JPS6348405B2 - - Google Patents
Info
- Publication number
- JPS6348405B2 JPS6348405B2 JP12870782A JP12870782A JPS6348405B2 JP S6348405 B2 JPS6348405 B2 JP S6348405B2 JP 12870782 A JP12870782 A JP 12870782A JP 12870782 A JP12870782 A JP 12870782A JP S6348405 B2 JPS6348405 B2 JP S6348405B2
- Authority
- JP
- Japan
- Prior art keywords
- coil
- magnetic field
- main coil
- compensation
- persistent current
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
- G01R33/381—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using electromagnets
- G01R33/3815—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using electromagnets with superconducting coils, e.g. power supply therefor
Landscapes
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Magnetic Resonance Imaging Apparatus (AREA)
Description
この発明は、永久電流モードで運転される超電
導マグネツト、特に超電導マグネツトの発生する
磁界の均一度の時間的な変化防止に関するもので
ある。
従来、この種の装置として第１図に示すものが
あつた。第１図において１は超電導マグネツト、
２は主コイル、３は主コイル２が発生する磁界の
均一度を向上させるための補償コイルである。
以下、２ａは主コイル２の永久電流スイツチ、
２ｂは永久電流スイツチ２ａヒータ、２ｃは引出
線であり、２ｄは主コイル２と永久電流スイツチ
２ａからなる閉回路を示す。また、３ａは補償コ
イル３の永久電流スイツチ、３ｂは永久電流スイ
ツチ３ａのヒータ、３ｃは引出線であり、３ｄは
補償コイル３と永久電流スイツチ３ａからなる閉
回路を示している。主コイル２の両端子間にはヒ
ータ２ｂを備えた永久電流スイツチ２ａが接続さ
れており、この永久電流スイツチ２ａの両端には
引出線２ｃが接続されている。また、主コイル２
の周囲を取り巻くように補償コイル３が巻かれて
おり、主コイル２と同様に補償コイル３の両端子
間には、ヒータ３ｂを備えた永久電流スイツチ３
ａが接続されており、さらにこの両端には引出線
３ｃが接続されている。第２図には、第１図に示
した従来装置が永久電流モードで運転されている
状態での、閉回路２ｄおよび３ｄの等価回路２
d′および３d′がそれぞれ示されている。等価回路
２d′のRM、LMはそれぞれ閉回路２ｄの純抵抗分、
リアクタンス分、また等価回路３d′のRC、MCは
それぞれ閉回路３ｄの純抵抗分とリアクタンス分
を示している。なお、インダクタンスLM、LCは
相互誘導の影響も考慮した等価的なインダクタン
スであり、また、第１図の超電導マグネツトは通
常超電導状態、例えば液体ヘリウム温度において
運転されるものである。
次に動作について説明する。第１図において主
コイル２を永久電流モードで運転するためには、
まずヒータ２ｂに通電し、永久電流スイツチ２ａ
を加熱することにより有限の抵抗をもたせ、続い
て、引出線２ｃに直流電源（図示しない）を接続
し、主コイル２を励磁する。その後ヒータ２ｂの
通電を中止すると、永久電流スイツチ２ａが超電
導状態となり、引出線２ｃにとりつけられた直流
電源（図示しない）を切り離すことにより、主コ
イル２と永久電流スイツチ２ａからなる永久電流
モードの閉回路２ｄが実現される。
この時、閉回路２ｄに流れる電流すなわち、主
コイル２の発生磁界は、等価回路２d′より、時間
ｔと共にexp（−RM／LMｔ）の割合で減衰してゆく。
上述した操作と同様に、補償コイル３のヒータ
３ｂを通電し、引出線３ｃに直流電源（図示しな
い）を接続して補償コイル３を励磁させ、その後
ヒータ３ｂへの通電を中止し、引出線３ｃに取り
付けられた直流電源を切り離すことにより、補償
コイル３もまた永久電流モードとなる。よつて、
補償コイル３と永久電流スイツチ３ａからなる永
久電流モードの閉回路３ｄに流れる電流、すなわ
ち、補償コイル３の発生磁界は、等価回路３d′よ
りexp（−RC／LCｔ）の割合で減衰することになる。
しかるに、超電導マグネツト１内の任意の点Z0
（図示しない）における主コイル２による磁界H→M
（Ｚ０）は、
同様にして、主コイル２の磁界を均一にするた
めの補償コイル３によるこの任意の点Z0での磁界
H→C(Z0)は
The present invention relates to a superconducting magnet operated in persistent current mode, and more particularly to preventing temporal changes in the uniformity of the magnetic field generated by the superconducting magnet. Conventionally, there has been a device of this type as shown in FIG. In Fig. 1, 1 is a superconducting magnet,
2 is a main coil, and 3 is a compensation coil for improving the uniformity of the magnetic field generated by the main coil 2. Hereinafter, 2a is the persistent current switch of the main coil 2,
2b is a heater of the persistent current switch 2a, 2c is a leader wire, and 2d is a closed circuit consisting of the main coil 2 and the persistent current switch 2a. Further, 3a is a persistent current switch of the compensation coil 3, 3b is a heater of the persistent current switch 3a, 3c is a lead wire, and 3d is a closed circuit consisting of the compensation coil 3 and the persistent current switch 3a. A persistent current switch 2a equipped with a heater 2b is connected between both terminals of the main coil 2, and a lead wire 2c is connected to both ends of the persistent current switch 2a. Also, main coil 2
A compensation coil 3 is wound around the main coil 2, and a persistent current switch 3 equipped with a heater 3b is connected between both terminals of the compensation coil 3 like the main coil 2.
