arXiv subjects

Alexander Pukhov

Publications and source records attributed to Alexander Pukhov.

At least 37 records · Page 2Linked to original sources

arXiv2024

Adiabatic sheath model for beam-driven blowout plasma channels

In plasma wakefield accelerators, the structure of the blowout sheath is vital for the blowout radius and the electromagnetic field distribution inside the blowout. Previous theories assume artificial distribution functions for the sheath, which are either inaccurate or require prior knowledge of parameters. In this study, we develop an adiabatic sheath model based on force balancing, which leads to a self-consistent form of the sheath distribution. This model gives a better estimate of the blowout channel balancing radius than previous models.

physics.plasm-ph↗

arXiv2024

Preservation of $^3\mkern-2mu$He ion polarization after laser-plasma acceleration

The preservation of nuclear spin alignment in plasmas is a prerequisite for important applications, such as energy production through polarized fusion or the acceleration of polarized particle beams. Although this conservation property has been the basis of numerous theoretical papers, it has never been experimentally confirmed. Here, we report on first experimental data from a polarized $^3\mkern-2mu$He target heated by a PW laser pulse, showing evidence for persistence of the nuclear polarization after acceleration to MeV energies. The finding also validates the concept of using pre-polarized targets for experiments at high-power laser facilities.

physics.plasm-ph↗

arXiv2024

Preliminary Investigation of a Higgs Factory based on Proton-Driven Plasma Wakefield Acceleration

A Higgs Factory is considered the highest priority next collider project by the high-energy physics community. Very advanced designs based on radio-frequency cavities exist, and variations on this approach are still being developed. Recently, an option based on electron-bunch driven plasma wakefield acceleration has also been proposed. In this article, we discuss a further option based on proton-driven plasma wakefield acceleration. This option has significant potential advantages due to the high energy of the plasma wakefield driver, simplifying the plasma acceleration stage. Its success will depend on further developments in producing compact high-energy proton bunches at a high rate, which would also make possible a broad range of synergistic particle-physics research.

physics.acc-ph↗

arXiv2024

Production and magnetic self-confinement of $e^-e^+$ plasma by an extremely intense laser pulse incident on a structured solid target

We propose an all-optical, single-laser-pulse scheme for generating dense, relativistic, strongly-magnetized electron-positron pair plasma. The scheme involves the interaction of an extremely intense ($I \gtrsim \SI{e24}{\watt/\cm^2}$) circularly polarized laser pulse with a solid-density target containing a conical cavity. Through full-scale three-dimensional particle-in-cell (PIC) simulations that account for quantum electrodynamical effects, it is shown that this interaction results in two significant outcomes: first, the generation of quasi-static axial magnetic fields reaching tens of gigagauss due to the inverse Faraday effect; and second, the production of large quantities of electron-positron pairs (up to $\num{e13}$) via the Breit-Wheeler process. The $e^-e^+$ plasma becomes trapped in the magnetic field and remains confined for hundreds of femtoseconds, far exceeding the laser timescale. The dependency of pair plasma parameters, as well as the efficiency of plasma production and confinement, is discussed in relation to the properties of the laser pulse and the target. Realizing this scheme experimentally would enable the investigation of physical processes relevant to extreme astrophysical environments.

physics.plasm-ph↗

arXiv2024

Wakefield-driven filamentation of warm beams in plasma

Charged and quasi-neutral beams propagating through an unmagnetised plasma are subject to numerous collisionless instabilities on the small scale of the plasma skin depth. The electrostatic two-stream instability, driven by longitudinal and transverse wakefields, dominates for dilute beams. This leads to modulation of the beam along the propagation direction and, for wide beams, transverse filamentation. A three-dimensional spatiotemporal two-stream theory for warm beams with a finite extent is developed. Unlike the cold beam limit, diffusion due to a finite emittance gives rise to a dominant wavenumber, and a cut-off wavenumber above which filamentation is suppressed. Particle-in-cell simulations with quasineutral electron-positron beams in the relativistic regime give excellent agreement with the theoretical model. This work provides deeper insights into the effect of diffusion on filamentation of finite beams, crucial for comprehending plasma-based accelerators in laboratory and cosmic settings.

physics.plasm-ph↗

arXiv2024

Elevating electron energy gain and betatron X-ray emission in proton-driven wakefield acceleration

