RU2422939C1 - Method of generating two-dimensional linear electric field and device for realising said method - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: invention relates to mass-spectrometry based on movement of charged particles in two-dimensional linear high-frequency electric fields, and can be used to improve design of mass analysers and improve analytical and commercial characteristics thereof. The device for generating such fields has flat electrodes with potential distribution which is discrete and linear on one coordinate. In order to improve the design and system for high-frequency powering analysers, electric fields which are linear on two coordinates are generated using two discrete electrodes made from thin metal filaments with opposite potential and three continuous earthed electrodes. The required field in the working area of the analyser is generated through non-uniform distribution of coordinates of the filaments in planes of the discrete electrodes, where charges on the electrodes along one of the axis are distributed according to a discrete linear law. ^ EFFECT: improved design of analysers with two-dimensional linear electric fields, enabling their use in making energy and mass analysers. ^ 2 cl, 1 dwg

Description

The invention relates to the field of mass spectrometry, which is based on the movement of charged particles in two-dimensional linear high-frequency electric fields, and can be used to improve the design of mass spectrometric devices and improve their analytical and commercial characteristics. Mac analyzers with hyperbolic electrodes are ineffective for the formation of two-dimensional linear electric fields with working areas extended along one coordinate [1]. Analyzers with flat electrodes with a discrete linear potential distribution [2] and with a linearly distributed capacity of discrete elements [3] solve this problem. The technical task of the invention is to improve the structural and technological characteristics of devices for the formation of two-dimensional linear electric fields using systems with flat discrete electrodes.

The formation of two-dimensional linear electric field in the working area of the analyzer with the dimensions 2 _0, y _0, L along the axes X, Y, Z ₀ when y >> x ₀ may be accomplished as in [2,3], using a system of planar discrete and solid electrodes. It is known from electrostatics that the electric field of a system of charges is determined on the basis of the principle of superposition as the sum of the fields created by individual charges. In this case, the problem of the formation of electric fields with a given potential distribution in a certain region of space can be solved by creating the required distribution of surface charges at the boundaries of this region. For the case of a two-dimensional linear field, extended along one axis Y, the problem is reduced to creating on the surfaces x = x ₀ and x = -x ₀ linear distributions of charge densities of opposite sign along the coordinate y. It is difficult to create the practically required charge distribution on a continuous conducting surface. The problem is solved using conductive surfaces consisting of many discrete elements [2,3]. From the point of view of practical implementation, discrete conducting surfaces consisting of identical equipotential elements are of interest. The required one-dimensional charge distribution on flat surfaces in this case is formed by changing the density of elements of the discrete surface along one coordinate. For the formation of a two-dimensional linear electric field with a working region extended along the Y axis, it is sufficient to use two flat, discrete along the y coordinate, conducting surfaces x = x ₀ and x = -x ₀ . In a first approximation, if we do not take into account the electrostatic interactions between surface elements, the distribution of charge densities and element densities on discrete surfaces along the y coordinate, we can assume that the proportionality relation is related to each other. It follows that for the formation of a linear electric field along the X and Y axes, the coordinates y _{i of the} elements of discrete surfaces x = x ₀ and x = -x ₀ must be calculated by the formula

where y ₁ is the coordinate of the first element, i is the serial number of the discrete elements of the surfaces. The formula is valid provided that the size d of the discrete elements in the x and y coordinates is much smaller than the distances between them. In this case, thin metal filaments of a round or other cross section can be used as discrete elements of the conductive surfaces parallel to the Z axis.

