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The characterization of an electron–positron beam generated from the interaction of a multi-GeV electron beam with a lead plate is performed using GEANT4 simulations. The dependence of the positron beam size on driver electron beam energy and lead converter thickness is investigated in detail. A pancake-like positron beam structure is generated with a monoenergetic multi-GeV driver electron beam, with the results indicating that a 5 GeV driver electron beam with 1 nC charge can generate a positron beam with a density of 1015–1016 cm−3 at one radiation length of lead. In addition, we find that electron–positron beams generated using above-GeV electron beams have neutralities greater than 0.3 at one radiation length of lead, whereas neutralities of 0.2 are observed when using a 200 MeV electron beam. The possibility of observing plasma instabilities in experiments is also examined by comparing the plasma skin depth with the electron–positron beam size. A quasi-neutral electron–positron plasma can be produced in the interaction between a 1 nC, 5 GeV electron beam and lead with a thickness of five radiation lengths. Our findings will aid in analyzing and interpreting laser-produced electron–positron plasma for laboratory astrophysics research. [ABSTRACT FROM AUTHOR]

A design study has been performed for a positron beam with an energy of 500 MeV to be realized at the applied physics area of the Mainz Microtron MAMI. Positrons will be created after pair conversion of bremsstrahlung, produced by the 855 MeV electron beam at MAMI in a tungsten converter target. From the two conceivable geometries (1) pair conversion in the bremsstrahlung converter target itself, and (2) bremsstrahlung pair conversion in a separated lead foil, the former was considered in detail. Positrons will be energy selected within an outside open electron beam-line bending magnet, and bent back by an additional sector magnet. Magnetic focusing elements in between are designed to prepare in a well shielded positron target chamber about 6 m away from the target a beam with horizontal and vertical emittances of ϵ v = 0.055 π mm mrad (1 σ ), and ϵ h = 0.12 π mm mrad (1 σ ), respectively, for a 10 μ m thick amorphous tungsten target and negligible momentum spread. At an accepted positron band width of 1 MeV, spots are expected vertically with an angular spread of 0.064 mrad and a size of 5.0 mm (FWHM), and horizontally with an angular spread of 0.64 mrad and a size of 7.7 mm (FWHM). The positron yield amounts to 13.1 per second, 1 MeV positron energy band width, and 1 nA electron beam current. [ABSTRACT FROM AUTHOR]

The stability of plasma-based accelerators against transverse misalignments and asymmetries of the drive beam is crucial for their applicability. Without stabilizing mechanisms, even small initial offsets of the drive beam centroid can couple coherently to the plasma wake, grow, and ultimately lead to emittance degradation or beam loss for a trailing witness beam. In this work, we demonstrate the intrinsic stability of a beam propagating in a plasma column. This result is relevant in the context of plasma-based positron acceleration, where a wakefield suitable for the transport and acceleration of a positron witness beam is generated in a plasma column by means of an electron drive beam. The stable propagation of the drive beam is a necessary condition for the experimental implementation of this scheme. The differences and similarities of stabilizing mechanisms in a plasma column compared to a homogeneous plasma are identified via theory and particle-in-cell simulations. Experimental tolerances are given, demonstrating the experimental feasibility of the scheme. [ABSTRACT FROM AUTHOR]

The positron source is one of the most important parts of the circular electron–positron collider (CEPC) linear accelerator. The design goal is to obtain a 3 nC bunch charge positron beam from a 4 GeV primary electron beam with an intensity of 10 nC/bunch. In this study, an all-solid-state, high-current pulse power system was developed to drive a flux concentrator to capture positrons by generating a magnetic field with a peak value of 6 T. Based on the inductive load topology circuit, the optimized parameters were designed to generate a pulse current with a high peak value and a high rise rate pulse current. In addition, a non-reverse voltage was realized to protect the solid-state switch components. For the characteristics of the long-distance transmission between the pulse power supply and the load in the system, the influences of the cable distribution parameters on the pulse were analyzed, and the design of the damping circuit was proposed to suppress the high-frequency ripples of the peak pulse current. An optimized coaxial discharge structure was designed to reduce the stray parameters in the main circuit. The design was verified through simulations and experiments, and the results demonstrated that the developed prototype successfully generated an ideal half-sinusoidal pulse current with a peak value of 15 kA, and a front pulsewidth of $2.5 ~\mu \text{s}$ at a repetition rate of 50 Hz. The pulse repetition stability is better than 0.1%. The final output was consistent with the theoretical analysis. The system can be applied in the CEPC positron source, which also provides a reference for the subsequent development of a positron source system at research facilities. [ABSTRACT FROM AUTHOR]