The long proton beams present at CERN have the potential to evolve into a train of microbunches through the self-modulation instability process. The resonant wakefield generated by a periodic train of proton microbunches can establish a high acceleration field within the plasma, facilitating electron acceleration. This paper investigates the impact of plasma density on resonant wakefield excitation, thus influencing acceleration of a witness electron bunch and its corresponding betatron radiation within the wakefield. Various scenarios involving different plasma densities are explored through particle-in-cell simulations. The peak wakefield in each scenario is calculated by considering a long pre-modulated proton driver with a fixed peak current. Subsequently, the study delves into the witness beam acceleration in the wakefield and its radiation emission. Elevated plasma density increases both the number of microbunches and the accelerating gradient of each microbunch, consequently resulting in heightened resonant wakefield. Nevertheless, the scaling is disrupted by the saturation of the resonant wakefield due to the nonlinearities. The simulation results reveal that at high plasma densities an intense and broadband radiation spectrum extending into the domain of the hard X-rays and gamma rays is generated. Furthermore, in such instances, the energy gain of the witness beam is significantly enhanced. The impact of wakefield on the witness energy gain and the corresponding radiation spectrum is clearly evident at extremely elevated densities.

physics.acc-ph↗

arXiv2024

Stable high-transformer ratio beam-wakefield acceleration in cusp plasma channels

Wakefield excitation by structured electron bunches in hollow gaps between plasma wedges is studied using three-dimensional particle-in-cell simulations. The main part of the electron bunch has a triangular current distribution in the longitudinal direction with a smooth head and short tail. These bunches propagate stably in the hollow gap while being attached to cusps of the plasma wedges. The excited wakefield profile may have a very high transformer ratio and allows to accelerate witness bunches to energies much higher than that of the driver bunch. Unlike round hollow channels, where asymmetric wakefields are difficult to avoid, no deleterious transverse beam break-up (BBU) is observed in the gap between cusp-shaped plasma layers.

physics.plasm-ph↗

arXiv2023

Spin-polarized ${}^3$He shock waves from a solid-gas composite target at high laser intensities

We investigate Collisionless Shock Acceleration of spin-polarized ${}^3$He for laser pulses with normalized vector potentials in the range $a_0 = 100-200$. The setup utilized in the 2D-PIC simulations consists of a solid Carbon foil that is placed in front of the main Helium target. The foil is heated by the laser pulse and shields the Helium from the highly oscillating fields. In turn, a shock wave with more homogeneous fields is induced, leading to highly polarized ion beams. We observe that the inclusion of radiation reaction into our simulations leads to a higher beam charge without affecting the polarization degree to a significant extent.

physics.plasm-ph↗

arXiv2023

The $Z_7$ model of three-component scalar dark matter

We investigate, for the first time, a scenario where the dark matter consists of three complex scalar fields that are stabilized by a single $Z_7$ symmetry. As an extension of the well-known scalar Higgs-portal, this $Z_7$ model is also subject to important restrictions arising from the relic density constraint and from direct detection experiments. Our goal in this paper is to find and characterize the viable regions of this model, and to analyze its detection prospects in future experiments. First, the processes that affect the relic densities are identified (they include semiannihilations and conversions) and then incorporated into the Boltzmann equations for the dark matter abundances, which are numerically solved with micrOMEGAs. By means of random scans of the parameter space, the regions consistent with current data, including the recent direct detection limit from the LZ experiment, are selected. Our results reveal that the $Z_7$ model is indeed viable over a wide range of dark matter masses and that both conversions and semiannihilations play an important role in determining the relic densities. Remarkably, we find that in many cases all three of the dark matter particles give rise to observable signals in future direct detection experiments, providing a suitable way to test this scenario.

hep-ph↗

arXiv2022

Co-scattering in micrOMEGAs: a case study for the singlet-triplet dark matter model

In scenarios with very small dark matter (DM) couplings and small mass splittings between the DM and other dark sector particles, so-called "co-scattering" or "conversion-driven freeze-out" can be the dominant mechanism for DM production. We present the inclusion of this mechanism in micrOMEGAs together with a case study of the phenomenological implications in the fermionic singlet-triplet model. For the latter, we focus on the transition between co-annihilation and co-scattering processes. We observe that co-scattering is needed to describe the thermal behaviour of the DM for very small couplings, opening up a new region in the parameter space of the model. The triplet states are often long-lived in this region; we therefore also discuss LHC constraints from long-lived signatures obtained with SModelS.

