RU2487449C1 - Solenoid coil of cesium atomic beam tube - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: solenoid coil of cesium atomic beam tube contains two identical coils placed inside the system of magnetic screens at both sides of U-type SHF resonator along its axial plane and equispaced from it; each coil represents a rectangular frame of linear conductors with bridges and at each side of the frame bridges are divided into two equal parts and incurved smoothly perpendicular to axial plane of the resonator, at that one part is incurved in direction to the resonator while the other one in the opposite direction; incurve height towards the resonator h1 and incurve height in the opposite direction 2 are defined be the following conditions: 2≤h1/H≤0.6, 0.4≤h2/H≤0.8, where H is the distance between frames. Ratio of the frame width S and distance between frames H is equal to H/S=tg30°.

EFFECT: capability to decrease of magnetic frequency shift and increase of frequency stability for cesium atomic beam tubes.

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Description

The invention relates to techniques for quantum frequency standards based on cesium atomic ray tubes (ALT) used in various navigation systems, including the GLONASS Russian global navigation satellite system. The navigational accuracy of the entire GLONASS system is determined by the metrological parameters of cesium ALT, which perform the function of high-quality frequency discriminators in frequency standards [1].

For GLONASS equipment of the new generation, the task is to increase the frequency maintenance accuracy by on-board standards by an order of magnitude up to the level of 1.0 · 10 ^-14 or less.

In cesium atomic ray tubes, in order to remove the degeneracy of the energy levels of cesium atoms in the drift space in the region of the microwave cavity, it is necessary to maintain a weak uniform magnetic field (field "C") with a strength of about 0.1 Oe, which creates a given spatial orientation of the magnetic moments of cesium atoms.

Field "C" is formed by a solenoid, which is installed together with the microwave cavity inside the multilayer magnetic casing, which serves to shield the ALT from the disturbing action of external magnetic fields.

In works on improving traditional cesium ALTs with magnetic selection of atomic states and new-generation laser ALTs, special attention is paid to the analysis of multifactor frequency shifts, including the magnetic frequency shift due to the inhomogeneity of the “C” field in the microwave cavity [2, 3]. In stationary devices of the metrological class, the non-uniformity of the magnetization field in the transit space of the microwave cavity can be reduced to a value of 4 · 10 ^-4 (0.04%) [4]. The characteristic dimensions of such devices are a length of about 2 meters (a cavity length of 1030 mm) and a diameter of about one meter. Onboard ALTs designed to operate as part of GLONASS satellites are very compact and have a length of 500 mm, a diameter of 120 mm, and a mass of 10 kg. The heterogeneity of the magnetization field in the flyby space of the microwave resonator of the onboard ALT is about 1.0%. Such heterogeneity leads to undesirable relative frequency shifts at the level Δf / f ₀₀ ~ 1 · 10 ^-12 , where f ₀₀ = 9191631770 Hz is the frequency of the working transition of cesium [3]. It is not possible to eliminate the indicated heterogeneity by increasing the size of the ALT, since for satellite devices the requirements for ensuring compactness and weight restrictions are very stringent.

In this regard, one of the urgent tasks in the design of onboard cesium ALT with high metrological characteristics is the development of a solenoid that creates a weak uniform magnetic field "C" with a minimal difference between the magnetic field strength in the areas of interaction of the atomic beam with the microwave field in spatially separated arms Microwave resonator and field strength in the transit space of the entire resonator.

The closest in technical essence to the proposed invention (prototype) is a cesium ALT solenoid [1, 5]. The solenoid is a system of rectangular frames, on the side surfaces of which coils are wound in the form of rectangular frames. The frames are arranged parallel and symmetrically with respect to the longitudinal plane of symmetry of the microwave cavity, made in the form of a rectangular waveguide with a cross section of 10 × 23 mm, which is given a U-shape by bending its ends along a narrow wall of the waveguide at an angle of 90 ° so that two resonators are formed spatially separated shoulder. Each arm is a segment of the waveguide in which at the distance of 23 mm (half the length of the standing wave in the waveguide, λ _in / 2) an antinode of the microwave magnetic field is created, the intensity vector of which is directed normal to the longitudinal plane of symmetry of the microwave resonator. In the same direction, the field strength vector “C” of the solenoid frame is oriented along the path of the cesium atomic beam. Each frame is formed by linear conductors with jumpers.