a is connected, and furthermore, a leader line 3c is connected to both ends of the lead wire 3c. FIG. 2 shows an equivalent circuit 2 of closed circuits 2d and 3d when the conventional device shown in FIG. 1 is operated in persistent current mode.
d' and 3d' are shown respectively. R M and L M of the equivalent circuit 2d' are the pure resistance of the closed circuit 2d, respectively.
The reactance component, and R C and M C of the equivalent circuit 3d' respectively indicate the pure resistance component and reactance component of the closed circuit 3d. Incidentally, the inductances L M and L C are equivalent inductances taking into account the influence of mutual induction, and the superconducting magnet shown in FIG. 1 is normally operated in a superconducting state, for example, at liquid helium temperature. Next, the operation will be explained. In order to operate the main coil 2 in persistent current mode in Fig. 1,
First, the heater 2b is energized, and the persistent current switch 2a is turned on.
A finite resistance is created by heating the lead wire 2c, and then a DC power source (not shown) is connected to the lead wire 2c to excite the main coil 2. After that, when the heater 2b is de-energized, the persistent current switch 2a becomes superconducting, and by disconnecting the DC power supply (not shown) attached to the leader wire 2c, the persistent current mode consisting of the main coil 2 and the persistent current switch 2a is activated. A closed circuit 2d is realized. At this time, the current flowing in the closed circuit 2d, that is, the magnetic field generated by the main coil 2, attenuates at a rate of exp(-R M /L M t) with time t from the equivalent circuit 2d'. Similar to the above-mentioned operation, the heater 3b of the compensation coil 3 is energized, a DC power source (not shown) is connected to the leader wire 3c to excite the compensation coil 3, and then the power to the heater 3b is stopped, and the leader wire 3c is energized. By disconnecting the DC power supply attached to 3c, the compensation coil 3 is also placed in persistent current mode. Then,
The current flowing in the closed circuit 3d in persistent current mode consisting of the compensation coil 3 and the persistent current switch 3a, that is, the magnetic field generated by the compensation coil 3, is attenuated at the rate of exp (-R C /L C t) from the equivalent circuit 3d'. I will do it. However, any point Z 0 in the superconducting magnet 1
Magnetic field H→ M due to main coil 2 at (not shown)
(Z0) is Similarly, the magnetic field at this arbitrary point Z 0 by the compensation coil 3 to make the magnetic field of the main coil 2 uniform
H→ C(Z0) is
【式】
となる。
従来の超電導マグネツトは以上のように構成さ
れているが、主コイル２と補償コイル３では、磁
界の時間的な減衰を表わす時定数が異なり、一般
に、LM／RM＝LC／RCとはならない。
従つて、主コイル２と補償コイル３とが各々発
生させる磁界は同じ割合では減衰してゆかず、そ
の結果、磁界の空間的均一度が時間的に低下して
ゆくという欠点があつた。
この発明は、上述したような従来のものの欠点
を除去するためになされたもので、主コイルおよ
び補償コイルの時定数を調整することにより磁界
の均一度が時間の経過と共に低下することを軽減
させることを目的としている。
以下、この発明の一実施例を説明する。この発
明の一実施例の構成要素は、第１図および第２図
の従来装置の一実施例と同じである。従来装置と
異なるところは第２図に示した等価回路２d′およ
び３d′の各回路定数間にLM／RM＝LC／RCの関係が成立
するように各コイルの時定数が調整されていると
ころである。
上述したように、この発明による超電導マグネ
ツトは、永久電流運転されている主コイル２の時
定数LM／RMと補償コイル３の時定数LC／RCを同一にす
るように、各回路定数RM、LM、RC、およびLCが
定められている。超電導マグネツト１内の任意の
点Z0（図示しない）に主コイル２が作る磁界
