Superconducting undulator magnetic field error correction method based on soft iron correction column

Abstract

The invention discloses a superconducting undulator magnetic field error correction method based on soft iron correction columns, and the method comprises the steps: 1), forming a blind hole in each magnetic pole, forming a through hole in an iron core corresponding to each magnetic pole as a correction hole, and arranging a soft iron correction column in each correction hole; magnetic field distribution on an axis in a superconducting state is measured; 2) selecting a plurality of correction magnetic pole groups, and adjusting the insertion depth of the soft iron correction column in the magnetic pole pair of each correction magnetic pole group; 3) operating the undulator in the superconducting state again and measuring the magnetic field distribution on the axis; obtaining a magnetic field correction value corresponding to the insertion depth adjustment amount h according to the magnetic field distribution as a calibration signal; 4) taking the magnetic field distribution in the superconducting state as a correction target and the calibration signal as a correction value, calculating the insertion depth adjustment amount of the soft iron correction column which enables the magnetic field error to be minimum, and the magnetic pole group and the polarity of the corresponding soft iron correction column to obtain a correction list, and 5) quantitatively adjusting the insertion depth of the soft iron correction column in the corresponding magnetic pole group according to the list.

Description

Technical Field

[0001] This invention belongs to the field of synchrotron radiation technology and relates to a method for correcting magnetic field errors in a superconducting undulator based on a soft iron correction column. Background Technology

[0002] Inserts are key components in specialized light sources that generate synchrotron radiation, and the quality of their magnetic field affects the axial brightness of the radiation source. Inserts can be classified into permanent magnet inserts and electromagnetic inserts according to their excitation method, and into oscillators and oscillators according to the undulator parameter K value. The correction method mentioned in this invention is applicable to electromagnetic superconducting oscillators. Superconducting inserts are typically made of superconducting wire with high current carrying capacity and have greater potential for peak magnetic field enhancement compared to permanent magnet inserts, making them a research hotspot in the fields of advanced synchrotron radiation sources and free-electron laser sources.

[0003] A superconducting undulator is a superconducting magnet structure with a short magnetic field period (approximately tens of millimeters) capable of generating a periodic magnetic field. The generated magnetic field originates from periodically wound superconducting coils. Typically, slots (half the period length) are evenly spaced on the iron core facing the working magnetic gap, and magnetic poles made of soft iron are inserted to form winding slots. The superconducting wire is wound slot by slot, with the winding direction of any two adjacent slots opposite, thus generating a periodic magnetic field under energized conditions. The magnetic poles are the peak positions of the periodic magnetic field generated by the superconducting coils and are also the key positions determining the quality of the magnetic field. The uniformity of the material, the consistency of the magnetic pole machining accuracy, and the consistency of the assembly accuracy of hundreds of magnetic poles with the iron core directly affect the magnetic field quality of the superconducting undulator and are also the root cause of its magnetic field errors.

[0004] Magnetic field error correction technology is an established technique for improving the magnetic field quality of inserts. Reducing magnetic field error can improve the magnetic field quality of the insert, thereby increasing the radiant brightness of the light source axis. Therefore, this invention proposes a novel method for correcting the magnetic field error of a superconducting undulator by adjusting the insertion depth of soft iron correction posts. Among the published literature and patents for superconducting inserts, the most similar implementation to this invention is the one proposed by NSRRC, which involves creating correction grooves on the back of the magnetic poles of the superconducting undulator magnet and changing the depth of the correction grooves by embedding different numbers of soft iron pieces, thereby adjusting the magnetic field error correction scheme of the superconducting undulator.

