Cherenkov Process Research Articles

Variation in linear susceptibility tensor at crystal surface probed by linear Cherenkov radiation

At the surfaces of crystals, linear susceptibility tensors would differ from their counterparts in the interior of the bulk crystal. However, this phenomenon has not been shown in a visible way yet. In previous researches, numerous types of nonlinear Cherenkov radiation based on different materials have been studied, while linear Cherenkov radiation is barely reported. We experimentally prove the generation of linear Cherenkov radiation on the potassium dihydrogen phosphate (KDP) crystal surface and theoretically analyze its phase-matching scheme. In our study, o-polarized light and e-polarized light can mutually convert through the linear Cherenkov process. According to this result, we figure out new nonzero elements at off-diagonal positions in the linear susceptibility tensor matrix at crystal surfaces, compared with the normal form of a bulk KDP.

Quasiclassical approach to synergic synchrotron–Cherenkov radiation in polarized vacuum

Photon emission by an ultrarelativistic charged particle in extremely strong magnetic field is analyzed, with vacuum polarization and photon recoil taken into account. Vacuum polarization is treated phenomenologically via refractive index. The photon emission occurs in the synergic (cooperative) synchrotron–Cherenkov process [J Schwinger et al 1976 Annals of Physics 96 303] which is similar to the synchrotron emission rather than to the Cherenkov one. For electrons, the effect of vacuum polarization on the emission spectrum is not evident at least below the probable onset of non-perturbative quantum electrodynamics (QED). However, the effect of vacuum polarization on the emission spectrum can be observable for muons already at γB/BS ≈ 30, with γ the muon Lorentz factor, B the magnetic field strength and BS the critical QED field. Nevertheless, vacuum polarization leads to only 10% enhancement of the maximum of the radiation spectrum.

Probability of radiation of twisted photons by cold relativistic particle bunches

The probability to detect a twisted photon produced by a cold relativistic particle bunch of charged particles is derived. The radiation of twisted photons by such particle bunches in stationary electromagnetic fields and in propagating electromagnetic waves is investigated. Several general properties of both incoherent and coherent contributions to the radiation probability of twisted photons are established. It is shown that the incoherent radiation by bunches of particles traversing normally an isotropic dispersive medium (the edge, transition, and Vavilov–Cherenkov radiations) and by bunches moving in a helical undulator does not depend on the azimuthal distribution of particles in the bunch and is the same as for round bunches. As for planar undulators, the incoherent radiation by particle bunches is the same as for the bunches symmetric under reflection with respect to the axis of a twisted photon detector. At high energies of detected twisted photons, this property is universal and holds for the forward incoherent radiation by any cold relativistic particle bunch. The coherent radiation of twisted photons by such particle bunches obeys the property that we call the addition rule. This rule provides a simple means to describe the properties of coherent radiation of twisted photons. Furthermore, the strong addition rule is established for the coherent radiation by sufficiently long helical bunches. The use of this rule allows one to elaborate superradiant pure sources of twisted photons. The coherent radiation by helical bunches is considered for the edge, transition, and Vavilov–Cherenkov processes and for particles moving in undulators and plane laser waves with circular polarization. In these cases, the sum rules are deduced for the total probability to detect a twisted photon and for the projection of the total angular momentum per photon. The explicit expressions for both incoherent and coherent interference factors are derived for several simple bunch profiles.

Improved inertial confinement fusion gamma reaction history 12C gamma-ray signal by direct subtraction.

The Gamma Reaction History (GRH) diagnostic located at the National Ignition Facility (NIF) measures time resolved gamma rays released from inertial confinement fusion experiments by converting the emitted gamma rays into Cherenkov light. Imploded capsules have a bright 4.4 MeV gamma ray from fusion neutrons inelastically scattering with carbon atoms in the remaining ablator. The strength of the 4.4 MeV gamma ray line is proportional to the capsule's carbon ablator areal density and can be used to understand the dynamics and energy budget of a carbon-based ablator capsule implosion. Historically, the GRH's four gas cells use the energy thresholding from the Cherenkov process to forward fit an estimation of the experiment's complete gamma ray spectrum by modeling the surrounding environment in order to estimate the 4.4 MeV neutron induced carbon gamma ray signal. However, the high number of variables, local minima, and uncertainties in detector sensitivities and relative timing had prevented the routine use of the forward fit to generate carbon areal density measurements. A new, more straightforward process of direct subtraction of deconvolved signals was developed to simplify the extraction of the carbon areal density. Beryllium capsules are used as a calibration to measure the capsule environment with no carbon signal. The proposed method is then used to appropriately subtract and isolate the carbon signal on shots with carbon ablators. The subtraction algorithm achieves good results across all major capsule campaigns, achieving similar results to the forward fit. This method is now routinely used to measure carbon areal density for NIF shots.

