Axial Spectrum Research Articles

INVESTIGATION OF LPG SOOTING DIFFUSION FLAME BY RAINBOW SCHLIEREN DEFLECTOMETRY

Rainbow schlieren deflectometry was employed to characterize the flame structure of unsteady laminar liquefied petroleum gas (LPG) jet diffusion flame. The schlieren images were acquired at 4000 Hz sampling rate for sooting LPG flame at Re = 500, and Abel inversion was employed to estimate local field refractive index difference. The a priori relationship between the refractive index difference and temperature was established using the opposed flow flame reactor concept. The peak temperature observed in the near-field region varies with axial location from 1000 K to 1700 K, which falls in the range of typical sooting flame. The sooting flame has depicted a typical flicker behavior of the unsteady laminar diffusion flame. Flicker behavior and flame puff formation could be attributed to the interaction of buoyancy-sustained outer vortical structure with the flame surface. It was observed that additional air entrainment during puff formation leads to higher temperatures in the puff (1700 K), which leads to better oxidation of carbon soot and its precursors at down-stream locations, a unique feature of sooting flames. Irrespective of whether space–time evolution at any axial location or frequency spectrum analysis of temporal signal of hue at any spatial location or the amplitude–time signal of decomposed mode from proper orthogonal decomposition (POD) analysis of color schlieren images, is employed the global unique flicker frequency of 13.33 Hz was observed in the near-field LPG diffusion flame. Interestingly the first two dominant energy modes of POD analysis correspond to flow features indicating strong ambient air entrainment pointing towards the role of outer vortical structures on flame flickering phenomena.

Syntheses, spectral aspects and biological studies of bromide and azide bridged box dimer copper(II) complexes of an NNO donor aroylhydrazone

A new NNO donor aroylhydrazone, di-2-pyridyl ketone-3-methoxybenzhydrazone (Hdkm) and three copper(II) complexes of Hdkm have been synthesized and characterized by different physicochemical techniques including single crystal X-ray diffraction technique. The structural analysis of copper(II) complexes revealed that a mononuclear bis coordinated complex [Cu(dkm)2] (1) and two monocoordinated Hdkm with dinuclear metal center [Cu(dkm)Br]2(2) and [Cu(dkm)N3]2(3) are formed. The coordination geometry of complex 1 is distorted octahedral with an N4O2 chromophore while complexes 2 and 3 are bromide and azide bridged box dimers respectively with distorted square pyramidal geometry. These complexes showed a axial spectra with g|| > g⊥ ≥ 2.0023. The antibacterial activity and cytotoxicity studies performed showed that these complexes display good activity.

Synthesis, Spectroscopic Characterization, Antibacterial and Short Term in vitro Cytotoxicity Studies of Copper(II) Complexes of Novel Tridentate N,N,S Donor Ligand 2-Benzoylpyridine-N(4),N(4)-(N,N-diethyl-N-methylamine-2,2'-diyl)thiosemicarbazone

A tridentate N,N,S-donor ligand, 2-benzoylpyridine-N(4),N(4)-(N,N-diethyl-N-methylamine-2,2'-diyl)thiosemicarbazone (Hbptsc) has been synthesized and characterized by elemental CHN analysis, UV-visible, FT-IR and 1H NMR spectroscopy. Copper(II) complexes of the ligand, Hbptsc synthesized have been characterized by elemental analysis, UV-visible spectra, FTIR spectra and EPR spectroscopic simulation. The complexes hold the stoichiometry of the type [CuLX] where X= Cl (1), NO3 (2), SO4 (3), N3 (4), SCN (5) confirmed by the molar conductivity studies of 10-3 M solutions in DMF at room temperature. The EPR spectra of the complexes recorded in DMF at 77 K shows an axial type spectra with two distinct g-values, g|| and g⊥ indicating a four coordinated planar geometry. The antimicrobial studies of the copper(II) complexes shows an appreciable activity against both gram positive and gram negative bacteria using streptomycin as positive control. The short term in vitro cytotoxicity studies following trypan blue dye exclusion method exhibits pronounced activity against the Dalton’s Lymphoma Ascites tumour cells extruded from the peritoneal cavity of mice.

