Bruker Switzerland Ag

Bruker Biospin Ag

Joerg Hinderer

Stephen Alfred March

Robert Schauwecker

Franck Borgnolutti

Patrick Wikus

Stephan Heiss

Rainer Pietig

Pierre-Alain Bovier

Marco Strobel

Dirk Wilhelm

Joost A B Lohman

Andreas Kraus

Dmitry Eshchenko

Hannes Grubinger

A method is provided for homogenizing a magnetic field profile of a superconductor magnet system having a cryostat with a room temperature bore, a superconductor bulk magnet with at least three axially stacked bulk sub-magnets, arranged coaxially with the room temperature bore, and a cryogenic cooling system for cooling the superconductor bulk magnet. The cryogenic cooling system independently controls the temperature of each bulk sub-magnet to provide different respective temperatures to the sub-magnets and thereby provide the sub-magnets with different relative currents such that a first subset of the bulk sub-magnets are almost magnetically saturated, and a second subset of the bulk sub-magnets are significantly away from magnetic saturation. By controlling a heating power and/or a cooling power at the bulk sub-magnets without measuring the temperatures of the bulk sub-magnets, the respective currents of the bulk sub-magnets are changed to increase a homogeneity of the field profile.

Method for homogenizing a magnetic field profile of a superconductor magnet system

A superconductor magnet system () includes a cryostat (), a superconductor bulk magnet (), and a cryogenic cooling system (). The bulk magnet () has at least N axially stacked bulk sub-magnets (-), with N&#x2265;3. Between each two axially neighboring bulk sub-magnets, an intermediate body (-) is arranged. The intermediate bodies (-) are made from a non-metallic thermal insulator material. The cryogenic cooling system () is adapted for independently controlling the temperature of each bulk sub-magnet (-), and has, for each bulk sub-magnet, a temperature sensor (-) for sensing the temperature of the respective bulk sub-magnet and an adjustment unit (-) for adjusting a heating power and/or a cooling power at the respective bulk sub-magnet.

Superconductor magnet system, with individual temperature control of axially stacked bulk sub-magnets

A superconductor bulk magnet magnetizing method providing a more homogenous trapped magnetic field includes: placing the bulk magnet inside a charger bore of an electrical charger magnet; placing a field correction unit inside a superconductor bore of the bulk magnet; applying an electrical current (I) to the charger magnet, to generate an externally applied magnetic field, wherein a temperature Tof the bulk magnet exceeds a bulk magnet critical temperature T; applying an auxiliary electrical current (I, . . . ) to the field correction unit, thus generating an auxiliary magnetic field applied to the bulk magnet from within the superconductor bore, wherein T&#x3e;T; lowering Tbelow T; turning off the electrical current at the charger magnet, wherein T&#x3c;T, and turning off the auxiliary electrical current at the field correction unit, wherein T&#x3c;T; and removing the bulk magnet from the charger bore while T&#x3c;T.

Method for magnetizing a superconductor bulk magnet, with generating an auxiliary magnetic field in the superconductor bore

Charging method for a superconductor magnet system with reduced stray field, weight and space includes: arranging the system within a charger magnet bore; with T&#x3e;Tand T&#x3e;T, applying a current Ito the charger magnet and increasing Ito a first current I&#x3e;0; lowering a main superconductor bulk magnet temperature Tto an operation temperature T, with T&#x3c;T, while keeping T&#x3e;T; lowering Ito a second current I&#x3c;0, thereby inducing a persistent current IPin the main magnet; lowering a shield magnet temperature Tto an operation temperature T, with T&#x3c;T; increasing Ito zero, thereby inducing a persistent current IPin the shield magnet; removing the magnet system from the charger bore, and keeping T&#x2264;Twith T&#x3c;Tand T&#x2264;Twith T&#x3c;T; where: T: main magnet critical temperature and T: shield magnet critical temperature.

Method for charging a superconductor magnet system, with a main superconductor bulk magnet and a shield superconductor bulk magnet

A superconductor magnet apparatus () includes a superconductor bulk magnet (), a cryostat () and a ferromagnetic shielding body (). The bulk magnet has a superconductor bore (), an axis (z) of rotational symmetry, and a maximum outer diameter ODin a plane perpendicular to the z axis. The superconductor bore has a minimum cross-sectional area Sin a plane perpendicular to the z axis. The cryostat has a room temperature bore (), the bulk magnet is arranged within the cryostat and the room temperature bore is arranged within the superconductor bore. The shielding body has a shielding bore (), the bulk magnet is arranged within the shielding bore and the shielding body extends beyond the bulk magnet at each axial end by at least OD/3. For an average cross-sectional area Sof the shielding body, S&#x2265;2.5*S, and the shielding body is arranged within the cryostat.

