Benjamin Haid

Quench and recovery of YBCO tape experimental and simulation results

This paper presents quench/recovery results, both experimental and simulation, of a 10-cm long YBCO test sample subjected to an over-current pulse. The sample was cooled by liquid nitrogen, either in a bath or forced through a narrow channel. Bath provides a better cooling than flow, at least for velocities of 3 and 5 cm/s used in the experiment.

A "permanent" high-temperature superconducting magnet operated in thermal communication with a mass of solid nitrogen

Abstract A new design for a portable “permanent” superconducting magnet system is explored. The design involves a persistent-mode high-temperature superconducting (HTS) magnet that is cooled by a solid heat capacitor. The system is an alternative to permanent low-temperature superconducting (LTS) magnet systems where the magnet is cooled by a bath of liquid helium. An apparatus was constructed to demonstrate stable operation of a permanent magnet wound with Bi2223/Ag conductor while in thermal communication with a mass of solid nitrogen. The apparatus includes a room-temperature bore and can function while it stands alone, detached from its cooling source, power supply, and vacuum pump. The magnet is operated in the 20–40 K temperature range. This apparatus is the first to demonstrate the operation of a superconducting magnet with a permissible temperature variation exceeding a few degrees kelvin. Models are developed to predict the experimental systems warming trend and magnetic field decay. The models are validated with a good agreement between simulations based on these models and experimental results. The results indicate that present HTS conductor critical current and index are not yet sufficient to provide field strengths and field decay time constants that are required for typical persistent-mode applications.

Design analysis of a solid nitrogen cooled “permanent” high-temperature superconducting magnet system

Abstract Potential performance advantages of a solid nitrogen cooled “permanent” high-temperature superconducting (SN2/HTS) magnet system over a liquid helium cooled low-temperature superconducting (LHe/LTS) system are explored. The SN2/HTS system design includes a second solid heat capacitor that cools a radiation shield. Recooling of the heat capacitors is performed with a demountable cryocooler. The SN2/HTS system offers both enhanced stability and improved portability over a LHe/LTS system. Design codes are constructed to compare the SN2/HTS system design with a LHe/LTS design for a general permanent superconducting magnet system employing a room temperature bore. The codes predict the system volume and mass that should be expected for a given set of design requirements, i.e. field strength and bore size, and a given set of conductor properties. The results indicate that present HTS conductor critical current and index are not yet sufficient for producing SN2/HTS systems of a size that is comparable with that expected for a LHe/LTS system; however, the conductor properties of Bi2223/Ag have been consistently improving, and new HTS conductors are expected to be developed in the near future. The codes are used to determine the minimum Bi2223/Ag conductor performance required for a SN2/HTS system to be competitive with a LHe/LTS system.

Thermal behavior of a solid nitrogen impregnated high-temperature superconducting pancake test coil under transient heating

This paper presents experimental and analytical results on a solid nitrogen impregnated high-temperature superconducting (HTS) test coil under transient heating. The test coil is a 1-layer, 10-turn single-pancake wound with Bi2223/Ag composite tape, 9-mm wide and 0.5-mm thick, with an average winding diameter of 105 mm. The solid nitrogen impregnating the 0.38-mm turn-to-turn radial gaps in the winding enhances the windings overall heat capacity significantly in the operating temperature range 30-40 K and thereby limits the test coils temperature rise when it is subjected to overcurrent pulses. The presence of solid nitrogen within the winding improves stability against fault-mode overcurrent pulses for HTS magnets used in electric power devices.

Design of the NIF Cryogenic Target System

Abstract The U.S. Department of Energy has embarked on a campaign to conduct credible fusion ignition experiments on the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory in 2010. The target assembly specified for this campaign requires the formation of a deuterium-tritium fuel ice layer in a 2-mm-diam capsule at the center of a 9-mm-long × 5-mm-diam cylinder, called a hohlraum. The ice layer must be formed and maintained at temperatures below 20 K. At laser shot time, the target is positioned at the center of the NIF target chamber, aligned to the laser beams, and held stable to <7-μm root-mean-square. We have completed the final design of the cryogenic target system and are currently integrating the devices necessary to create, characterize, and position the cryogenic target for ignition experiments.

Fabrication of Bi-2223 HTS magnet with a superconducting switch

A test pancake magnet, equipped with persistent superconducting switch, was fabricated with Bi-2223/Ag-Mg tape. The magnet was operated in persistent mode at 20 and 77 K. For large operating currents that forces the magnet to operate in the flux flow range, the field decays is exponentially with time. A simple circuit model is used to compute field decay time constants. It was also found that Pb-Sn solder joints are unsuitable for persistent mode operation.

Beneficial effect of solid nitrogen on a BSCCO-2223/Ag composite tape subjected to local heating

Abstract This paper presents results of a quench/recovery experiment for a BSCCO-2223/Ag composite tape in the presence or absence of a thin layer of solid nitrogen on each side of the tape. Voltage and temperature data were recorded for a 20-cm long BSCCO-2223/Ag tape operating in the range 20–55 K and subjected to a heat pulse of a 10–600 s duration applied over a short distance at its midpoint. The data clearly show that solid nitrogen is beneficial to the stability of high-temperature superconductors operating in this temperature range and subjected to transient heating disturbances.

A solid-nitrogen cooled Nb/sub 3/Sn NMR magnet operating in the range 8-10 K

This paper presents a reference design of a solid-nitrogen cooled 300-MHz/25 mm Nb/sub 3/Sn NMR magnet based on a novel design/operation concept. The magnet operates in the temperature range 8-10 K with its cryocooler thermally decoupled from the magnet and idled. A mass of solid nitrogen in thermal contact with the magnet prolongs the magnet warm-up time to 17 h, during which NMR measurement may be performed under a quiet environment free of the cryocoolers microphonics. At 10 K, the magnet is re-coupled to the cryocooler for recooling to 8 K and ready for another 17-h measurement.

Measurement of Total Condensation on a Shrouded Cryogenic Surface Using a Single Quartz Crystal Microbalance

Abstract A single quartz crystal microbalance (QCM) is cooled to 18 K to measure condensation rates inside of a retractable shroud enclosure. The shroud is designed to minimize condensate on fusion targets to be fielded at the National Ignition Facility (NIF). The shroud has a double-walled construction with an inner wall that may be cooled to 75 to 100 K. The QCM and the shroud system were mounted in a vacuum chamber and cooled using a cryocooler. Condensation rates were measured at various vacuum levels and compositions and with the shroud open or closed. A technique for measuring total condensate during the cooldown of the system with an accuracy of >1 × 10-6 g/cm2 was also demonstrated. The technique involves a separate measurement of the condensate-free crystal frequency as a function of temperature that is compared to the measurement for the cooldown trend of interest. The shroud significantly reduces the condensation rates of all gases and effectively eliminates H2O condensation.

D2 and D-T Liquid-Layer Target Shots at the National Ignition Facility

Abstract Experiments at the National Ignition Facility (NIF) using targets containing a deuterium-tritium (D-T) fuel layer have, until recently, required that a high-quality layer of solid D-T (herein referred to as an ice layer) be formed in the capsule. The development of a process to line the inner surface of a target capsule with a foam layer of a thickness that is typical of ice layers has resulted in the ability to field targets with liquid layers wetting the foam. Successful fielding of liquid-layer targets on NIF required not only a foam-lined capsule but also changes to the capsule filling process and the manner with which the inventory is maintained in the capsule. Additionally, changes to target heater power and the temperature drops across target components were required in order to achieve the desired range of shot temperatures. These changes and the target’s performance during four target shots on NIF are discussed.