The disadvantage of the prototype solenoid is the large heterogeneity of the “C” field at about 1%, which is more than an order of magnitude higher than the requirements for cesium ALT for the new generation GLONASS system equipment. The indicated field inhomogeneity “C” value does not decrease when tightening tolerances on the mutual arrangement of the frames of the solenoid, microwave resonator, and the system of magnetic screens, because it is associated with the influence of the local magnetic field that arises between the bridge jumpers and the end disks of the inner screen located near them. The local field sags along the central axis of the solenoid in the gaps between the jumpers of each frame. As a result, the field strength “C” in the arms of the microwave cavity through which the atomic cesium stream passes is reduced.

The technical result of the invention is to reduce the magnetic frequency shift and increase the frequency stability of cesium ALT.

The proposed cesium atomic beam tube solenoid contains two identical coils located inside the system of magnetic screens on both sides of the U-shaped microwave resonator along the longitudinal plane of its symmetry and equidistant from it, each coil is a rectangular frame of linear conductors with jumpers, each the sides of the jumper frame are divided into two equal parts and smoothly bent perpendicular to the longitudinal plane of symmetry of the resonator, one part is bent towards the resonator, and the other part in the direction from the resonator, the bend height h1 to the resonator and the bend height h2 from the resonator are determined from the conditions: 0.2≤h1 / Н≤0.6, 0.4≤h2 / H≤0.8, where Н is the distance between the frames, while the width of the frames S and the distance between the frames H are in the ratio H / S = tg30 °.

The use in the solenoid of frames with jumpers divided into two equal parts and smoothly bent perpendicular to the longitudinal plane of symmetry of the resonator in such a way that one part is bent towards the resonator and the other part away from the resonator, for which the bend height h1 to the resonator and the bend height h2 from the resonator are determined from the conditions: 0.2≤h1 / Н≤0.6, 0.4≤h2 / Н≤0.8, where Н is the distance between the frames, provides an increase in the uniformity of the "C" field and a decrease in the magnetic frequency shift of the cesium ALT.

The upper limit of the bend height h1 of the jumpers towards the resonator is limited by the outer diameter of the central vacuum tube inside the ALT housing for transporting the atomic beam.

The upper limit of the bend height h2 of the jumper frames in the direction from the resonator is limited by the inner diameter of the cylindrical part of the magnetic screen, in the cavity of which a solenoid is installed.

The fulfillment of the ratio H / S = tg30 ° for the width of the frames S and the distance between the frames H improves the uniformity of the field "C" over the cross section of the atomic beam and increases the frequency stability of cesium ALT.

The invention is illustrated by drawings.

Figure 1 shows the calculated computer model of the proposed solenoid with surrounding magnetic screens, where

- first magnetic screen 1,

- second magnetic screen 2,

- third magnetic screen 3,

- forming plates 10,

- the first frame of the solenoid 4,

- jumpers of the first frame, bent in the direction from the resonator 5,

- jumpers of the first frame, bent towards the resonator 6,

- the second frame of the solenoid 7,

- jumpers of the second frame, bent towards the resonator 8,

- jumpers of the second frame, bent in the direction from the resonator 9,

- line conductors A, B, C, D.

