Cerenkov Emission Research Articles

NOVEL SOUND PHENOMENA IN IMPURE SUPERFLUIDS

In the last decade, new techniques for producing impure superfluids with unique properties have been developed. This new class of systems includes superfluid helium confined to aerogel, HeII with different impurities, superfluids in Vycor glasses, and watergel. These systems exhibit very unusual properties including unexpected acoustic features. We discuss the sound properties of these systems and show that sound phenomena in impure superfluids are modified from those in pure superfluids. We calculate the coupling between temperature and pressure oscillations for impure superfluids and show that this coupling increases significantly. This leads to the existence in impure superfluids of such unusual sound phenomena as slow "pressure" waves and fast "temperature" waves. This also decreases the threshold values for nonlinear processes as compared to pure superfluids. Sound conversion, which has been observed in pure superfluids only by high intensity waves should be observed at moderate sound amplitude in impure superfluids. Cerenkov emission of second sound by first sound (which has never been observed in superfluids) could be observed in impure superfluids. Even the nature of the sound modes in impure superfluids turns out to be changed. We have also derived for the first time the nonlinear hydrodynamic equations for superfluid helium in aerogel.

Table-top water window transmission x-ray microscopy: Review of the key issues, and conceptual design of an instrument for biology

As it has been beautifully demonstrated in synchrotron facilities, water window transmission x-ray microscopy (WW-TXM) has a great potential for high resolution three dimensional (3D) tomographic imaging of frozen cells, without the cumbersome staining and slicing preparation needed by electron microscopy. However, the existing instruments do not exactly meet the expectations of cell biologists in terms of performance and accessibility: 3D images of entire cells grown on a flat substrate with details in the 50–80nm range are necessary for structural cell studies. Functional imaging is also a key issue. Specific molecular probes are widely used to achieve molecular imaging in optical and electron microscopy. The same demand applies to x-ray microscopy. Immediate availability of the observation technique within the biology laboratory is as important as its performance. Therefore, WW-TXM will develop on a wider scale only when table-top instruments become available. We present a detailed analysis of such a microscope. The source is clearly the key element. Laser created plasmas of carbon or nitrogen are a proven but expensive solution. Cerenkov emission in vanadium has been demonstrated as a potential monochromatic source, but we emphasize severe obstacles: huge thermal load and radiation protection. We show that oxygenKα line excitation by an electron beam is a realistic alternative. Being a purely monochromatic source, it would allow the use of a high efficiency mirror condenser, while laser plasmas imply spectral selection with the associated losses. We then describe the main elements of an affordable laboratory microscope, supported by numerical simulations and preliminary experimental work. We also show that functionalized quantum dots, currently used in fluorescence microscopy, are equally detectable with soft x-rays and would allow a dual modality observation. Finally, the expected performance of this prototype is discussed and confronted by the requirements of cell biology.

The relation between the lateral profile of giant extensive air showers and the age parameter

After performing extensive simulations with the code CoRSiKa, we have obtained an analytical description fitting with surprising accuracy the numerical densities up to distances larger than 5 km from the shower axis. This was achieved by using the hypergeometric formalism in place of the traditional NKG approach. The difficulty of cascade theory (validity limited to 3.5 Moliere radii), underlined with reason by the particle data group, is solved here, after overcoming the constraints of approximation B, to show that the distribution of lateral profiles at large distances is also correlated with the age parameter. This is an important step for a coherent interpretation of hybrid events recorded with both surface array and fluorescence telescopes, even with other information coming from Cerenkov or radio emission. A set of hypergeometric Gaussian functions, with a consistent relation between age parameter and total size, is proposed in the ultra-high-energy range (above 1 EeV) for electrons, muons and vertical equivalent muons.

Does the Iron Kα Line of Active Galactic Nuclei Arise from the Cerenkov Line–like Radiation?

When thermal relativistic electrons with isotropic distribution of velocities move in a gas region or impinge upon the surface of a cloud that consists of a dense gas or doped dusts, the Cerenkov effect produces peculiar atomic or ionic emission lines, which is known as the Cerenkov - like radiation. This newly recognized emission mechanism may find wide applications in high-energy astrophysics. In this paper we tentatively adopt this new emission mechanism to discuss the origin of the iron Kα feature of active galactic nuclei (AGNs). The motivation of this research is to attempt a solution to a problem encountered by the disk fluorescence line model, i.e. , the lack of temporal response of the observed iron Kα flux to the changes of the X-ray continuum flux. If the Cerenkov emission is indeed responsible significant ly for the iron Kα feature, the conventional scenario around the central supermassive black holes of AGNs would need to be modified to accomodate more energetic, more violent, and much denser environments than previously thought.

