A new approach to the theory of Cherenkov radiation based on relativistic generalization of the Landau criterion

Relativistic generalization of the Landau criterion is obtained which, in contrast to the classical Tamm-Frank and Ginzburg theories, determines the primary energy mechanism of emission of nonbremsstrahlung Cherenkov radiation. It is shown that Cherenkov radiation may correspond to a threshold energetically favorable conversion of the condensate (ultimately long-wavelength) elementary Bose perturbations of a medium into transverse Cherenkov photons emitted by the medium proper during its interaction with a sufficiently fast charged particle. The threshold conditions of emission are determined for a medium with an arbitrary refractive index n, including the case of isotropic plasma with n<1 for which the classical theory of Cherenkov radiation prohibits such direct and effective nonbremsstrahlung emission of these particular transverse high-frequency electromagnetic waves. It is established that these conditions of emission agree with the data of well-known experiments on the threshold for observation of Cherenkov radiation, whereas the classical theory only corresponds to the conditions of observation of the interference maximum of this radiation. The possibility of direct effective emission of nonbremsstrahlung Cherenkov radiation, not taken into account in the classical theory, is considered for many observed astrophysical phenomena (type III solar radio bursts, particle acceleration by radiation, etc.).     

填充等离子体的介质同轴波导中的切伦科夫辐射

 利用自洽线性场理论，导出了薄环形相对论电子注通过填充等离子体的介质同轴波导中的注波互作用色散方程，得到了注波互作用产生切伦科夫辐射的同步条件和波增长率。分析了填充等离子体后的波与电子注之间的能量交换及等离子体密度对色散特性、波增长率和注波能量交换的影响。分析结果表明：切伦科夫辐射是由沿介质同轴波导传播的慢波与沿薄环形相对论电子注传播的负能空间电荷波耦合所致，且其耦合强度与电子注的密度成正比；输出频率和波增长率随着填充等离子体密度的增大而提高；保持一定的输出频率，增大电子注的束流可得到高的微波输出功率。     

Cherenkov quartz calorimeter

A Cherenkov quartz detector possesses a high radiation resistance because of the radiation resistance of quartz fibers in which a light signal is formed and which are used to transfer signals to photodetectors. Owing to properties of Cherenkov radiation, such as the existence of a threshold with respect to the velocity of radiating charged particles and an instantaneous character of the radiation, this type of calorimeter is not sensitive to neutrons and the majority of radiative-decay products and generates a short signal within a narrow spatial region. In view of these special features of a Cherenkov quartz calorimeter, it is advantageous (with respect to other calorimetric methods) in detecting narrow jets of high-energy particles against the background of high-density energy fluxes, this being necessary, for example, in experiments at the Large Hadron Collider, which is presently under construction at CERN. The results obtained by measuring the radiation resistance of quartz fibers and the main features of a Cherenkov quartz calorimeter that were measured for prototypes are discussed in the present article.     

Possibility of using satellite-based detector for recording the Cherenkov light from ultrahigh-energy extensive atmospheric shower penetrating into ocean water

Various components of Cherenkov radiation are calculated which occur during development of a shower with a primary energy of 10²⁰ eV above the ocean surface. It is shown that, under conditions of the TUS experiment, a flare of the reflected Cherenkov photons at the end of the fluorescence track can be identified in showers with zenith angles up to 20°.     

Resonant diffusive radiation in random multilayered systems

We have theoretically shown that the yield of diffuse radiation generated by relativistic electrons passing random multilayered systems can be increased when a resonant condition is met. The resonant condition can be satisfied for the wavelength region representing visible light as well as soft X rays. The intensity of diffusive soft X rays for specific multilayered systems consisting of two components is compared with the intensity of Cherenkov radiation. For radiation at a photon energy of 99.4 eV, the intensity of resonant diffusive radiation (RDR) generated by 5-MeV electrons passing a Be/Si multilayer exceeds the intensity of Cherenkov radiation by a factor of ≈60 for electrons with the same energy passing a Si foil. For a photon energy of 453 eV and 13 MeV, electrons passing a Be/Ti multilayer generate RDR exceeding the Cherenkov radiation generated by electrons passing Ti foils by a factor ≈130.     

