JPH012635A - Cryogenic chamber for magnetic resonance - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Relationship to Related Applications This application is filed under pending U.S. Patent Application Serial No. 033.
No. 326, No. 033.293, No. 033.423,
No. 033.329 and No. 033゜330 and related a
do.

BACKGROUND OF THE INVENTION This invention relates to a direct contact thermal interface device for interconnecting a polygonal cryocooler and a magnetic resonance imaging cryostat.

A conventional magnetic resonance imaging cryostat typically uses two thermal radiation shields surrounding a helium container, with a superconducting magnet in the helium container and a cryostat in the helium container. Minimizes heat leakage from the outside.

The outer of the two shields is a storage container for liquid nitrogen, so that the temperature of this shield is maintained at approximately 80'K.

The inner shield uses vented helium gas for cooling,
Operates at 40'.

Two main attachment methods are used to connect cryocoolers to thermal shields within cryostats. The first relies on the thermal conductivity of the helium gas interface to reduce the interfacial resistance between the cryocooler and the radiation shield. In this format, a helium vessel is filled vertically and the cryogenic head of the cryocooler is suspended within a layered column of helium gas. A cryocooler heat station is then created with a ring attached to the shield. Interfacial resistance is minimized because a thin film of helium gas trapped between the heat station and the shield ring creates a heat transfer path.

This system requires a form of vertical mounting, and therefore lacks flexibility in positioning the cryocooler. Furthermore, it requires entering a helium container, so it costs quite a bit
as well as having to ensure some vacuum-tight seal upon entry. Furthermore, by entering the helium container, there is a risk of introducing mechanisms and sources of heat leakage into the helium container, such as thermo-acoustic imaging and solid-state conduction through the helium column. . Finally, there is a risk of direct communication between the surroundings and the helium vessel, creating a large heat leak that could lead to magnet quenching when the cryocooler has to be repaired. This is large.

The second method relies on contact pressure between two solid mating members to minimize interfacial resistance. In this type, the cryocooler is suspended in a well that is evacuated. The radiation shield uses the well as a heat station,
A means of applying appropriate interfacial pressure between the cryocooler and the cryostat is required. This approach gives Jlj the freedom to completely replace the cryocooler when it becomes convenient to repair it. However, the requirement for interfacial pressure results in a significant increase in the agility and cost of this interface, or a significant sacrifice in the thermal performance of the interface.

It is an object of this invention to provide a thermally efficient, low cost interface between a magnetic resonance imaging cryostat and a cryocooler.

Another object of this invention is to
The objective is to provide an interface through which the cryocooler can be accessed.

SUMMARY OF THE INVENTION One aspect of the present invention provides a cryostat for magnetic resonance that uses a vacuum vessel of the cryostat that has a limited opening. Inside the vacuum vessel is a radiation shield.

A cryocooler cold end housing having a heat φ stage and having a housing passes through an opening in the vacuum vessel of the cryostat and is hermetically secured thereto.

A housing forms part of the vacuum vessel. A stage of the housing at the cold end of the cryocooler is directly connected to the radiation shield. The internal parts of the cryocooler can be removed for maintenance without breaking the vacuum of the cryocooler.

Although the gist of the invention is specifically and clearly described in the claims, the features and advantages of the invention will be better understood from the following description of preferred embodiments with reference to the drawings.

DETAILED DESCRIPTION OF THE INVENTION Throughout the drawings, the same reference numerals are used for like parts, except that FIGS.
j 11 is shown. Closed axial bore 15
an outer closed cylindrical 2'J empty container 13,
It surrounds a closed cylindrical heat shield 17 of 80 K. A closed cylindrical heat shield 21 at 20 K and a closed cylindrical helium container 23 containing a magnet are nested inside the 80 K shield.
Both the shield and the helium container have a sealed axial bore therethrough. 80K and 2
Both shields are made of a non-magnetic, thermally conductive material such as aluminum and are shown in their entirety in FIGS. 3 and 4, respectively. The circular end face of the shield is fixed by bolts 27 to an aluminum ring 25, which ring
As shown in FIGS. 3 and 4, it is welded to the end of the cylindrical shield. Helium container 23 is made of a non-magnetic, thermally conductive material such as aluminum and is shown in its entirety in FIG. The hem is welded in place to the circular end face or cylinder of the ram container. The vacuum vessel 13, which also acts as a ferromagnetic shield, is made of a rolled mild steel plate, and the axial hollow portion 15 is made of non-magnetic stainless steel.

