimized with this system as functions of beam parameters in multidimensional spaces for any positron capture section.

First Simultaneous Detection of Electron and Positron Bunches at the Positron Capture Section of the SuperKEKB Factory

The direct simultaneous detection of electron and positron bunch signals was successfully performed for the first time with wideband pickups and a detection system at the positron capture section of the SuperKEKB factory. The time interval between the electron and positron bunches, their bunch lengths, and bunch intensities depending on the phase of accelerating structures were measured to investigate their capture process and to maximally optimize the positron intensity. The results show that the time intervals were measured in the range of 135–265 ps, and the line-order switch of the electron and positron bunches in the axial direction was clearly observed as a function of the phase. The positron (electron) intensity was maximized at the optimal phase (180 deg shifted from the optimum). These series of measurements have never been experimentally conducted so far. It is demonstrated that the positron intensity can be systematically optimized with this system as functions of beam parameters in multidimensional spaces for any positron capture section.

SOURCE OF POSITRONS ON THE BASE OF LINAC LUE-40

The results of the numeral studies of the source of positrons for NSC KIPT are presented. The positrons are to produce from conversion of the 40 MeV electrons. The bunches of such electrons will be provided by the linac LUE-40. The estimations of yield of the positrons, their spectrum, and spatial-angular distribution are produced. The possibility of the spectrum modification with help of the RF resonator adjusted to the sub-harmonics of the RF frequency is proposed. It is shown that the use of such device allows to substantially increase the number of positrons with small energy. It allows to promote efficiency of the moderation process and increase yield of the slow mono energetic positrons. The optimal parameters of conversion target have been defined. The preliminary calculations of the system of forming the positron bunch are presented as well.