Magnetic shimming configuration with optimized turn geometry and electrical circuitry
View Patent ↗A magnetic shimming configuration for a high-field magnet having optimized turn geometry and electrical circuitry. The present invention accomplishes this by combining the corrective functionalities of the standard X and ZX shims into two single, simplified electrical circuits and conductors, optimized for field strength as a function of turn location. The standard Y and ZY shims were also replaced with two single, simplified circuits and conductor that is corrective of the Y and ZY fields. The new configuration also eliminates the need of additional “second, outboard turns” of the traditional X, ZX, Y, and ZY shims, located further away from the mid-plane.
1. A shim assembly for improving magnetic field uniformity in an electromagnet having a central axis, a central bore which is aligned with said central axis and which is bounded by a cylindrical wall, a mid-plane which is orthogonal to said central axis, a z-axis lying along said central axis, an x-axis lying in said mid-plane and orthogonal to said z-axis, and a y-axis lying in said mid-plane and orthogonal to said z-axis and said x-axis, said shim assembly comprising:
a. an A circuit having an A circuit loop which surrounds the −x axis;
b. wherein the majority of said A circuit loop lies on the −z side of said mid-plane;
c. a B circuit having a B circuit loop which surrounds the −x axis;
d. wherein all of said B circuit loop lies on said −z side of said mid-plane;
e. a C circuit having a C circuit loop which surrounds said y axis;
f. wherein the majority of said C circuit loop lies on the −z side of said mid-plane;
g. a D circuit having a D circuit loop which follows the same path as said C circuit, except that said D circuit is translated in the −z direction with respect to said C circuit so that all of said D circuit lies on the −z side of said mid-plane;
h. an E circuit having a first E circuit loop and a second E circuit loop, wherein said first E circuit loop surrounds the +z-axis and said second E circuit loop surrounds the −z-axis;
i. wherein said first E circuit loop lies on the +z side of said mid-plane and said second E circuit loop lies on said −z side of said mid-plane;
j. an F circuit having a first plurality of F circuit loops, a second plurality of F circuit loops, and a third plurality of F circuit loops; and
k. wherein said first plurality of F circuit loops lies on said +z side of said mid-plane, said second plurality of F circuit loops lies proximate said mid-plane, and said third plurality of F circuit loops lies on said −z side of said mid-plane.
2. A shim assembly as recited in claim 1 , wherein said A circuit loop, said B circuit loop, said C circuit loop, said D circuit loop, said E circuit loop, said first plurality of F circuit loops, said second plurality of F circuit loops, and said third plurality of F circuit loops are all located proximate said cylindrical wall bounding said central bore, with said circuit loops lying on a side of said cylindrical wall which is opposite said central axis.
3. A shim assembly as recited in claim 1 , further comprising a Z0 shim coil.
4. A shim assembly as recited in claim 1 , wherein:
a. the electrical current in said A circuit loop flows in a clockwise direction when viewed on an azimuthal plot;
b. the electrical current in said B circuit loop flows in a clockwise direction when viewed on an azimuthal plot;
c. the electrical current in said C circuit loop flows in a clockwise direction when viewed on an azimuthal plot;
d. the electrical current in said D circuit loop flows in a clockwise direction when viewed on an azimuthal plot;
e. the electrical current in said first E circuit loop flows in the direction of the x-axis cross the y-axis;
f. the electrical current in said second E circuit loop flows in the direction of the y-axis cross the x-axis;
g. the electrical current in said first plurality of F circuit loops flows in the direction of the y-axis cross the x-axis;
h. the electrical current in said second plurality of F circuit loops flows in the direction of the x-axis cross the y-axis; and
i. the electrical current in said third plurality of F circuit loops flows in the direction of the y-axis cross the x-axis.
5. A shim assembly as recited in claim 4 , wherein said A circuit loop, said B circuit loop, said C circuit loop, said D circuit loop, said E circuit loop, said first plurality of F circuit loops, said second plurality of F circuit loops, and said third plurality of F circuit loops are all located proximate said cylindrical wall bounding said central bore, with said circuit loops lying on a side of said cylindrical wall which is opposite said central axis.
6. A shim assembly as recited in claim 4 , wherein:
a. each of said current loops is located proximate said cylindrical wall bounding said central bore, with said current loops lying on a side of said cylindrical wall which is opposite said central axis;
b. each of said current loops is located a distance “a” from said central axis;
c. each point in each of said current loops can be defined by a ratio of its position along said z-axis divided by its distance “a” from said central axis, with said ratio being known as “z/a ratio”, and its azimuthal position in degrees from said x-axis;
d. said A circuit loop lies
i. between a z/a ratio of about +0.4 and a z/a ratio of about −4.0,
ii. between an azimuthal position of about 90 degrees and about 270 degrees;
e. said B circuit loop lies
i. between a z/a ratio of about −0.2 and a z/a ratio of about −4.2,
ii. between an azimuthal position of about 90 degrees and about 270 degrees;
f. said C circuit loop lies
i. between a z/a ratio of about +0.4 and a z/a ratio of about −3.8,
ii. between an azimuthal position of about 0 degrees and about 180 degrees;
g. said D circuit loop lies
i. between a z/a ratio of about −0.2 and a z/a ratio of about −4.0,
ii. between an azimuthal position of about 0 degrees and about 180 degrees;
h. said E circuit loop lies between a z/a ratio of about +0.6 and a z/a ratio of about −0.6;
i. said first plurality of F circuit loops lies between a z/a ratio of about +1.2 and a z/a ratio of about +0.6;
j. said second plurality of F circuit loops lies proximate a z/a ratio of 0.0; and
k. said third plurality of F circuit loops lies between a z/a ratio of −0.6 and −1.2.