[0005] Existing technologies indirectly adjust the effective depth of the correction groove by changing the number of pre-embedded soft iron sheets, as shown in Figure 1. The effective adjustment depth of the correction groove depends on the number of pre-embedded soft iron sheets removed, thus the adjustment amount is discrete. Furthermore, soft iron sheets are soft, and in existing technologies, the thickness of the soft iron sheets is 1 mm. The adjustment accuracy of this method is determined by the thickness of a single layer of soft iron sheets, thus limiting the correction accuracy. Moreover, existing solutions require machining a wide, narrow, and deep groove and preparing dozens of 1 mm thick soft iron sheets to be pre-embedded in the correction groove. This technology suffers from high machining difficulty, complex integration and installation processes, and high parts management costs. Finally, in the error correction stage, removing several wide, narrow, and thin sheets from the wide, narrow, and deep groove is inefficient. Summary of the Invention

[0006] To address the problems existing in the prior art, the purpose of this invention is to provide a method for correcting the magnetic field error of a superconducting undulator based on a soft iron correction column, which can accurately compensate for the half-cycle magnetic field integral error of the superconducting undulator, thereby improving the magnetic field quality of the device.

[0007] This invention achieves local magnetic field error correction in a superconducting undulator by adjusting the insertion depth of the soft iron correction post. The magnetic field error in the undulator's main period can be entirely compensated by adjusting the insertion depth of the soft iron correction post. This method improves the consistency of the half-cycle magnetic field distribution, reduces the magnetic field error in the undulator's main period, and enhances the undulator's magnetic field quality. This magnetic field error correction method is technically implemented based on the structure of the correction magnetic poles, the layout of the undulator magnets, and the adjustment method of the soft iron correction post insertion depth.

[0008] As shown in Figure 2, the technical solution proposed in this invention involves pre-drilling blind holes and embedding soft iron correction posts within the correction magnetic pole. By adjusting the insertion depth of the soft iron correction posts within the correction magnetic pole, continuous and precise adjustment can be achieved. On one hand, this achieves high efficiency by transitioning from "discrete adjustment" to "continuous adjustment" and from "limited adjustment precision" to "precise adjustment." On the other hand, the technical solution proposed in this invention not only reduces processing difficulty and simplifies assembly and integration processes but also significantly improves the operability of the correction process and increases work efficiency.

[0009] The technical solution of this invention is as follows: A method for correcting the magnetic field error of a superconducting undulator based on a soft iron correction column, comprising the following steps: 1) A blind hole is opened on each magnetic pole in the superconducting undulator, and a through hole is opened on the iron core corresponding to each magnetic pole as a calibration hole. A soft iron calibration post is set in each calibration hole for insertion into the blind hole of the corresponding magnetic pole, and the insertion depth in the blind hole is adjustable; when the superconducting undulator is operating stably in the superconducting state, the magnetic field distribution on the axis of the superconducting undulator is measured. 2) The superconducting undulator is shut down and allowed to warm up to an operable room temperature environment. Several magnetic pole groups in the superconducting undulator whose correction signals do not interfere with each other are selected as correction magnetic pole groups. The insertion depth of the soft iron correction column in the pair of magnetic poles with positive or negative polarity in each selected correction magnetic pole group is adjusted and the insertion depth adjustment amount h of the soft correction column is recorded. The magnetic pole group includes two pairs of magnetic poles with opposite polarities adjacent to each other in the same magnetic field period. 3) Run the superconducting undulator in the superconducting state again and measure the magnetic field distribution on the axis of the superconducting undulator; subtract the magnetic field distribution measured after the soft iron correction column is inserted into the magnetic field distribution measured in step 1) from the magnetic field distribution measured in step 1) to obtain the magnetic field correction amount corresponding to the insertion depth adjustment amount h, which is used as the calibration signal. 4) Using the magnetic field distribution of the superconducting undulator when it is stably operating in the superconducting state as the correction target and the calibration signal as the correction quantity, the insertion depth adjustment of the soft iron correction column that minimizes the magnetic field error of the superconducting undulator, as well as the magnetic pole group and polarity of the corresponding soft iron correction column, are calculated based on the principle of magnetic field superposition to obtain a correction list. 5) Shut down the superconducting undulator and allow it to warm up to an operable room temperature environment. Quantitatively adjust the insertion depth of the soft iron correction post in the corresponding magnetic pole group according to the calibration list. 6) Run the superconducting undulator in the superconducting state again and measure the magnetic field distribution on the axis of the superconducting undulator; 7) Calculate the magnetic field error of the superconducting undulator based on the magnetic field distribution measured in step 6); 8) If the magnetic field error meets the set index requirements, the correction ends; otherwise, proceed from step 4) to step 8) until the magnetic field error meets the index requirements.