Enhanced Čerenkov second-harmonic generation in a planar nonlinear waveguide that reproduces a one-dimensional photonic bandgap structure

Second-harmonic generation in the Cerenkov configuration is investigated under conditions for which the use of a linear grating fabricated on top of the waveguide reproduces a photonic bandgap structure. The fundamental mode of the guide at the fundamental frequency is tuned at the photonic band-edge resonance, thus producing great confinement and enhancement of the electromagnetic field inside the structure. The conversion efficiency achieved in both the forward and the backward directions is at least 1 order of magnitude greater than that of a conventional Cerenkov emission in a waveguide of the same length. An analysis of the tolerances of the grating period on the conversion efficiency is presented.

An overview of observations by the Cassini radio and plasma wave investigation at Earth

On August 18, 1999, the Cassini spacecraft flew by Earth at an altitude of 1186 km on its way to Saturn. Although the flyby was performed exclusively to provide the spacecraft with sufficient velocity to get to Saturn, the radio and plasma wave science (RPWS) instrument, along with several others, was operated to gain valuable calibration data and to validate the operation of a number of capabilities. In addition, an opportunity to study the terrestrial radio and plasma wave environment with a highly capable instrument on a swift fly‐through of the magnetosphere was afforded by the encounter. This paper provides an overview of the RPWS observations at Earth, including the identification of a number of magnetospheric plasma wave modes, an accurate measurement of the plasma density over a significant portion of the trajectory using the natural wave spectrum in addition to a relaxation sounder and Langmuir probe, the detection of natural and human‐produced radio emissions, and the validation of the capability to measure the wave normal angle and Poynting flux of whistler‐mode chorus emissions. The results include the observation of a double‐banded structure at closest approach including a band of Cerenkov emission bounded by electron plasma and upper hybrid frequencies and an electron cyclotron harmonic band just above the second harmonic of the electron cyclotron frequency. In the near‐Earth plasma sheet, evidence for electron phase space holes is observed, similar to those first reported by Geotail in the magnetotail. The wave normal analysis confirms the Polar result that chorus is generated very close to the magnetic equator and propagates to higher latitudes. The integrated power flux of auroral kilometric radiation is also used to identify a series of substorms observed during the outbound passage through the magnetotail.

Radiation-induced absorption and luminescence in specially hardened large-core silica optical fibers

Radiation-induced absorption and luminescence are measured in the visible spectral region in H/sub 2/-loaded and as-drawn fibers with KU and KS-4V silicas in the core in the process of /spl gamma/-irradiation (/sup 60/Co-source). The induced absorption in H/sub 2/-loaded fibers is shown to be much lower than in as-drawn fibers, at least up to 1.2 MGy. A 'blue' band prevails in the luminescence spectra of all the fibers. Its intensity is greater in a KS-4V fiber than in a KU fiber. It is also somewhat greater in H/sub 2/-loaded fibers than in unloaded ones, The luminescence lifetime in a KU fiber has been measured under excitation with a pulsed reactor to be 100 /spl mu/s at /spl lambda/=488 nm and 60 /spl mu/s at /spl lambda/=633 nm. It is concluded that the 'blue' radioluminescence cannot be attributed either to relaxation of the oxygen-deficient center or to Cerenkov emission. A fabrication technology of radiation-hardened H/sub 2/-containing fibers with a hermetic aluminum coating is reported. Such fibers appear to be the best candidates for various applications in radiation environments.

Cerenkov generation of high-frequency confined acoustic phonons in quantum wells

We analyze the Cerenkov emission of high-frequency confined acoustic phonons by drifting electrons in a quantum well. We find that the electron drift can cause strong phonon amplification (generation). A general formula for the gain coefficient α is obtained as a function of the phonon frequency and the structure parameters. The gain coefficient increases sharply in the short-wave region. For the example of a Si/SiGe/Si device, it is shown that the amplification coefficients of the order of hundreds of cm−1 can be achieved in the subterahertz frequency range.

New Paradigm for the Self-Consistent Modeling of Wave-Particle and Wave-Wave Interactions in the Saturation of Electromagnetically Driven Parametric Instabilities

We introduce two new and complementary simulation models, which have domains of quantitative agreement, for the self-consistent evolution of the electron distribution, Langmuir decay cascades, and Langmuir collapse. In our reduced-description particle-in-cell (RPIC) simulations, Langmuir decay cascades and cycles of collapse are seen for the first time in particle simulation. The velocity distribution in our Zakharov model is evolved using quasilinear diffusion plus Cerenkov emission loss and agrees in expected domains with the RPIC results. These techniques promise to solve long known problems in the standard simulations of laser-plasma instabilities.