Tachyonic Cherenkov radiation in the absorptive aether

Dissipative tachyonic Cherenkov densities are derived and tested by performing a spectral fit to the γ-ray flux of supernova remnant (SNR) RX J1713.7 − 3946, measured over five frequency decades up to 100 TeV. The manifestly covariant formalism of tachyonic Maxwell–Proca radiation fields is developed in the spacetime aether, starting with the complex Lagrangian coupled to dispersive and dissipative permeability tensors. The spectral energy and flux densities of the radiation field are extracted by time averaging, the energy conservation law is derived, and the energy dissipation caused by the complex frequency-dependent permeabilities of the aether is quantified. The tachyonic mass-square in the field equations gives rise to transversally/longitudinally propagating flux components, with differing attenuation lengths determined by the imaginary part of the transversal/longitudinal dispersion relation. The spectral fit is performed with the classical tachyonic Cherenkov flux radiated by the shell-shocked electron plasma of SNR RX J1713.7 − 3946, exhibiting subexponential spectral decay.     

Measuring the distribution of particles according to their velocity in accelerator beams on the basis of Cherenkov radiation in the optical and microwave range

Methods for measuring the energy spectra of powerful beams of charged particles and their bunches according to the dependence of the intensity of Cherenkov radiation on the refractive index of the radiator (with and without using of dispersion) are considered. The methods are practically nondestructive. In the case of special demands on the Cherenkov radiation collection system, beam spectra with unknown angular distributions can be measured. Uncharged particle spectra are determined from the secondary charged particles spectra.     

Energy Losses of a Charged Particle due to Excitation of Helicons in Plasma-Like Media

We study the energy lost by a particle moving along the helical line in a static magnetic field due to Vavilov–Cherenkov radiation of volume and surface helicons. It is found that the energy losses related to excitation of volume helicons are equivalent to the energy losses of a magnetic moment created due to the charge rotation. The magnetic moment moves at a constant velocity along the magnetic field. It is shown that collisionless damping of volume helicons in plasmas is based on the Cherenkov radiation of magnetic moment. Radiation of surface helicons by a particle does not correspond to the energy losses of a moving magnetic moment. This is related to the fact that not only magnetic (H) waves but also electric (E) waves contribute to the excitation of surface helicons, which leads to an increase in the energy losses of a particle.     

Waves in resonant random media

Electromagnetic properties of resonant inhomogeneous media are investigated. A new type of transverse electromagnetic wave arising due to the effective spatial dispersion is studied. It is shown that scattering on the fluctuations of the resonant frequency of the medium shifts the Cherenkov threshold and reduces the intensity of the Cherenkov radiation.     

The factor of suppression of Cherenkov radiation from electron-positron pairs produced by a hard γ photon

Cherenkov radiation from electron-positron pairs produced by hard γ photons is considered. The radiation yield is shown to be suppressed when the distance between an electron and a positron is less than the wavelength. This effect depends on the γ-photon energy and radiation intensity.     

Nonlinear optical terahertz wave sources

We developed a Cherenkov phase-matching method for monochromatic THz-wave generation using the DFG, process with a lithium niobate crystal, which resulted in both high conversion efficiency and wide tunability. Although THz-wave generation by Cherenkov phase matching has been demonstrated using femtosecond pumping pulses, producing very high peak power, these THz-wave sources are not monochromatic. Our method generates monochromatic and tunable THz, waves using a nanosecond pulsed laser source. We also show that Cherenkov radiation with waveguide structure is an effective strategy for achieving extremely wide tunable THz-wave source. We fabricated MgO-doped lithium niobate slab waveguide and demonstrated difference frequency generation of THz-wave generation with Cherenkov phase matching. Extremely frequency-widened THz-wave generation, from 0.1 to 7 THz was observed.     

Investigation of coherent Vavilov-Cherenkov radiation in the millimeter wavelength range generated in PTFE and paraffin target

In this paper, we present an experimental observation of coherent Cherenkov radiation in the millimeter wavelength range. Coherent Cherenkov radiation is generated by a 6.1-MeV bunched electron beam passing by dielectric targets (PTFE and paraffin). The characteristics of Cherenkov and diffraction radiation measured under the same conditions are compared. The experiment is carried out with the electron beam of the microtron at Tomsk Polytechnic University.     

On the polarization characteristics of Cherenkov radiation from a dielectric screen

The Cherenkov effect is a well-known phenomenon and its properties are widely used in many fields of physics. However, some features of the polarization characteristics of Cherenkov radiation that appears when charged particles pass near azimuthally asymmetric, finite dielectric targets are still poorly studied. This problem is solved in this work. The polarization characteristics of Cherenkov radiation in the case of a rectangular dielectric screen are analyzed using the Stokes approach. Owing to the azimuthal asymmetry of the target, radiation acquires an elliptic polarization whose rotation direction and inclination angle depend both on the direction of radiation propagation and on the dielectric properties of a substance. The results demonstrate that the Cherenkov effect can be used to create sources of elliptically polarized radiation with the controlled direction of polarization rotation.     