For a long time the necessity of having intense positron beams to get a high rate of events with fixed targets as with e+e− collisions, led to conventional positron sources using high energy and high intensity electron beams generating bremsstrahlung photons in thick high Z targets. The inconveniences for such scheme, heat load and large emittance, are underlined. Alternative ways aiming to provide a high number of photons impinging on rather thin conversion targets have been developed: they are using magnetic undulators, laser Compton backscattering and channeling radiation in axially oriented crystals. A brief description of these methods is given. However, the emphasis is put here on the channeling radiation. The advantages of channeling radiation, described by M.Kumakhov and others, were confirmed by many simulations and experiments. We are reporting, hereafter, on two schemes: positron all-crystal converters involving thick crystals where photon radiation and e+e− pair creation are occurring in the crystal and hybrid sources where the two functions are separated. With the hybrid scheme, including a thin crystal-radiator and a thick amorphous-converter, the heat load and the local deposited energy density can be lowered. Simulations and experiments related to these two schemes are reported. Further developments concerning the converter, granular instead of bulk, are providing additional advantages. The promising, already gathered results led to consider these kinds of positron sources for future e-e+ colliders. More physicists, from different laboratories, concerned by the studies on positron sources are now contributing in this field. [ABSTRACT FROM AUTHOR]

In this work, we simulated the distributions of positrons with different kinetic energies as a function of linear transverse and angular deflections from the electron beam axis and the exit time produced upon normal incidence of "needle-like" "instantaneous" electron beams with kinetic energies E– = 55, 220, 1000 MeV on optimal converter targets (at the exit from the converters). The calculation results are compared with the available published data and experimental requirements. [ABSTRACT FROM AUTHOR]

In this paper, we report the characteristics of the generated beams, the extracted electron beam and the beam of secondary electrons/positrons, of the LPI accelerator complex Pakhra as of November 2019 for testing and calibrating detectors used in large accelerator and astrophysical experiments. At energies of 250–500 MeV of the electron beam ejected into Hall 1 from the S-25R synchrotron, its energy resolution is δ ~ 1% and the intensity can be changed by collimators in the range of 103–1010 s–1. The quasi-monochromatic beam of secondary electrons produced in Hall 2 typically has an energy in the range of 50–300 MeV, a corresponding energy resolution of δ = 14–2%, and an intensity of ~ 102 s–1. The performed simulation of the characteristics of the secondary positron beam allowed selecting the optimal geometry of the setup and showed good agreement with the experimental data obtained later. [ABSTRACT FROM AUTHOR]

Particle-in-cell simulations of jets of electrons and positrons in an ambient electron–proton plasma have revealed an acceleration of positrons at the expense of electron kinetic energy. We show that a filamentation instability, between an unmagnetized ambient electron–proton plasma at rest and a beam of pair plasma that moves through it at a non-relativistic speed, indeed results in preferential positron acceleration. Filaments form that are filled predominantly with particles with the same direction of their electric current vector. Positron filaments are separated by electromagnetic fields from beam electron filaments. Some particles can cross the field boundary and enter the filament of the other species. Positron filaments can neutralize their net charge by collecting the electrons of the ambient plasma, while protons cannot easily follow the beam electron filaments. Positron filaments can thus be compressed to a higher density and temperature than the beam electron filaments. Filament mergers, which take place after the exponential growth phase of the instability has ended, lead to an expansion of the beam electron filaments, which amplifies the magnetic field they generate and induces an electric field in this filament. Beam electrons lose a substantial fraction of their kinetic energy to the electric field. Some positrons in the beam electron filament are accelerated by the induced electric field to almost twice their initial speed. The simulations show that a weaker electric field is induced in the positron filament and particles in this filament hardly change their speed. [ABSTRACT FROM AUTHOR]