Cerenkov emissions of ion acoustic‐like waves generated by electron beams emitted during TSS 1R

During the Tethered Satellite System reflight the Spacecraft Particle Correlation Experiment detected fluxes of energetic electrons and ions that were simultaneously modulated at low frequencies during firings of both the fast pulsed electron gun (FPEG) and the electron generator assembly (EGA). The modulations have been interpreted as signatures of large‐amplitude, ion acoustic‐like waves excited in Cerenkov interactions between electron beams and ambient plasmas as the shuttle moved at supersonic speeds across the ionospheric magnetic field. We present examples of particle modulations observed during steady beam emissions. Measurements show that (1) most electron modulations were at frequencies of several hundred Hertz and (2) ions modulated at similar frequencies appeared at spectral energy peaks during shuttle negative charging events. Detection of modulated ion fluxes confirms the Cerenkov emission hypothesis. Observed frequency variations indicate that the EGA beam underwent more spatial spreading than the FPEG beam.

Influence of restraint stress on IL-1 β messenger RNA expression in the rat brain induced by peripheral lipopolysccharide injection

Single-mode optical fibres (SMFs) are required for ITER in-vessel applications as transport fibres to deliver the signal at wavelength λ = 1.55 µm from/to optical fibre sensors. The paper describes the first comparison study of radiation resistance of six pure-silica-core SMFs of different manufacturers performed in the process of fission-reactor irradiation in the conditions corresponding to the whole ITER lifetime (fast-neutron fluence, flux, γ-dose and dose rate of up to 1.8·1020n/cm2, 1.08·1014n/(cm2·s), 2.32 GGy and 1.39 kGy/s, respectively, temperature of 170–190 °C and vacuum pumping). Polyimide- and acrylate-coated SMFs failed mechanically during the irradiation; therefore, only metal-coated fibres can be considered for the in-vessel applications. Induced optical loss in all three metal-coated SMFs (copper- and aluminum-coated ones) at the fast-neutron fluence of 1·1020n/cm2 was found to lie in the range ~1.5–4 dB/m, the lower value of this range allowing the employment of at least 10-m-long transport fibre lengths in the in-vessel applications, assuming the dynamic range of 30 dB. The temperature-dependent microbending optical loss in metal-coated SMFs is discussed, of which the contribution to the total induced loss may be comparable in value to the radiation-induced absorption of light. Neither radiation-induced luminescence, nor Cerenkov emission was detected in the SMFs in the near-infrared range.

A search for lunar radio Cerenkov emission from high-energy neutrinos

A search for erenkov emission in the radio-frequency range resulting from the particle cascade of an ultrahigh-energy neutrino on the near surface of the Moon is described. The expected pulse of 1-ns duration, dispersed by propagation through the Earth's ionosphere, with an amplitude of approximately 400 Jy was not detected in approximately 10 h of observations.

Gamma-Ray Astronomy: Extension beyond the GeV domain by ground-based observations

Gamma-Ray Astronomy, originated with the OSO-3, SAS-2 and COS-B satellites, has been renewed during the last three years by Compton-GRO's discovery of tens of Galactic and extra-galactic sources up to ≈ 10 GeV. Also in the last three years, a ground-based observing technique has emerged for TeV gamma rays: the identification of gamma-induced air showers via their Cerenkov emission. Extrapolating this technique down to the present limit of satellite observations has become a realistic goal, allowing fundamental questions to be tackled which would remain open until the individual spectra were extended.

Soliton collisions in optical birefringent fibers

Soliton collisions in birefringent optical fibers have been investigated numerically. It is found that soliton collisions can be divided into three kinds of behavior depending on the value of the linear birefringence. Both soliton mixing and soliton center-frequency shifts have been studied in detail. A new kind of soliton state has been found. The Cerenkov emission generated by soliton collision has also been found numerically.