7. A shim assembly as recited in claim 6 wherein said A circuit loop, said B circuit loop, said C circuit loop, said D circuit loop, said E circuit loop, said first plurality of F circuit loops, said second plurality of F circuit loops, and said third plurality of F circuit loops intersect only at a plurality of crossing points.
8. A shim assembly as recited in claim 6 , further comprising a Z0 shim coil.
9. A shim assembly as recited in claim 6 , wherein said A circuit loop, said B circuit loop, said C circuit loop, said D circuit loop, said E circuit loop, said first plurality of F circuit loops, said second plurality of F circuit loops, and said third plurality of F circuit loops are all located proximate said cylindrical wall bounding said central bore, with said circuit loops lying on a side of said cylindrical wall which is opposite said central axis.
10. A shim assembly as recited in claim 9 wherein said A circuit loop, said B circuit loop, said C circuit loop, said D circuit loop, said E circuit loop, said first plurality of F circuit loops, said second plurality of F circuit loops, and said third plurality of F circuit loops intersect only at a plurality of crossing points.
11. A shim assembly for improving magnetic field uniformity in an electromagnet having a central axis, a central bore which is aligned with said central axis and which is bounded by a cylindrical wall, a mid-plane which is orthogonal to said central axis, a z axis lying along said central axis, an x-axis lying in said mid-plane and orthogonal to said z-axis, and a y-axis lying in said mid-plane and orthogonal to said z-axis and said x-axis, said shim assembly comprising:
a. an X+ZX shim;
b. an X−ZX shim;
c. a Y+ZY shim;
d. a Y−ZY shim;
e. a Z shim; and
f. a Z2 shim.
12. A shim assembly as recited in claim 11 wherein said X+ZX shim, said X−ZX shim, said Y+ZY shim, said Y−ZY shim, said Z shim, and said Z2 shim intersect only at a plurality of crossing points.
13. A shim assembly as recited in claim 11 , further comprising a Z0 shim coil.
14. A shim assembly as recited in claim 11 , wherein said X+ZX, X−ZX shim, said Y+ZY shim, said Y−ZY shim, said Z shim, and said Z2 shim are all located proximate said cylindrical wall bounding said central bore, with said shims lying on a side of said cylindrical wall which is opposite said central axis.
15. A shim assembly as recited in claim 14 wherein said X+ZX shim, said X−ZX shim, said Y+ZY shim, said Y−ZY shim, said Z shim, and said Z2 shim intersect only at a plurality of crossing points.
16. A shim assembly as recited in claim 14 , wherein:
a. each of said shims contains a current loop located proximate said cylindrical wall bounding said central bore, with said current loops lying on a side of said cylindrical wall which is opposite said central axis;
b. each of said current loops is located a distance “a” from said central axis;
c. each point in each of said current loops can be defined by a ratio of its position along said z-axis divided by its distance “a” from said central axis, with said ratio being known as “z/a ratio”, and its azimuthal position in degrees from said x-axis;
d. said X+ZX shim contains a current loop lying
i. between a z/a ratio of about +0.4 and a z/a ratio of about −4.0,
ii. between an azimuthal position of about 90 degrees and about 270 degrees;
e. said X−ZX shim contains a current loop lying
i. between a z/a ratio of about −0.2 and a z/a ratio of about −4.2,
ii. between an azimuthal position of about 90 degrees and about 270 degrees;
f. said Y+ZY shim contains a circuit loop lying
i. between a z/a ratio of about +0.4 and a z/a ratio of about −3.8,
ii. between an azimuthal position of about 0 degrees and about 180 degrees;
g. said Y−ZY shim contains a circuit loop lying
i. between a z/a ratio of about −0.2 and a z/a ratio of about −4.0,
ii. between an azimuthal position of about 0 degrees and about 180 degrees;
h. said Z shim contains a circuit loop lying between a z/a ratio of about +0.6 and a z/a ratio of about −0.6;
i. said Z2 shim contains a first plurality of circuit loops lying between a z/a ratio of about +1.2 and a z/a ratio of about +0.6;
j. said Z2 shim contains a second plurality of circuit loops lying proximate a z/a ratio of 0.0; and
k. said Z2 shim contains a third plurality of circuit loops lying between a z/a ratio of −0.6 and −1.2.
17. A shim assembly as recited in claim 16 wherein said X+ZX shim, said X−ZX shim, said Y+ZY shim, said Y−ZY shim, said Z shim, and said Z2 shim intersect only at a plurality of crossing points.
18. A shim assembly as recited in claim 16 , further comprising a Z0 shim coil.
19. A shim assembly as recited in claim 16 , wherein said X+ZX shim, said X−ZX shim, said Y+ZY shim, said Y−ZY shim, said Z shim, and said Z2 shim are all located proximate said cylindrical wall bounding said central bore, with said shims lying on a side of said cylindrical wall which is opposite said central axis.
20. A shim assembly as recited in claim 19 wherein said X+ZX shim, said X−ZX shim, said Y+ZY shim, said Y−ZY shim, said Z shim, and said Z2 shim intersect only at a plurality of crossing points.