传输损耗对条形波导中切伦科夫倍频的影响

基于耦合模理论,分析了考虑传输损耗的条皮导中切伦科夫（Cherenkov)二次谐波（SHG）的问题。结果表明,转换效率具有指数性质和饱和性质。这一结果不同于未考虑传输损耗时转换效率所具有的线性性质,这对于切伦科夫频率倍频器的研制中参数的优化具有重要的意义。     

Modern trends in methods of charged particle identification at high energies

The survey is devoted to methods of charged particle identification at high energies that are based on measurements of the angle of Cherenkov radiation (ring imaging Cherenkov counters — RICH), of time of flight (TOF) and propagation (TOP), and of ionization energy loss (dE/dx). As an example, some operating spectrometers are considered (LHCb, ALICE, COMPASS, Belle, and BaBar) together with proposed ones (Belle-2 and PANDA) in which new achievements of recent years are introduced.     

Waves in resonant random media

Abstract

Electromagnetic properties of resonant inhomogeneous media are investigated. A new type of transverse electromagnetic wave arising due to the effective spatial dispersion is studied. It is shown that scattering on the fluctuations of the resonant frequency of the medium shifts the Cherenkov threshold and reduces the intensity of the Cherenkov radiation.     

Generation of Microwave Pulses with a Carrier Frequency of 3.8 GHz and a Length of 75 ns by a Relativistic Cherenkov Microwave Oscillator without a Guiding Magnetic Field

In the experiment with an electron energy of ≈500 keV, the long-pulse (~300T, where T is the oscillation period) the generation regime of a relativistic Cherenkov microwave oscillator without a guiding magnetic field at a carrier frequency of 3.8 GHz has been obtained. A high-power microwave radiation pulse length of ~75 ns, a peak generation power of 210 ± 30 MW, and a power conversion efficiency of 9 ± 2% were attained.     

Interaction of a modulated electron beam with a magnetoactive plasma

Experimental results concerning the interaction of a modulated electron beam with a magnetoactive plasma in the whistler frequency range are reported. It was shown experimentally that when a beam is injected into the plasma, waves can be generated by two possible mechanisms: Cherenkov emission of whistlers by the modulated beam, and transition radiation from the beam injection point. In the case of weak beam currents (N _b/N ₀)≪⁻⁴) the Cherenkov resonance radiation is more than an order of magnitude stronger than the transition radiation; the Cherenkov emission efficiency decreases at high beam currents. The transformation of the distribution function of the beam is investigated for the case of weak beam currents. It is shown that in the case of the Cherenkov interaction with whistlers the beam is retarded and the beam distribution function becomes wider and acquires a plateau region. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 6, 378–382 (25 March 1998)     

Angular distribution of Cherenkov radiation from relativistic heavy ions taking into account deceleration in the radiator

Numerical methods are used to study the dependence of the structure and the width of the angular distribution of Vavilov-Cherenkov radiation with a fixed wavelength in the vicinity of the Cherenkov cone on the radiator parameters (thickness and refractive index), as well as on the parameters of the relativistic heavy ion beam (charge and initial energy). The deceleration of relativistic heavy ions in the radiator, which decreases the velocity of ions, modifies the condition of structural interference of the waves emitted from various segments of the trajectory; as a result, a complex distribution of Vavilov-Cherenkov radiation appears. The main quantity is the stopping power of a thin layer of the radiator (average loss of the ion energy), which is calculated by the Bethe-Bloch formula and using the SRIM code package. A simple formula is obtained to estimate the angular distribution width of Cherenkov radiation (with a fixed wavelength) from relativistic heavy ions taking into account the deceleration in the radiator. The measurement of this width can provide direct information on the charge of the ion that passes through the radiator, which extends the potentialities of Cherenkov detectors. The isotopic effect (dependence of the angular distribution of Vavilov-Cherenkov radiation on the ion mass) is also considered.     

The monochromatization of a beam of charged particles by Cherenkov interaction

The possibility of monochromatization of a real beam of charged particles (possessing energy spread and angle divergence) as a result of Cherenkov interaction with laser radiation in a medium is shown. The refraction index of the medium, the Cherenkov angle and the intensity of the wave, necessary for this effect are determined by the initial parameters of the beam. For the real parameters of the beam of charged particles and the laser radiation the degree of monochromatization reaches several orders. A method of raising the monochromaticy of the charged particles of a beam is suggested.