Numerical and Monte Carlo study of positron production in a hybrid scheme based on 〈1 0 0〉 axial channeling radiation in a Si single crystal

The non-conventional (hybrid) scheme of a positron source using GeV electron beams is investigated by means of our Mathematica and GEANT4 simulation codes. Axial channeling radiation (CR) is generated in a Si single crystal (radiator) and subsequently converted into e+–e− pairs in an amorphous tungsten (W) target (converter).We will present numerical calculations of axial CR spectra from relativistic electrons of different energies channeled in a Si single crystal. Applying both the dipole and non-dipole approach, comparison reveals a striking difference between obtained energy distributions of axial CR.Positron spectra obtained by pair production and captured by an adiabatic matching device (AMD) are simulated using GEANT4 toolkit. The AMD provides an axial magnetic field of upstream decreasing strength between the converter and the aperture of some pre-accelerating structure (linac). We also present Monte-Carlo simulation results of positron-beam emittance and transverse beam-density distribution behind the W converter and behind the AMD.

On the inverse spectrum problem of neutron stars

In this work we revisit axial perturbations of spherically symmetric and non-rotating neutron stars. Although it has been object of many studies, it still offers new insights that are of potential interest for more realistic scenarios or in the study exotic compact objects, which have drawn much attention recently. By using WKB theory, we first derive a new Bohr–Sommerfeld rule that allows to investigate the quasi-normal mode spectrum and address the inverse spectrum problem. The pure analytical treatment of the wave equation is rather involved, because it requires the solution of the TOV equations and the non-trivial tortoise coordinate transformation depending on the underlying space-time. Therefore we provide an easy way to construct potentials that simplifies the analytical treatment, but still captures the relevant physics. The approximated potential can be used for calculations of the axial perturbation spectrum. These results are also useful in the treatment of the inverse problem. We demonstrate this by reconstructing the time–time component of the metric throughout the star and constraining the equation of state in the central region. Our method also provides an analytical explanation of the empirically known asteroseismology relation that connects the fundamental QNM and radius of a neutron star with its compactness.

Pyridine-2,6-Dicarboxylic Acid Esters (pydicR2) as O,N,O-Pincer Ligands in CuII Complexes

The pyridine-2,6-carboxylic esters pydicR2 with R = Me or Ph form the unprecedented mononuclear CuII complexes [Cu(pydicR2)Cl3]− in one-pot reactions starting from pyridine-2,6-carboxychloride pydicCl2, CuII chloride, and NEt3 in MeOH or PhOH solution under non-aqueous conditions. The triethylammonium salts (HNEt3)[Cu(pydicR2)Cl3] were isolated. The methyl derivative could be crystallized to allow a XRD structure determination. Both structures were optimized using DFT calculations in various surroundings ranging from gas phase and the non-coordinating solvent CH2Cl2 to the weakly coordinating acetone and well-coordinating solvents acetonitrile (MeCN) or dimethylformamide (DMF), while detailed calculation showed the charge distribution, dipole moments, and HOMO–LUMO gap energies changing upon solvation. According to these calculations, the ion pairs and the anionic CuII complexes were stable, which shows only Cu–Cl bond elongation and weakening of the charge transfer between the anionic complex and the cation as solvents become polar. Synthesis attempts in the presence of water yielded the CuII complexes [Cu(pydic)(OH2)2]n and [Cu(OH2)6][{Cu(pydic)}2(µ-Cl)2], which results from pydicCl2 hydrolysis. Alternatively, the new pydic(IPh)2 (IPh = 2-iodo-phenyl) ester ligand was synthesized and reacted with anhydrous CuCl2, which yields the new binuclear complex [{Cu(pydic(IPh)2)Cl}2(µ-Cl)2]. EPR spectroscopy of the solid compounds reveals typical axial spectra in line with the observed and DFT calculated geometries. Cyclic voltammetry and UV–vis absorption spectroscopy in solution are in line with un-dissociated complex species [Cu(pydicR2)Cl3]−.

Structural characterization, thermal investigation and biological activity of metal complexes containing Schiff Base ligand (Z)‐3‐(1‐((4,6‐dimethyl‐1H‐pyrazolo[3,4‐b] pyridin‐3‐yl)imino)ethyl)‐4‐hydroxy‐6‐methyl‐2H‐pyran‐2‐one

