Persistent mode Liquid helium free Robust Bi Magnets for MRI and GHz NMR

Superconducting magnets are required for MRI systems that can operate at elevated temperatures and with higher magnetic field without the expensive and in many places unavailable liquid helium that is required with Low Temperature Superconductors LTS and for enabling NMR instruments to operate above the T LTS field limit High Temperature Superconductors HTS provide the best options for advancing the performance of these instruments at the lower cost elevated temperatures of mechanical refrigeration provided they can be made with the required form strength uniformity and current density into persistent current coils The Magnet Technology Division MTD of the MIT Francis Bitter Magnet Laboratory FBML our partner in this Phase I STTR Program was first to recognize and propose to the NIH in that HTS based conductors must be incorporated into MRI and NMR magnets in order to surpass these limits Among HTS conductors only wire can provide superior Je in much higher operating temperatures and magnetic fields while in principle enabling wire forms for example round and rectangular that are proven to work with LTS However in order to meet this demand coils must be developed with improved wire stress and bend tolerance in long lengths to allow for simpler coil fabrication and operation with large Lorentz forces capability for superconducting joints to allow much lower costs and more uniform fields via persistent current operation modes and high uniform current densities in layer wound configurations Solid Material Solutions SMS is now developing coiled forms of strong rectangular wire with focus in this program on a first of its kind persistent mode HTS coil that is made with strong wire and superconducting joints Firstly SMS with its partner the MTD at MIT FBML will develop a superconducting joint technique for its strong rectangular high current density wire Joint configuration melt texture parameters and wire joint Ic s will be investigated based on the results of a preliminary study that has already demonstrated that a superconducting joint can be produced between wire ends Secondly the technique will be applied to develop superconducting joints and a prototype persistent current switch Joints will be prepared between reinforced wire ends and heat treatments completed followed by Ic tests of joints as well as coiled wire sections Using the best samples a method for switching to persistent mode will be established with heaters and with field decay rates characterized to demonstrate that persistent current carrying joints can be achieved with coiled strong wire Thirdly a first persistent mode demonstration HTS coil will be designed produced and tested based on our strong wire and coil making know how This coil will be designed and built so that it can generate a central field of up to about T at or below Ic with loop closing superconducting joints and heater to allow switching to persistent mode It will be tested at K in driven current mode up to Ic and then with a background field for a total field of andgt T It will then be charged to different current levels followed by switching to persistent mode Tests will be completed to measure its field decay rates in background fields up to about T in order to characterize persistent mode properties and demonstrate our capability to produce and operate strong wire based coils in persistent mode When fully developed this advance will enable the practical production of persistent mode HTS magnets based on our superconductor for use in liquid He free and higher field MRI as well as andgt GHz NMR systems Superconducting magnets are required that enable MRI systems to operate at higher than K without the expensive and in many places unavailable liquid He LHe that is currently used with Low Temperature Superconductors LTS and for NMR instruments that operate at field levels above the T LTS limit High Temperature Superconductors HTS provide the best options for advancing MRI systems to operating temperatures that are attained with LHE free refrigeration provided they can be made with the required from strength uniformity and current density Je into persistent current coils Analysts forecast global NMR sales to grow by about annually for the next years driven largely by the start of sales of andgt GHz systems that require HTS based field boosting magnets and global MRI sales to grow above $ B yr in the same timeframe Solid Material Solutions plans to develop and sell products into these markets Among HTS conductors only Tc K can provide superior Je in much higher operating temperatures and magnetic fields in wire forms for example round and rectangular that are proven to work with LTS Among round rectangular wire candidates MgB like Nb Sn also loses its ability to carry current at the high fields and temperatures possible with preventing its use at conditions accessible by despite the low cost of its constituents In the next step coils must be developed with improved wire stress and bend tolerance in long lengths capability for superconducting joints and persistent current operation modes and high uniform current densities in layer wound configurations Solid Material Solutions SMS is developing coiled forms of its strong rectangular wire with focus in this program on a first of its kind persistent mode HTS coil that is made with superconducting joints As a first and most significant step this program will prove the technology for making superconducting joints in high Je coils comprised of strong wires so that following reaction the coil is capable of persistent mode operation MRI application Liquid He free MRI will be realized when HTS based wires such as not tapes are fully developed that can operate at much higher temperatures than Nb Sn or NbTi for example above K However the wire for this must be similar in robustness form quality and with persistent current joint capability to NbTi and Nb Sn NMR application Highest field NMR magnets generate about T using a combination of LTS NbTi and Nb Sn solenoids that are operated near their upper field limits pushing all LTS magnets as far as they can go to attain GHz However it is widely agreed that both solution and magic angle spinning MAS solid state NMR will benefit greatly from andgt GHz levels Recent data on several proteins indicated that for solution NMR resolution is optimized in the range of GHz whereas for magic angle spinning MAS solid state NMR optimal field is simply the highest field possible The Magnet Technology Division MTD of the MIT Francis Bitter Magnet Laboratory FBML our partner in this Phase I STTR Program was first to propose to the NIH in that HTS based conductors must be incorporated into NMR magnets in order to surpass GHz Over the past year SMS has advanced the status of its strong long length rectangular and round wire capability As well SMS has developed a capability to fabricate these wires into compact coils by wind and react as is currently done with Nb Sn for NMR and into large diameter coils by react and wind for MRI as is done with NbTi In the first part of this Phase STTR program SMS will develop a superconducting joint technique for its strong rectangular high Je wire Joint configuration melt texture parameters and wire joint Je s will be investigated based on the results of a preliminary study that has already demonstrated that a superconducting joint can be produced In the second part the technique will be applied to develop superconducting joints and a prototype persistent current switch in coiled wire Joints will be prepared between reinforced wire ends followed by Ic tests of joints as well as coiled wire sections Using the best samples a method for switching to persistent mode will be established with heaters and with field decay rates characterized to demonstrate that persistent current carrying joints can be achieved In the third part a first persistent mode HTS coil will be designed produced and tested based on our strong wire and coil making know how This coil will be designed and built so that it can generate a central field of up to about T at or below Ic with loop closing superconducting joints and heater to allow switching to persistent mode It will be tested at K in driven current mode up to Ic and then with a background field for a total field of andgt T It will then be switched to persistent mode and tests completed to measure its field decay rates in background fields up to about T in order to demonstrate basic capability to produce and operate strong wire based coils in persistent mode When fully developed in a Phase program this advance will enable the practical production of persistent mode HTS magnets based on our superconductor for use in liquid He free and higher field MRI as well as andgt GHz NMR systems