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1. Fiberglass Reinforcement of High Field Pulsed Magnets

1. Fiberglass Reinforcement of High Field Pulsed Magnets. and. 2. Development of a High Pressure System for use at Low Temperatures and High Fields. David Barbee ’04 Advisor: Prof. Charles Agosta. Outline. A little about superconductivity and pulsed field magnets

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1. Fiberglass Reinforcement of High Field Pulsed Magnets

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  1. 1. Fiberglass Reinforcement of High Field Pulsed Magnets and 2. Development of a High Pressure System for use at Low Temperatures and High Fields David Barbee ’04 Advisor: Prof. Charles Agosta

  2. Outline • A little about superconductivity and pulsed field magnets • Getting fiberglass on a magnets • Creating high pressures

  3. Pulsed Field Magnets • Why do we need pulsed magnets? To study the behavior of high field superconductors: the critical field (Hc2), vortex state, and the spin-magnetic field interaction. Studying these phenomena provides a better understanding of the mechanisms behind superconductivity (Ginzburg-Landau, BCS Theory.) In the normal metallic state the motion of the electrons in a High magnetic field provides information about the effective electron mass, scattering time, and fermi surface via Haas von Alphen and Shubnikov de Haas oscillations.

  4. Pulsed Field Magnets How do we make pulsed field magnets? By tightly winding several hundred turns (700) of copper wire around a delrin rod. The rod will eventually be removed to create the bore of the magnet. • How are these pulsed fields created? By dumping the energy in a capacitor bank into the magnet, creating roughly 5,000 – 10,000 amps of current in the copper wire. The magnet can be treated as a solenoid to first approximation. B = μ0NI/L = 4π · 10E-7 Tm/A · 700 turns · 5000 A / 0.1 m = 44 T 44 tesla! Won’t that produce some large lorentz forces?

  5. A Few Calculations • Can copper wire alone handle the forces? Hoop stress calculation for ½ loop: dF = I B R dθ F = ∫ dF sin(θ) = IBR ∫ sin(θ) dθ F = 2 · 5,000 A · 40 T · 0.025 m Max Force on Cu wire = 10,000 N (8th Layer for most recent magnet) Fnet Current Field Properties of copper wire: Tensile strength of Cu wire = 70 ksi (480 MPa) Area of Cu wire = 4.8E-6 m2 Breaking force of Cu wire = 2200 N 1.7 mm 2.8 mm Copper wire alone will not work, extra reinforcement is necessary.

  6. Reinforcement of Magnets • How do we “safely” make magnets? - wires held in place to prevent rubbing, - reinforce the magnet with something of high tensile strength to prevent hoops from stretching. • There are two methods of winding to fix the • wires in place: • Wet-winding – painting epoxy on every layer of the magnet as it is wound. Requires a great deal of external reinforcement. 2. Dry-winding – magnet is first wound, then epoxy impregnates the magnet. Allows for internal reinforcement via fiberglass. Our lab has already made and destroyed wet-wound magnets. The most dependable and highest field magnet in our lab is the Leuven magnet, which was made using the dry-wind technique. We will make dry wound magnets because of the success of the Leuven magnet. We therefore need internal fiberglass reinforcement

  7. The Wonders of Fiberglass • Maximum tensile strength of 4890 MPa (709 ksi) Best case scenario, 0.7 mm (0.028”) of S-glass needed to reinforce the magnet at the greatest force (8th layer),neglecting copper’s strength. • Electrical resistivity of 9.0E12 Ω·cm fiberglass is a great insulator, reducing the chances of a short between wires. • How do we get it on the magnet? 0.7 mm A flywinder is needed to wind the fiberglass onto the magnet being wound because the magnet must be kept under constant tension while being wound. 1.7 mm 2.8 mm

  8. The Flywinder Capable of quickly and accurately applying fiberglass from the spindle to a magnet as the magnet is being wound. The guiding posts are necessary to accurately position and wind the fiberglass. A single flywinder is capable of only applying fiberglass to EVERY OTHER LAYER due to interference by the copper wire (see picture.) When the flywinder is idle it is in the way of winding! Need to get the flywinder out of the way. Original