Dual Cherenkov and Scintillation Response to High-Energy Electrons of Rare-Earth-Doped Silica Fibers

The simultaneous readout of photons emitted due to Cherenkov and scintillation processes is a promising feature of SiO${}_{2}$:Ce optical fibers, suggesting applications in innovative radiation sensors for calorimetry in high-energy physics, as well as radiation monitoring in medicine, security, and industrial controls. This study presents a detailed characterization of the scintillation properties of doped silica fibers exposed to high-energy electrons, and demonstrates the feasibility of a simultaneous dual-readout approach.

One dimensional Cherenkov processes in ferromagnetic insulator

One dimensional Cherenkov processes in ferromagnetic insulators are studied with perturbation theory under the constraint condition of conservation of energy and momentum. It is shown that the magnon-phonon interaction channels are limited and wave number dependent, which result in, respectively, 1/k2 and 1/k4 dependence of the lifetime and the relaxation time of long wavelength magnons. The reciprocal of relaxation time between magnons and phonons, 1/τmp, is found to be a linearly increasing function of the temperature in the high temperature regime. Based on the Sanders-Walton model, we further show that when a thermal (phonon) gradient is applied along the system, the temperature difference between the phonon bath and the magnons with wave-vector k becomes more pronounced as k decreases.

Vacuum Cherenkov radiation for Lorentz-violating fermions

The current work focuses on the process of vacuum Cherenkov radiation for Lorentz-violating fermions that are described by the minimal Standard-Model Extension (SME). To date, most considerations of this important hypothetical process have been restricted to Lorentz-violating photons, as the necessary theoretical tools for the SME fermion sector have not been available. With their development in a very recent paper, we are now in a position to compute the decay rates based on a modified Dirac theory. Two realizations of the Cherenkov process are studied. In the first scenario, the spin projection of the incoming fermion is assumed to be conserved, and in the second, the spin projection is allowed to flip. The first type of process is shown to be still forbidden for the dimensionful $a$ and $b$ coefficients where there are strong indications that it is energetically disallowed for the $H$ coefficients, as well. However, it is rendered possible for the dimensionless $c$, $d$, $e$, $f$, and $g$ coefficients. For large initial fermion energies, the decay rates for the $c$ and $d$ coefficients were found to grow linearly with momentum and to be linearly suppressed by the smallness of the Lorentz-violating coefficient where for the $e$, $f$, and $g$ coefficients this suppression is even quadratic. The decay rates vanish in the vicinity of the threshold, as expected. The decay including a fermion spin flip plays a role for the spin-nondegenerate operators and it was found to occur for the dimensionful $b$ and $H$ coefficients as well as for the dimensionless $d$ and $g$. The characteristics of this process differ much from the properties of the spin-conserving one, e.g., there is no threshold. Based on experimental data of ultra-high-energy cosmic rays, new constraints on Lorentz violation in the quark sector are obtained from the thresholds.

Opticks : GPU Optical Photon Simulation for Particle Physics using NVIDIA® OptiX™

Opticks is an open source project that integrates the NVIDIA OptiX GPU ray tracing engine with Geant4 toolkit based simulations. Massive parallelism brings drastic performance improvements with optical photon simulation speedup expected to exceed 1000 times Geant4 when using workstation GPUs. Optical photon simulation time becomes effectively zero compared to the rest of the simulation. Optical photons from scintillation and Cherenkov processes are allocated, generated and propagated entirely on the GPU, minimizing transfer overheads and allowing CPU memory usage to be restricted to optical photons that hit photomultiplier tubes or other photon detectors. Collecting hits into standard Geant4 hit collections then allows the rest of the simulation chain to proceed unmodified. Optical physics processes of scattering, absorption, scintillator reemission and boundary processes are implemented in CUDA OptiX programs based on the Geant4 implementations. Wavelength dependent material and surface properties as well as inverse cumulative distribution functions for reemission are interleaved into GPU textures providing fast interpolated property lookup or wavelength generation. Geometry is provided to OptiX in the form of CUDA programs that return bounding boxes for each primitive and ray geometry intersection positions. Some critical parts of the geometry such as photomultiplier tubes have been implemented analytically with the remainder being tessellated. OptiX handles the creation and application of a choice of acceleration structures such as boundary volume hierarchies and the transparent use of multiple GPUs. OptiX supports interoperation with OpenGL and CUDA Thrust that has enabled unprecedented visualisations of photon propagations to be developed using OpenGL geometry shaders to provide interactive time scrubbing and CUDA Thrust photon indexing to enable interactive history selection.