hep-ph↗

arXiv2022

Relativistic Topological Waves from Cherenkov and Doppler Resonances in Self-Magnetized Laser Plasmas

Strong magnetic fields at plasma-plasma interfaces can be naturally produced in laser-plasma interactions. Using theoretical analysis and fully three-dimensional particle-in-cell simulations, we demonstrate that relativistic topological waves can be generated via Cherenkov and Doppler resonances in the interaction of intense femtosecond laser pulses with near-critical-density plasmas. At the self-magnetized plasma-plasma interface, a new slow-wave branch appears. Its phase velocity is much smaller than the group velocity of the laser pulse and the electron beam velocity. Therefore, the Cherenkov resonance condition can be easily satisfied. Furthermore, since electrons undergo betatron oscillations, Doppler resonances may also occur and are responsible for the excitation of several frequency-shifted branches observed in our simulations. After the passage of the laser pulse, we observe a fast remnant mode with relativistic amplitude and frequency close to the local plasma frequency. This mode continues to accelerate electrons further for many tens of laser periods even after the laser pulse has left the plasma.

physics.plasm-ph↗

arXiv2022

Decoding Dark Matter at future $e^+ e^-$ colliders

We explore the potential of the $e^+ e^-$ colliders to discover dark matter and determine its properties such as mass and the spin. For this purpose we study spin zero and spin one-half cases of dark matter, $D$ which belongs to $SU(2)$ weak doublet and therefore has the charged doublet partner, $D^+$. For the case of scalar dark matter we chose Inert Doublet Model, while for the case of fermion dark matter we suggest the new minimal fermion dark matter model with only three parameters. We choose two benchmarks for the models under study which provide the correct amount of observed DM relic density and consistent with the current DM searches. We focus on the particular process $e^+ e^- \to D^+ D^- \to D D W^+ W^- \to DD(q \bar{q})(μ^\pmν)$ at 500 GeV ILC collider which gives rise to the "di-jet +$μ$ + missing $E_T$" signature and study it at the level of fast detector simulation, taking into account Bremsstrahlung and ISR effects. We have found that two kinematical observables -- the energy of the muon, $E_μ$, and the angular distribution of $W$-boson, reconstructed from di-jet, $\cosθ_{jj}$ are very powerful in determination of DM mass and spin, respectively. In particular we have demonstrated that in case of fermion DM, the masses can be measured with a few percent accuracy already at 500 fb$^{-1}$ integrated luminosity. At the same time, the scalar DM model which has about an order of magnitude lower signal, requires about factor of 40 higher luminosity to reach the same accuracy in the mass measurement. We have found that one can distinguish fermion and scalar DM scenarios with about 2 ab$^{-1}$ total integrated luminosity or less without using the information on the cross sections for benchmarks under study.

hep-ph↗

arXiv2022

Acceleration of spin-polarized proton beams via two parallel laser pulses

We present a setup for highly polarized proton beams using two parallel propagating laser pulses that have a carrier envelope phase difference of $π$. This mechanism is examined utilizing particle-in-cell simulations and compared to a single-pulse setup commonly used for magnetic vortex acceleration. We find that the use of the dual-pulse setup allows for peak energies of 124 MeV and good angular spread for two pulses with normalized laser vector potential $a_0 = 100$. Compared to a single pulse, we further observe higher polarization of the accelerated bunch.

physics.plasm-ph↗

arXiv2022

Acceleration of an electron bunch with a non-Gaussian transverse profile in a quasilinear plasma wakefield

Beam-driven plasma wakefield accelerators typically use the external injection scheme to ensure controllable beam quality at injection. However, the externally injected witness bunch may exhibit a non-Gaussian transverse density distribution. Using particle-in-cell simulations, we show that the common beam quality factors, such as the normalized RMS emittance and beam radius, do not strongly depend on the initial transverse shapes of the witness beam. Nonetheless, a beam with a highly-peaked transverse spatial profile can achieve a higher fraction of the total beam charge in the core. The same effect can be seen when the witness beam's transverse momentum profile has a peaked non-Gaussian distribution. In addition, we find that an initially non-axisymmetric beam becomes symmetric due to the interaction with the plasma wakefield, and so it does not cause a detrimental effect for the beam acceleration.