A new series of metal complexes containing Co(II), Pd(II), Fe(III) chloride and Cu(II) salts (chloride, bromide, sulphate and perchlorate) have been prepared with Schiff base ligand (HL). The synthesized compounds were elucidated using elemental analyses, spectral techniques, molar conductance, magnetic measurements and thermogravimetric studies. The analytical data established (1 M:1 L) stoichiometry for complexes (1), (2), (4), (6) and (7) as well as (1 M:2 L) and (2 M:3 L) stoichiometry for complexes (5) and (3), respectively. As a result, the ligand HL coordinates in complexes (1), (2), (4), (6) as a monobasic tridentate ONN moiety via the oxygen atom of the deprotonated phenolic OH, the nitrogen atoms of the azomethine and the imine group in pyrazolopyridine ring. While, it behaves as a neutral bidentate in complexes (3,7), chelates via oxygen and nitrogen atoms of enolic OH and azomethine groups. Also, in complex (5) Cu2+ ion binds via NO sits of two ligand molecules in its monobasic and neutral forms. The magnetic moment and electronic spectral data proposed octahedral structure for complexes (2, 3 and 7) as well as triagonal bipyramidal and square pyramidal geometry for complexes (1 and 4), while, chelates (5) and (6) possess square planar geometry. TG/DTG studies confirmed the chemical formula for these complexes and established the thermal decomposition processes ended with the formation of metal or metal oxides contaminated with carbon residue. An axial electron spin resonance spectra were suggested for Cu(II) complexes pointing to 2B1g as a ground state with hyperfine structure for complex (4). In vitro antibacterial and antioxidant activities were performed for HL ligand and its metal complexes. The biological studies indicate that complex (3) has better antibacterial activity compared to the ligand and the other complexes.

MmSTORM: Multimodal localization based super-resolution microscopy

Super-resolution localization microscopy provides a powerful tool to study biochemical mechanisms at single molecule level. Although the lateral position of the fluorescent dye molecules can be determined routinely with high precision, measurement of other modalities such as 3D and multicolor without the degradation of the original super-resolved image is still in the focus. In this paper a dual-objective multimodal single molecule localization microscopy (SMLM) technique has been developed, optimized and tested. The proposed optical arrangement can be implemented onto a conventional inverted microscope without serious system modification. The performance of the method was tested using fluorescence beads, F-actin filaments and sarcomere structures. It was shown that the proposed imaging method does not degrade the image quality of the original SMLM 2D image but could provide information on the axial position or emission spectra of the dye molecules.

Synthesis and Reduction of Bimetallic Methyl-Bridged Rare-Earth Metal Complexes, [(C5H4SiMe3)2Ln(μ-CH3)]2 (Ln = Y, Tb, Dy).

The complexes [Cp′2Ln(μ-CH3)]2, (Cp′ = C5H4SiMe3; Ln = Y, Tb, Dy) were reduced to determine if these methyl-bridged complexes would form mixed valent 4fn5d1 Ln(II)/4fn Ln(III) compounds or bimetallic 4fn5d1 Ln(II) compounds containing 5d1–5d1 metal–metal bonds upon reduction. Reaction of the known bridged-chloride complexes, [Cp′2Ln(μ-Cl)]2, 1-Ln (Ln = Y, Tb, Dy), with MeLi forms the bridged-methyl complexes [Cp′2Ln(μ-CH3)]2, 2-Ln, which were crystallographically characterized for Tb and Dy. KC8 reduction of 2-Ln in the presence of 2.2.2-cryptand produced 3-Y, 3-Tb, and 3-Dy, which exhibited intense dark colors and broad absorbance peaks around 400 nm with molar extinction coefficients of 1700, 2300, and 1800 M–1 cm–1, respectively, which are characteristics of Ln(II) ions. The dark maroon 3-Y product had an axial electron paramagnetic resonance spectrum at 77 K (g1 = 1.99, A1 = 17.9 G; g2 = 2.00, A2 = 17.7 G) and a two-line isotropic spectrum at 273 K (g = 1.99, A = 18.4 G), which indicates that an Y(II) ion is present. Although these results are indicative of Ln(II) ions present in the solution, crystallographic evidence was not obtained to establish the structure of these complexes.

Wave propagation in initially-stressed elastic rods

This paper presents a study of incremental wave motion in elastic media with initial stress. Alternative formulations of the governing equations are examined as independent developments as well as special cases of a general theory in which the strain energy function is written in terms of deformation and initial stress. An application to a straight rod of circular cross is considered by means of a semidiscrete finite-element approximation that enables us to explore the effects of initial axial tension on the torsional, axial and flexural spectra and, furthermore, suggest paths toward estimation of the coefficients arising in the general theory.