Ingot iron may be used instead of rolled mild steel.

The end face of the rolled steel plate of the vacuum vessel is welded to the stainless steel bore 15 and a predetermined position of the cylindrical shell of the rolled steel plate. All welds in the steel of the ferromagnetic shield shall be vacuum-tight. The inner surface of the shield is treated with an anti-Q+'i agent to reduce outgassing in vacuum. A rust preventive coating that is effective in reducing outgassing is Bond R1123, available from Sealed Air Corporation.
5 and context. Alternatively, in an unshielded embodiment, the entire vacuum vessel can be made of non-magnetic stainless steel.

Next, regarding Figures 2, 6, 7, and 9, the extremely low 111! A radial support device for the helium container inside the tank is described. The helium container 23 is radially supported within the vacuum container 13 by eight fiber-reinforced plastic support straps 31 . Four straps are on each circular side of the helium container 23. By selecting 19-combination, which is mainly composed of unidirectional fibers with a fiber volume ratio of 60% in epoxy 7-trix, fiber-reinforced plastic; performance. The fibers should have high strength, high modulus, and low thermal conductivity at cryogenic temperatures. Suitable fiber families for this application include alumina, graphite, silicon carbide, and S-nitrate. The strap of the preferred embodiment is formed as an elongated loop of S-2 fiber glass impregnated with SCI-REZ-081 Stainless Steel epoxy abrasive, available from Structural Refinery Industries, Inc. of California. The four straps 31 at each end of the helium container 8 are in the same plane and are aligned with the circular end face of the cylindrical vacuum container 13. The straps at each end of the helium container are The middle 1' of the outer vacuum vessel is arranged symmetrically with respect to the plane.

Each strap extends from a pin 33 held in a clevis 35. It is fixed by a U-link 35 or a threaded rod 41 to a block 37 welded to the helium container 21. One end of the threaded rod 41 is threaded into the U-link 35, and the other end passes through an opening in the block 37 and is fixed by a nut 43 and a lock nut. The other end of the strap 31 passes through the second end of a spherical support 45 which is fitted into a recess in the vacuum vessel 13. This spherical support body rotates,
The straps are properly aligned 11., thus compensating for manufacturing part variations. This consistent alignment ensures that the strap is evenly supported across its width;
The maximum fatigue life is thus achieved. The U-link, threaded rod and spherical support body are made of non-magnetic H-grade, preferably stainless steel. Block 37 is made of non-magnetic material.
Preferably made of aluminum.

A mild steel cover 47 is welded to the opening of the vacuum vessel to maintain the vacuum state. Each of the four straps 31 at the end of the helium container 2- forms an angle of 45° with the water shell surface. At the end of the circular valley of the helium container 2-, two straps are locked near the top of the helium container and two near the bottom. The top strap extends at a 45" angle from the water surface and the bottom strap extends at a 45" angle in one direction from the horizontal plane. One bottom strap under the force of the helium container. The straps and one top strap pass through the vacuum vessel horizontally near the IB face, and the top strap on one side of the helium vessel and the bottom strap on the other side pass through the vacuum vessel on the opposite side. Close to the horizontal plane and pass through the vacuum vessel. None of the straps intersect. Strap 31 is 20K and 80K.
It also passes through the opening in the g-shield.

The straps 31 use braided copper cables 51 and 53 to respectively use the 20K and 110K shields as heat stations to block the heat due to conduction 4 transmitted from the vacuum vessel 13 at room temperature. Strap 51 which acts as a heat station. ．． one support strap 31 with 53
is shown in FIG.