Figure 2 shows the proposed solenoid and its location relative to the magnetic screens and the U-shaped microwave resonator in the planes Y = 0 (a) and Z = const (b), where

- first magnetic screen 1,

- second magnetic screen 2,

- third magnetic screen 3,

- the first frame of the solenoid 4,

- jumpers of the first frame, bent in the direction from the resonator 5,

- jumpers of the first frame, bent towards the resonator 6,

- the second frame of the solenoid 7,

- jumpers of the second frame, bent towards the resonator 8,

- jumpers of the second frame, bent in the direction from the resonator 9,

- forming plates 10,

- microwave resonator 11,

- the input gap of the microwave resonator 12,

- the output of the energy of the microwave cavity 13,

- a rectangular hole 14 in the wall of the microwave cavity.

Figure 3 shows the calculation results of the proposed solenoid in the form of isolines of the module of the field strength in the planes Y = 0 (a) and X = 0 (b), where

- first magnetic screen 1,

- second magnetic screen 2,

- third magnetic screen 3,

- forming plates 10,

- the first frame of the solenoid 4,

- jumpers of the first frame, bent in the direction from the resonator 5,

- jumpers of the first frame, bent towards the resonator 6,

- the second frame of the solenoid 7,

- jumpers of the second frame, bent towards the resonator 8,

- jumpers of the second frame, bent in the direction from the resonator 9,

- isolines of the field strength module 15.

Figure 4 shows the results of calculating the axial distribution function of the relative deviation of the field strength modulus at the current point Z from the field in the center of the frames Z = Z0 for the proposed design of the solenoid (curve 1) and the design of the prototype solenoid (curve 2).

Example.

The solenoid consists of two coils with a width of S = 55.4 mm, a length of L = 213 mm, a bend height of the bridges h1 = 7.5 mm and h2 = 11.4 mm. Each coil is wound on a caprolon frame in the form of a plate with a profile for bends. The coil is wound around the perimeter of the side surfaces of the frame with an insulated wire in one direction. An even number of ampere turns is wound, which ensures equal currents in the separated bent parts of the jumpers. Coils are installed on both sides of the resonator along the longitudinal plane of its symmetry at a distance of H = 32 mm between them. In this case, the ratio 32 / 55.4 = tg30 ° is fulfilled.

The solenoid operates as follows.

Direct current passes through the linear conductors A, B, C, D and jumpers 5, 6, 8, 9 of the frames 4, 7 and creates a magnetic field "C" in the solenoid. The direction of the current density vector in the conductors is shown by the arrows in figure 1.

Field “C” is created by a system of 4-line conductors A, B, C, D, the cross-section centers of which pass through the vertices of the rectangle with sides H and S. In conductors A, B of both frames, the current flows in one direction, and in conductors C, D - in the opposite direction. The field lines of the field of linear conductors with current envelope each pair of conductors A, B and C, D and are oriented perpendicular to the longitudinal plane of symmetry of the frames X = 0 and the wide side of the ribbon atomic beam passing through vertical rectangular holes 14 in the walls of the microwave resonator 11.

At the ends of the frames, the field “C” of the linear conductors A, B, C, D is added with the local fields of the jumpers 5, 6, 8, 9 located in the same plane Z = const at a close distance from the end disk of the inner screen 1. Due to the same current direction in the jumpers 5, 6, 8, 9 at the edges of each frame, the lines of force go around the jumpers and create a local field that is opposite to the field “C”. The intensity of the local field and the degree of permeability (along the Z axis) towards the center of the solenoid depend on the magnitude of the current and the distance (along the X axis) between the jumpers. In each frame with bent bent jumpers, the current value of the jumpers is reduced by 2 times and the distance between the jumpers is approximately halved. This reduces the intensity of the local field and its permeability to the end region of the frames, in which the gaps of the microwave cavity are located. As a result, the uniformity of the “C” field increases over the entire length of the resonator system — in the cavity gaps and in the region of the drift of the atomic beam between the gaps. The possibility of implementing the invention is confirmed by computer simulation of two design variants of the solenoid, one of which corresponded to the prototype [1, 5], and the other to the invention.