Scintillating Glasses for Total Absorption Dual Readout Calorimetry

Scintillating glasses are a potentially cheaper alternative to crystal - based calorimetry with common problems related to light collection, detection and processing. As such, their use and development are part of more extensive R&D aimed at investigating the potential of total absorption, combined with the readout (DR) technique, for hadron calorimetry. A recent series of measurements, using cosmic and particle beams from the Fermilab test beam facility and scintillating glass with the characteristics required for application of the DR technique, serve to illustrate the problems addressed and the progress achieved by this R&D. Alternative solutions for light collection (conventional and silicon photomultipliers) and signal processing are compared, the separate contributions of scintillation and Cherenkov processes to the signal are evaluated and results are compared to simulation.

Quartz plate calorimeter prototype with wavelength shifting fibers

The quartz plate calorimeters are considered as hadronic calorimeter options for upgrading Large Hadron Collider experiments. Previous studies have shown that quartz can resist up to 12 MGy of proton irradiation. Using uniformly distributed wavelength shifting fibers embedded the quartz plates are shown to solve the problem of low visible light production on Cherenkov process. Here, we report the performance tests of a 20-layer quartz plate calorimeter prototype, which is constructed with this approach. The calorimeter prototype was tested at CERN H2 area in hadronic and electromagnetic configuration, at various energies of pion and electron beams. We report the beam test and simulation results of this prototype, we also discuss future improvement directions on manufacturing radiation hard wavelength shifting fibers for this type of hadronic calorimeter design.

The discovery of Cherenkov radiation and its use in the detection of extensive air showers

Cascades of charged particles are created when high-energy cosmic rays enter the earth's atmosphere: these 'extensive air-showers' are studied to gain information on the energy spectrum, arrival direction distribution and mass composition of the particles above 1014 eV where direct observations using instruments carried by balloons or satellites become impractical. Detection of light in the visible and ultra-violet ranges of the electromagnetic spectrum plays a key role in this work, the two processes involved being the emission of Cherenkov light and the production of fluorescence radiation. In this paper I will outline some of the history of the discovery of the Cherenkov process and describe the use to which it has been put in the study of extensive air-showers at ground level.

Nonlinear interaction of charged particles with nonplane counterpropagating laser pulses of relativistic intensities

The nonlinear threshold phenomena of particle reflection and capture of electrons in the induced Compton process that have previously been revealed in the case of plane monochromatic counterpropagating waves, take place also with the actual nonplane laser pulses of ultrashort duration and lead to particle acceleration. In contrast to analogous phenomena in the induced Cherenkov and undulator processes, the Compton reflection-capture mechanism with laser pulses of relativistic intensities practically may be realized for arbitrary initial energies of particles. The acceleration effect for particles initially in rest is explored numerically, taking into account the significance of this case connected with the relativistic electron bunches of high densities, which currently may be realized by relativistic lasers on the ultrathin solid foils where the electrons initially are almost in rest.

Cherenkov radiation of shear Alfvén waves

A calculation is presented of the radiation pattern of shear Alfvén waves excited by a burst of charged particles propagating along the confinement magnetic field. The characteristic wake patterns are obtained for the inertial and kinetic regimes of wave propagation. In the inertial regime, the waves are only excited by particles moving slower than the Alfvén speed. The radiated wake exhibits an inverted V-shape due to the backward-wave nature of the modes. In the kinetic regime, particles moving faster as well as slower than the Alfvén speed can radiate propagating modes. The super Alfvénic particles, however, excite modes with relatively short transverse scales. The motorboat type of wake of the kinetic modes is more typical of the Cherenkov process obtained in scalar dielectrics. The predictions are in agreement with experimental observations [B. Van Compernolle et al., Phys. Plasmas 13, 09112 (2006)] and computer simulations [F. S. Tsung et al., Phys. Plasmas 14, 042101 (2007)] in which a burst of fast electrons generated by resonant absorption in a magnetized plasma excites a pulse of large-amplitude Alfvén waves.

