Experimental study on the acceptance of a quadrupole mass filter

The acceptance of a quadrupole mass filter is studied by means of a small alkali ion source movable under vacuum. Experimental results are in agreement with Dawson's theoretical calculations.     

Acceptance and transmittance of a quadrupole mass filter with amplitude modulation of RF voltage with allowance for an edge field

A method for calculating the acceptance of a quadrupole mass filter with amplitude modulation of rf voltage is developed. The key factor in determining the transformation of the phase ellipse by edge fields is taking into account the phase shift of the rf field during motion of ions in the input edge field. The variation of the combined acceptance depending on the axial energy of ions (or the transit time of ions through the edge field) is in conformity with the rated transmittance, which is an indirect indication of the correctness of the proposed approach.     

Spatial harmonics of the field in a quadrupole mass filter with circular electrodes

The amplitudes of the spatial harmonics of the field are calculated for given displacements of the electrodes in a quadrupole mass filter relative to their optimum positions. The cases of radial and angular displacements of the electrodes, asymmetries in voltage supplied to the electrodes, and nonidentical rod diameters are considered. These data are required for calculating the actual shape of the mass peaks and will be useful in designing mass filters. Zh. Tekh. Fiz. 69, 96–101 (October 1999)     

Acceptance of the quadrupole mass filter in the upper stability island under biharmonic excitation

Dynamic characteristics of the quadrupole mass filter (QMF) with the parametric resonance excitation of ion oscillations by a low additional HF voltage are studied by numerical methods. The upper stability island formed by instability bands that follow the isolines of stability parameters of the unperturbed first stability band is considered. Isolines of characteristic indices on the island’s parameter plane are calculated. Ion trajectories at characteristic points near the x and y island boundaries, which have the form of beats, are presented. Parameters of the ellipses are determined as functions of the initial phase at which the ions enter the HF field. These parameters are shown to be periodic with a period of π with respect to the phase shift between the main and additional HF voltages. As a result, the QMF acceptance and, consequently, transmittance have maxima as functions of the phase shift. Therefore, to increase the QMF transmittance, the biharmonic signal must be synchronized.     

Simulation of ion-optical systems for mass spectrometers with a quadrupole mass filter

Ion-optical systems with intermediate focusing and parallel extraction of the ion beam are simulated. The systems may be integrated with a quadrupole mass filter in order to improve the analytical properties of the latter.     

Acceptance and transmission of a quadrupole mass filter with a prefilter

We have proposed an analytical model of a quadrupole mass filter with an additional rf quadrupole (prefilter) at its entry, which is based on the model of a transient field in the region between the edges of the mass filter electrodes and the prefilter electrodes. The characteristics of the complex mass filter have been investigated by the methods of phase space dynamics. In the presence of the entrance prefilter, instead of the entrance diaphragm, the y acceptance increases by 1.5 times relative to the x acceptance. Upon an increase in the ion residence time in the fringing field, the y acceptance contour exhibits the tendency to rotation on the phase plane, while the x acceptance contour is broadened in the x coordinate. The transmission function increases and oscillates upon an increase in the ion residence time in the fringing field. The result of numerical experiment using the SIMION 8 software differs from the result of analytical calculation by 14% for the x acceptance and by 35% for the y acceptance.     

A detailed study of the quadrupole mass filter operating with no d.c. component of the rods

A report is given of the results of an extensive series of measurements of the quadrupole mass spectrometer performance when operating in the retarding mode. It is shown that this mode has some significant advantages over conventional operation for the mass range 40–500 a.m.u. In particular, there is less dependence upon mechanical imperfections in the quadrupole lens assembly, with consequent improvement in long term stability. Also, because the analyser operates without any applied d.c. voltage, the defocussing action at its entrance is reduced and therefore mass discrimination reduced. Satellite peaks have been identified as arising from third- and fourth-order disturbances in the quadrupole field. Mapping the position of these satellites over the whole stability region helps the understanding of the effect of field imperfections.     