Computer simulation was performed using a three-dimensional mathematical model in which: the actual dimensions of the multilayer magnetic screen, the configuration of the conductors (frames) in different designs of the solenoids, the current value in the conductors of the solenoids (the product of the average current density by the cross-sectional area of the conductor), the direction of the current density vector along the conductors, magnetic characteristics (HV curves) of the shield materials (permalloy) and forming plates (iron - armco). The geometric dimensions are given in millimeters and marked on the axes of the Cartesian coordinate system XYZ in figure 2 and figure 3. The current value is set in milliamperes. The magnetic field strength is set in oersteds. The coordinate origin is chosen in the center of the rectangular hole in the input plane of the end disk of the screen 3. The coordinate axis Z is directed along the central axis of symmetry (X = Y = 0) of the screens and frames of the solenoid along the cesium atoms. The X and Y axes are directed, respectively, along the width and length of the rectangular hole in the screen 3. As a result of computer simulation, the magnetic field distributions are calculated for different design variants of the solenoid in the entire region of cesium ALT, including the internal cavity of screen 1, where the solenoid is located.

Figure 1 shows the calculated computer model (3D) of the proposed solenoid with bent bent jumpers surrounded by magnetic screens. The arrows indicate the direction of the DC density vector. Frames 4 and 7 with bent bent jumpers are located at the same distance from the plane X = 0. The bends of the jumpers in two frames are made according to the rule of mirror image frames relative to their central plane of symmetry X = 0. The centers of the cross-sections of the linear conductors of the frames (cross-section 2 × 2 mm ² ) are located at the vertices A, B, C, D of the rectangle with sides S and H, which are respectively taken as the width of the frames and the distance between the frames.

Figure 3 shows the results of computer simulation of the proposed design of the solenoid with bent bent jumpers in the form of a family of isolines of the magnetic field strength module. Shown are fragments of the computational domain in two planes Y = 0 (Fig. 3a) and X = 0 (Fig. 3b). The contour map shows the location of the end disks of the screens 1, 2, 3, the forming plates 10, the linear conductors and the bent bent jumpers 5, 6, 8, 9. The current in the linear conductors of the frames 4, 7 is 27 mA, and in each jumper - 13.5 mA The direction of the current density vector is shown as one-sided arrows (if a projection of one conductor with a given direction of the current density vector is shown) and as two-sided arrows (if combined projections of two conductors with the opposite direction of the current density vector are shown). The modulus of the field strength vector for each curve from the shown family is determined by scales with a changing black intensity, located on the left side of the drawings. The upper and lower boundaries of each scale correspond to the maximum and minimum field strengths in the considered calculation area. Their values are indicated above and below each scale. In the calculation, the number of field strength isolines is set equal to 50, which determines the value of the interval between isolines. On the map of isolines in the plane Y = 0 in FIG. 3a, it is seen that the magnetic field of the jumpers with current is concentrated near the centers of the jumpers: the isolines surround the centers of the jumpers and the corresponding field strength decreases as the isoline moves from the center of the bridge. Near the surface of the disk screen 1 with a central circular hole and forming plates 10, the field strength drops to zero. Between the centers of the jumpers, part of the isolines of the field sags to the right of the plane of arrangement of the centers of the jumpers towards the center of the frames. The greatest danger is the sagging of the local field between the jumpers 6 and 8, which are at a minimum and equal distance from the central plane of symmetry of the frames X = 0 along the path of the atomic beam. The depth of the "dip" of the local field of the jumpers in this region is reflected by the position of the contour line 15, the modulus of which is accurate to the division of the scale is equal to the modulus of the field "C" in the center of the linear conductors of the frames. On the map of isolines in fig.3b shows that in the region of the passage of the atomic beam in the plane X = 0 there is a gradual change in the field strength along the Z axis from zero to a constant field "C" equal to 0.0959 Oersted, indicated on the top of the scale. It is also seen that the transition region of the local field of the jumpers does not reach the cavity arm — the plane Z = Z1pez, indicated in FIG. 2a.

