SU448524A1 - Superconducting magnet operating in a "frozen flow" mode - Google Patents

Description

The invention relates to a technique of magnetic measurements and can be used in high resolution nuclear magnetic resonance spectroscopy. Orthogonal superconducting windings are known to eliminate residual gradients operating in a frozen flow mode. They include main, compensating and orthogonal correction windings, superconducting thermal switches, protective circuits with diodes, a cryostat with liquid helium. Compensation windings are wound on the ends of the main and orthogonal corrective windings. The main and compensating windings are connected in series. The main winding is broken into several sections. Two diodes are connected in parallel to each section, and the anode of one diode is connected to the cathode of the other. thermal key, the same keys are connected-in parallel to each compensating winding. The known magnet requires the use of four current sources to establish the magnetic field and correct its axial component. The main current source establishes the current connected in series to the main and collector windings. The remaining sources are connected separately to the main and compensating windings, their purpose is to adjust the current I in these windings in such a way that the axial residual gradient of the magnetic field is minimized. During the adjustment process, the superconductor and other thermal keys are normally In this state, the main source of current must be switched on. At the same time, its temporal stability must not be lower than 10 in chao in order for the main magnetic field to not change in an uncontrolled manner, which could make it difficult to achieve the required homogeneity of the magnetized CkJHOBHHM The source of the axial neody of the breed is the shift J of the main winding attributable to the center of the column i ffleHgHpjiiixr windings. This leads to the fact that the compensator of the windings is the size of the uniform floor area and led The reason for homogeneity is less compared to that when the symmetry centers of the main and compensating windings coincide. The lack of orthogonal corrective oytok wound inside the main winding in close proximity to the field to be corrected and connected through the secondary winding of the DC transformer, the primary winding of which is connected in series with the main and compensating windings, is that if there are magnetic fields, the source of which can be the studied objects or additional correcting windings, for example, on the sensor of a nuclear magnetic field spectrometer onansa in correct ruyuschih orthogonal windings due to the small inductance of the secondary winding of the transformer and the DC is induced parasitic current and cos given by orthogonal correcting coils varies gradients. Thus, the most significant disadvantages of a known magnet are as follows. The connection scheme of thermal superconducting keys with windings allows for the adjustment of axial residual gradients by adjusting the currents in the compensating coils only when the main winding and the compensating windings are fed with current from the main source. This makes it difficult to establish the region of optimal magnetic uniformity with an uncontrolled change in the current of the main source (rectifier) due to its insufficient time stability. Adjusting the currents in the compensating windings does not allow the axial gradients of the magnetic field to be fully corrected, caused by a shift in the symmetry of the main winding relative to compensating for the magnetic field and low temperature. in orthogonal corrective windings under the influence of extraneous electrical disturbances, the currents are corrected. The purpose of the invention is to eliminate the influence of the instability factor of the main current source on the choice of the optimal area of a uniform magnetic field, reducing the correlation of radial gradients from electromagnetic disturbances and increasing the uniformity of the magnetic field by more accurate alignment of the centers of symmetry of the compensating and main currents. To do this, in the proposed device, the main, compensating and orthogonal correction windings are connected in series and in parallel they are connected to a thermal superconducting key. The other two heat- output keys are connected in parallel to the compensating windings, which are wound on separate frames with the possibility of moving along the main winding axis during the adjustment process. The proposed superconducting magnet design reduces residual axial gradients, eliminates the dependence of corrective radial gradients created by orthogonal windings on magnetic disturbances, and corrects axial homogeneity when the magnetic system is operating in a frozen flow with a main current source, which makes it easier to find the optimal homogeneous field areas and does not require the use of a highly stable main current source. Figure 1 shows the electrical circuit of the superconducting magnet; 2, its construction, longitudinal section. The proposed superconducting magnet contains the main winding I; compensating winding 2; orthogonal corrective windings 3; main current source 4; ballast resistor 5 in the main current source circuit; switch 6; protective circuits from diodes 7 and resistors 8; thermal superconducting key 9 of the main current source with electric heater 10; thermal keys II with heater 12 compensating windings; additional current sources 13 for compensating windings; ballast resistors 14; turning off 15; frames 16 of compensating windings with fasteners 17; guide frame 18 with fasteners 19: half-ring gaskets 20; frame 21 of the main winding; The superconducting magnet empties a cryostat and pours liquid helium into it. The current is passed through the heaters 10.12 of superconducting keys 9.11 and transforms them to normal

condition. Then switch 6 is turned on and smoothly increases the current from the main source 4 through series-connected windings 1.2 3. When the required magnetic field is reached, turn off the current flowing through the heater of the thermal switch 9 and transfer it from normal to superconducting the

The superconducting magnet operates in frozen flow mode. Thus, the temporary instability of the main current source 4 is eliminated. After that, the switches 15 are turned on, smoothly regulate the current from the sources 13 and thereby change the current by the values of one

the winding winding and the other. The current corresponds to the lower axial gradients of the superconducting magnet.

When the currents in the compensating windings change by values, and from sources 13, the currents in the main winding change automatically. These changes are inversely proportional to the main and compensating windings, but they are three to four times less and.Then they turn off

the current from the heaters 12 of the heat switches II and transfer them from the normal to the superconducting state, turn off the current sources 4 of 13 with the switches 6 and TB. The LEDs with the corrected gradients work, thus, in the frozen flow mode.

The main, compensating and orthogonal windings of the magnet are connected in series and made of superconducting wires (alloys

or ).

The number of corrective orthogonal windings 3 depends on the number

residual radial gradients

etc. which need to be corrected

set the number of turns corrective

coil is determined in the process of adjusting the magnetic system:

where is the current flowing through the main, compensating and correcting orthogonal windings.

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The Invention

Superconducting magnet, operating in a frozen flow mode, containing superconducting solenoid main windings placed in a cryostat, consisting of several sections, two compensating windings connected in series with the main winding and placed at the ends of its frame, orthogonal corrective windings, thermal superconducting switches and protective circuits connected in parallel to the windings, and sources of current, which are distinguished by the fact that, in order to eliminate the influence (the instability factor of the main current source on the choice of optimal th field of the homogeneous magnit0 Nogo AMPs, depending reduce radial gradients of the correcting solenoid: brightening) uscheny and increasing the uniformity of the magnetic field more accurate registration.

5 centers of compensation of the compensating and main windings, the main one, the compensating and orthogonal corrective windings are connected in series with the main current source,

0 in parallel with which one of the superconducting thermal switches is connected via superconducting connections, and the other two superconducting thermal switches through superconducting

5 connections are connected in parallel to the compensating windings, each of which is made on a separate frame with the possibility of movement along the axis of the main winding.

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