Vibration Traits and Mechanism Analysis of an Engine Blades Fracture Failure

For the failure of twice centrifugal wheel blade fracture of an engine, the paper obtained the vibration traits of the fracture failure by analyzing the gross trend, time domain wave type, axial trajectory map and frequency spectrum diagram of the vibration signals at the failure time. The failure mechanism was analysed systematically based on the failure analysis of the fracture vane, the vibration characteristic analysis and stress distributing research of the vane. Finally, the paper verified the failure mechanism through the vane dynamic stress measurement test.

Investigation on Axial Displacement Fault Mechanism Based on Dynamic Characteristic Coefficients Identification of Tilting-Pad Thrust Bearing

To prevent the thrust bearing damage faults, the thrust bearing pad temperature and the static axial displacement variation are usually monitored and cared about, but axial vibration caused by axial dynamic excitation can also result in the severe rubbing. An electric oil pump system with overflow valve is designed on a similar industrial centrifugal compressor test-rig to apply the axial low-frequency excitation from 3 to 7 Hz, and the axial and radial vibration response amplitudes are analyzed. Then, the stiffness and damping coefficients of tilting-pad thrust bearing (TPTB) are identified by instrumental variable filter (IVF) algorithm to reveal the mechanism of TPTB dynamic characteristics affecting axial vibration. Finally, a fault case about surge and the rubbing of thrust bearing is studied. Compared with axial vibration, radial vibration does not directly correlate to axial excitation, and the axial frequency spectrum is an effective method to diagnose axial displacement faults; the static axial load, the dynamic excitation amplitude and the excitation frequency all exert influence on thrust bearing dynamic characteristics and axial vibration response. The research results can guide the design of thrust bearings and help to diagnose the axial displacement faults, while the test device and method can be used to measure the static and dynamic characteristics of thrust bearings.

Quasi-two-dimensional nonlinear evolution of helical magnetorotational instability in a magnetized Taylor–Couette flow

Magnetorotational instability (MRI) is one of the fundamental processes in astrophysics, driving angular momentum transport and mass accretion in a wide variety of cosmic objects. Despite much theoretical/numerical and experimental efforts over the last decades, its saturation mechanism and amplitude, which sets the angular momentum transport rate, remains not well understood, especially in the limit of high resistivity, or small magnetic Prandtl numbers typical to interiors (dead zones) of protoplanetary disks, liquid cores of planets and liquid metals in laboratory. Using direct numerical simulations, in this paper we investigate the nonlinear development and saturation properties of the helical magnetorotational instability (HMRI)—a relative of the standard MRI—in a magnetized Taylor–Couette flow at very low magnetic Prandtl number (correspondingly at low magnetic Reynolds number) relevant to liquid metals. For simplicity, the ratio of azimuthal field to axial field is kept fixed. From the linear theory of HMRI, it is known that the Elsasser number, or interaction parameter determines its growth rate and plays a special role in the dynamics. We show that this parameter is also important in the nonlinear problem. By increasing its value, a sudden transition from weakly nonlinear, where the system is slightly above the linear stability threshold, to strongly nonlinear, or turbulent regime occurs. We calculate the azimuthal and axial energy spectra corresponding to these two regimes and show that they differ qualitatively. Remarkably, the nonlinear state remains in all cases nearly axisymmetric suggesting that this HMRI-driven turbulence is quasi two-dimensional in nature. Although the contribution of non-axisymmetric modes increases moderately with the Elsasser number, their total energy remains much smaller than that of the axisymmetric ones.

Synthesis, spectral characterization, thermal studies and biological activity of (Z)‐5‐((1,5‐dimethyl‐3‐oxo‐2‐phenyl‐2,3‐dihydro‐1H‐pyrazol‐4‐yl)diazenyl)‐6‐hydroxy‐2‐mercaptopyrimidin‐4(3H)‐one and its metal complexes