Strap 51°53 that acts as a heat station
are secured to either side of the loops of the one-summer strap 31 with thermally conductive epoxy at locations along the length of the strap 31. The straps 51.53 are secured to the shield by rivets passing through holes in the braid. Adjustment of the nut 43 in the block 37 changes the tension of the strap. The symmetrical arrangement of the radial supports ensures that the axial centerline of the helium volume moves relative to the axial centerline of the outer vacuum vessel when the outer vacuum vessel undergoes a small temperature thinning. It is guaranteed that there will be no. If the outer vacuum container performs a self-shielding effect on the magnet in the helium container and attempts to maintain the homogeneity of the magnetic field in the bore of the magnet necessary for imaging, then the distance between the two center lines □ This is important because we cannot allow relative motion of .

Next, with reference to FIGS. 6, 7, and 10, the axial support device for the helium container 23 in the extremely hot bath will be described. A helium container 23 is axially supported from the vacuum container 13 by four composite straps 55. Strap 55 is formed as an elongated loop of the same material that radially supports the helium container, but is half as wide. A strap 55 extends along a horizontal plane passing through the center of the cylindrical helium container. One end of each of the four straps 55 is supported by a pin 57, and the strap 55
passes around it. A pin is held by a U-link 61, which is fixed to a threaded rod 63. Threaded rods for the two straps pass through one circular surface of the vacuum vessel, and a nut 65 and a lock nut, not shown in the drawings, are threaded onto the threaded rod 63 to adjust the tension. Threaded rods for the remaining two straps pass through the circular surface on the opposite side of the vacuum vessel and are similarly secured. The straps 55 are connected to the helium container by looping the other end of each strap through one of four cap-shaped flanged trunnions 67 extending radially from the helium container. The trunnions 67 are on a horizontal lower surface passing through the center of the cylinder, and the two trunnions on either side of the center plane of the cylinder are arranged symmetrically in the axial direction. The axial position of the trunnion on the people side of the center plane is determined by the amount of preload that will be applied to the strap by heat shrinkage of the helium container after the strap is installed. The farther the trunnion is from the centerline, the greater the contraction toward the center of the cylinder. Support straps 55 pass through the openings in the 29 K and 80 K shields and provide heat stations for the 20 K and 80 K shields by means of braided copper cables 71, 73, respectively. Straps 71, 73 are attached to either side of the loops of the 112 merged strap 55 at locations along the length of the straps. FIG. 11 shows an axial support strap 5 with straps 71, 73 acting as a heat station.
5 is shown. A strap serving as a heat station is secured to the shield by rivets. Connections using U-links 61 and trunnions 67 allow straps 55 to rotate, thereby compensating for manufacturing variations.

At 80 , the shield 17 is supported radially from the helium container 23 by a tubular strut 75 . The struts 75 are in compression and are attached to aluminum blocks 7 welded to the helium container at three locations on each circular face of the helium container.
It is fixed at 4. The struts have internal threads on each end.
T-there's a threaded rod extending from it. A single post extends from each side in the vertical direction, passes through the 20 IC shield, and is secured to the goK shield. The other two pillars 7
5 are attached to each of the helium vessels, equidistant from each other and from the vertical struts, passing through a 20Ki shield and fixed to the shield at 80. The two pillars are water (1'
, and the horizontal b passing through the center of the shield is fixed. Each strut 75 provides a heat station for the 20Kfi shield with braided cables 76. 8
The shield at 0 is axially supported by two wooden posts 77 located at one end of the container, as shown in FIG.

This strut is secured to the circular face of the helium vessel by a threaded rod and to the axial support cover 78 by two nuts that thread through the 20 K shield and into threaded rods extending from the end of the strut 77. Support (177 is the braided cable 79
Therefore, the 20KM shield will be a heat station.

All struts 75 and 77 are made of non-magnetic material with a small heat conduction hole, and are made of a thin walled G with internal grooves at both ends.
-10CR sentinel-preferably a fiber tube.

Referring to FIG. 7, the shield 21 is supported by 80I<shield 17 at 20 by six non-magnetic supports. These supports have low thermal conductivity and are preferably made of 010 steel fiber glass T-11Q80 (0/90 steel poxy laminate with holes). or 20, an aluminum plate extending from the circular surface of the shield.
It is fixed to the block 81 with nuts and bolts. The rest of the plates 80 are fixed in spacer blocks 83 inside the shield. Blocks 81, 83 ensure that the plate 80 extends across the circular surface of the shield. Three tentative 80s at each end are equally spaced from each other in the circumferential horn direction, and one sag is attached to the 80, and from the bottom of the fourth shield to the seventh
20 as shown in the figure, extending vertically to the bottom of the shield.