Counterstreaming electron beams drifting along the magnetic field in electron–proton plasmas may lead to the generation of electrostatic (ES) waves and structures widely observed in planetary magnetospheres. In electron–positron plasmas, streaming electron/positron beams along the background magnetic field may first result in ES waves followed by the electromagnetic (EM) waves with substantial magnetic field perturbations, as shown by Jao and Hau [Phys. Rev. E 98, 013203 (2018)]. In this study, we examine the formation of ES and EM waves driven by current free counterstreaming electron beams in electron–ion background plasmas and current free electron–positron beams in electron–proton–positron background plasmas based on one-dimensional EM particle-in-cell simulations with the drift velocity being along the background magnetic field. For the former cases, the effects of ion-to-electron mass ratios are examined, which have implications for two- and three-dimensional particle in cell simulations with reduced mass ratios. For the latter cases, the effects of positrons are examined, which have applications to astrophysical plasma environments and laboratory experiments. It is shown that the presence of positrons or light ions may shorten the occurrence times between the ES and EM waves driven by current free electron beam instability. The EM waves have relatively longer wavelengths as compared to the ES waves and the magnetic field evolution resembles parallel proton firehose instability. The effects of positrons, background compositions, and ion-to-electron mass ratios on the occurrence of ES and EM waves are consistent with the linear fluid theory. [ABSTRACT FROM AUTHOR]

The nonlinear features of Ion Acoustic (IA) waves are studied in a fully relativistic three-dimensional (3-D) plasma system with consideration of effect of both positron beam and trapped electrons. We consider a set of 3-D magnetised hydrodynamic equations with pressure expansion for our plasma model along with kinetic Vlasov equation for electrons. Applying the perturbative expansion technique, a Modified Korteweg-de Vries (m-KdV)-like equation is derived, exhibiting the evolution of small amplitude IA waves in plasma. The modified coefficient of nonlinear term in K-dV equation has arrived due to impact of vortex-like distribution of electrons. An analytical and numerical investigation of the nonlinear evolution equations is exhibited with external magnetic field effects, the time derivative pressure expansion as well as other parameters like relativistic effect, mass variation, beam velocity and temperature effect have been taken into consideration. The presence of vortex like trapped electron distribution and positron beam governs the influence of soliton structure quite significantly. The present result should help us to understand the experiments that involve particle trapping and also the salient features of astrophysical environment like ionospheric plasma together with situations in plasma describing the electrostatic solitary structures usually seen in antimatter-related environment in interplanetary region. [ABSTRACT FROM AUTHOR]

A new system for measuring the position of the beam in a pulsed transport channel from the VEPP-3 storage ring to the VEPP-4M collider is discussed, which provides measurement of the position and intensity of an electron or positron beam in one span. For reliable operation of the experimental complex, it is necessary to continuously monitor the beam trajectory in a non-destructive manner, as well as to measure the possible losses of the beam charge. In 2018, new sensors and new electronics of the beam position measurement system were developed, manufactured, and installed in the transportation channel, which provide much greater accuracy compared to the old system. In the new system, it was possible to almost completely eliminate interference and to achieve measurement accuracy better than 0.02 mm, which is more than enough for optimal tuning of the channel optics and achieving high bypass efficiency. The design of the sensor, the structure and the main features of the construction of electronics are described, the accuracy of measurements is analyzed, and some results of the operation of the new system in the channel are given. [ABSTRACT FROM AUTHOR]

TeV center-of-mass energy electron-positron linear colliders comprising seamlessly staged capillary laser-plasma accelerators are presented. A moderate intensity laser pulse coupled with the single electromagnetic hybrid mode in a gas-filled capillary can generate plasma waves in the linear regime, where laser wakefields can accelerate equally focused electron and positron beams. In multiple stage capillary accelerators, a particle beam with respect to the laser wakefield can undergo consecutive acceleration up to TeV energies, associated with continuous transverse focusing in a beam size down to a nanometer level, being capable of a promising electron-positron linear collider with very high luminosities of the order of 10 3 4 cm − 2 s − 1 . The transverse and longitudinal beam dynamics of beam particles in plasma wakefields with the effects of radiation reaction and multiple Coulomb scattering are investigated numerically to estimate the luminosities in beam-beam collisions with the effects of beamstrahlung radiation and bunch disruption. [ABSTRACT FROM AUTHOR]