Superconducting magnet apparatus and method for magnetizing a superconductor bulk magnet by field cooling through a ferromagnetic shield

A magnet assembly () with a cryostat () has a superconducting magnet coil system (), an active cooling device () for the coil system, and current leads () for charging the coil system. The current leads have at least one normal-conducting region (), wherein multiple cold reservoirs () are thermally coupled to the current leads along the normal-conducting region thereof, in order to absorb heat the normal-conducting region during charging of the magnet coil system. The current leads have a variable cross-sectional area B in the normal-conducting region along the extension direction thereof, wherein at least over a predominant fraction of their overall length in the normal-conducting region, the cross-sectional area B decreases from a cold end () toward a warm end (). This provides a magnet assembly requiring reduced cooling power during charging, with less heat introduced into the magnet coil system in normal operation.

Magnet assembly with cryostat and magnet coil system, with cold reservoirs on the current leads

A cryostat system is kept at a cryogenic operating temperature without providing or supplying cryogenic fluids by a cryocooler. The cryostat system includes a superconducting magnet arrangement and a heat sink apparatus to prolong the time before the superconducting magnet arrangement quenches/returns to the normally conducting state if active cooling fails. The heat sink apparatus includes magnetocaloric material and is thermally connected to the superconducting magnet arrangement and/or to parts of the cryostat system through which ambient heat can flow to the superconducting magnet arrangement. In this way, the cryostat system can be operated in a truly 'cryogen-free' manner while maintaining a sufficiently long time to quench in the event of potential operational malfunctions.

Cryogen-free magnet system comprising a magnetocaloric heat sink

A cryostat arrangement includes a superconducting magnet to be cooled by an active cryocooler. The cryocooler includes a coolant circuit with a compressor, a cold head, and a cold finger in thermal contact with the magnet. A volumetric vessel containing cryogenic fluid is thermally coupled to the magnet. The volumetric vessel is connected to the coolant circuit by a pressure-resistant line. A fluidic component influences the flow rate through the line in a defined manner such that the cryogenic fluid flows between the volumetric vessel and the coolant circuit with a time constant of at least 15 minutes. The cryostat can be operated in a 'cryogen-free' manner and permits a sufficiently long time to quench in the event of operational malfunctions.

Cryogen-free magnet system comprising a heat sink connected to the gas circuit of a cryocooler

A superconducting magnet assembly includes a cryostat, a vacuum vessel and a refrigeration stage. An NMR probe using the assembly includes comprises cooled probe components, a two-stage cryocooler, and a counter flow heat exchanger. A cooling circuit guides coolant from one outlet of the counter flow heat exchanger back to an inlet of the counter flow heat exchanger via the second cooling stage, a cooled probe component, and a heat exchanger in the cryostat or a heat exchanger in a helium suspension tube. Both the intake temperature of the coolant flowing into the heat exchanger in the cryostat or in the suspension tube and the return flow temperature of the emerging coolant are at least 5 K lower than the operating temperature of the first cooling stage. Excess cooling capacity of the cryocooler reduces the evaporation rate of liquid helium or cools a superconducting magnet in a cryogen-free cryostat.

NMR apparatus comprising a superconducting magnet assembly and cooled probe components

An NMR apparatus includes a superconducting magnet assembly, a cryostat having a vacuum vessel, a refrigeration stage that can be operated at a temperature of &#x3c;100 K, and a magnet coil system that comprises a cold bore into which a room temperature access of the cryostat engages. The NMR apparatus also includes an NMR probe with probe components cooled to an operating temperature of &#x3c;100 K. The probe components are arranged between the cold bore and the room temperature access into the cold bore, radially inside the cold bore but outside the room temperature access. The vacuum vessel includes an opening that can be closed by a lock valve. A lock chamber is directly connected to the opening, such that the cooled probe components can be installed and/or removed through the opening and lock valve without breaking the vacuum in the vacuum vessel of the cryostat.

Introducing an NMR apparatus comprising cooled probe components via a vacuum lock

A DNP apparatus includes a cryostat () having an opening () and a loading path for a sample (), the loading path extending from the opening to a sample receptacle (), with a cryomagnet and a microwave source () as well as a configuration for supplying microwave radiation from the microwave source to the sample, which comprises a microwave path extending directly to the sample. The microwave path extends spatially separately from the loading path and the configuration for supplying microwave radiation has at least one microwave feed-through passing through one or more walls of the cryostat. The microwave path is incident on the sample from a direction opposite to the loading path or from a sideward direction at right angles to or at an inclination with respect to the axis of the loading path. This leads to simple and efficient polarization of the electron spins in the sample.

DNP apparatus

A method for converting a cryostat configuration () having a first container () with a liquid helium bath () and a second container () which is filled with liquid nitrogen () is characterized in that a cooling medium () which is in a gaseous state at a temperature of 60K and a pressure of 1 bar, is introduced into the second container and is cooled by a refrigerator () by means of a cooling circuit (), the coolant lines of which are guided into the second container, to an operating temperature of &#x2266;60K. With this retrofit for existing cryostat configurations that utilize both liquid helium and also liquid nitrogen for cooling a superconducting coil, use of liquid nitrogen can be completely avoided and the evaporation rate of the liquid helium can also be considerably reduced without having to re-liquefy the cryogens used.

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Waldshut-Tiengen, Germany

Joerg Hinderer