SHIMMING DEVICE FOR SUPERCONDUCTING MAGNET

• US 20120176136A1
• Filed: 07/05/2010
• Published: 07/12/2012
• Est. Priority Date: 07/03/2009
• Status: Active Grant

• Current Assignee: National Institute for Materials Science
• Original Assignee: National Institute for Materials Science
• Inventors: Shimizu, Tadashi, Shinagawa, Hideyuki, Ohki, Shinobu
• Granted Patent: US 9,075,120 B2
• Time in Patent Office: Days
• US Class Current: 324/322
• CPC Class Codes: G01R 33/3815 with superconducting coils, e.g. power supply therefor
• CPC Class Codes: G01R 33/3875 using correction coil assemblies, e.g. active shimming
• CPC Class Codes: G01R 33/389 Field stabilisation , e.g. by field measurements and control means or indirectly by current stabilisation

Abstract

This shimming device sequentially records a history of conducted shim setting, momentarily dynamically calculates compensation values corresponding to the record by the aid of a characteristic function, and dynamically controls the shim coil by the aid of the compensation values thus obtained, to thereby compensate the magnetic field fluctuation of the superconducting magnet which is attributable to the setting of the shim, and stabilizes the magnetic field, in an NMR superconducting magnet. This device includes shim setting recording means (230) that records a set value of the shim, a type of set operation, the operation amount of the setting, and a time at which the setting is conducted, in association with each other for each setting; generating compensation function supply means (210) that supplies a generating compensation function that is a function having the type of the operation, the operation amount, and the amount of time as factors, and is set so as to approximately compensate a magnetic field fluctuation attributable to individual setting; compensation value computing means (240) that refers to the generating compensation function supply means (210) and the shim setting recording means (230), computes a compensation value at the time t by the aid of a compensation function configured by those means, and outputs the computation result; shim coil driving means (300) that drives the shim coil (400) by the aid of a sum of the compensation value obtained by the compensation value computing means (240), and a latest set value.

Claims

1. A shimming device that compensates stability and homogeneity of a magnetic field of a superconducting magnet with a shim coil, wherein at least one term of the shim is controlled by the following means (1) to (4).

(1) shim setting recording means that records, when the setting of the shim is conducted, a set value u of the shim, a type w of set operation, operation amount s of setting, and the time t of setting, by associating the setting finally conducted with an index N−

1 so as to be referred to as (w_n, u_n, s_n, t_n) by the aid of an index n which is a value of 0 to N−

1 where the number of times of setting is N;

(2) generating compensation function supply means that supplies a generating compensation function “

f^w(s,t′

)”

that is a function having the type w of the operation, the operation amount s, and the amount of time t′

as arguments, which has a property to become 0 when the amount of time t′

is infinite, and is set so as to approximately compensate a magnetic field fluctuation attributable to individual setting;

(3) compensation value calculating means that calculates a compensation value at the time t by the aid of a compensation function assuming that symbol “

Σ

”

represents a sum of n (0, 1, 2 . . . N−

1), and the compensation function “

g(t)”

is a function of the time t which is expressed as “

g(t)=Σ

f^wn (s_n, t−

t_n)”

by the generating compensation function and the setting of the shim conducted before the time t; and

(4) shim coil driving means that drives the shim coil by the aid of a sum of the compensation value obtained by the compensation value calculating means, and a latest set value u<sub>N−

1</sub>.

2. The shimming device according to claim 1, wherein the generating compensation function is expressed as “

f^w_s=_s0(t′

)×

h(s/s₀)”

assuming that the generating compensation function “

f^w(s₀, t′

)”

when the operation amount s of setting has a specific value s₀ is a species compensation function “

f^w_s=_s0(t′

)”

which is a function of the amount of time t′

, the operation amount s of setting is normalized by the aid of s₀, and a polynomial function h of the normalized operation amount “

s/s₀”

is h(s/s₀).

3. (canceled)