(Z)‐5‐((1,5‐Dimethyl‐3‐oxo‐2‐phenyl‐2,3‐dihydro‐1H‐pyrazol‐4‐yl)diazenyl)‐6‐hydroxy‐2‐mercaptopyrimidin‐4(3H)‐one (H3L) was exploited as a ligand for the synthesis of a series of metal complexes, where the metal was Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Pd(II), Cr(III) and Ru(III). The structural features of the ligand and the synthesized complexes were characterized using various analytical, spectral and thermal measurements. Infrared spectra showed that the ligand coordinates to all metal ions in a neutral keto–enol–thiol manner. It behaves in a tetradentate fashion in all binuclear complexes except the Cr(III) complex, where it is hexadentate, and in a tridentate fashion in mononuclear complexes. The azo group participates in chelation only in the case of binuclear complexes. All complexes exhibit octahedral geometry except Pd(II) and Cu(II) acetate which are square planar and square pyramidal, respectively. Kinetic parameters were computed from thermal decomposition data. Axial electron spin resonance spectra were obtained for Cu(II) complexes indicating ()1as a ground state with smallg||values affording strong interaction between the ligand and metal ions. The biological measurements reveal that the ligand has antioxidant activity relative to the metal complexes, while the metal complexes have cytotoxicity in comparison to the free ligand.

On the emerging flow from a dual-axial counter-rotating swirler; LES simulation and spectral transition

The LES of a dual counter-rotating axial swirler in a confined rectangular configuration was performed under cold flow conditions. As the first objective of this paper, the grids were constructed based on a primary RANS simulation and then refined relative the Kolmogorov length scale using a field function. This greatly aided the construction of a very fine and effective grid whereby all the required criteria for an LES could be met. For the sake of validation, results in terms of mean structures were compared to existing 2D PIV experimental data using water as the working fluid. The achievement of very good agreement between the results has presented the opportunity to study the flow behavior in unsteady state conditions. The available experimental facility suffers from a similar drawback and always results in measurements a few millimeters after the flare down to downstream, while the region before the flare with high swirling interaction remains inaccessible. The second objective of this study was to study the flow behavior merely within the region before the flare location. Previous investigations have shown that the inner axial swirler greatly reduces the interaction with the outer counter-rotating swirler; a few millimeters away from the swirler, there is no sign of the inner swirler motion. Additionally, previous studies have related the formation of Precessing Vortex Core (PVC) within the central core to the peaks of the pressure or axial velocity spectrum. In addition, in some cases, up to two distinct peaks have been reported at the swirler mouth [1–3]. However, the spectrum analysis under iso-thermal conditions at the region inside the swirler, where the inner swirler dominates the flow, showed a higher potential for instabilities, with three to four distinct peaks. It was observed that, moving forward, the number of peaks is decreased, and in certain areas where the experimental measurement is applicable, the number of peaks decreased to two and one distinct points. In addition, the co-variance of the identified regions of axial and tangential velocity showed a higher correlation. The data show that the central axis corresponds to a lack of peaks of instabilities, whereas further away in the radial direction, several peaks exist. These results both emphasize the importance of the region inside the swirler where the primitive mixture of fuel and swirling air is constructed and aid in identifying the source of instabilities.

Orthogonal time-of-flight mass spectrometry of an ion beam with a broad kinetic energy profile.

A combined experimental and modeling effort is undertaken to assess a detection system composed of an orthogonal extraction time-of-flight (TOF) mass spectrometer coupled to a continuous ion source emitting an ion beam with kinetic energy of several hundred eV. The continuous ion source comprises an electrospray capillary system employing an undiluted ionic liquid emitting directly into vacuum. The resulting ion beam consists of ions with kinetic energy distributions of width greater than a hundred of eV and mass-to-charge (m/q) ratios ranging from 111 to 500 000 amu/q. In particular, the investigation aims to demonstrate the kinetic energy resolution along the ion beam axis (axial) of orthogonally extracted ions in measurements of the axial kinetic energy-specific mass spectrum, mass flow rate, and total ion current. The described instrument is capable of simultaneous measurement of a broad m/q range in a single acquisition cycle with approximately 25 eV/q axial kinetic energy resolution. Mass resolutions of ∼340 (M/ΔM, FWHM) were obtained for ions at m/q = 1974. Comparison of the orthogonally extracted TOF mass spectrum to mass flow and ion current measurements obtained with a quartz-crystal microbalance and Faraday cup, respectively, shows reasonable numeric agreement and qualitative agreement in the trend as a function of energy defect.