[0010] Preferably, the magnetic field error is a phase error or a trajectory error.

[0011] Preferably, the material of the soft iron correction column is a soft magnetic material.

[0012] Preferably, the magnetic field distribution on the axis of the superconducting undulator is measured using a HALL sensor.

[0013] Preferably, the insertion depth adjustment of the soft iron correction column that minimizes the magnetic field error of the superconducting undulator is calculated using the simulated annealing method.

[0014] Preferably, the correction hole and the blind hole have the same diameter and are coaxial.

[0015] Key aspects of this invention include: 1) The soft iron correction column made of soft iron materials such as DT4 proposed in this invention is a key component for realizing magnetic field error correction; 2) The correction magnetic pole proposed in this invention, which includes a correction hole and a soft iron correction post, is a key structure that generates a magnetic field correction amount by adjusting the insertion depth of the soft iron correction post, and is also a key structure for continuously adjustable insertion depth. 3) The superconducting undulator magnet structure composed of correcting magnetic poles proposed in this invention is the basic structure for realizing this correction method; 4) The method proposed in this invention for symmetrically adjusting the insertion depth of the soft iron correction column in a pair of correction magnetic poles is a key method for achieving magnetic field error correction; 5) The method proposed in this invention for adjusting the insertion depth of the soft iron correction post within the correction magnetic pole with positive polarity is a method for obtaining a negative correction signal; 6) The method proposed in this invention for adjusting the insertion depth of the soft iron correction post within the correction magnetic pole with negative polarity is a method for obtaining a positive correction signal; 7) The method proposed in this invention, which involves adjusting the insertion depth of the soft iron correction posts of the positive or negative polarity correction magnetic poles in all correction magnetic pole groups on a undulator in pairs, is the basic method for correcting the overall magnetic field error of a superconducting undulator.

[0016] The advantages of this invention are as follows: From a theoretical perspective, this invention offers the advantage of high-precision correction of local magnetic field errors. Simulation results show that the correction method provides a strong magnetic field error correction signal with a relatively narrow distribution along the beam motion direction. Therefore, it can accurately compensate for half-cycle magnetic field integration errors, thereby effectively improving the uniformity between half-cycle magnetic field integrals in the superconducting undulator. From a technical implementation perspective, this invention proposes a technical solution that uses the insertion depth of the correction column to achieve magnetic field error adjustment, giving the correction method the advantages of continuous and precise adjustment. Finally, this invention boasts advantages such as simple processing, concise procedures, and easy operation in the manufacturing process, integration, and magnetic field error correction. Attached Figure Description

[0017] Figure 1(a) is a partial front view of the existing technical solution before the adjustment of the upper beam magnet.

[0018] Figure 1(b) is a partial front view of the upper beam magnet after adjustment in the existing technical solution.

[0019] Figure 1(c) is a partial top view of the back of the upper beam magnet in the existing technical solution.

[0020] Figure 2(a) is a partial front view of the upper beam magnet before adjustment in the technical solution of this application.

[0021] Figure 2(b) is a partial front view of the upper beam magnet after adjustment in the technical solution of this application.

[0022] Figure 2(c) is a partial top view of the back of the upper beam magnet in the technical solution of this application.

[0023] Figure 3 This is a schematic diagram of the magnetic poles of a conventional superconducting undulator and the magnetic poles of the superconducting undulator of this invention within a periodic magnetic field structure.

[0024] Figure 4 This is a schematic diagram of the structure of a superconducting undulator magnet composed of corrective magnetic poles and the magnetic field it generates.

[0025] Figure 5 A schematic diagram showing the insertion depth of the soft iron correction post within a pair of correction magnetic poles with positive polarity and the amount of magnetic field correction generated therefrom.

[0026] Figure 6 A schematic diagram showing the insertion depth of the soft iron correction post within the pair of correction magnetic poles with negative polarity and the amount of magnetic field correction generated.