The radial length of the wetted plate between the bolt holes is adjusted to compensate for the relative shrinkage of the aluminum 20K and 5oKs shields when cooled and reduce the stress on the tent. The kari is thick enough to have a supporting effect in the direction of the support.

A two-part misalignment washer 38 is used at each screw attachment point to the strap 31.55 and post 75. These washers are made of non-magnetic material,
Preferably made of stainless steel to compensate for misalignment due to manufacturing component variations. These washers ensure that the straps and struts are installed in proper alignment, thus avoiding the addition of potentially damaging cartons to the supports during assembly. The washer can rotate up to 5°.

1u combined support 1jf straps 31, 55 and strut 75
．． By installing 77 heat stations!
(The temperature along the combined straps and struts can be changed.Thermal conductivity of the straps and struts is -
At lower temperatures, the layer becomes even smaller, making it even smaller! The heat station action of a portion of the wrap and struts reduces the amount of heat conducted through the straps and struts by making the length of the strap lower at lower temperatures than it would otherwise be. Decrease. By blocking heat and redirecting it to the shield, heat transfer to the helium container is significantly reduced.

FIG. 12 shows a superconducting electromagnet 85 in a helium container. The helium container is partially filled with liquid helium through the filling tube 87 shown in FIG. 1, which is provided outside the vacuum container.

A fill boat 86 is coupled to a fill tube 87, which
1 (shield, 20 K) and enters the lower part of the helium container as shown in FIGS. 3, 4, and 5. Referring to FIG. line 9
1 is wound around the outside of a non-magnetic cylindrical coil winding 'C293 by directly applying tension. The former is machined with grooves for receiving the separate main coils. In FIG. 12, six separate main coils are shown. Preferably, the former is made of fiberglass. The number of coils to be installed is
It depends on the uniformity of the magnetic field over a given imaging volume desired in the bore of the magnet. If the uniformity of the magnetic field is to be further increased, -more coils are required. Since it is easier to machine grooves in the fiber glass former than to modify castings or forgings, increasing the number of coils can improve the uniformity of the magnetic field of the magnet in the magnet's bore. The gender can be easily changed, and the increase in manufacturing costs is minimal.

The main coils are preferably wound sequentially from one end of the winding form to the other, and the coils are connected in series, but more complicated winding orders can easily be used. To explain about FIGS. 12 to 15, the thickness in the circumferential direction is 0.
The superconducting wire is lined with a thin film of anti-friction material such as 0.005 to 0.010 inch polytetrafluoroethylene (PTFE) tape 95 to create a low friction interface between the superconducting wire winding 91 and the coil former. . Alternatively, a PTFE or molybdenum disulfide coating may be applied to the surface of the coil former to contact the superconducting wire.

Superconducting wires are typically bare wires with a rectangular cross section, and can be comprised of superconducting filaments embedded in a copper matrix.

The superconducting wire is electrically insulated by helically wrapping a heat-resistant aromatic polyamide fiber lace-wrap tape, such as Nomex Lace-wrap Tape 95, to about 50% coverage. At this time, half of the surface of the wire is in contact with liquid helium during operation of the magnet and is cooled by boiling of the nucleation pool.

The stability of the superconductor is determined by the heat dissipation into the liquid helium as the current passes from the filament of the superconductor to the steel matrix, if there is frictional heating due to the movement of the wire that energizes the magnet. The electromagnetic loading on each coil then exerts a radially outward force along with an axial force that attracts the coil toward the center plane of the magnet. The axial force of the coil is supported by the circumferential groove. The radial force is the hoop tension of the superconducting wire and
The bulk is partially supported by lapped turns 97 of stainless steel wire. The lap turns of wire are separated from the outer surface of the coil by a thin sheet 101 of high dielectric strength material. The material retains its properties even at liquid helium temperatures. As dielectric material, fiberglass sheets or laminated plastics can be used. The sheet 101 is machined with an axial groove 103 on the side facing the coil before it is placed in position. The sheets can be applied in two or three pieces circumferentially. As before, a PTFE lining 105 is used on the side of the sheet 101 that contacts the superconducting wire 91. The sheet 101 is axially separated from the walls of the coil groove by a radially extending spacer 107. The spacers create a ventilation path for the axial grooves in the sheet 101 between adjacent spacers.