осевого распределения величины относительного отклонения модуля напряженности поля в текущей точке Z от его значения в центре рамок Z0, рассчитанные на оси соленоида и атомного пучка (X=Y=0). По оси ординат отложена величина функции F(Z) в процентах. Также отмечены положения входной (Z1peз) и выходной (Z2peз) плоскостей зазора СВЧ-резонатора, отмеченные выше на фиг.2а. Максимальное по абсолютной величине значение функции F(Z) на любом заданном отрезке вдоль оси Z определяет величину коэффициента неоднородности поля на этом участке. На длине участка Z1peз≤Z≤Z0, равной половине длины СВЧ-резонатора, значение коэффициента неоднородности является показателем качества поля «С» и в идеальном однородном поле его величина равна нулю. Расчет функций F(Z) выполнен для предлагаемого соленоида с раздвоенными загнутыми перемычками (кривая 1 на фиг.4) и соленоида-прототипа с прямоугольными рамками (кривая 2 на фиг.4) при одинаковых параметрах: ширине рамок S=55.4 мм и расстоянии между рамками Н=32 мм в соответствии с условием H/S=tg30°, длине рамок L=213 мм и токах в линейных проводниках рамок 27 мА и перемычках 13.5 мА. Высоты загибов раздвоенных перемычек рамок заданы равными h1=7.5 мм и h2=11.4 мм. Из приведенных расчетов видно, что максимумы функций F(Z) для обеих конструкций соленоидов расположены на отрезке Z1peз≤Z≤Z2peз в области резонатора. Для соленоида-прототипа (кривая 2 на фиг.4) функция F(Z) достигает своего максимума +0.85% и затем медленно спадает по направлению к центру рамок Z0, так что коэффициент неоднородности поля «С» соленоида-прототипа составляет 0.85%. Полученная расчетная величина коэффициента неоднородности близка к минимальной величине 1.0%, полученной экспериментально в цезиевой АЛТ с соленоидом-прототипом при жестких требованиях на соосность между токонесущими проводниками (катушками соленоида) и магнитными экранами.Figure 4 shows the functions $$F\left(Z\right)=\left(\left|H\left(Z\right)\right|-{\left|H\right|}_{Z0}\right)/{\left|H\right|}_{\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="00000003.png,00000005.png"\; state="\{\{state\}\}">Z</figure-callout>}0}$$

the axial distribution of the relative deviation of the field strength modulus at the current point Z from its value in the center of the frames Z0 calculated on the axis of the solenoid and atomic beam (X = Y = 0). The ordinate shows the value of the function F (Z) in percent. Also marked are the positions of the input (Z1pez) and output (Z2pez) clearance planes of the microwave cavity, noted above in FIG. 2a. The maximum value of the function F (Z) in absolute value on any given interval along the Z axis determines the magnitude of the field inhomogeneity coefficient in this region. On the length of the section Z1pez≤Z≤Z0 equal to half the length of the microwave resonator, the value of the heterogeneity coefficient is an indicator of the quality of the field "C" and in an ideal uniform field its value is zero. The calculation of the functions F (Z) was performed for the proposed solenoid with bent bent jumpers (curve 1 in figure 4) and the prototype solenoid with rectangular frames (curve 2 in figure 4) with the same parameters: the frame width S = 55.4 mm and the distance between frames H = 32 mm in accordance with the condition H / S = tg30 °, the length of the frames L = 213 mm and the currents in the linear conductors of the frames 27 mA and jumpers 13.5 mA. The bend heights of the bifurcated frame jumpers are set equal to h1 = 7.5 mm and h2 = 11.4 mm. It can be seen from the above calculations that the maxima of the functions F (Z) for both designs of the solenoids are located on the segment Z1pez≤Z≤Z2pez in the resonator region. For the prototype solenoid (curve 2 in FIG. 4), the F (Z) function reaches its maximum of + 0.85% and then slowly decreases towards the center of the Z0 frames, so that the heterogeneity coefficient of the “C” field of the prototype solenoid is 0.85%. The calculated value of the inhomogeneity coefficient is close to the minimum value of 1.0% obtained experimentally in a cesium ALT with a prototype solenoid with stringent requirements for alignment between current-carrying conductors (solenoid coils) and magnetic shields.