[0027] Figure 7 This is a flowchart of the magnetic field error correction method of the present invention. Detailed Implementation

[0028] The present invention will now be described in further detail with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0029] Unlike permanent magnet undulators, the magnetic poles of a superconducting undulator are fixed components and cannot be adjusted. This invention corrects the magnetic field error of the superconducting undulator by adjusting the insertion depth of the correction post embedded in the magnetic pole. As shown in "Adjustment Depth" in Figure 2(b).

[0030] like Figure 3 As shown, the corrected magnetic pole proposed in this invention is a novel magnetic pole structure, different from the conventional undulator magnetic pole. Conventional magnetic poles are the commonly used magnetic pole structures internationally, such as... Figure 3 As shown on the left, it lacks magnetic field error correction capability. The correction magnetic pole consists of a correction hole and a soft iron correction post made of soft magnetic material such as DT4. The soft iron correction post can move continuously in the Y-direction within the correction hole, thus the correction magnetic pole has continuous magnetic field error correction capability. To achieve both positive and negative correction within the same magnetic field cycle (one magnetic field cycle includes one positive peak and one negative peak), this invention proposes a correction magnetic pole group. The correction magnetic pole group consists of two pairs of adjacent correction magnetic poles with opposite polarities within the same magnetic field cycle, such as... Figure 3 The positive polarity of magnetic pole pair 1 and the negative polarity of magnetic pole pair 2 (a total of 4 magnetic poles) together form a corrected magnetic pole group.

[0031] like Figure 4As shown, the superconducting undulator magnet structure applicable to the magnetic field error adjustment technology of this invention is mainly composed of a set of correction magnetic poles. Typically, a complete superconducting undulator consists of hundreds of superconducting coils and alternating magnetic poles. Only three magnetic field cycles are shown here, where the polarity of correction magnetic pole pairs 1, 3, and 5 is positive, and the polarity of correction magnetic pole pairs 2, 4, and 6 is negative.

[0032] like Figure 5 As shown, by adjusting the insertion depth of the soft iron correction post within the positive polarity correction magnetic pole pair, such as symmetrically increasing the distance between the two correction posts within the No. 3 correction magnetic pole pair, a result can be achieved as shown. Figure 5 The magnetic field error correction signal shown on the right is a negative correction value.

[0033] like Figure 6 As shown, by adjusting the insertion depth of the soft iron correction post within the negative polarity correction pole pair, such as symmetrically increasing the distance between the two correction posts within the No. 4 correction pole pair, a result can be achieved as shown. Figure 6 The correction value shown on the right is a positive magnetic field error correction signal.

[0034] like Figure 7 As shown, for a complete superconducting undulator magnet equipped with the aforementioned corrective magnetic pole structure of this invention, the magnetic field error correction process is as follows: 1) When the superconducting undulator is operating stably in the low-temperature environment of the superconducting state, the magnetic field distribution on the axis of the superconducting undulator can be measured using a HALL sensor. 2) When the superconducting undulator is shut down and warmed to an operable room temperature, select several non-interfering magnetic pole groups as calibration magnetic pole groups. Adjust the insertion depth of the soft iron calibration column in the positive or negative polarity calibration magnetic pole pair in each selected calibration magnetic pole group and record the insertion depth adjustment amount h of the soft calibration column to obtain the calibration signal. The selected calibration magnetic pole groups can be adjusted simultaneously to obtain multiple calibration signals at once. The average value of each calibration signal is taken as the final calibration signal. 3) After adjustment, when the superconducting undulator is running again in the cryogenic environment of the superconducting state, the magnetic field distribution on its axis is measured. Data processing is performed; the magnetic field measured after adjusting the insertion depth of the soft iron correction post is subtracted from the magnetic field measured before adjustment to obtain the magnetic field correction amount corresponding to the adjustment amount h of the correction post insertion depth, i.e., the calibration signal. Typically, the adjustment amount of the insertion depth and the magnetic field correction amount have a linear or known correlation; based on this correlation, the insertion depth adjustment amount corresponding to any desired correction amount can be obtained. 4) Taking the magnetic field distribution of the superconducting undulator when it is stably operating in the superconducting state as the correction target and the calibration signal as the basis for calculating the correction amount, based on the principle of magnetic field superposition, the program calculates the insertion depth adjustment of the soft iron correction column that minimizes the magnetic field error of the superconducting undulator, as well as the position and polarity of the correction magnetic pole group where the soft iron correction column is located, i.e., the correction list; usually, logical algorithms such as simulated annealing are used, mainly to improve the calculation efficiency; 5) In an operable ambient temperature environment, adjust the insertion depth of the soft iron correction post at the specific correction magnetic pole group position of the superconducting undulator quantitatively according to the calibration list. 6) After adjustment, when the superconducting undulator is running stably again in the low-temperature environment of the superconducting state, the magnetic field distribution is measured and the phase error or trajectory error is calculated based on this to assess whether the error has been reduced to the required level. 7) If the target requirements are met, the correction ends; if not, continue iterating from step 4) to step 7) until the target requirements are met.

