Nathaniel Pogue

Accelerator-driven subcritical fission in molten salt core: Closing the nuclear fuel cycle for green nuclear energy

A technology for accelerator-driven subcritical fission in a molten salt core (ADSMS) is being developed as a basis for the destruction of the transuranics in used nuclear fuel. The molten salt fuel is a eutectic mixture of NaCl and the chlorides of the transuranics and fission products. The core is driven by proton beams from a strong-focusing cyclotron stack. This approach uniquely provides an intrinsically safe means to drive a core fueled only with transuranics, thereby eliminating competing breeding terms.

Texturing of Micaceous Superconductor Powder and Fabrication of Wire to Preserve the Texture

The Bi-based high-temperature superconductors are micaceous: grains cleave preferentially in the ab plane when fractured, so that powders consist of thin platelets. Superconducting current transport is similarly planar, and supercurrent flow is largely limited to the ab plane. We report studies of two methods to align the particles of such powder in a thin layer so that most particles are aligned with parallel ab planes. We are developing a `jelly-roll method for wire fabrication that could preserve this desirable texture.

Ultra-Gradient Test Cavity for Testing SRF Wafer Samples

A 1.3 GHz test cavity has been designed to test wafer samples of superconducting materials. This mushroom shaped cavity, operating in TE01 mode, creates a unique distribution of surface fields. The surface magnetic field on the sample wafer is 3.75 times greater than elsewhere on the Niobium cavity surface. This field design is made possible through dielectrically loading the cavity by locating a hemisphere of ultra-pure sapphire just above the sample wafer. The sapphire pulls the fields away from the walls so the maximum field the Nb surface sees is 25% of the surface field on the sample. In this manner, it should be possible to drive the sample wafer well beyond the BCS limit for Niobium while still maintaining a respectable Q. The sapphires purity must be tested for its loss tangent and dielectric constant to finalize the design of the mushroom test cavity. A sapphire loaded CEBAF cavity has been constructed and tested. The results on the dielectric constant and loss tangent will be presented.

MAGNETIC ORIENTATION OF BI‐2212 POWDER

The Accelerator Lab at Texas A&M is developing a method of texturing Bi‐2212 powder for an oriented powder multifilament round wire. Results of preliminary experiments relating to the orientation of Bi‐2212 powders by magnetic fields are presented.

Strong Focusing Cyclotron and Its Applications

A Strong Focusing cyclotron has been developed by the Accelerator Research Lab at Texas A&M to produce up to 10 mA of proton beam at 800 MeV. The cyclotron has several innovations that allow it to achieve such high levels of power. The first is the superconducting RF cavities that provide sufficient gain to separate the orbits by a minimum of 6 cm. This space allows for beam transport channels to be place along every orbit and provide continuous quadrupole focusing. Additionally, a trim dipole is added to the channel to allow for corrections to the main dipole. This document will show the new BTC design that allows for the cyclotron to be greatly simplified. The main dipole is kept below saturation and is shaped to levitate the poles. The main dipole, along with the RF cavity, are designed such that several cyclotrons could be stacked on top of one another. This design provides the high power beam required for several applications. These applications include accelerator driven systems, neutron damage facilities, and medical isotope production. Texas A&M has developed two designs for ADS fission: an isoburner and an isobreeder. Both of these designs will be expounded on within the document. A design for a neutron damage facility and it capabilities are presented as well as a medical isotope production design. The SFC has great potential to revolutionize these fields and be of great service to the US.

Superconducting Test Cavity With Dielectric Concentrator for High Q, High Surface Field

A superconducting test cavity and cryostat are being developed to support the testing of round wafer samples of new superconducting materials. The cavity is designed to test these samples in surface fields up to and beyond the BCS limit of Nb. The design is optimized to produce maximum surface field on the sample compared with that elsewhere in the cavity. It operates in the TE011 mode. A dielectric hemisphere of low-loss sapphire is located just above the wafer surface and serves to concentrate the surface field. The sapphire is cooled by a column of superfluid He, with sufficient heat transport to maintain high Q throughout the rf pulse. It should be possible to test a sample to twice the BCS limit of Nb while measuring the rf surface resistance of the sample.

First Results of the SRF Wafer Test Cavity for the Characterization of Superconductors

The wafer test cavity was designed as a short sample test system that could create a reproducible environment for the testing of superconducting materials above the Bardeen-Cooper- Schrieffer limit of niobium. The results of the sapphire test cavity showed that the dielectric was too lossy, and thus, the original design had to be altered to make operation feasible with current hardware and achieve ~200 mT. The new design was fabricated at Thomas Jefferson National Accelerator Facility and was cryogenically tested. After four tests, the cavity was able to produce a 6.6-mT field with a Q of 3.96 * 108. Although lower than anticipated, in comparison to other TE01 cavities, this result is quite encouraging. Multipacting and coupling were limitations, but current work is pursuing the elimination of these complications. This document will expound upon the new design, mathematical simulations, testing of the cavity, complications, results, and future work.

Superconducting Sector Dipole for a Strong Focusing Cyclotron

A superconducting strong focusing cyclotron (SFC) is being developed for high current applications. The dipole magnetic field required for isochronous operation is provided by sector magnets utilizing a common warm-iron flux return and levitated cold-iron pole design. The sector magnets utilize MgB2 superconducting cable operating at 15-20 K. The sector dipoles for a 100 MeV SFC were modeled to provide for isochronous operation. The field distribution, fringe fields, forces and torques in the dipole were calculated.

WAFER TEST CAVITY -Linking Surface Microstructure to RF Performance: a ‘Short-­Sample Test Facility’ for characterizing superconducting materials for SRF cavities.

The Wafer Test cavity was designed to create a short sample test system to determine the properties of the superconducting materials and S-I-S hetero-structures. The project, funded by ARRA, was successful in accomplishing several goals to achieving a high gradient test system for SRF research and development. The project led to the design and construction of the two unique cavities that each severed unique purposes: the Wafer test Cavity and the Sapphire Test cavity. The Sapphire Cavity was constructed first to determine the properties of large single crystal sapphires in an SRF environment. The data obtained from the cavity greatly altered the design of the Wafer Cavity and provided the necessary information to ascertain the Wafer Test cavity’s performance.

Design of a

A superconducting strong-focusing cyclotron is being developed for high current applications. Alternating-gradient focusing is provided by ~ 6 T/m superconducting beam transport channels which lie in the sectors along the arced beam trajectory of each orbit of the cyclotron. The ~ 1 T sector dipoles, corrector dipoles, and Panofsky type quadrupoles utilize MgB2 superconductor operating around 15-20 K. The operating temperature provides a valuable margin for a cost-effective cryogenic design, and large thermal stability in the event of occasional heat loads from intercepted beam or other sources. The main dipole windings are designed with sufficiently large curvature so that they can be fabricated using react-and-wind procedure; the quadrupole windings require small-radius end bends and so must be fabricated using wind-and-react procedure. Initial magnetic modeling on the end field region is presented.