A strong magnetic field synchrocyclotron and its magnetic field shim method
A cyclotron and strong magnetic field technology, which is applied in the direction of magnetic resonance accelerators, accelerators, electrical components, etc., can solve the problems of increasing the difficulty of frequency curve matching, so as to improve the matching degree, reduce the beam loss, and reduce the number of shims Effect
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Embodiment approach 1
[0038] A schematic flow chart of the magnetic field shimming method for a strong magnetic field synchrocyclotron provided in an embodiment of the present application is as follows figure 1 As shown, the following steps S1-S9 are included.
[0039] Actual shimming amount acquisition step S1: Acquire the actually required shimming magnetic field amount. In this step S1 , it can be measured by, for example, a four-dimensional motion magnetometer to obtain the actual required amount of shimming magnetic field.
[0040]Shape function construction step S3: Within the radius range that can be processed, the continuous curve is equivalent to a series of rectangular blocks with fixed radial width but height to be obtained, and the shape function of the continuous curve is constructed, wherein the shape function indicates that each rectangular block corresponds to The magnetic field change amount of , the radius range includes multiple radius values r.
[0041] Specifically, in step...
Embodiment approach 2
[0070] Such as Figure 5 As shown, it is a schematic flow chart of the magnetic field shim method provided by another embodiment of the present application, which is similar to the aforementioned embodiment 1, the difference is that there may be certain errors in the linear approximation in step S3, therefore, in this embodiment In the method, an error removal step S8 is also included after the rectangle height calculation step S7 and before the processing step S9. In step S8, the calculation formula involved in step S5 is solved according to the shape function, and the height vector H corresponding to all the rectangular blocks in the rectangular height calculation step S7 is solved to obtain the magnetic field change corresponding to a series of rectangular blocks, and the magnetic field change is obtained The difference with the actual required shimming magnetic field value is used as the newly required shimming magnetic field value and returned to the rectangular height ca...
Embodiment approach 3
[0081] In the aforementioned step S7, sometimes due to ill-conditioned matrix (det(F T For the problem of F)≈0), the solved rectangular block height vector H fluctuates greatly, and the formed curve is difficult to process in engineering practice. Based on this, this embodiment proposes a method to improve the first two embodiments, by artificially increasing the matrix F T The value of the diagonal of F, that is
[0082] H=(F T F+κI) -1 (F T ΔB)
[0083] Among them, I is the unit matrix, and κ is a constant, which needs to be determined after measuring the calculation accuracy and calculating the smoothness of the shimming curve through the weight of experience.
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