  9. The Computer/Controllers • Two parameters needed for flywinder: • Number of revolutions needed for the • flywinder to traverse the magnet. • The rate (rev/s) to turn the flywinder and • apply fiberglass. • Program allows for 4 movements: winding • fiberglass (both lateral and rotational motion) • moving the flywinder forward and backward, • and rotating only the flywinder. Computer communicates with daisy chained controllers through a modem port and addresses each controller specifically and simultaneously through a 25-pin D-connector. A linear dependence exists between the rotational velocity and the change in diameter of fiberglass wound, meaning that we can specify the desired thickness of fiberglass between layers. The controllers are fixed on a giant aluminum heatsink and powered by a 75 volt power supply

  10. Look at it go!

  11. Results • Two magnets have been successfully wound and impgregnated. • The first was an overall test of the fiberglass/epoxy system and proved the system worked as advertised. • The second has been further reinforced with steel ribbon and pulsed at liquid nitrogen temperature. A maximum field of 35 T has been reached out of a theoretical 44 T. • We are now able to quickly and easily create our own magnets with customizable field characteristics. Magnet 1 Magnet 2

  12. Future Work for the FlywindingProject • Development of another flywinder for winding fiberglass on every layer of copper. • Another flywinder must first be built (5” ID bearing not necessary!) • The new flywinder must be attached somehow to the coil winder’s horizontal threaded rod for lateral movement. • The stepper motor controllers must be readdressed and the program modified to control at least one more motor. • Extension rods must be implemented in the winding frame setup to allow for the new flywinder to keep out of the way when idle.

  13. Superconductors at high pressure • What happens as pressure is increased? • As the pressure increases two things happen: • The interlayer spacing of the SC is decreased due to the • compression of the lattice. • The electron density increases and affects the electron-electron • interaction (destructive to superconductivity.) -Critical field is changed -Effective mass, scattering time, fermi surface changed.

  14. Bringing SC’s to High Pressure • How are high pressures reached? • SC samples brought to high pressures via diamond anvil cells (DAC) • or metal cells. • DAC’s theoretically good to 25-50 kbar (our experiences, up to 5 kbar). • Difficult to work with because pressure is difficult to set (in press) • and maintain when not at STP. • Metal cells will not work in our setup, eddy current heating. • General rule to keep metal out of 50 T. We want a system and nonconductive cell capable of changing pressure in situ and capable of reaching 2 kbar (~30 ksi).

  15. What we got from Duke Donated by Horst Meyer Highlights: • a frame with most components 40 yrs • old and nonfunctioning • system leaked like crazy • overly elaborate for what we needed. • all unnecessary components • removed from previous system: • ~12 valves  5 valves • 5 gauges  3 gauges • removed ~5 feet of excess tubing • removed 10 connecting blocks/ • valves • all O-rings in system changed: in • valves, the pressure generator • new 1/8” and 1/16” tubing used to • make connections Front Back

  16. How do we get to high pressure? Our pressure limitations: Tank alone can give 2,500 psi Hand Pump – 20,000 psi Pressure Head – 20,000 psi Gauges – 20,000 psi Safety Heads – 30,000 psi (Burst Valves) Pressure Generator – 30,000 psi • What pressure is the tubing good to? Treat as a thick walled vessel: Pburst = Tstr*log(OD/ID) Typical tensile strength of S.S: 600 MPa (87 ksi) Theoretical Burst Pressures: 1/8” OD, 0.020” – 70 ksi 1/16” OD, 0.020” – 40 ksi Low temperature should increase the tensile strength allowing even greater pressure.

  17. Results thus far Cells cracked at a variety of pressures, but system did not leak. Currently limited only by cell design. 12,600 PSI ~ 4,000 PSI Results are favorable, we can already study several different superconductors at these pressures. 13,600 PSI (~0.8 kbar) k-(ET)2-Cu(NCS)2 has a predicted critical pressure of 2.2 kbar, meaning that this range is already very useful to us. The critical field is already reduced by a factor of 3 at 1.5 kbar

  18. Quite a bit of work to be done • More accurate measurement - Manganin wire gauge, strain gauge • Electrical feed through for closed cell design • Pressure experiments on superconductors – verifying/calibrating • More cell design • Testing the system and cell at liquid helium temperatures Are the system and cell in hydrostatic equilibrium?

  19. Acknowledgements:Vincent Ciarametaro, Luiz de Viveros, Geoff Esper,Katholike University – Leuven, Belguim Special Thanks to: Chuck Agosta, Joel Norton, Vin Ciarametaro, Mike Viotti, Catalin Martin, Izabela Mihut, and Charles Gatete Funded by: National Science Foundation, Stanley Geschwind Memorial Fund

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