The crystallographic and magnetic properties of the LaNi5--x Fex (1 ≤ x ≤ 1.4) and LaNi5--xMn x (... more The crystallographic and magnetic properties of the LaNi5--x Fex (1 ≤ x ≤ 1.4) and LaNi5--xMn x (x = 0, 1, 1.5, and 2) compounds have been studied by x-ray and neutron diffraction, SQUID and Mossbauer spectroscopy (LaNi 5--xFex only). All of the samples crystallized in the hexagonal CaCu5-type structure with space group P6/mmm. Both Fe and Mn atoms preferentially occupy the 3g site in these compounds. The LaNi 5--xFex samples exhibit ferromagnetic properties for x ≥ 1.2. The different magnetic behavior observed in LaNi4Fe suggests the coexistence of both short and long range magnetic ordering. The magnetic structure of LaNi5--xMnx for x = 1.5 and 2 is described by a ferrimagnetic model. A ferromagnetic model gives the best fit of the neutron diffraction data for LaNi4Mn. Calculations of the nearest-neighbor environments suggest that the difference between the magnetic structures of LaNi5--xMnx is due to the Mn dilution. The electronic structures of the LaNi5--xFe x compounds with x = 1 and 2 have been modeled by the orthogonalized linear combination of atomic orbitals (OLCAO) method. Calculations of magnetic moments, total energy, which is related to the preference of Fe occupying the 3g site, and total density of states are consistent with the results from SQUID measurements, neutron diffraction data, and Mossbauer spectroscopy. The spin-polarized photoemission measurements did not provide quality data due to a sample magnetization problem caused by the low remanence of the samples. Spin-independent photoemission spectra for YCo5, NdCo5, and LaNi3.65Fe1.35 are presented.
Energen, Inc. has designed, built, and demonstrated several fast and slow tuners based on its mag... more Energen, Inc. has designed, built, and demonstrated several fast and slow tuners based on its magnetostrictive actuators and stepper motor. These tuners are designed for Superconducting Radio Frequency (SRF) cavities, which are important structures in particle accelerators that support a wide spectrum of disciplines, including nuclear and high-energy physics and free electron lasers (FEL). In the past two years, Energen's work has focused on magnetostrictive fast tuners for microphonics and Lorentz detuning compensation on elliptical-cell and spoke-loaded cavities. These tuners were custom designed to meet specific requirements, which included a few to 100 micron stroke range, hundreds to kilohertz operation frequency, and cryogenic temperature operation in vacuum or liquid helium. These tuners have been tested in house and at different laboratories, such as DESY, Argonne National Lab, and Jefferson Lab. Some recent results are presented in this paper.
IEEE Transactions on Applied Superconductivity, 2005
Energen, Inc. has demonstrated new tuners based on magnetostrictive actuators to address SRF cavi... more Energen, Inc. has demonstrated new tuners based on magnetostrictive actuators to address SRF cavity fast tuning requirements for next-generation particle accelerators. Prototype fast tuners were fabricated and delivered to DESY, Argonne National Lab and Jefferson Lab. Results are reported from tests at Jefferson Laboratory, which were done under realistic operating conditions. In these tests, Energen's fast tuner was found to have a tuning range double the required 1200 Hz and provided precise, nanometer-resolution motion. Slow tuner results have been reported in earlier papers.
The crystallographic and magnetic properties of the LaNi5--x Fex (1 ≤ x ≤ 1.4) and LaNi5--xMn x (... more The crystallographic and magnetic properties of the LaNi5--x Fex (1 ≤ x ≤ 1.4) and LaNi5--xMn x (x = 0, 1, 1.5, and 2) compounds have been studied by x-ray and neutron diffraction, SQUID and Mossbauer spectroscopy (LaNi 5--xFex only). All of the samples crystallized in the hexagonal CaCu5-type structure with space group P6/mmm. Both Fe and Mn atoms preferentially occupy the 3g site in these compounds. The LaNi 5--xFex samples exhibit ferromagnetic properties for x ≥ 1.2. The different magnetic behavior observed in LaNi4Fe suggests the coexistence of both short and long range magnetic ordering. The magnetic structure of LaNi5--xMnx for x = 1.5 and 2 is described by a ferrimagnetic model. A ferromagnetic model gives the best fit of the neutron diffraction data for LaNi4Mn. Calculations of the nearest-neighbor environments suggest that the difference between the magnetic structures of LaNi5--xMnx is due to the Mn dilution. The electronic structures of the LaNi5--xFe x compounds with x = 1 and 2 have been modeled by the orthogonalized linear combination of atomic orbitals (OLCAO) method. Calculations of magnetic moments, total energy, which is related to the preference of Fe occupying the 3g site, and total density of states are consistent with the results from SQUID measurements, neutron diffraction data, and Mossbauer spectroscopy. The spin-polarized photoemission measurements did not provide quality data due to a sample magnetization problem caused by the low remanence of the samples. Spin-independent photoemission spectra for YCo5, NdCo5, and LaNi3.65Fe1.35 are presented.
Energen, Inc. has designed, built, and demonstrated several fast and slow tuners based on its mag... more Energen, Inc. has designed, built, and demonstrated several fast and slow tuners based on its magnetostrictive actuators and stepper motor. These tuners are designed for Superconducting Radio Frequency (SRF) cavities, which are important structures in particle accelerators that support a wide spectrum of disciplines, including nuclear and high-energy physics and free electron lasers (FEL). In the past two years, Energen's work has focused on magnetostrictive fast tuners for microphonics and Lorentz detuning compensation on elliptical-cell and spoke-loaded cavities. These tuners were custom designed to meet specific requirements, which included a few to 100 micron stroke range, hundreds to kilohertz operation frequency, and cryogenic temperature operation in vacuum or liquid helium. These tuners have been tested in house and at different laboratories, such as DESY, Argonne National Lab, and Jefferson Lab. Some recent results are presented in this paper.
IEEE Transactions on Applied Superconductivity, 2005
Energen, Inc. has demonstrated new tuners based on magnetostrictive actuators to address SRF cavi... more Energen, Inc. has demonstrated new tuners based on magnetostrictive actuators to address SRF cavity fast tuning requirements for next-generation particle accelerators. Prototype fast tuners were fabricated and delivered to DESY, Argonne National Lab and Jefferson Lab. Results are reported from tests at Jefferson Laboratory, which were done under realistic operating conditions. In these tests, Energen's fast tuner was found to have a tuning range double the required 1200 Hz and provided precise, nanometer-resolution motion. Slow tuner results have been reported in earlier papers.
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Papers by Chiu-Ying Tai