Beam diagnostics is important to guarantee good quality of beam in a particle accelerator. Both the electron and positron run in the tunnel in some modern electron–positron colliders such as circular electron–positron collider (CEPC) to be built and Beijing Electron–Positron Collider II (BEPC II). To measure the electron and positron beams, picking-up these two different bunches in real time is a notable concern. As the time interval between adjacent electron and positron bunches is quite small, for example, 6 ns in CEPC, high-speed switch electronics is required. This paper presents the prototype design of a high-speed radio frequency (RF) electronics that can pick up nanosecond positron–electron beam bunches with a switching time of fewer than 6 ns. Fast separation of electron and positron is achieved based on RF switches and precise delay adjustment of the controlling signals (∼10 ps). Initial tests have been conducted in the laboratory to evaluate the performance of electronics; the results indicate that this circuit can successfully pick up the bunch signal within a time interval of 6 ns, which makes it possible to further measure the electron and positron beams simultaneously. [ABSTRACT FROM AUTHOR]

Accelerator-based searches for dark matter are aiming for high sensitivity and need an experimental setup with high luminosity. This field of research is often called intensity frontier physics. One of the best motivated portals of interaction between dark matter and ordinary matter is a dark photon which could be observed as a resonance in the invariant mass of the decay products. Electron–positron collisions are known to be the cleanest interaction for such a study. In this paper we propose a scheme for a collider which allows for a luminosity of a few orders of magnitude higher than could be obtained in a conventional symmetric collider and with a few times higher accessible mass than is possible using a positron beam and a fixed target approach. The key concept is based on asymmetric energies: a high-energy circulating positron beam and a low-energy high-intensity electron beam, and optimization of the beam interaction region. We present here a configuration of a collision region of 10 MeV electron and 4 GeV positron beams. [ABSTRACT FROM AUTHOR]

A scheme for positron plasma wakefield acceleration using hollow or donut-shaped electron driver beams is studied. An annular-shaped, electron-free region forms around the hollow driver beam, creating a favorable region (longitudinal field is accelerating and transverse field is focusing) for positron acceleration. For Facility for Advanced Accelerator Experimental Tests (FACET)-like parameters, the hollow beam driver produces accelerating gradients on the order of 10 GV/m. The accelerating gradient increases linearly with the total charge in the driver beam. Simulations show acceleration of a 23-GeV positron beam to 35.4 GeV with a maximum energy spread of 0.4% and very small emittance over a plasma length of 140 cm is possible. [ABSTRACT FROM AUTHOR]

Plasma wakefield acceleration in the blowout regime is particularly promising for high-energy acceleration of electron beams because of its potential to simultaneously provide large acceleration gradients and high energy transfer efficiency while maintaining excellent beam quality. However, no equivalent regime for positron acceleration in plasma wakes has been discovered to date. We show that after a short propagation distance, an asymmetric electron beam drives a stable wakefield in a hollow plasma channel that can be both accelerating and focusing for a positron beam. A high charge positron bunch placed at a suitable distance behind the drive bunch can beam-load or flatten the longitudinal wakefield and enhance the transverse focusing force, leading to high efficiency and narrow energy spread acceleration of the positrons. Three-dimensional quasistatic particle-in-cell simulations show that an over 30% energy extraction efficiency from the wake to the positrons and a 1% level energy spread can be simultaneously obtained. Further optimization is feasible. [ABSTRACT FROM AUTHOR]

Injectors and in particular the positron production systems are a crucial element in linear and circular colliders. The proposed FCC-ee injector linac accelerates both electrons and positrons up to 6 GeV in order to be injected into the Pre-Booster Ring (PBR) with a high intensity of 3.5 nC per bunch for the Z running mode. The current design baseline of the FCC-ee injector linac is based on the SuperKEKB scheme, in which the electron and the positron beams share the same linacs with a fixed target configuration on-axis hole for electron beam passage. One of the main drawbacks of this scheme is the positron production efficiency at the exit of the injector linac. In order to achieve a better performance and a higher positron yield, in this paper we study different bypass injection options. Start-to-end design and optimization for beam production, acceleration and transport from the feeding electron source to the positron damping ring are also being presented. [ABSTRACT FROM AUTHOR]

Plasma wakefield acceleration of positron beams in the wake of a dense electron beam (in the blowout regime) is numerically analyzed. The acceleration is possible only if the energy content of the wakefield is not very high. This is in contrast to electron acceleration, for which the optimum performance requires driver currents and wave energies to be as high as possible. For positrons, the efficiency of plasma-to-witness energy exchange can amount to several tens percent, but high efficiencies require precise location of the positron beam and sophisticated beam shapes. Unlike an electron witness, the positron always gets an energy spread of about several percent caused by the transverse inhomogeneity of the accelerating field. [ABSTRACT FROM AUTHOR]