HM(Z0)は[Formula] becomes. Conventional superconducting magnets are constructed as described above, but the main coil 2 and the compensation coil 3 have different time constants representing the temporal attenuation of the magnetic field, and in general, L M /R M =L C /R C It is not. Therefore, the magnetic fields generated by the main coil 2 and the compensation coil 3 do not attenuate at the same rate, and as a result, the spatial uniformity of the magnetic fields deteriorates over time. This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and by adjusting the time constants of the main coil and the compensation coil, the deterioration of the uniformity of the magnetic field over time is alleviated. The purpose is to An embodiment of this invention will be described below. The components of an embodiment of the present invention are the same as the embodiment of the conventional apparatus shown in FIGS. 1 and 2. The difference from the conventional device is that the time constant of each coil is adjusted so that the relationship L M /R M = L C /R C is established between the circuit constants of equivalent circuits 2d' and 3d' shown in Figure 2. This is where it is being done. As described above, in the superconducting magnet according to the present invention, each circuit is adjusted so that the time constant L M /R M of the main coil 2 and the time constant L C /R C of the compensation coil 3, which are operated with persistent current, are made the same. Constants R M , L M , R C , and L C are defined. Magnetic field created by the main coil 2 at an arbitrary point Z 0 (not shown) in the superconducting magnet 1
H M(Z0) is
【式】
同様にして、主コイル２の作る磁界を均一にす
るために、補償コイル３がこの任意の点Z0につく
る磁界H→C(Z0)は[Formula] Similarly, in order to make the magnetic field created by the main coil 2 uniform, the magnetic field H→ C(Z0) created by the compensation coil 3 at this arbitrary point Z 0 is
【式】
で示される。任意の点Z0には、両コイルの合成磁
界が加わり、この合成磁界をH→(Z0)とすると、
H→(Z0)＝H→M(Z0)＋H→C(Z0)
となる。従つて両コイルの時定数が等しい時、
LM／RM＝LC／RC＝τとすれば任意の点Z0における磁界
H(Z0)は、
で示される。すなわち、任意の点Z0の磁界の絶対
値は時間と共に変化するが、主コイル２による磁
界と補償コイル２による磁界との割合は常に一定
である。主コイル２が任意点Z0に発生する不均一
磁界の大きさは、主コイルのその点での発生磁界
のの絶対値に比例する。従つてこの均一磁界を取
り除くための補償コイル３の磁界も、主コイルの
発生磁界の絶対値に比例する。すなわちこの実施
例の如く主コイル２の発生磁界と補償コイル３の
発生磁界との割合が一定ならば、補償コイル３
は、補償すべき不均一磁界を完全に取り除いてお
り、また時間的な減衰の割合が等しいので磁界の
均一度は時間と共に変化しない。
なお、上記実施例では補償コイルが１個とりつ
けられ、その補償コイルが主コイルの軸方向の１
次の磁界変化を補償するものである場合について
説明したが、補償コイルは主コイルの軸と直角方
向の磁界補償用のものでもよく、補償すべき磁界
変化の次数について制限はない。また、主コイル
の形状については、ノツチコイルがとりつけられ
た場合であつてもよく、いずれの場合も上記実施
例と同様の効果を奏する。
さらに、上記実施例では主コイルと補償コイル
の時定数の関係をLM／RM＝LC／RCとしたが｜（LM／RM）
−
（LC／RC）｜≪１の場合でも十分同様の効果を奏す
る。
以上のように、この発明によれば、主コイルと
補償コイルとの時定数を一致、または十分近づけ
ることにより、磁界の均一度の時間的な変化をな
くすか、あるいは十分小さくできる効果がある。[Formula] A composite magnetic field of both coils is applied to an arbitrary point Z 0 , and if this composite magnetic field is H→ (Z0) , then H→ (Z0) = H→ M(Z0) +H→ C(Z0) . Therefore, when the time constants of both coils are equal,
If L M /R M =L C /R C =τ, the magnetic field H (Z0) at any point Z 0 is It is indicated by. That is, although the absolute value of the magnetic field at any point Z 0 changes with time, the ratio of the magnetic field due to the main coil 2 and the magnetic field due to the compensation coil 2 is always constant. The magnitude of the non-uniform magnetic field generated by the main coil 2 at an arbitrary point Z 0 is proportional to the absolute value of the generated magnetic field at that point of the main coil. Therefore, the magnetic field of the compensation coil 3 for removing this uniform magnetic field is also proportional to the absolute value of the magnetic field generated by the main coil. That is, if the ratio of the magnetic field generated by the main coil 2 and the magnetic field generated by the compensation coil 3 is constant as in this embodiment, the compensation coil 3
completely eliminates the non-uniform magnetic field to be compensated for, and the uniformity of the magnetic field does not change over time because the rate of temporal attenuation is equal. In addition, in the above embodiment, one compensation coil is installed, and the compensation coil is attached to one side of the main coil in the axial direction.
