Large Transverse Dimensions Research Articles

Measurement of the electron beam profile by the multiangle scanning method

Nowadays, ionizing radiation beams with relatively large transverse dimensions are widely used not only for research purposes but also in technological processes related to metal and food treatment, as well as medical instrument sterilization. Thus, control of beam characteristics is required, and in particular, the intensity distribution in the transverse plane must be accurately measured. The multiangle scanning method, based on mathematical transformations, allows overcoming the limitations of modern detectors used for these purposes. In this study, the method was applied to an electron beam. A detection system based on scintillating fiber was used. The beam profile was measured using the proposed method and a conventional detector — a film dosimeter. Experimental results allowto conclude that the beam intensity distribution obtained using the multiangle scanning method is close to the results obtained using a film dosimeter, which is most often used in medical institutions. Thus, we can consider the multiangle scanning method as an effective approach for determining the intensity distribution of an electron beam.

A Miniaturized Anechoic Chamber: Omnidirectional Impedance Matching Based on Truncated Spatial Kramers–Kronig Medium

AbstractSpatial Kramers–Kronig (KK) medium provides a new platform to achieve omnidirectionally reflectionless absorption without using any gain elements. However, impedance‐matched spatial KK media realized in previous experiments generally have flat geometries with large transverse dimensions. Realizing finite spatial KK absorbers in free space background is important for many practical applications but has not been demonstrated experimentally thus far. Here, the concept of spatial KK relation to cylindrical coordinates is extended and a double‐resonance space‐frequency KK permittivity profile is implemented in a circular geometry. Omnidirectional impedance matching to free space is achieved by truncating the spatial KK absorber at the boundary where the relative permittivity is unity. For the experimental verification, a two‐dimensional 6.6‐wavelength‐diameter doughnut‐shaped anechoic chamber is implemented using the designed spatial KK medium. The measured electric field distributions and experimental imaging confirm the omnidirectionally reflectionless property, demonstrating that this miniaturized anechoic chamber is suitable for electrically small scatterer measurements and imaging. The proposed finite spatial KK absorber and fabricated miniaturized anechoic chamber show great promises for electromagnetic shielding and compatibility.

Electron Orbital Motion and the Threshold Voltage for Spatial-Harmonic Magnetrons

The Buneman-Hartree relation is a condition that determines the excitation of oscillations in magnetrons. However, experiments of different years indicate that for a whole class of similar generators, it is not accurate enough. In particular, this is observed for the so-called spatial-harmonic magnetrons, which have significant advantages over conventional ones in millimeter and subterahertz ranges. The operating parameters of these generators are close to the Hull cutoff parabola, i.e., they have substantially larger transverse dimensions of the interaction space for the same values of the operating voltage and magnetic field, and accordingly, a larger-sized slow-wave system is possible. The results obtained in the development of spatial-harmonic magnetrons for radars can serve to estimate the limits of applicability of the Buneman-Hartree condition. Experiments show that the initial voltage at which generation occurs is significantly higher than the value calculated from the conventional formula. Probable causes are a change in the pattern of motion of an electron near the Hull cutoff parabola and the possibility of exciting gyroresonances. The analysis of the experiments fully confirms that even for millimeter-band magnetrons operating under purely drift (conventional) resonance, an analytical model that takes into account the orbital motion of electrons more accurately describes the physical processes near the cutoff parabola and significantly improves the accuracy of the choice of generator parameters and operating modes.

Structure of Energy Fluxes in Topological Three-Dimensional Dissipative Solitons

The internal structure of dissipative topological solitons has been revealed by example of three-dimensional dissipative optical solitons with one open and one closed dislocation lines of a wavefront. This structure is manifested in the existence of critical points, lines, and surfaces in the field of electromagnetic energy fluxes (Poynting vector). The conservation of the topological characteristics of such solitons, which can be formed in a homogeneous laser medium with saturated amplification and absorption or in lasers with quite large longitudinal and transverse dimensions, provides additional capabilities for information applications.

High-efficiency room-temperature ZnSe:Fe2+ laser with a high pulsed radiation energy

Characteristics of a ZnSe:Fe2+ laser operating at room temperature of active polycrystalline elements with large transversal dimensions are investigated. The active elements had a shape of plates with diameters D = 25–63 mm and width of ~4 mm, doped from two sides with iron ions by the diffusion method. The plates were doped in the process of hot isostatic pressing at an argon pressure of 100 MPa and temperature of 1250 °C for 75–151 h. The laser was pumped by a non-chain electrodischarge HF laser operated in a single-pulse mode. The employment of active elements with greater transversal dimensions resulted in a suppressed transversal parasitic oscillation at large diameters of the pumping spot. The generation energy of 1.43 J with the slope efficiency ηslope = 53 % and the total efficiency with respect to the energy absorbed in an active element ηabs ≈ 48 % was obtained on the sample of diameter D = 63 mm.