Analysis of the quadrupole mass filter with quadrupole excitation by the envelope equation method

The method of the envelope equation has been developed to describe the stability of the motion of ions in a quadrupole mass filter in the presence of periodic excitations of the feeding voltage. Dynamic equations that describe the variations in the envelope of ion vibrations in the vicinity of the vertex of the first common stability region have been obtained and reduced to the form of the Mathieu equations. The splitting of the stability diagram of the motion of ions into stability islands due to excitation has been described. The results of the approximate theory have been confirmed by an exact analysis of the stability diagram for rational values of the relative excitation frequency. The boundaries of the applicability domain for the developed theory limited by first-order resonances have been determined.     

Concept of the effective potential in describing the motion of ions in a quadrupole mass filter

We propose a generalization of the effective potential theory for the motion of particles in a rapidly oscillating electric field for the stability parameters lying near the boundary of the diagram where the standard effective potential theory is inapplicable. We derive the dynamic equations describing the variation of the envelope of ion oscillations for the motion of ions near the stability vertex of the first zone of the quadrupole mass filter. We reduce them to the form of the Hamilton equations for oscillations of a material particle in the field of potential forces. We obtain expressions for the effective potential well. It is shown that in spite of the high kinetic energy of oscillations, the depth of the effective potential well for ions in the quadrupole is less than 1 eV in the case of filtration with a mass resolution exceeding 200 units. The acceptance of the mass filter is calculated as a function of the stability parameters and the resolving power.     

Effect of an electric field on the limits of liquid stability

When electric fields are applied to metastable liquids, the energy barrier for nucleation of the vapor phase will increase. Reported observations of field-induced nucleation should not be used to infer stability limits of bulk liquids.     

Effect of a weak static magnetic field on nitrogen-14 quadrupole resonance in the case of an axially symmetric electric field gradient tensor

The application of a weak static B₀ magnetic field (less than 1 mT) may produce a well-defined splitting of the ¹⁴N Quadrupole Resonance line when the electric field gradient tensor at the nitrogen nucleus level is of axial symmetry. It is theoretically shown and experimentally confirmed that the actual splitting (when it exists) as well as the line-shape and the signal intensity depends on three factors: (i) the amplitude of B₀, (ii) the amplitude and pulse duration of the radio-frequency field, B₁, used for detecting the NQR signal, and (iii) the relative orientation of B₀ and B₁. For instance, when B₀ is parallel to B₁ and regardless of the B₀ value, the signal intensity is three times larger than when B₀ is perpendicular to B₁. This point is of some importance in practice since NQR measurements are almost always performed in the earth field. Moreover, in the course of this study, it has been recognized that important pieces of information regarding line-shape are contained in data points at the beginning of the free induction decay (fid) which, in practice, are eliminated for avoiding spurious signals due to probe ringing. It has been found that these data points can generally be retrieved by linear prediction (LP) procedures. As a further LP benefit, the signal intensity loss (by about a factor of three) is regained.     

SHF频段超宽带高温超导滤波器的研制

针对超宽带通信系统的发展趋势,采用1/4波长短截线结构设计了一个工作于超高频(SHF)频段的超宽带高温超导滤波器,滤波器的中心频率为4.2 GHz,相对带宽为50%,讨论了1/4波长短截线结构滤波器的设计原理,给出了所设计超宽带滤波器的理论曲线、模拟仿真结果。实际制作的超宽带高温超导滤波器的测量曲线与模拟仿真曲线基本吻合,得到了满意的结果。     

Approximate calculation of the resolving power of a quadrupole mass filter as a function of the number of ion oscillations

The paper presents a theoretical solution to the investigated problem. The final relation is in qualitative agreement with that found experimentally in earlier papers; quantitatively, however, it gives a smaller number of ion oscillations in the quadrupole field for obtaining the necessary resolving power than does the experimental relation. Simultaneously, it points to the existence of other parameters influencing this dependence. It follows from a comparison of the theory and experiment that there probably exists another process not theoretically explained so far, which influences the experimental data.     

