RU2509386C1 - Solenoid - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: external magnetic conductor of armour type comprises a cylindrical side shell and two end flanges in the form of truncated cones. The cross section of the external magnetic conductor is equal-sized along the entire length of the power lines of the magnetic field passing through it, which provides for high radial homogeneity of magnetic field in the working space of the solenoid. The solenoid winding is partitioned and made of a tubular conductor. To ensure axial homogeneity of the magnetic field, the number of turns in sections increases as the turns move away from the centre.

EFFECT: increased efficiency of conversion of electric current into magnetic field during optimisation of material consumption and electric energy for development of magnetic fields of medium and high levels.

8 dwg

Description

The present invention relates to the technique of electromagnets creating uniform magnetic fields of medium and high levels of magnitude with a large axial and radial extent, with a high uniformity. Such devices are needed for experimental physics and for creating a workspace for autoresonant acceleration or generation.

The aim of the invention is to provide a device with a uniform magnetic field in a cylindrical volume and efficiently converting the energy of electric current into a magnetic field.

The essence of the invention consists in the use of a tubular conductor for the manufacture of a solenoid winding in the room of the solenoid in an external armored magnetic circuit.

An analogue of the invention is the synchrotron electromagnet, see A. Vorobyov and others. "1.5 GeV Synchrotron TPI." M .: Atomizdat, 1963, p. 43. The electromagnet field winding is made of a copper tube with a diameter of 22 mm with an inner diameter of 12 mm, which was insulated with a nickel tape. All sections of the winding are connected electrically in series. The winding was fed by a pulsed source with a power of 63.7 MV · A at a voltage of 12,400 volts and a current of 5140 amperes in a pulse with a duration of 0.084 seconds and a repetition rate of 2 Hz. The pulsed current density in the winding reached 19 A / mm ² . The average power consumption in an electromagnet was 500 kVA.

To cool the winding, all its sections were hydraulically connected in parallel and water was supplied under a pressure of 10 atm. In the nominal mode, the copper in the windings was heated to 60 ° C.

The second analogue of the invention is the microtron electromagnet, see S.P. Kapitsa, V.N. Melekhin. Mikrotron M .: Nauka, 1969. Microtrons with armored type electromagnets are known. Structurally, they consist of two identical annular windings that are mounted on other opposing poles, which are externally supported by an annular reverse magnetic circuit, Fig. 8. The axial gap between the poles is about 100 mm, and the diameter of the poles is 700-2000 mm. The magnitude of the magnetic field is 1-3 kOe, and the heterogeneity in the working space is 0.5-0.01%. Windings are performed by a copper bus, natural cooling.

The disadvantage of both analogues is that they cannot be directly applied to create a magnetic field in a cylindrical extended volume. However, methods for constructing windings and magnetic circuits can be applied in the present invention.

The first prototype of the invention is the solenoid S.P. Kapitsa, see the collection "Electronics of high power", Academy of Sciences of the USSR, M., 1963, pp. 109-118. An essential feature of this device is an increase in the magnetomotive force of the winding at its ends. The winding was made of copper tape 25 mm wide, 0.4 to 0.2 mm thick as the winding section moved away from the center to the periphery. The winding sections consisted of paired cassettes with counter winding and their serial electrical connection. When moving away from the center to the periphery, the number of turns in the rolls increased stepwise while maintaining the outer size of the winding, which was 332 mm, and the inner was 150 mm. For cooling, the winding was placed in a cylindrical casing with a diameter of 410 mm, through which transformer oil was circulated under a pressure of 3 atm. At a rated power supply mode of a 36 kW solenoid, a voltage of 378 V and a current of 110 A, the average copper temperature was 29 ° C. The current density in the winding increased from 5.5 A / mm ² for median to 11 A / mm ² for end cartridges. With a total length of the solenoid of 727 mm, a uniform field on the axis of the solenoid was in the area of 370 mm with a uniformity of 0.06%. The maximum level of the operating mode was 4500 oersted.

The main disadvantage of this prototype in the small relative length of a homogeneous working field: 370/727 = 495. This is unacceptable for an autoresonant accelerator, the injector and the output device need to be placed somewhere.

The second prototype of the invention is a device, see Kapitsa P.L. Filimonov S.I. "A solenoid that creates a magnetic field of up to 20 kilo-oersted in a volume of 5 liters and consumes 500 kilowatts." Collection 6 "Electronics of high power" No. 6. M.: Science 1969, p. 147-160.