1/Nperturbations in superstring bit models

We develop the 1/N expansion for stable string bit models, focusing on a model with bit creation operators carrying only transverse spinor indices a=1,...,s. At leading order (1/N=0), this model produces a (discretized) lightcone string with a "transverse space' of $s$ Grassmann worldsheet fields. Higher orders in the 1/N expansion are shown to be determined by the overlap of a single large closed chain (discretized string) with two smaller closed chains. In the models studied here, the overlap is not accompanied with operator insertions at the break/join point. Then the requirement that the discretized overlap have a smooth continuum limit leads to the critical Grassmann "dimension" of s=24. This "protostring", a Grassmann analog of the bosonic string, is unusual, because it has no large transverse dimensions. It is a string moving in one space dimension and there are neither tachyons nor massless particles. The protostring, derived from our pure spinor string bit model, has 24 Grassmann dimensions, 16 of which could be bosonized to form 8 compactified bosonic dimensions, leaving 8 Grassmann dimensions--the worldsheet content of the superstring. If the transverse space of the protostring could be "decompactified", string bit models might provide an appealing and solid foundation for superstring theory.

Experimental Study of Tsunami-Type Waves Impact on Soil near Foundation of Offshore Gravitational-Type Platforms

The need to study the problem of seabed local scour near offshore platforms has arisen in Russian Federation in connection with the activation of oil and gas production from fields located in coastal areas of seas (in accordance with the Energy Strategy for the period up to 2030, approved by the Government of the Russian Federation on November 13, 2009, No1715-p). Operation of offshore platforms is characterized by a number of features: shallow water areas; severe storm conditions; large transverse dimensions of structures that cause waves diffraction; the variety of used structure forms; the way of platform mounting on the seabed. During platform operation in the shallow waters, its basement soil is under an intense impact of sea waves, currents, as well as jets from engine of coming and berthing ships. The structure disturbs the natural wave flow. Near the platform, flow velocity increases, there are vortexes breakaway from platform corner edges. Scour holes appear and progress near platform foundation. Their location and measure depend on the parameters of external impacts, on the water depth, on the shape and dimensions of the foundation block.

High-Power, Low-Noise 1.5-μm Slab-Coupled Optical Waveguide (SCOW) Emitters: Physics, Devices, and Applications

We review the development of a new class of high-power, edge-emitting, semiconductor optical gain medium based on the slab-coupled optical waveguide (SCOW) concept. We restrict the scope to InP-based devices incorporating either InGaAsP or InGaAlAs quantum-well active regions and operating in the 1.5-μm-wavelength region. Key properties of the SCOW gain medium include large transverse optical mode dimensions (>;5 × 5 μm), ultralow optical confinement factor (Γ ~ 0.25-1%), and small internal loss coefficient (αi ~ 0.5 cm-1). These properties have enabled the realization of 1) packaged Watt-class semiconductor optical amplifiers (SOAs) having low-noise figure (4-5 dB), 2) monolithic passively mode-locked lasers generating 0.25-W average output power, 3) external-cavity fiber-ring actively mode-locked lasers exhibiting residual timing jitter of <;10 fs (1Hz to Nyquist), and 4) single-frequency external-cavity lasers producing 0.37-W output power with Gaussian (Lorentzian) linewidth of 35 kHz (1.75 kHz) and relative intensity noise (RIN) <; -160 dB/Hz from 200 kHz to 10 GHz. We provide an overview the SCOW design principles, describe simulation results that quantify the performance limitations due to confinement factor, linear optical loss mechanisms, and nonlinear two-photon absorption (TPA) loss, and review the SCOW devices that have been demonstrated and applications that these devices are expected to enable.

The LHCb RICH silica aerogel performance with LHC data

In the LHCb experiment at the Large Hadron Collider, powerful charged particle identification is performed by Ring Imaging CHerenkov (RICH) technology. In order to cover the full geometric acceptance and the wide momentum range (1–100 GeV/ c), two detectors with three Cherenkov radiators have been designed and installed. In the medium (10–40 GeV/ c) and high (30–100 GeV/ c) momentum ranges, gas radiators are used (C 4F 10 and CF 4, respectively). In the low momentum range (1–10 GeV/ c), pion, kaon and proton separation is performed with solid silica aerogel radiator. A set of 16 tiles, with large transverse dimensions of up to 200 × 200 mm 2 and nominal refractive index 1.03 have been produced and integrated in the detector. These tiles have excellent optical properties and homogeneity of the refractive index at the percent level within the tile. The first data collected at the LHC are used to investigate the behaviour of the RICH; preliminary results of the performance of silica aerogel are presented and discussed.