physics.acc-ph↗

arXiv2022

QED Effects at Grazing Incidence on Solid-State-Targets

New laser facilities will reach intensities of $10^{23} \textrm{W cm}^{-2}$. This advance enables novel experimental setups in the study of laser-plasma interaction. In these setups with extreme fields quantum electrodynamic (QED) effects like photon emission via non-linear Compton scattering and Breit-Wheeler pair production become important. We study high-intensity lasers grazing the surface of a solid-state target by two-dimensional particle-in-cell simulations with QED effects included. The two laser beams collide at the target surface at a grazing angle. Due to the fields near the target surface electrons are extracted and accelerated. Finally, the extracted electrons collide with the counter-propagating laser, which triggers many QED effects and leads to a QED cascade under a sufficient laser intensity. Here, the processes are studied for various laser intensities and angles of incidence and finally compared to a seeded vacuum cascade. Our results show that the proposed target can yield many order of magnitude more secondary particles and develop a QED cascade at lower laser intensities than the seeded vacuum alone.

physics.plasm-ph↗

arXiv2022

The $B$ Anomalies, the $U_1$ Leptoquark and Dark Matter

The present-day $B$-anomalies involving $b \to s μ^+ μ^-$ or $b \to c τ^- {\barν}$ transitions can all be explained with the addition of a vector $U_1$ leptoquark with a mass of $M_{U_1} \ge 1.8$ TeV. In the scalar singlet dark matter model (SSDMM), the DM is a scalar $S$ that couples to the Higgs via $λ_{hS} \, S^2|H|^2$. We update the fit to the data and find that the SSDMM is now viable only for $M_S \ge 1.6$ TeV. In this paper, we assume that the DM also couples to the $U_1$ via $λ_{U_1 S} \, S^2 \, U_{1μ}^{\dagger} U^μ_1$. In addition to leading to DM annihilation via $S S \to U_1 {\bar U}_1$, this coupling generates $SSgg$ and $SSγγ$ couplings at one loop. Although naively divergent, these loop diagrams can be calculated under the assumption that the $U_1$ is a gauge boson of a group broken at the TeV scale. With this DM-$U_1$ coupling term, there are additional contributions to the various DM observables (relic density, direct and indirect detection). We find that the constraints on the SSDMM are relaxed for both heavy DM ($M_S \ge M_{U_1}$) and light DM ($M_S < M_{U_1}$).

hep-ph↗

arXiv2022

The AWAKE Run 2 programme and beyond

Plasma wakefield acceleration is a promising technology to reduce the size of particle accelerators. Use of high energy protons to drive wakefields in plasma has been demonstrated during Run 1 of the AWAKE programme at CERN. Protons of energy 400 GeV drove wakefields that accelerated electrons to 2 GeV in under 10 m of plasma. The AWAKE collaboration is now embarking on Run 2 with the main aims to demonstrate stable accelerating gradients of 0.5-1 GV/m, preserve emittance of the electron bunches during acceleration and develop plasma sources scalable to 100s of metres and beyond. By the end of Run 2, the AWAKE scheme should be able to provide electron beams for particle physics experiments and several possible experiments have already been evaluated. This article summarises the programme of AWAKE Run 2 and how it will be achieved as well as the possible application of the AWAKE scheme to novel particle physics experiments.

physics.acc-ph↗

arXiv2022

Simulation study of betatron radiation in AWAKE Run 2 experiment

The spectroscopy of betatron radiation from the focusing plasma column can work as a powerful non-invasive beam diagnostic method for plasma wakefield acceleration experiments such as the AWAKE. In this paper, the effects of radial size mismatch and off-axis injection on the beam dynamics, as well as the spectral features of the betatron radiation emitted by the witness electron bunch in the quasi-linear proton-driven plasma wakefield are studied. It is shown that the evolution of the critical betatron photon energy and the overall photon angular distribution can effectively reveal the initial injection conditions of the witness electron bunch. The possibility of using this method for the diagnostics of the seed electron bunch in the proton self-modulation stage of AWAKE Run 2 is also discussed.

physics.acc-ph↗