The essence of this device is that the winding was made of two groups of roll cassettes separated by a gap of 32 mm. The current density in copper increased to 32 A / mm ² . The windings of each half of the solenoid were cooled by separate casings, through which distilled water circulated.

The second significant difference was the use of an external jugular type magnetic core made of steel plates 90 mm thick over the entire width of the winding 540 mm with a thickness of the winding 100 mm. With a total winding length of 406 mm, the working field of 30 kilo-ested was on a 200 mm section with a uniformity of 5.5%, which is also unacceptable for autoresonance devices.

The author-applicant met with interest and enthusiasm these prototypes at the end of 1969, when he presented his post-graduate work to the authors of autoresonance A. Kolomensky. and Lebedev A.N. DAN USSR, 145.1259, 1962.

The third prototype of the present invention is a device of three coils placed in an external armored magnetic circuit, see candidate diss. Ishkov A.P. "An experimental study of an autoresonant electron accelerator" TPI, Tomsk, 1969.

In essence, the system of three coils was a modification of two Helmholtz coils, which provide high uniformity of the magnetic field on their axis and in the adjacent region. The direct use of Helmholtz coils was irrational due to their large transverse size and, accordingly, the high power of their power. The length of the region of a uniform magnetic field of 200 mm was already given by the size of the accelerating system. The task was solved by the use of an average coil. The use of an external armored magnetic circuit solved the problem of reducing power supply.

From a modern position, the disadvantage of this device is the small thickness of the end flanges of the magnetic circuit and the presence of large holes in them, i.e. irrational form of the magnetic circuit.

The fourth prototype of the invention is the patent RU 2364000, “Ishkova homogeneous solenoid”, which most closely corresponds to the task of creating a uniform magnetic field in a cylindrical volume. However, there are drawbacks to it. The winding is uniform along its axis and has no means of compensating for the decrease in the magnetic field at its peripheral ends. The design of the magnetic circuit also does not take into account the specific structure of the initial magnetic field created by the winding at the ends. In general, the device of this prototype will be justified only for small desktop devices. For large structures, this prototype is irrational.

As an example, the present invention is presented in figure 1. The device consists of a partitioned winding 1 and an external magnetic circuit of armor type 2.

The winding of the solenoid 1 is symmetrical with respect to the median plane passing through the center of the solenoid, and each section of the winding consists of paired rolls 3, Fig.2. Rolls 3 in the section are wound counter-copper tube of flat shape 4 with an internal channel 5 for the circulation of cooling water. Inside the section, the coils are connected by an oblique turn 5, and outside the adjacent sections are connected by oblique turns 7, from which the nozzles 8 pass in isolation through the cylindrical part of the magnetic circuit 12. Then they supply circulating water through the insulating sleeves 9 to the collector pipes 10 and 11, Fig. 3.

The armored magnetic circuit 2 consists of a cylindrical side shell 13 of constant thickness Δ and end flanges 13 in the form of truncated cones with a height h> Δ. The inner radius of the cylindrical side shell 13 is equal to R, and the inner radius of the solenoid r. The conical shape of the end flanges 13 will provide an equal section of the armored type 2 magnetic circuit along the entire length of the magnetic lines 14. This will make it possible to rationally use the material to create large solenoids and to prevent the appearance of scattered magnetic fields around the solenoids. The thickness of the cylindrical side shell 12 is equal to or comparable with the radial thickness of the coil of the solenoid 1 Δ = R-r. The diameter of the smaller base of the end flanges 13 is equal to the inner diameter of the solenoid winding.

The invention operates as follows.

According to Laplace’s law, each element of the electric current creates a magnetic field element at a given point in the surrounding space.

$$d\overrightarrow{B}=k\cdot \frac{i[d\ell \times \overrightarrow{r}]}{{\mathrm{<figure-callout\; id="3"\; label="r"\; filenames="00000015.png"\; state="\{\{state\}\}">r</figure-callout>}}^3}/\mathrm{one}/$$

where dℓ is an electric current element of value i,

- радиус-вектор заданной точки окружающего пространства, $$\overrightarrow{r}$$

is the radius vector of a given point in the surrounding space,

k is a coefficient depending on the choice of unit dimension.