Ageing tests and recovery procedures of silica aerogel

Silica aerogel has been extensively used in RICH detectors for the identification of charged particles over the momentum range between 1 and 10 GeV / c . Tiles of hygroscopic aerogel with large transverse dimensions ( 20 × 20 cm 2 ) and refractive index n = 1.03 have recently been produced for use in the LHCb experiment, allowing pion–kaon identification up to 10 GeV / c . The tiles have excellent optical properties (clarity factor better than 0.006 μ m 4 / cm and homogeneity σ ( n - 1 ) / ( n - 1 ) ∼ 1 % within the tile). Extensive R&D tests on aerogel samples have been performed. Samples have been exposed to intense irradiation (proton, neutron and gamma), to humid air, to standard black varnish (used to paint the inner surface of RICH detectors), and to C 4F 10 and CO 2 gases. The optical properties of the aerogel have been monitored during these tests and, when required, recovery procedures have been investigated and applied. In particular, regeneration of the tiles has been realized through exposure to dry atmosphere (gaseous N 2) or through baking for several hours at 500 ∘ C . The measurements demonstrate that the optical properties have been successfully restored to their values at the production stage, and in no case permanent degradation has been observed.

Structure and rheology of organoclay suspensions

We have characterized a montmorillonite-based organoclay dispersed in three different nonaqueous solvents using a combination of x-ray scattering, small-angle neutron scattering (SANS), and ultrasmall angle neutron scattering (USANS), together with rheological measurements. Consistent with these measurements, we present a structural model for the incompletely dispersed clay as consisting of randomly oriented tactoids made of partially overlapping clay sheets, with transverse dimensions of several microns. Intersheet correlation peaks are visible in x-ray scattering, and quantitatively fit by our model structure factor. SANS and USANS together show a power law of about -3 over a wide range of wave numbers below the intersheet correlation peak. Our model relates this power law to a power law distribution of the number of locally overlapping layers in a tactoid. The rheology data show that both storage and loss moduli, as well as yield stress, scale with a power law in volume fraction of about three. Equating the gel onset composition with the overlap of randomly oriented tactoids and taking into account the large transverse dimensions of the tactoids, we predict the gel point to be at or below 0.006 volume fraction organoclay. This is consistent with the rheology data.

Wave propagation in tunnels in a MIMO context—a theoretical and experimental study

MIMO (Multiple-Input Multiple-Output) techniques, based on multiple antennas at both the transmitting and receiving sites, use multipath propagation to transform the overall channel into numerous independent virtual channels. However, when the link is made in a long tunnel, the number of reflecting objects between, or near, the transmitter and the receiver is often quite low. In addition, due to the large transverse dimensions of the tunnel compared to the wavelength, the tunnel acts like a lossy oversized waveguide. In such situations, the concept of spatial diversity must be replaced by the concept of modal diversity. This article uses theoretical and experimental results to show the conditions in which MIMO techniques allow the ergodic capacity of the channel to be increased. To cite this article: M. Lienard et al., C. R. Physique 7 (2006).

Status and characterisation of COMPASS RICH-1

COMPASS RICH-1, a gas-radiator RICH detector with large transversal dimensions, which makes use of MWPC with CsI photocathodes as photon detectors, is in operation at COMPASS since 2001. The behaviour of the detector components is optimised and fully understood. The characterisation of the detector is now complete. We report about the detector status and its response in the COMPASS environment.

Results from COMPASS RICH-1

COMPASS RICH-1, designed in 1996 for hadron identification at high momenta in the COMPASS large angle spectrometer, is a large acceptance gaseous RICH with a 3 m thick C 4 F 10 radiator. MWPCs with CsI photocathodes are used as VUV photon detectors and the image focalization is provided by a large UV mirror wall. π /K are separated in the several 10 GeV/ c domain. The main characteristics of the detector are the large acceptance resulting in very large transversal dimensions, the use of far UV photon detectors, which implies VUV transparency of the radiator gas and good VUV mirror reflectance and the high rate capabilities, made possible by the read-out system architecture. The detector description, the various technological achievements and present performances are given. In particular, preliminary RICH-1 performances obtained analysing the data from the 2002 and 2003 runs are presented.