Forward THz radiation emission by femtosecond filamentation in gases: theory and experiment

A transition–Cherenkov electromagnetic emission by a femtosecond laser pulse propagating in a self-induced plasma channel in air has been very recently proposed as mechanism for production of terahertz (THz) radiation in the forward direction. In this paper, we study in detail the theory of the transition–Cherenkov process. The theoretical model is developed and compared with recent experimental results for several gases.

Nonlinear interaction of charged particles with strong laser pulses in a gaseous media

The charged particles nonlinear dynamics in the field of a strong electromagnetic wave pulse of finite duration and certain form of the envelope, in the refractive medium with a constant and variable refraction indexes, is investigated by means of numerical integration of the classical relativistic equations of motion. The particle energy dependence on the pulse intensity manifests the nonlinear threshold phenomenon of a particle reflection and capture by actual laser pulses in dielectric-gaseous media that takes place for a plane electromagnetic wave in the induced Cherenkov process. Laser acceleration of the particles in the result of the reflection from the pulse envelope and in the capture regime with the variable refraction index along the pulse propagation direction is investigated.

Coherent x-ray source due to the quantum reflection of an electron beam from a laser-field phase lattice.

Within the scope of relativistic quantum theory for electron-laser interaction in a medium and using the resonant approximation for the two degenerated states of an electron in a monochromatic radiation field, a nonperturbative solution of the Dirac equation is obtained. The multiphoton cross sections of the electrons' coherent scattering on the plane monochromatic wave at the Cherenkov resonance are obtained, taking into account the specificity of an induced Cherenkov process and spin-laser interaction as well. As a result of coherent reflection from the "phase lattice" of a slowed plane wave in a medium, electron beam quantum modulation at high frequencies occurs. So, a coherent x-ray source in an induced Cherenkov process is expected, since such a beam is a potential source of coherent radiation itself.

Quantum theory of the nonlinear stimulated Cherenkov process

On the basis of nonperturbative solutions of relativistic quantum equations a zone structure of the charged scalar and spinor particle states in the field of a monochromatic wave in a dielectric medium is found, independent of the field strength. For spinor particles the zone structure appears in the absence of charge interaction as well.

Quantum theory of induced Cherenkov processes at exact resonance

Perturbation theory at exact resonance in the stimulated Cherenkov process is developed. Utilizing the secular equation, because of the double degeneracy of the particle states in the longitudinal momentum, the dynamics of scalar as well as spinor particles in the presence of a plane electromagnetic wave field in a medium is described. The corresponding zone structure is confirmed.

Nonlinear quantum theory of interaction of charged particles and monochromatic radiation in a medium

We study the quantum theory of nonlinear interaction of charged particles and a given field of plane-transverse electromagnetic radiation in a medium. Using the exact solution of the generalized Lame equation, we find the nonlinear solution of the Mathieu equation to which the relativistic quantum equation of particle motion in the field of a monochromatic wave in the medium reduces if one ignores the spin-spin interaction (the Klein-Gordon equation).We study the stability of solutions of the generalized Lame equation and find a class of bounded solutions corresponding to the wave function of the particle. On the basis of this solution we establish that the particle states in a stimulated Cherenkov process form bands. Depending on the wave intensity and polarization, such a band structure describes both bound particle-wave states (capture) and states in the continuous spectrum. It is obvious that in a plasma there can be no such bands, since bound states of a particle with a transverse wave whose phase velocity vph is higher than c are impossible in this case. The method developed in the paper can be applied to a broad class of problems reducible to the solution of the Mathieu equation.

Cherenkov radiation of longitudinal photons by neutrinos

In a relativistic plasma, neutrinos can emit plasmons by the Cherenkov process which is kinematically allowed for a range of frequencies for which the refractive index is greater than one. We calculate the rate of energy emission by this process. We compute the energy deposited in a stalled supernova shock wave by the Cherenkov process and find that it is much smaller than the Bethe-Wilson mechanism.