Spacer 107 is constructed of fiberglass material. C)1
An axial groove at 07 allows helium vapor to escape from the inside of the coil to the ventilation passage between adjacent spacers in the event of magnet quenching.

The overlapping winding 97 is used not only to support the superconducting wire 91 during the operation of the wire, but also to prevent the turns of the superconductor from buckling and riding on each other as a result of transient heat generation during the quenching state of the magnet. In order to restrain it so that it does not occur, it is wrapped under tension. For example, when using a 0.5T magnet and the coil former has an inner diameter of 46.5 inches and an outer diameter of 50 1/8 inches, the superconductor winding is wound with a tension of 30 pounds, and On the other hand, city wraps are wrapped with a tension of 40 pounds.

The fiber glass winding form 93 has a smaller elastic modulus than the superconductor 91 and the lap winding 97, so when sufficient tension is applied to the superconductor and the lap winding and an electromagnetic load is applied, the coil will not wind. It can prevent it from separating from the mold. Furthermore, by controlling the direction in which the fibers of the fiber glass are wound, the fiber glass can be wound in such a way that the thermal shrinkage in the circumferential direction is smaller than both the superconductor and lap winding. . A fiberglass former was wound onto a mandrel using fiberglass filaments of E-glass wet-layered with epoxy. A circumferential winding layer forming a 90° loop is followed by a +45° layer and a −
The winding pattern is made up of four layers of 45° layers, followed by a circumferential wire layer, followed by four layers of 10 and -45° until the desired thickness is reached. It was used until it was achieved. As a result, the tension in the winding and the 11t winding increases at lower temperatures, further preventing the coil and former from separating when the superconducting magnet is energized! 1- Do.

Since the 1r winding is electromagnetically tightly coupled to the coil,
During the quenching condition, a significant portion of the coil's energy is dissipated by the circulating current in the lap windings. For this reason,
The lap windings of the coil act as a magnet protection circuit during quenching. During quenching, in order to make the distribution of the induced current in the lap winding circuit uniform, the first and last conductors are electrically connected between two plates 111 and 113 fixed to the winding form as shown in FIG. must be short-circuited. These bars are manufactured from a non-magnetic abrasive material such as brass, but the crossed ends of a 1R spiral wire are made with -r smaller than the diameter of the wire.
-2 Firmly compress into the formed groove. Plate 111,
113 are fastened to each other by a screw connection member. The square footage of stainless steel for each main coil is:
This electrically corresponds to one shorted turn.

With the integral shield, the outer container 13 of the cryostat can be
Acts as a ferromagnetic shield for the R magnet.

Since the geometry of the cryogenic chamber is determined by the cryogenic and vacuum conditions, the superconducting main winding must be synthesized to maximize the homogeneity of the magnetic field in the presence of a ferromagnetic shield. . In FIG. 16, a portion of the shield 13 is shown relative to the location of the main coil 91 as well as the volume at the center of the bore where high uniformity of the magnetic field is desired. The non-magnetic radiation shield 17.21, the helium container 23 and the support are not shown in the drawing since their presence does not affect the determination of the magnetic field. The process for manufacturing a one-piece shielded magnetic resonance magnet in which the outer container of the cryostat acts as a ferromagnetic shield is shown in FIG.

First, as shown in block 123, the cryostat condition 4 is
Based on the vacuum conditions of the outer vacuum vessel of the cryogenic chamber,
Determine the shape of the shield. At block 125, a first approximation of the number of coils, their axial and radial positions, and the number of ampere turns for the magnet with the desired field strength is selected. This first approximation may be an air-core design for magnets with the same field strength. At block 131,
A finite element analysis of the main coil and iron shield was performed using a finite element algorithm on a VAX-like computer manufactured by the Digital Equipment Company. Determine the axial magnetic flux density at various points of interest in a highly uniform volume within the borehole. This H finite element algorithm also determines the magnetization of the iron shield. At decision block 133, the peak ppm error between various points within the volume of high uniformity of axial magnetic flux density is examined to see if there are any deviations. pp
If the m error does not reach the minimum value, in block 135, the magnetization of the shield is adjusted to a spherical scale ([by performing a spherical number expansion of one function,
The magnetic field uniformity determines the contribution of the axial magnetic flux density of the shield at each point of interest within the volume 127.

