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Cooldown time is one of the major factors in the conduction-cooled superconducting magnet system. Cooldown time means a time cooling a superconducting magnet from room temperature to cryogenic temperature within a stipulated amount of time. The estimation of cooldown time seeks the elapsed time to cool the superconducting magnet by cryocooler during initial cooldown process. This procedure includes the modeling of properties of low temperature superconductor, the dimensions of superconducting magnet, the cryogenic loads, the thermal link between magnet and cryocooler, and the available refrigerating capacity of cryocooler. This method is applied to the conduction-cooled superconducting magnet system developed by ourselves for accuracy confirmation. The effects of magnetic field, size of magnet and thermal link on the initial cooldown are also discussed. [ABSTRACT FROM AUTHOR]

The cryocooler directly cooled low temperature superconducting magnet is designed, fabricated and tested at the Korea Basic Science Institute (KBSI) for the crystal growth application. The magnet has one solenoidal configuration with a copper former which has a 52 mm room temperature bore. A two-stage 4 K GM cryocooler with 1.5 W refrigeration power is employed to cool the magnet from room temperature to liquid helium temperature. A pair of the binary current lead, a series combination of a normal conductor in the high temperature section and an HTS conductor in the low temperature section, is used for this application. The paper presents the process of design, fabrication and charging test. Also, the performance of the conduction cooled superconducting magnet system is discussed with respect to the supplied current and contact resistance. [ABSTRACT FROM AUTHOR]

The conduction-cooled superconducting magnet with operating current of 180 A is designed, fabricated, and tested for material control application. The superconducting magnet has the effective standard warm bore of 52 mm and the maximum central field of 3 Tesla. Since magnetic field gradient should be larger at the end rather than at the center of the magnet for material control, we developed design method to optimize magnet for this purpose. The safety of the superconducting magnet is evaluated, taking into account the electro-magnetic field, heat and structure, and the superconducting coil is successfully wound by the wet-winding method. The superconducting coil is installed in the cryostat maintaining high vacuum and cooled by a two-stage GM cryocooler. The performance of the conduction-cooled superconducting magnet is discussed with respect to the supplied current, joule heating, and cooling medium. [ABSTRACT FROM AUTHOR]

A closed-loop cooling concept for 21 T Fourier transform ion cyclotron resonance (FT-ICR) superconducting magnets is presented. In the magnet system, low temperature superconducting coils are immersed in a subcooled 1.8 K bath, which is connected to the saturated helium reservoir through the weight load relief valve. Saturated liquid helium is refrigerated by a Joule-Thomson (JT) heat exchanger and flows through the JT valve, isenthalpically dropping its pressure to approximately 1.6 kPa, corresponding to a saturation temperature of 1.8 K. Helium gas exhausted from JT pump is liquefied by a two-stage cryocooler located after the vapor purify system. In the present paper, the amount of heat budget is determined and the structural design of cryostat is carried out by the relevant analyses. The position of a cryocooler in the magnet system is investigated, taking into account the requirement of magnetic field for normal performance. Helium liquefaction system, a key component of the closed-loop cooling system, is fabricated and tested in order to demonstrate the feasibility of our new cryogenic cooling for high field magnets. [ABSTRACT FROM AUTHOR]

The development of the semi-retractable current leads for a 21 T Fourier Transform Ion Cyclotron Resonance (FT-ICR) superconducting magnet system is presented. The semi-retractable current leads are composed of a normal metal element, conducting the current from room temperature to intermediate temperature, and an HTS element, conducting the current down to liquid helium temperature. An HTS element is partly immersed in liquid helium and the joint between the normal metal and HTS element is continuously refrigerated by a cryocooler. After magnet energization the metal element is disengaged from the HTS element without breaking vacuum to the insulating vacuum space. In the paper, the optimized dimensions of the leads are presented in order to minimize the thermal heat load when carrying operational current with some margin. The intermediate block with a lockable set point and the insulating vacuum system are fabricated and the adaptability and reliability are tested during engage and disengage performance. The effects of vacuum level and performance cycle on the electrical contact resistance in a lockable set are also investigated. [ABSTRACT FROM AUTHOR]

A new concept of current leads for a 21 T Fourier Transform Ion Cyclotron Resonance (FT-ICR) superconducting magnet system is presented. The binary current lead, a series combination of a normal conductor in the high-temperature section and an HTS conductor in the low-temperature section, is employed. The HTS section is partly immersed in liquid helium and the joint between the normal metal and HTS conductor is cooled by the contact with a cryocooler. After excitation, the normal metal conductor section is thermally disengaged from the HTS section without disturbance to the insulating vacuum space and without requiring complete removal of the current leads. The present paper describes the so-called semi-retractable current leads for a 21 T FT-1CR magnet system application. The optimized dimensions of the leads are presented in order to minimize the thermal heat load when carrying operational current with some margin. [ABSTRACT FROM AUTHOR]