Although the case has been described in which the compensation coil compensates for the following magnetic field change, the compensation coil may be one for magnetic field compensation in a direction perpendicular to the axis of the main coil, and there is no restriction on the order of the magnetic field change to be compensated for. Further, regarding the shape of the main coil, a notch coil may be attached, and in either case, the same effects as in the above embodiments are achieved. Furthermore, in the above embodiment, the relationship between the time constants of the main coil and the compensation coil is L M /R M = L C /R C | (L M /R M )
− (L C /R C ) | << 1, the same effect can be achieved. As described above, according to the present invention, by making the time constants of the main coil and the compensation coil the same or sufficiently close to each other, there is an effect that the temporal change in the uniformity of the magnetic field can be eliminated or sufficiently reduced.
第１図超電導マグネツトの構成図、第２図は第
１図の主コイルおよび補償コイルを含む閉回路の
それぞれの等価回路図である。
１……超電導マグネツト、２……主コイル、３
……補償コイル、２ａ，３ａ……永久電流スイツ
チ、２ｂ，３ｂ……ヒータ、２ｃ，３ｃ……引出
線。なお、図中、同一符号は同一又は相当部分を
示す。
FIG. 1 is a block diagram of a superconducting magnet, and FIG. 2 is an equivalent circuit diagram of a closed circuit including a main coil and a compensation coil shown in FIG. 1...Superconducting magnet, 2...Main coil, 3
...compensation coil, 2a, 3a...persistent current switch, 2b, 3b...heater, 2c, 3c...lead wire. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.
Claims (1)
イルが発生する磁界の空間的な均一度を高めるた
めに取付けた補償コイル群と、上記主コイルおよ
び上記補償コイル群を永久電流運転するための各
コイルの永久電流スイツチとから成る超電導マグ
ネツトにおいて、永久電流運転時の上記主コイル
の時定数と上記補償コイル群の各コイルの時定数
とをできる限り同一値にもしくは同一値にするこ
とを特徴とした超電導マグネツト。1. A main coil that generates the main magnetic field, a group of compensation coils installed to improve the spatial uniformity of the magnetic field generated by this main coil, and a group of compensation coils that operate the main coil and the compensation coil group with persistent current. A superconducting magnet comprising a persistent current switch of a coil, characterized in that the time constant of the main coil during persistent current operation and the time constant of each coil of the compensation coil group are made to be the same value as much as possible or the same value. superconducting magnet.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP12870782A JPS5918618A (en) | 1982-07-21 | 1982-07-21 | Superconductive magnet |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP12870782A JPS5918618A (en) | 1982-07-21 | 1982-07-21 | Superconductive magnet |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS5918618A JPS5918618A (en) | 1984-01-31 |
| JPS6348405B2 true JPS6348405B2 (en) | 1988-09-29 |
Family
ID=14991433
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP12870782A Granted JPS5918618A (en) | 1982-07-21 | 1982-07-21 | Superconductive magnet |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS5918618A (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4656447A (en) * | 1984-06-27 | 1987-04-07 | General Electric Company | Superconducting filter coils for high homogeneity magnetic field |
| GB9016184D0 (en) * | 1990-07-24 | 1990-09-05 | Oxford Magnet Tech | Magnet assembly |
| JP2000277322A (en) * | 1999-03-26 | 2000-10-06 | Toshiba Corp | High-temperature superconducting coil, high-temperature superconducting magnet using the same, and high-temperature superconducting magnet system |
| CN104730475B (en) * | 2013-12-23 | 2020-07-07 | Ge医疗系统环球技术有限公司 | Magnetic field adjusting system and method and magnetic resonance imaging system |
-
1982
- 1982-07-21 JP JP12870782A patent/JPS5918618A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5918618A (en) | 1984-01-31 |
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