[0035] Although specific embodiments of the invention have been disclosed for illustrative purposes to aid in understanding and implementing the invention, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the invention should not be limited to the content disclosed in the preferred embodiments, and the scope of protection claimed by the invention is defined by the claims.

Claims

1. A method for correcting magnetic field error of a superconducting undulator based on soft iron correction columns, comprising the steps of: 1) drilling a blind hole on each magnetic pole in the superconducting undulator, drilling a through hole on the corresponding iron core as a correction hole, and setting a soft iron correction column in each correction hole for insertion into the blind hole of the corresponding magnetic pole and adjustable in insertion depth in the blind hole; measuring the magnetic field distribution on the axis of the superconducting undulator when the superconducting undulator is stably operated in a superconducting state; 2) stopping the superconducting undulator and warming it to an operable normal temperature environment, selecting a plurality of magnetic pole groups in the superconducting undulator as correction magnetic pole groups, the magnetic pole groups being selected such that the correction signals of the magnetic pole groups do not interfere with each other, adjusting the insertion depth of the soft iron correction column in each pair of magnetic poles with positive polarity or negative polarity in each selected correction magnetic pole group and recording the insertion depth adjustment amount h of the soft iron correction column; the magnetic pole groups include two pairs of adjacent magnetic poles with opposite polarities in the same magnetic field period; 3) operating the superconducting undulator in a superconducting state again and measuring the magnetic field distribution on the axis of the superconducting undulator; subtracting the measured magnetic field distribution after the insertion depth adjustment of the soft iron correction column from the measured magnetic field distribution in step 1) to obtain a magnetic field correction amount corresponding to the insertion depth adjustment amount h of the soft iron correction column, as a calibration signal; 4) taking the magnetic field distribution when the superconducting undulator is stably operated in a superconducting state as a correction target and the calibration signal as a correction amount, and calculating the insertion depth adjustment amount of the soft iron correction column, the magnetic pole group and the polarity corresponding to the soft iron correction column based on the principle of magnetic field superposition to minimize the magnetic field error of the superconducting undulator, to obtain a correction list; 5) stopping the superconducting undulator and warming it to an operable normal temperature environment, and adjusting the insertion depth of the soft iron correction column in the corresponding magnetic pole group according to the correction list; 6) operating the superconducting undulator in a superconducting state again and measuring the magnetic field distribution on the axis of the superconducting undulator; 7) calculating the magnetic field error of the superconducting undulator based on the measured magnetic field distribution in step 6); 8) if the magnetic field error meets the set index requirements, the correction is ended; otherwise, steps 4) to 8) are executed until the magnetic field error meets the index requirements.

2. The method of claim 1, wherein, The magnetic field error is a phase error or a trajectory error.

3. The method of claim 2, wherein, The material of the soft iron correction column is a soft magnetic material.

4. The method according to claim 1 or 2 or 3, characterized in that, The HALL sensor is used to measure the magnetic field distribution on the axis of the superconducting undulator.

5. The method according to claim 1 or 2 or 3, characterized in that, The simulated annealing method is used to calculate the insertion depth adjustment amount of the soft iron correction column to minimize the magnetic field error of the superconducting undulator.

6. The method according to claim 1 or 2 or 3, characterized in that, The correction hole and the blind hole have the same diameter and are coaxial.

Images