For the case of filaments of circular cross section, an analyzer with a linear electric field along the X and Y axes created by charges discontinuously distributed over the coordinate y is shown in FIG. 1. The analyzer consists of two flat discrete electrodes 1 and 2, located in the planes x = x ₀ and x = -x ₀ , composed of metal threads parallel to the Z axis of length L and diameter d << x ₀ , two solid electrodes 3 and 4 with dimensions y ₀ and L along the axes Y and Z located in the planes x = x ₀ + h and x = -x ₀ -h and one continuous electrode 5 with dimensions 2x ₀ and L along the axes X and Z, located in the plane y = 0 . The electrodes 3, 4 and 5 are grounded, and the antiphase potentials -φ and φ are applied to the electrodes 1 and 2. Electrodes 3 and 4 act as screens, and 1, 2, and 5 are field-forming electrodes of the analyzer. If the diameters and potentials of the filaments are equal, the density of charge distribution on them will be the same. If the coordinates of the centers of the threads are determined by the formula (1), the charge density distribution on the electrodes 1 and 2 along the Y axis will be described by a discrete-linear law. In this case, an electric field close to linear in the x and y coordinates is formed in the analyzer's working area x <x ₀ .

The degree of linearity of the field is limited by the discreteness of the electrodes, electrostatic bonds between the elements of the electrodes and the final dimensions of the electrodes along the coordinate y. Deviations of the field from the linear one due to the discreteness of the electrodes can be reduced to the required level by limiting the size of the analyzer working area along the X axis. The nonlinearity of the electric field arising for two other reasons is minimized by correcting the coordinate distribution of the filaments by adding to (1) a polynomial function of the form

The coefficients a ₀ , a ₁ , a _2, a _{3 ...} for given geometric parameters x ₀ , y ₀ , d and h are determined in the process of computer simulation of the electric field in an analyzer with flat electrodes from conducting wires according to the criterion of the minimum deviation of the calculated potential distribution in the working regions | x | <x ₁ , y <y ₁ from a two-dimensional linear distribution.

The technological design of the proposed analyzer with flat continuous and discrete electrodes made of thin metal filaments and a simple method of electric power supply make it possible to create effective devices for focusing, energy and mass analysis of charged particles with high analytical and commercial characteristics on its basis.

The drawing shows a diagram of a charged particle analyzer with a two-dimensional linear electric field along the X and Y axes, 1, 2 - flat discrete electrodes of thin metal filaments; 3, 4 - flat grounded shielding electrodes; 5 - flat grounded field-forming electrode.

LITERATURE

1. Mamontov E.V., Gurov V.S., Filippov I.V., Dyatlov R.N. Time-of-flight separation of ions by specific charge in high-frequency fields with a quadratic potential distribution // Zh. - 2007. - T.77. - Issue 7. - S.139-142.

2. Mamontov E.V., Filippov I.V. The method of mass-selective analysis of ions by time of flight and a device for its implementation // Patent for the invention No. 23237245 from 05/03/2006.

3. Gurov V.S., Mamontov E.V., Diaghilev A.A. Electrode systems with a discrete linear distribution of the RF potential // Mass spectrometry. - 2007. - T.4. - No. 2. - S.139-142.

Claims (2)

1. A method of forming a two-dimensional linear electric field, comprising establishing the boundaries of the field plane parallel to Z axis conductive surfaces with dimensions 2x _0, y _0, and L along the axes X, Y and Z, characterized in that the conductor used as two discrete with opposite potentials φ and -φ, the surfaces x = x ₀ and x = -x ₀ , composed of thin conductive threads parallel to the Z axis and located at different distances from each other along the Y axis, and three continuous grounded surfaces x = x ₀ + h and x = -x ₀ - h and y = 0. 2. Device for the formation of a two-dimensional linear electric field, containing electrodes parallel to the Z axis, length L, where L> 2x ₀ , with potentials applied to them, characterized in that two discrete located in the planes x = x ₀ and x = -x _{0 are used} made up of thin metal filaments parallel to the Z axis with coordinates proportional to the square root of the number of filaments, an electrode with a size of ₀ on the Y axis with opposite potentials φ and -φ applied to them, and three solid grounded electrodes, two of which are of size y ₀ p about the Y axis are located in the planes x = x ₀ + h and x = -x ₀ -h and one with size 2 (x ₀ + h) along the X axis is located in the plane y = 0.