Abstract: A new kind of positron sources for future linear colliders, where the converter is an aligned tungsten crystal, oriented on the 〈111〉-axis, has been studied at CERN in the WA103 experiment with tertiary electron beams from the SPS. In such sources the photons resulting from channeling radiation and coherent bremsstrahlung create the e+e− pairs. Electron beams, of 6 and 10GeV, were impinging on different kinds of targets: a 4mm thick crystal, a 8mm thick crystal and a compound target made of 4mm crystal followed by 4mm amorphous disk. An amorphous tungsten target 20mm thick was also used for the sake of comparison with the 8mm crystal and to check the ability of the detection system to provide the correct track reconstruction. The charged particles coming out from the target were detected in a drift chamber immersed partially in a magnetic field. The reconstruction of the particle trajectories provided the energy and angular spectrum of the positrons in a rather wide energy range (up to 150MeV) and angular domain (up to 30°). The experimental approach presented in this article provides a full description of this kind of source. A presentation of the measured positron distribution in momentum space (longitudinal versus transverse) is given to allow an easy determination of the available yield for a given momentum acceptance. Results on photons, measured downstream of the positron detector, are also presented. A significant enhancement of photon and positron production is clearly observed. This enhancement, for a 10GeV incident beam, is of 4 for the 4mm thick crystal and larger than 2 for the 8mm thick crystal. Another important result concerns the validation of the simulations for the crystals, for which a quite good agreement was met between the simulations and the experiment, for positrons as well as for photons. These results are presented after a short presentation of the experimental setup and of the track reconstruction procedure. [Copyright &y& Elsevier]

The performance characteristics of a plane parallel chamber were investigated on beams of slow muons and positrons, as well as on an electron beam from a 106Ru β source. The chamber was filled with CO2 or a gas mixture of Ar (30%) + CO2(70%) at atmospheric pressure. The amplitude spectra of charged particles and the efficiency of their detection were measured. The muon and positron momenta were ∼27 MeV/ c. It was shown that the muon detection efficiency of the plane parallel chamber with a 1-mm gas gap and CO2 (100%) used as a working gas was as high as 99%, while that of the chamber with a 0.4-mm gas gap and a working gas mixture of Ar(30%) + CO2(70%) was 88%. This result, along with the detector's high response speed, allows the plane parallel chamber to be used as an active target being developed for a future experiment (FAMILON) on searching for neutrinoless muon decay with the release of a scalar Goldstone's boson (µ → eα). [ABSTRACT FROM AUTHOR]

Positron acceleration in plasma wakefield faces significant challenges, as the positron beam must be pre-generated and precisely coupled into the wakefield and, most critically, suffers from defocusing issues. Here we propose a scheme that utilizes laser-driven electrons to produce, inject, and accelerate positrons in a single setup. The high-charge electron beam from wakefield acceleration creates copious electron–positron pairs via the Bethe–Heitler process, followed by enormous coherent transition radiation due to the electrons' exiting from the metallic foil. Simulation results show that the coherent transition radiation field reaches up to tens of GV m−1, which captures and accelerates the positrons to cut-off energy of 1.5 GeV with energy peak of 500 MeV (energy spread ~ 24.3%). An external longitudinal magnetic field of 30 T is also applied to guide the electrons and positrons during the acceleration process. This proposed method offers a promising way to obtain GeV fast positron sources. Generation of high-energy positron beams is more complex than for electrons, requiring positrons to be pre-generated and compensation of defocusing effects. Here, a system allowing positron creation, injection and acceleration in a single setup is considered theoretically. [ABSTRACT FROM AUTHOR]

We report on an indirect and non-invasive method to simultaneously characterise the energy-dependent emittance and source size of ultra-relativistic positron beams generated during the propagation of a laser-wakefield accelerated electron beam through a high-Z converter target. The strong correlation of the geometrical emittance of the positrons with that of the scattered electrons allows the former to be inferred, with high accuracy, from monitoring the latter. The technique has been tested in a proof-of-principle experiment where, for 100 MeV positrons, we infer geometrical emittances and source sizes of the order of 3 µm and 150 µm, respectively. This is consistent with the numerically predicted possibility of achieving sub-µm geometrical emittances and micron-scale source sizes at the GeV level. [ABSTRACT FROM AUTHOR]