The desired contribution by the coil is determined by subtracting the shield's deviation from the axial magnetic flux density from the identified axial magnetic flux density. Desired drop! 7 is not the axial magnetic flux density determined by finite element analysis, but for example 0°5
Since it uses a specified axial magnetic flux density called Tesla, it is not an actual contribution. At block 137, the design of the main coil is modified to take into account the iron bias approximation determined by subtracting the calculated iron contribution from the magnetic flux density in the identified axis ()j. The coils are synthesized using the iterative Newton-Raphson method. The 1'l FI-1 degree of this composition is twice the number of coil pairs. This means that each coil pair has two degrees of freedom, either the radial position is constant but variable axial position and the number of ampere turns, or the number of ampere turns is constant but variable. This is because positions in the axial direction and in the radial direction are allowed. For example, the magnet G of six coils has six degrees of freedom. The axial magnetic flux density B7 at any given point in space is measured using Biot-Savart's law. To achieve a -like magnetic field in the volume of interest, choose as many points as there are degrees of freedom within the volume of interest and determine the axial magnetic flux density at these points. after that,
If desired, the radial position is constant but the axial position and number of ampere turns or the number of ampere turns is constant but variable axial position and radial position of the coil pair. The parameters are determined using the Newton-Raphson method. - Once the coil has been resynthesized using a suitable algorithm in the computer, block 131
, the finite element solution F for the shape of the coil and constant iron shield is
Execute a loaf. When approximating the iron contribution by +-1, resynthesizing the coils, and applying the nail limit element solution +Ii to the 11 synthesized coils and constant iron shield geometry, at decision block 133: Continue until no further changes in the peak ppm of the calculated magnetic field within the volume of interest are observed. The next step in block 141 is to fabricate the coil according to the most recent resynthesis and then block 1
43, the coils are positioned within a single shield.

1, 3, 4, and 5, the 20K and 80I (iQ shields are cooled by the evaporation of helium from the helium container 23. While moving back and forth in the axial direction, , a vent line 157 passes circumferentially around each shield and then through a vent 155 to the vacuum vessel after absorbing heat while passing through a serpentine path to reach the outside of the cryostat. Filling and venting orientations are not shown in Figures 6 and 7. With reference to Figures 1 and 18, extra cooling is provided by a two-stage cryocooler. The cryocooler housing 161 is shown with its internal working parts removed. During operation, the two-stage cryocooler is coupled to two shields 17.21 and Improving the thermal performance of the vessel 11.The mounting of the cryocooler is shown as being near one end of the vacuum vessel near the base, but it can be oriented in any direction. The cryocooler is coupled to the cryostat using a direct interface.The cryocooler's cold head housing is connected to the two heat stations 163. 165, and the cryocoolers attached to these are maintained at temperatures of 80 K and 20 K, respectively.The cryohead housing is mounted directly within the vacuum space of the cryostat 11. A flange 167 of the cryocooler housing 161 is welded to the vacuum vessel so that the cold end is within the vacuum of the cryocooler.Heat stations 163 and 165 in the cryocooler housing each have a There is a direct connection to the thermal radiation shield 17.21 via a braided copper cable 169.171.

Cables 169, 171 are sized to minimize thermal resistance while allowing rotational movement between the shield and the cryocooler's cold head housing.

One end of the braided cable 171 is connected to the heat of the cryogenic cooler.
Welded to station 165, the other end of the braided cable is bolted to shield 21. Therefore, the total thermal interface resistance is composed of the resistance of the weld zone, the braided cable, and the bolted joint [1]. Using electron beam welding, the copper braid is substantially fused to the heat station, eliminating thermal contact resistance. To accommodate the cold end housing, a portion of the shield at 80 is cut away from the shield.
The modification is made by welding an adapter piece 173 to the shield 17 which creates a place for inserting the cold end.