In the proposed solenoid with bent bent jumpers (curve 1 in Fig. 4), the maximum of the function F (Z) in the resonator Z1pez≤Z≤Z2pez is + 0.05%, after which the function F (Z) quickly drops to zero towards the center of the frames. The heterogeneity coefficient of the formed field “C” in this case is 0.05%. The calculations showed that, when the indicated ratio H / S = tg30 ° is fulfilled, the functions F (Z) calculated from the lines of intersection of the planes X = ± 1.0 mm and Y = ± 2.5 mm at the boundaries of the cross section of the atomic beam, up to the 5th of the sign coincide with the function F (Z) calculated for the center of the atomic beam X = Y = 0. In the same cases when the angle in the indicated ratio varies within 30 ° ± 1 °, the inhomogeneity of the field “C” in the cross section of the atomic beam varies within 0.05 ± 0.02%.

Thus, the proposed design of the solenoid allows more than an order to reduce the heterogeneity of the field "C" in the microwave cavity to the level achieved in stationary ALT metrological class. This will ensure a decrease in the magnetic frequency shift in onboard cesium ALTs intended for use in the equipment of a new generation of the GLONASS system. The proposed design of the solenoid may also find application in ALTs operating on other atomic fluxes, including fluxes of rubidium, thallium, magnesium and silver atoms.

Information sources

1. Atomic beam cesium tubes / E.N. Pokrovsky and others // Electronic technology. Ser. 1. Microwave technology. - 2009. - Issue 3 (502). S.4-16 (prototype).

2. An atomic beam tube with increased resistance to magnetic fields. / E.N.Abramov et al. // Electronic Technology. Ser. 1. Microwave technology. - 1992. - Issue 2 (446). S.11-14.

3. Prediction of metrological characteristics and optimization of the parameters of atomic beam tubes. V.K. Kurakin. Candidate dissertation, VNIIFTRI, M., 1973.

4. A. Makdissi, E. de Clercq. Evaluation of the accuracy of the optically pumped cesium beam primary frequency standard of the BNM-LPTF // Metrologia, 2001, 38, 409-425.

5. Atomic beam cesium tubes / I.I. Samartsev /. Collection of lectures in VI volumes under the general editorship of Doctor of Technical Sciences A.N. Koroleva. FSUE NPP ISTOK Volume I, Part 2. Atomic Beam Tubes. 2005, p.205-223 (prototype).

6. Cesium atomic beam tube with optical selection of atomic states at the entrance to the microwave cavity / S. A. Pleshanov et al. // Electronic Engineering. Ser. 1. Microwave technology. - 2007 .-- Issue 1 (489). S.87-92.

Claims (1)

A cesium atomic beam tube solenoid containing two identical coils located inside the system of magnetic screens on both sides of the U-shaped microwave resonator along the longitudinal plane of its symmetry and equidistant from it, each coil is a rectangular frame of linear conductors with jumpers, characterized in that on each side of the frame the jumpers are divided into two equal parts and smoothly bent perpendicular to the longitudinal plane of symmetry of the resonator, one part is bent towards the resonator, and the narrow part in the direction from the resonator, the bend height h1 to the resonator and the bend height h2 from the resonator are determined from the conditions: 0.2≤h1 / H≤0.6, 0.4≤h2 / H≤0.8, where N is the distance between the frames, while the width of the frames S and the distance between the frames H are in the ratio H / S = tg30 °.

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