The use of stability bands to improve the performance of quadrupole mass filters

The possibility of increasing the resolving power of quadrupole mass filters has been discussed. It has been shown that the limitations associated with the finite time of flight imposed by Von Zahn’s rule are modified while using the islands of stability that appear when quadrupole is excited by the additional signals. By calculation of the exponential increment of growth of the oscillation amplitude the effect of the acceleration of mass separation and improvement of the peak shape, when the islands of stability are used for ion filtering, is explained. The case of the excitation by two signals at different frequencies has been studied theoretically. The conditions under which suppression of the first order resonance for one of the directions of motion is obtained. The direct modeling of the peak shape of the mass filter shows the possibility of obtaining a resolution of 10,000 with a time of flight of ions through the quadrupole of 100 cycles of the main RF supply, and low sensitivity of the new operating mode to the nonlinear field distortions in the quadrupoles with rods of circular cross sections.     

Determination of the field singularity index at the edge of a gyrotropic structure

Physicotechnical Institute, Tomsk University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, No. 10, pp. 1350–1352, October, 1994.     

Effect of a magnetic field on the dipole echo in glasses caused by nuclear quadrupole moments

The effect of a magnetic field on the amplitude of the dipole echo in glasses at a temperature of about 10 mK caused by the presence of nonspherical nuclei with electric quadrupole moments in the glass has been considered theoretically. It has been shown that in this case, the two-level systems (TLSs) that determine the properties of glasses at low temperatures are transformed into more complicated multilevel systems. These systems have new properties as compared to usual TLSs and, in particular, exhibit oscillations of the electric dipole echo amplitude in the magnetic field. A general formula that describes the echo amplitude in an arbitrarily split TLS has been derived in perturbation theory. Detailed analytic and numerical analysis of the formula has been performed. The theory agrees qualitatively and quantitatively well with the experimental data.     

Laser spectroscopy on molecular beam with a time-of-flight mass spectrometer operating in a strong magnetic field

Experimental set-up for studying effects of a strong magnetic field on a structure and a decay dynamics of molecules, was designed and constructed. A vacuum chamber, in which a molecular beam propagated, was mounted in a bore of a superconducting magnet. Laser light crossed the molecular beam in the magnetic field and excited the molecules. Fragment or parent ions produced through sequential decay processes, were extracted by an electric field parallel to the magnetic field and detected by a microchannel plate. By measuring the time-of-flight from the photo-excitation to the ion-detection, a species of ions —mass and charge state— was identified. A performance of the set-up was demonstrated using the resonance enhanced multiphoton ionization process through the X²Π-A²Σ⁺ transition of nitric oxide (NO) molecules. A mass resolution m/Δm ≥180±6 was obtained in the field up to 10 T. This was the first successful result demonstrating the sufficient mass resolution obtained by the time-of-flight technique in the strong magnetic field up to 10 T. Parent NO⁺ ions were selectively detected by the mass spectrometer and the ion current was measured as a function of the frequency of the laser light. Rotational transition lines were measured with a sufficient S/N ratio in the field up to 10 T.     

Effect of an electric field on the surface tension of a liquid at low temperatures

An external electric field changes the dispersion law of waves on the surface of a liquid. Besides the usual capillary term (∝k ³, k is the wave number) and gravitational term (∝k), a term quadratic in the wave vector appears in the expression for the square of the frequency in a homogeneous field. These excitations are associated with the variation of the coefficient of surface tension of the liquid at low temperatures. In the case of a large field tangent to the surface, the correction is proportional to T ^8/3, unlike the T ^7/3 correction in the absence of a field. Zh. éksp. Teor. Fiz. 111, 1369–1372 (April 1997)     

Luttinger liquid at the edge of undoped graphene in a strong magnetic field

We demonstrate that an undoped two-dimensional carbon plane (graphene) whose bulk is in the integer quantum Hall regime supports a nonchiral Luttinger liquid at an armchair edge. This behavior arises due to the unusual dispersion of the noninteracting edge states, causing a crossing of bands with different valley and spin indices at the edge. We demonstrate that this stabilizes a domain wall structure with a spontaneously ordered phase degree of freedom. This coherent domain wall supports gapless charged excitations, and has a power law tunneling I-V with a nonintegral exponent. In proximity to a bulk lead, the edge may undergo a quantum phase transition between the Luttinger liquid phase and a metallic state.