Heat station 163 is welded to cable 169. Cable 169 is welded to a ring-shaped adapter 175 that is bolted to adapter 173. The braided cable 171 used in the preferred embodiment has small wire dimensions (
AW136). The pressure between the shield and the braid at the bolted joint can be increased by increasing the number of bolts to ill. Thus, the thermal performance of the interface can be controlled at minimal cost and without the same additional complexity.

By using a common vacuum between the cryostat and the cryocooler, and by welding the flange of the cryocooler housing to the vacuum vessel, the risk of vacuum disturbance is minimized. The helium container is a large ultra-low 7.1! A pump is included which freezes any air or moisture within the vacuum space and helps maintain a high vacuum within the cryostat and therefore the ultra-low IAa cooler. When the cryocooler needs repair or maintenance, the internal parts of the cryocooler can be removed from the housing 161 without breaking the vacuum.

When assembling the cryostat, the axial support straps are looped over one trunnion each having a capped flange 67. A strap 71 that acts as a heat station is secured to the 2oKa shield. A helium container 23 containing a magnet 85 is placed inside the two shields 17 and 21 within the vacuum container 13. The 80 K vessel is fitted with a multilayer insulator 177 seen in FIGS. 9 and 10. The shield and the circular end of the vacuum vessel are not yet in place. A radial support strap 31 to which a strap acting as a heat station is secured is inserted through an opening in the vacuum vessel and held by a spherical support 45. Radial straps pass through openings in the 80K and 20Ki7 shields and are welded to the circular face of the helium container 37
The strap is fixed. Tension in radial support strap: J! 1 section, and center the helium volume 2: (in the vacuum container.

Installation 1 of this invention allows the helium container to be directly observed, so the helium container is surrounded by a cylinder, and a probe must be used to confirm the position of the helium container. Positioning is easier and more reliable than with a support device that requires Tubular branch! +
75 is fixed to block 74 of the helium container, passes through the shield at 20, and the other end is fixed to the shield at 80.

Straps 51.53 with heat stations of radial support straps 31 are fixed to the '8 shield at 20K and 80. A strap 76 is secured to the shield at 20 which acts as a heat station for the tubular struts. The opening in the shield through which the radial strap passes is closed by a thin sheet 181 of heat reflective material, such as aluminized mylar.

An axial strut 77 is fixed to one circular end of the helium container. At 20, the circular end plates of the shield are secured to the ring 25 by screws 27, the radial straps '14 pass through openings in the circular ends, and the axial struts 77 pass through one circular end. A heat station cable 79 is fixed to the 20KM shield.

A sheet of heat reflective material 181 is placed around each strap passing through the 20 K shield. A spacer block 83 is fixed inside the shield at 80 and a temporary 80 is attached to it. A braided cable 171 is melted in the heat station 165 of the cryocooler, but this is exposed to the shield 21 at 20!・It is tightened.

The circular ends of the shield 80 are covered with a multi-layer insulation 177, fixed to each end of the shield 801. An axial strut 77 is fixed to the cover 78 of the axial support. Directional support straps 55 are fixed to the circular ends of the shield to the heat station acting cables 73 or 80. Adapter pieces 175 at the interface of the cryocooler are fixed in place. The ends of the cover 65.47 are welded in place to adjust the tension of the axial support wrap.The cover 65.47 is welded in place, after which the vacuum vessel can be evacuated.

The radial and axial cross-belt support system used in this invention allows the helium container to be filled with body helium at the end, and the shield at 20K and 80K for normal operation. ! It is designed to have that design tension at certain times. Extremely low lH
The vessels are transported at low temperatures by evacuating the vacuum container. However, during field operations, damage to the cryostat may occur, requiring the cryostat to be returned to the factory. The composite strap support device can act to support the container even when the cryostat is not at operating temperature, and fatigue loads do not adversely affect the design life of the support device.

The suspension system for the shield allows for assembly into the laminar bow by simply bolting the plates in place without the need for equivalent tension adjustments.

However, the .../I- orientation of the radial support strap is 1 [
It is essential. As long as the symmetry between two axes (not necessarily vertical and horizontal axes) 90° apart, both of which are perpendicular to the axial centerline of the cryogenic chamber, is maintained. The overall shape of the strap can be rotated about a longitudinal axis.