Results from COMPASS RICH-1

COMPASS RICH-1, designed in 1996 for hadron identification at high momenta in the COMPASS large angle spectrometer, is a large acceptance gaseous RICH with a 3 m thick C 4 F 10 radiator. MWPCs with CsI photocathodes are used as VUV photon detectors and the image focalization is provided by a large UV mirror wall. π /K are separated in the several 10 GeV/ c domain. The main characteristics of the detector are the large acceptance resulting in very large transversal dimensions, the use of far UV photon detectors, which implies VUV transparency of the radiator gas and good VUV mirror reflectance and the high rate capabilities, made possible by the read-out system architecture. The detector description, the various technological achievements and present performances are given. In particular, preliminary RICH-1 performances obtained analysing the data from the 2002 and 2003 runs are presented.

An asymptotic analysis for determining concentration uncertainty in aquifer transport

Transport of a conservative solute takes place by advection and by pore-scale dispersion in a formation of spatially variable logconductivity Y( x )= ln K( x ). The latter is modeled as a normal stationary random space function, characterized by a few statistical parameters, like the mean 〈 Y〉, the variance σ Y 2, the horizontal and vertical integral scales I h and I v . The local solute concentration C( x ,t), a random function of space and time, is characterized by its statistical moments, like, e.g. the mean 〈 C〉 and the standard deviation σ C . A simplified analysis for determining the concentration uncertainty is proposed. The proposed methodology, valid for nonreactive solutes, is based on a few simplifications, the most important being: (i) large transverse dimensions of the injected plume compared to the logconductivity correlation lengths, (ii) mild heterogeneity of the hydraulic properties, which allows for the use of the first-order analysis, (iii) highly anisotropic formations, and (iv) mean uniform flow. The concentration uncertainty is represented through the coefficient of variation CV C = σ C /〈 C〉 at the plume center, where the expected concentration is maximum. Results for CV C are illustrated as function of time and on two dimensionless parameters: Ω=I v 2/(I hα dT) and Λ=L 1/ A 11I h , where L 1 is the longitudinal dimension of the initial plume, A 11 is the longitudinal macro dispersivity, and α dT is the local transverse dispersivity. Summary graphs lead to a quick and simple estimate of the time-dependent concentration uncertainty, as well as its peak and its setting time (i.e. the time needed to reach the peak coefficient of variation). The methodology and its results can be used to assess the concentration uncertainty at the plume center. The problem is quite important when dealing with contaminant prediction and risk analysis.

Theory of relativistic-electron transition radiation in a thin metal target

An analysis is made of the transition radiation of a relativistic electron in a thin metal target in the infrared wavelength range. It is shown that in this case, the spatial transverse dimensions responsible for forming the radiation may have macroscopic dimensions comparable with the size of the target and allowance for this effect may lead to significant distortion of the transition-radiation spectrum compared with a target having infinitely large transverse dimensions.

D-brane recoil and supersymmetry breaking as a relaxation process

We propose a new mechanism for the formation of conical singularities on D-branes by means of recoil resulting from scattering of closed string states propagating in the (large) transverse dimensions. By viewing the (spatial part of the) four-dimensional world as a 3-brane with large transverse dimensions the above mechanism can lead to supersymmetry obstruction at the TeV scale. The vacuum remains supersymmetric while the mass spectrum picks up a supersymmetry obstructing mass splitting. The state with “broken” supersymmetry is not an equilibrium ground state, but is rather an excited state of the D-brane which relaxes to the supersymmetric ground state asymptotically in (cosmic) time.

Scales of string theory

I review the arguments in favour of/against the traditional hypothesis that the Planck, string and compactification scales are all within a couple of orders of magnitude of each other. I explain how the extreme brane-world scenario, with TeV type I scale and two large (near millimetric) transverse dimensions, creates conditions analogous to those of the energy desert and is thus naturally singled out. I comment on the puzzle of gauge coupling unification in this context.

Low-scale closed strings and their duals

We study large dimensions and low string scale in four-dimensional compactifications of type II theories of closed strings at weak coupling. We find that the fundamental string scale, together with all compact dimensions, can be at the TeV, while the smallness of the string coupling accounts for the weakness of gravitational interactions. This is in contrast to the situation recently studied in type I theories, where the string scale can be lowered only at the expense of introducing large transverse dimensions felt by gravity only. As a result, in these type II strings, there are no strong gravity effects at the TeV, and the main experimental signature is the production of Kaluza-Klein excitations with gauge interactions. In the context of type IIB theories, we find a new possibility providing a first instance of large non-transverse dimensions at weak coupling: two of the internal dimensions seen by gauge interactions can be at the TeV, with the string scale and all other dimensions at intermediate energies of the order of 10 11 GeV, where gravity becomes also strong. Finally, using duality, we provide a perturbative description for the generic case of large dimensions in the heterotic string. In particular, we show that the two type II theories above describe the cases of one and two heterotic large dimensions. A new M-theory derivation of heterotic-type II duality is instrumental for this discussion.