For the center of a circular coil with current in the GHS system, this formula has the form $$d\overrightarrow{B}=\frac{{\displaystyle \int uo}}{\mathrm{four}\beta \pi }\frac{id\mathrm{<figure-callout\; id="2"\; label="l\; r"\; filenames="00000015.png,00000020.png"\; state="\{\{state\}\}">\ell \; </figure-callout>}}{r^{}}/2/$$

The magnetic field at the center of this circular current is determined by the integral

$$\overrightarrow{B}={\displaystyle \int dB=\frac{{\mu }_o}{2}\frac{i}{r}}/3/$$

see Saveliev I.V. "The course of general physics", t.2, p.129-134.

Figure 4 presents the scheme for calculating the magnetic field at a point spaced from the center of the circular current at a distance x. Consider the triangle oxA. It has three sides x, δ, R and an angle φ between the sides x and R. According to the cosine theorem, we can determine the length of the side of the triangle opposite the angle φ.

$$\delta =x^2+R^2-2Rx\cos \varphi ./\mathrm{four}/$$

The magnetic field element at point x created by the current element at point A in the GHS system will be

$$dB=\frac{{\mu }_o}{\mathrm{four}\pi }\frac{id\ell }{{\delta }^2}=\frac{{\mu }_o}{\mathrm{four}\pi }i\frac{Rd\mathrm{<figure-callout\; id="2"\; label="\phi \; \delta "\; filenames="00000015.png,00000020.png"\; state="\{\{state\}\}">\varphi \; </figure-callout>}}{{\delta }^{}}/5/$$

After substitution, we obtain the integral for determining the magnetic field at the desired point

$$B\left(x\right)=\frac{{\mathrm{<figure-callout\; id="2"\; label="\mu \; o"\; filenames="00000015.png,00000020.png"\; state="\{\{state\}\}">\mu \; </figure-callout>}}_o}{2\pi }{\displaystyle \underset{0}{\overset{\pi }{\int }}\frac{Rd\varphi }{R^2+x^2-2Rx\cos \varphi }}./6/$$

Without losing generality of reasoning, we can put R = 1, then the integral will be simplified for calculations

$$B\left(x\right)=\frac{{\mathrm{<figure-callout\; id="2"\; label="\mu \; o"\; filenames="00000015.png,00000020.png"\; state="\{\{state\}\}">\mu \; </figure-callout>}}_o}{2\pi }{\displaystyle \underset{0}{\overset{\pi }{\int }}\frac{d\varphi }{\mathrm{one}+x^2-2Rx\cos \varphi }}./7/$$

Figure 5 shows a diagram of the calculation of the magnetic field in the space adjacent to the circular current. The desired integral has the form

$$B\left(x,z\right)=\frac{{\mathrm{<figure-callout\; id="2"\; label="\mu \; o"\; filenames="00000015.png,00000020.png"\; state="\{\{state\}\}">\mu \; </figure-callout>}}_o}{2\pi }{\displaystyle \underset{0}{\overset{\pi }{\int }}\frac{d\varphi }{\mathrm{one}+x^2+z^2-2Rx\cos \varphi }}./8/$$

For a solenoid, the circular current can be represented by the product

$$i=jdrdz,/9/$$

where j is the current density in its winding.

The magnetic field inside the solenoid will now be represented by a triple integral

$$B_z\left(x,z\right)=\frac{{\mu }_o}{\pi }{\displaystyle \underset{0}{\overset{\pi }{\int }}{\displaystyle \underset{r}{\overset{R}{\int }}{\displaystyle \underset{-\frac{z_o}{2}}{\overset{\frac{z_o}{2}}{\int }}\frac{jRd\varphi drd\mathrm{<figure-callout\; id="2"\; label="z\; R"\; filenames="00000015.png,00000020.png"\; state="\{\{state\}\}">z\; </figure-callout>}}{R^{}}}}}./10/$$

where r is the inner radius of the coil of the solenoid,

R is the outer radius of the coil of the solenoid,

z ₀ is the length of the solenoid.

To study the relative distribution of the magnetic field inside the solenoid, we should set R = 1, then the integral will be simplified

$$B_z\left(x,z\right)=\frac{{\mu }_o}{\pi }{\displaystyle \underset{0}{\overset{\pi }{\int }}{\displaystyle \underset{\mathrm{one}}{\overset{\mu \Delta }{\int }}{\displaystyle \underset{-\frac{z_o}{2}}{\overset{\frac{z_o}{2}}{\int }}\frac{d\varphi drdz}{\mathrm{one}+x^2+z^2-2x\cos \varphi }}}}./\mathrm{eleven}/$$

where Δ is the radial thickness of the solenoid winding.

x is the distance of the investigated point from the axis of the solenoid.