Helical Cerenkov effect, a novel radiation source

The observability of the helical Cerenkov effect as a novel radiation source is discussed. Depending on the value of the index of refraction of the medium, the strength of the uniform magnetic field, and the electron beam energy, helical Cerenkov radiation can occur in the same spectral regions as the ordinary Cerenkov effect, that is, from microwave to visible wavelengths. From the kinematics point of view, I argue that for a microwave wavelength of 10/sup -1/cm this effect should be observable in a medium with an index of refraction of 1.4, with a beam energy of 3 MeV, and a uniform magnetic field of 4 T. On the specific level, however, for the sake of simplicity, I discuss the observability of this effect for visible light with the central wavelength of 5/spl times/10/sup -5/ cm which can be achieved with 2 MeV in beam energy, silica aerogel as a medium (with an index of refraction of 1.075), and uniform magnetic fields from 5 to 10 T. For a 10-T magnetic field, I calculate that in the visible region of 250 to 750 nm an electron will produce a photon per 10 cm of traveled length. As to the stimulated helical Cerenkov emission, I estimate that respectable gains are possible even if the beam passes close to the dielectric rather than through it. In addition to being potentially a new radiation source, the helical Cerenkov effect could possibly be used as a detector of radiation by energetic electrons that are trapped in a medium by strong magnetic fields.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Operation of the sapphire Cerenkov laser

First operation of a sapphire-based Cerenkov free electron laser is reported. It is a tunable source of coherent millimeter and submillimeter radiation. The phase velocity of light in sapphire is about one-tenth of that in free space so that Cerenkov radiation is obtained at modest electron beam energies. In addition to its role as a Cerenkov coupler, the sapphire forms a high Q resonator obviating external mirrors. The spontaneous Cerenkov emission is well-confined by this resonator and can build to watts of power. Measured tuning and threshold currents are presented and compared with the predictions of free electron laser theory.

Measurement of long-pulse relativistic electron beam perpendicular- to-parallel velocity ratio by Cerenkov emission and radiation darkening on a glass plate

We report measurements of the ratio of the perpendicular velocity to the parallel velocity, α= v⊥ /v∥, of a relativistic electron beam gyrating in a magnetic field by the use of (1) Cerenkov emission from a glass plate, detected by a gated microchannel plate image intensifier camera, and (2) electron-beam-induced radiation darkening pattern on the same glass plate. The measurements are based on a direct determination of the Larmor radius of an electron beam of known energy. Experiments were performed on a long-pulse electron beam accelerator with e-beam diode parameters: VD = 0.6–0.9 MV, pulse length=0.5–1 μs, ID = 1–10 kA. The experimental value of α agrees with simulation results from particle trajectory codes as well as theoretical predictions from Busch’s theorem and adiabatic theory.

Icemand: Microwave detection of ultra-high energy neutrinos in ice

A muon from an ultra-high energy neutrino interaction produces an electromagnetic shower of considerable length. Coherent Cerenkov emission at microwave frequencies from the electric charge imbalance developing in such a shower serves as an efficient signal of the event. We discuss detecting upward going UHE neutrinos ( E ν ⪆ 10 15eV ) in the antarctic ice by detecting this microwave signal with comparatively cheap and simple antennas located on the ice surface. We conclude that a pilot experiment to measure UHE neutrinos from point sources such as Cygnus X - 3 is feasible.

Coherent Cerenkov radiation from the Spacelab 2 electron beam

During the Spacelab 2 mission, a spacecraft called the Plasma Diagnostics Package (PDP) was released from the space shuttle to investigate the surrounding plasma environment. During an interval when the shuttle and PDP were magnetically connected, a continuous 1‐keV/50‐mA electron beam was ejected along a field line from an electron generator on board the shuttle. As the PDP flew by the beam, the PDP plasma wave instrument detected intense whistler mode radiation originating from the beam. It is believed that coherent Cerenkov radiation from bunches of beam electrons is responsible for the whistler mode radiation, where an electrostatic beam‐plasma instability forms the coherently radiating bunches. In this paper a detailed model of the coherent Cerenkov emission process is presented. A one‐dimensional computer simulation of the beam is used to model the expected phase space structure of the electrons, and power emitted from Cerenkov radiation is computed using an analytical expression. The calculated power from the modeled 200‐m beam segment is ∼5 × 10−8 W/Hz, which can easily account for the measured whistler mode wave power. The inclusion of coherent effects in the beam increases the wave powers by nearly 90 dB above incoherent power levels. These calculations demonstrate that a spontaneous emission process, alone, can account for the observed whistler mode wave powers.

The origin of the hump in the Cerenkov lateral distribution in gamma-ray showers and a possible means of separating them from proton showers

The lateral distribution of Cerenkov photons emitted by 100 GeV electromagnetic cascades is calculated using a detailed Monte Carlo procedure. The calculated lateral distribution shows a prominent hump at a distance of about 135 m from the core. The nature and origin of this hump are investigated analytically as well as through Monte Carlo calculations and it is shown to be due to electrons of energy >1 GeV, above which the root mean square scattering angle is less than the Cerenkov emission angle. The conditions under which such a hump can arise are derived. Arguments are given to show that such a hump is not present in proton showers of comparable energy. Possible implications for identification of gamma rays against the cosmic-ray background are discussed.