Performance Evaluation of Current Leads for a 5 Tesla Electromagnetic Properties Measurement System

The development of the Electromagnetic Property Measurement System is underway at the Korea Basic Science Institute. The Electromagnetic Property Measurement System is used for electrical, thermal, and magnetic specimen property measurements in variable magnetic fields and temperatures with a low-temperature superconducting magnet. To activate low-temperature superconducting magnet that operates with liquid helium, we propose the use of vapor-cooled current leads. The low-temperature superconducting magnet is connected to the power supply at room temperature through a pair of current leads. Accordingly, heat inflows through the current leads and represents one of the major contributory factors of the entire heat inflow. Therefore, design optimization and evaluation of the current leads is necessary to minimize heat and liquid helium consumption. Vapor-cooled, and hybrid current leads were designed and fabricated, and testing in liquid helium cryostat was conducted. The low-temperature superconducting magnet was charged with electrical current up to the operating level, and the liquid helium boil-off rate was measured with respect to the supplied electrical current level. The performances of the two current leads were accessed based on the thermal load and boil-off rate of the liquid helium. The experimental and analyzed liquid helium boil-off rates associated with the current leads were in close agreement.

Установка для измерения времени жизни нейтрона с большой гравитационной ловушкой при низкой температуре

Currently the most accurate measurements of neutron lifetime are being performed at the Petersburg Nuclear Physics Institute with ultracold neutrons (UCNs) stored in a gravitational trap. A modified setup with a large gravitational trap and cooling to 10–15 K is presented. The results of measurements of temperature dependence of UCN losses in collisions with walls, which were coated with a perfluorinated grease (Fomblin UT 18), at 300–77 K, are detailed. The probable heat inflow to the trap is estimated, and the feasibility of cooling to indicated temperatures in experiments with the modified setup is demonstrated.

Modeling the influence of magnetospheric heat fluxes on the electron temperature in the subauroral ionosphere

We present results of modeling of the electron temperature distribution in the F region of the subauroral ionosphere for different helio-geomagnetic conditions with consideration for magnetospheric heat fluxes. It is shown that under quiet geomagnetic condi-tions during a winter period in the dawn and dusk sec-tors “hot” zones with a higher electron temperature are formed, and under disturbed geomagnetic conditions an annular “hot” region is formed in a time interval 04–06 UT as a result of heat inflow from Earth’s magnetosphere along magnetic field lines. The analysis of the DE-2 satellite data demonstrates that such zones can be formed during geomagnetic disturbances.

Modeling the influence of magnetospheric heat fluxes on the electron temperature in the subauroral ionosphere

We present results of modeling of the electron temperature distribution in the F region of the subauroral ionosphere for different helio-geomagnetic conditions with consideration for magnetospheric heat fluxes. It is shown that under quiet geomagnetic condi-tions during a winter period in the dawn and dusk sec-tors “hot” zones with a higher electron temperature are formed, and under disturbed geomagnetic conditions an annular “hot” region is formed in a time interval 04–06 UT as a result of heat inflow from Earth’s magnetosphere along magnetic field lines. The analysis of the DE-2 satellite data demonstrates that such zones can be formed during geomagnetic disturbances.

Linear baroclinic instability in the presence of heat inflow from the lower boundary

A linear Eady model with a parameterization of heat influx from the lower boundary is studied analytically in order to obtain the characteristics of baroclinic normal modes modified by this non-adiabatic source. The results display a secondary maximum of growth rate at high wave numbers and a range of absolutely unstable waves, thus suggesting that the property observed among mid-latitude explosive cyclones of being near-stationary in the phase of maximum growth may be captured by this representation of the air-sea energy exchange.