As a thermal interface that interconnects the cryocooler and the magnetic resonance cryostat, it is inexpensive and effective, and the cryocooler can be repaired without breaking the vacuum of the cryocooler. This is an explanation of the thermal interface that makes it possible to

Although the invention has been described in terms of preferred embodiments, it will be obvious that various modifications may be made within the scope of the invention. It is therefore intended that the appended claims cover all such modifications that fall within the scope of this invention.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a cryogenic chamber for magnetic resonance imaging of the present invention, FIG. 2 is an end sectional view of FIG. 1, and FIG. 3 is a 80I (radiant heat shielding FIG. 4 is a perspective view of the heat shield at 20 of the cryostat for magnetic resonance imaging, FIG. 5 is a perspective view of the helium container of the cryostat for magnetic resonance imaging, and FIG. FIG. 7 is a perspective view with a portion of one end of the cryogenic chamber for magnetic resonance imaging shown in FIG. 1 cut away; Figure 8 is a perspective view of a radial support strap with a braided cable serving as a heat station of the present invention; Figure 9 is a perspective view of a cable serving as a heat station in a magnetic ultralow bath; FIG. 10 is a partial cut away perspective view of the cryostat showing the attachment of one end of the radial suspension strap and the attachment of one end of the radial suspension strap; FIG. FIG. 11 is a perspective view of an axial support strap with two braided cables acting as a heat station of the present invention, and FIG. 12 is a cross-sectional view with a portion of FIG. 5 cut away, showing a superconducting electromagnet according to the present invention. Figure 13 shows a partial cross-section perpendicular to the axis of the magnet winding support with superconducting wire and stainless steel wire in place; Figure 15 is a radial cross-sectional view of a portion of a magnet winding support type with a conductive wire but without a stainless steel irI winding. FIG. 16 is a cross-sectional view of the cryogenic chamber showing the relative positions of the vacuum vessel acting as a single shield, the magnet windings, and the volume of high uniformity of the desired magnetic field; FIG. The figure is a block diagram showing the process of making an MR magnet with one shield, and Figure 18 is a cross-sectional view of the cryostat showing the interface with the cryocooler. ゛Explanation of main symbols 13: Vacuum Container 17.21: Shield 161: Housing

Claims (6)

[Claims] 1. a cryocooler vacuum vessel defining an aperture, a radiation shield inside the vacuum vessel, and a cryocooler cold end having a heat station and including a housing, the housing comprising: a cryocooler cold end having a heat station and including a housing; through an opening in the vacuum vessel of the cryostat and is hermetically fixed to the vacuum vessel to form a part of the vacuum vessel, and a heat station in the housing at the cold end of the cryocooler is directly connected to the radiation shield. For this reason, the cryogenic chamber for magnetic resonance is designed to allow the internal parts of the cryogenic cooler to be removed without destroying the vacuum of the cryogenic chamber. 2. Magnetic resonance according to claim 1, characterized in that one end of a heat transfer connector is fixed to a heat station of a housing of a cold end of a cryocooler, and the other end of the connector is fixed to said radiation shield by a threaded coupling member. cryogenic chamber. 3. 3. A magnetic resonance cryostat as claimed in claim 2, wherein the cryocooler housing is welded to an opening of the cryostat. 4. a cryostat vacuum vessel defining an aperture; two radiation shields encased within the vacuum vessel; and a two-stage cryocooler cold end having two heat stations and including a housing. the housing is hermetically secured to the vacuum vessel through an opening in the cryocooler to form a portion of the vacuum vessel, and a heat station for each of the housings at the cold end of the cryocooler is provided. A cryogenic chamber for magnetic resonance in which the internal parts of the cryogenic cooler can be taken out without destroying the vacuum of the cryogenic chamber, since the cryogenic chamber is directly connected to one radiation shield. 5. 5. The magnetic device of claim 4, wherein one end of the heat transfer connector is secured to each heat station of the cryocooler cold end housing, and the other end of the connector is secured to the radiation shield by a threaded coupling member. Cryogenic chamber for resonance. 6. 6. The cryostat for magnetic resonance according to claim 5, wherein the housing of the cryocooler is welded to the opening of the cryostat.