Table 1 presents the results of a computer calculation of the distribution of the magnetic field of a circular current according to formula 8.

Thus, the magnetic field in the plane of the circular current radially grows progressively, and axially decreases hollow. Within z≤0.5, the field retains radial growth, and for z> 0.5 the field decreases both axially and radially.

Table 2 shows the results of a computer calculation of the magnetic field of a solenoid with parameters R = z = 1.0 at a uniform current density in its winding.

An analysis of the contents of Table 2 shows that the magnetic field inside the solenoid radially increases by an order of magnitude, and axially hollow decreases. It can be seen that the steepness of field changes in the solenoid is weaker than that of a single circular current. A solenoid is a system of many single circular currents, so they have such a similarity of the structures of magnetic fields.

Figure 6 presents a graph of the radial distribution of the magnetic field of a circular current, which is built according to table 1.

Figure 7 presents a family of lines constructed according to table 2, which represent the structure of the magnetic field inside the solenoid with a uniform winding.

Thus, the solenoid itself creates an inhomogeneous magnetic field. The axial decrease in the magnetic field can be compensated within certain limits by increasing the number of turns at the ends of the winding, which is done in the first prototype.

Eliminate or weaken the radial growth of the magnetic field in the solenoid is represented only by the use of an external magnetic circuit. In the third prototype, weakened radial inhomogeneity of the magnetic field from 3% to 1% in the working area of the solenoid, which is adjacent to the axis of symmetry of the solenoid, is achieved.

In the present invention, the design and parameters of the external magnetic circuit are consistent with the dimensions of the exciting winding. Along the lines of the magnetic field, the cross section of the external magnetic circuit is the same and sufficient to preserve the entire magnetic flux generated by the exciting coil. Due to the use of end flanges of the magnetic circuit in the form of truncated cones, the central and axial magnetic lines of the magnetic field pass more in the magnetic circuit than the peripheral lines of the magnetic field, so they are more amplified than peripheral. The magnetic flux is enhanced by reducing the magnetic resistance of the magnetic circuit outside the solenoid due to the use of effective magnetic materials for the external magnetic circuit. In the second prototype, the relative magnetic permeability of the material of the magnetic circuit was 20,000. In the third prototype, the use of an accurate magnetic circuit of steel St-3 made it possible to reduce the current in the winding from 280 A to 105 A.

The use of a tubular conductor for the manufacture of a solenoid winding increases the efficiency of heat removal from each element of the winding. This increases the operational parameters of the solenoid.

On Fig presents the magnetic system of the second analogue, the microtron, which achieves a radial uniformity of the magnetic field of 0.5-0.1%. This is achieved and ensured by the fact that in a microtron magnetic field lines extend mainly in the body of the magnetic circuit and only 1/10 pass in the interpolar gap.

In the present invention, the working space of the solenoid accounts for 1 / 3-1 / 4 of the entire length of the lines of the magnetic field. Therefore, for the solenoid presented in Table 2 with the parameters R = Z ₀ = 1, one can expect radial uniformity 3-4 times worse than the microtron uniformity, i.e. 2% -0.4%.

Of course, convincing arguments require a reliable experiment.

It should be noted that with an increase in the length of the solenoid, the radial uniformity of the magnetic field will decrease, and with a shortening of the solenoid, it will improve accordingly. With the length of the solenoid Z = 0.1, it will turn / degenerate / into a microtron.

The main results

1. The development of solenoids over the past 50 years is considered.

2. An integral formula of the structure of the magnetic field in the solenoid is obtained.

3. The formula of a solenoid creating a uniform magnetic field is proposed.

Claims (1)

 A solenoid consisting of a winding, an external magnetic circuit and a water cooling system, characterized in that the winding is made of paired cassettes with a rectangular tubular conductor and electrically connected in series, and hydraulically connected in parallel with insulating sleeves to a water cooling system; the external armored magnetic circuit consists of a cylindrical side shell and end flanges in the form of truncated cones, the cross section of the external armored magnetic circuit along the entire length of the magnetic lines passing through it is equal.

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