Superconducting Magnet Systems

With over three decades of experience and a worldwide installation base, Janis Research Company is a recognized leader in the design and manufacture of superconducting magnet systems.  Janis' renowned SuperVariTemp insert operates from 1.5 K - 325 K, and is featured in the SuperVariMag, OptiMag and SuperOptiMag systems and is also available as an independent insert for use with existing magnets. Janis also offers a variety of superconducting magnet systems that offer a room temperature bore (with inserts that reach 800 K), He-3 systems that reach less than 0.280 K, dilution refrigerator systems that reach below 10 mK, along with a variety of other systems that are designed for specific applications.  These state of the art systems feature integrated designs for the cryostat, magnet, temperature controller and programmable power supply, together with a complete line of ancillary equipment.  Janis Research's approach to superconducting magnet system design provides a variety of technical and cost benefits.

By maintaining flexibility over the specification and integration of the magnet, electronics, temperature controller and cryostat, Janis is able to offer magnet systems with performance characteristics tailored to individual experimental and budgetary requirements.

Janis' staff of physicists and engineers has extensive experience in the design and operation of superconducting magnet systems and is uniquely qualified to assist you with every step of your system purchase, from experimental design through post-installation support. All systems are fully integrated and liquid helium tested at our Wilmington, Massachusetts facility; installation, start-up and training are available.

Magnets

For magnetic fields of 5-9 Tesla at 4.2 K, our superconducting coils are wound from multifilamentary NbTi copper composite conductor, bonded in epoxy. This process provides maximum stability, and is guaranteed to eliminate flux jumping and associated heat generation. Used in conjunction with an optional Lambda point refrigerator, these magnets reach fields up to 11 Tesla at 2.2 K. Many of these magnets are available in a low current version for optimized helium consumption.

For magnetic fields of above 12 Tesla the magnets are wound in multiple sections; the outer being of copper stabilized filamentary NbTi, and the inner sections of filamentary NbSn (doped) conductor. The coils are vacuum impregnated with epoxy resin to form a composite structure of excellent strength and insulation. Most magnets are supplied with persistent current switches and diode and/or resistor protection circuits.

Compensation coils reduce the field at a distance close to the center for Mössbauer experiments or for locating the mixing chamber of a dilution refrigerator. Gradient and modulation superconducting coils are supplied for Faraday Balance and de Haas van Alphen studies, respectively. Standard magnetic field homogeneities range from 0.5% to 0.01% over a 1 cm diameter sphere (or larger volume); higher homogeneity magnets (1 part in 105 or better) are also available for special applications.

In general, the bore size of the magnet (or coil separation in a split Helmholtz pair) is determined by the size of the sample chamber. Larger size sample chambers and better field homogeneities require a larger number of windings and larger size magnets (and larger dewars), which translates into a higher system cost. The cost also increases with the maximum field required. It is therefore important to clearly define the system requirements in order to optimize the purchasing power for a specific budget. 

The link below will download a word document containing several questions that will help our engineers determine the best system for your requirements.  Please take a moment to fill it out and email it back to sales@janis.com

• Magnet requirements questionnaire (Word document, 40 KB)

Standard System Features:

• Top sample loading and exchange at all temperatures;
   

• Effortless sample rotation and translation about the vertical axis at all temperatures, with options for rotation about a horizontal axis;
   

• Field-independent thermometry;
   

• The Janis SuperVariTemp system, with provision for a temperature control thermometer at the heat exchanger;
   

• Vapor cooled/superconducting high current magnet leads;
   

• Superconducting magnets with persistent mode operation providing field stabilities of 20 ppm/hr;
   

• Carefully designed magnet support inside the helium reservoir, with optical access through the dewar vacuum space (OptiMag and SuperOptiMag systems);
   

• Built-in superconducting liquid helium level sensors, providing continuous or timed level monitoring;
   

• Readily accessible and interchangeable sample chambers.

Complete Systems Include:

• Programmable magnet power supply with computer interface and bi-polar operation;
   

• Temperature controller with field independent thermometry;
   

• Liquid helium transfer lines;
   

• Cryogenic Hall probe and Gaussmeter;
   

• Automatic nitrogen filling mechanism;
   

• Vacuum pumping stations.

* Room temperature bore systems can be combined with variable temperature cryostats to operate in temperature ranges between 1.5 K and 800 K.
 

The Janis Research SuperVariTemp (SVT) cryostat is a key component of all SuperVariMag, OptiMag and SuperOptiMag systems. By controlling the temperature of the flowing helium vapor in which samples are immersed, the SVT allows for precise monitoring and control of sample temperature over a 1.5-325 K range, while eliminating the need for thermal anchoring and sample mount heating. The helium flow rate and heater are balanced to provide operation over the range of 4.2 K - 325 K; automatic temperature controllers equipped with field independent thermometers provide accurate and precise temperature control.

The SVT cryostat allows full use of the cooling power of escaping helium vapor as it exits the sample chamber. The sample chamber is thermally isolated from the helium reservoir by the dewar vacuum, thereby eliminating heat conduction into the reservoir. Precise sample temperature is measured through the use of a thermometer attached to the sample holder. Operation to 1.5 K is made possible by immersing the sample in liquid helium and reducing the pressure with a mechanical vacuum pump. The SVT's unique design also allows sample cooling in flowing helium vapor to approximately 2 K for extended operation below 4.2 K without the need to monitor or replenish the helium level in the sample chamber. For optical experiments, this presents the least interference to the incoming and scattered beams.

The SVT insert is available as an accessory for existing superconducting magnets. A custom designed SVT cryostat can be matched to the dimensions of an existing open neck dewar and magnet bore. Drawing liquid helium from the main magnet reservoir, the SVT insert will provide temperatures of 1.5K - 325 K without the need for pumping on the main reservoir.

It is also available in a high stability or a high temperature static gas insert option for applications requiring a high stability region, continuous operation above 100 K, or high sensitivity experiments that preclude locating the sample in a flowing helium vapor. Special sample positioners can also be supplied for temperatures of 400 K or higher along with optional wiring and cold, detachable wiring stages.