The effects of magnetic field topology on secondary neutron spectra in Magnetized Liner Inertial Fusion

The Magnetized Liner Inertial Fusion (MagLIF) concept involves the compression of a magnetized fuel such that the stagnated fuel contains a magnetic field that can suppress heat flow losses and confine α particles. Magnetic confinement of α particles reduces the fuel ρR required for ignition. Recent work [1,2] has demonstrated that the magnitude of the magnetic field in deuterium fuel can be inferred from the yields and spectra of secondary DT neutrons. In this work we investigate the potential for using the shape of the secondary neutron spectra to diagnose the magnetic field topology in the stagnated fuel. Three different field topologies that could possibly occur in MagLIF experiments are studied: (1) a cylindrical fuel column containing axial and azimuthal magnetic field components, (2) a fuel column which is pinched at the ends to form a magnetic mirror and (3) a fuel column that has a helical tube shape with magnetic field lines following the helical path of the tube’s axis. Each topology is motivated by observations from experimental or simulated MagLIF data. For each topology we use a multi-physics model to investigate the shapes of the secondary neutron spectra emitted from a steady-state stagnated fuel column. It is found that the azimuthal and helical topologies are more suitable than the mirror topology for reproducing an asymmetry in the axial spectra that was observed in experiments. Gorgon MHD simulations of the MagLIF implosion in 1D are also carried out. These show that sufficient azimuthal magnetic field can penetrate from the liner into the fuel to qualitatively reproduce the observed spectral asymmetry.

COMPARISON OF NON-RADIOGRAPHIC SPONDYLOARTHRITIS VERSUS ANKYLOSING SPONDYLITIS PATIENTS UNDERGOING BIOLOGICAL THERAPY – DATA FROM A ROMANIAN COHORT

Both non-radiographic spondyloarthritis (nr-SpA) and ankylosing spondylitis (AS) are medical conditions that belong to the axial spondyloarthritis spectrum; these two terms reveal the extent of sacroiliitis assessed by conventional x-ray or MRI. According to the latest classification criteria (ASAS, 2009), clinicians are able to differentiate patients with nr-SpA from AS and to follow their disease progression. The present study aims to compare the two patient categories undergoing biological therapy with an anti-TNF agent and indicate distinct disease features. We included 94 patients in treatment with IFX, ADL, ETA or GOL and monitored clinical, biological and disease activity parameters. The nr-SpA subgroup included a higher percentage of female patients; AS patients presented higher values of the CRP at follow-up visits; there were no significant differences between the two groups regarding the HLA-B27 presence, uveitis history or smoking status. Patients with an inactive disease status had a lower BMI, shorter disease duration and an early initiation of biological therapy, so that we suggest a close and regular monitoring of these two entities.

Developing an optional multiple repeated load test to evaluate permanent deformation of asphalt mixtures based on axle load spectrum

An optional multiple repeated load (OMRL) test, capable of simulating the axial load spectrum in real pavement, was developed to evaluate the rutting susceptibility of asphalt mixture. This new test was conducted at the temperature of 60°C under multiple stresses determined by a simplified axle load spectrum considering the pavement management system (PMS). A pre-stage dynamic creep test was employed to determine the loading cycles of the first increment. Two kinds of asphalt mixtures were compared in the OMRL test with varying orders of multiple stresses and they were also tested in dynamic creep test under five different loading levels. As the test results show, loading sequences have a significant impact on the high-temperature performance of asphalt mixtures. The curve of permanent strain rate versus stress level could fit well with a power-law model in the dynamic creep test, and a similar result can be obtained by the OMRL test. However, the OMRL test shows higher efficiency than the traditional dynamic creep test. Besides, the secondary stage of the OMRL test fits a broken-line model since various stress levels are conducted on the specimen. The newly proposed lowest average strain rate (LASR) and multiple flow number (MFN) could evaluate the rutting resistance of asphalt mixtures under a more realistic loading condition. Overall, this OMRL test provides a better understanding of the rutting behavior of asphalt mixtures to improve the mix design and field performance.

Possibilities for Continuous Frequency Tuning in Terahertz Gyrotrons with Nontunable Electrodynamic Systems

Large ohmic losses in the cavities of terahertz gyrotrons may lead to the overlapping of the axial mode spectra. In a number of gyrotron experiments, this effect has been used to provide a fairly broadband frequency tuning by changing appropriately the operating magnetic field and/or accelerating voltage of the gyrotron. Similar to the systems with nonfixed axial structure of the RF electromagnetic field and low diffraction quality, which are due to weak reflections of the operating wave from the collector end of the electrodynamic system, this changing leads to a monotonic change in the axial index of the operating wave and transition from the gyrotron regime to the gyro-BWO regime. According to a theoretical comparison of these two methods performed on the basis of generalization of self-consistent gyrotron equations with allowance for variations in the axial electron momenta, low-reflection systems can provide a higher efficiency and monotonicity of the frequency tuning.