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Closed-Loop Cryogenic Cooling for a 21 T FT-ICR Magnet System
Choi, Y.S.,Kim, D.L.,Painter, T.A.,Markiewicz, W.D.,Lee, B.S.,Yang, H.S.,Yoo, J.S. IEEE 2008 IEEE transactions on applied superconductivity Vol.18 No.2
<P>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.</P>
Semi-Retractable Current Leads for a 21 T FT-ICR Magnet System
Choi, Y.S.,Painter, T.A.,Kim, D.L.,Bole, S.T.,Adkins, T. IEEE 2008 IEEE transactions on applied superconductivity Vol.18 No.2
<P>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.</P>
Choi, Y.S.,Kim, D.L.,Lee, B.S.,Yang, H.S.,Painter, T.A.,Miller, J.R. 한국초전도저온학회 2006 한국초전도저온공학회논문지 Vol.8 No.1
A closed-loop cryogenic cooling system for high field magnets is presented. This design is motivated by our recent development of cooling system for 21 tesla Fourier Transform ion Cyclotron Resonance (FT-ICR) superconducting magnets without any replenishment of cryogen. The low temperature superconducting magnets are immersed in a subcooled 1.8 K bath, which is connected hydraulically to the 4.2 K reservoir through a narrow channel. Saturated liquid helium is cooled by Joule-Thomson heat exchanger and flows through the JT valve, isenthalpically dropping its pressure to approximately 1 6 kPa, corresponding saturation temperature of 1.8 K. Helium gas exhausted from pump is now recondensed by two-stage cryocooler located after vapor purify system. The amount of cryogenic Heat loads and required mass flow rate through closed-loop are estimated by a relevant heat transfer analysis, from which dimensions of JT heat exchanger and He II heat exchanger are determined. The detailed design of cryocooler heat exchanger for helium recondensing is performed. The effect of cryogenic loads, especially superfluid heat leak through the gap of weight load relief valve, on the dimensions of cryogenic system is also investigated.
Semi-Retractable Current Lead Cooled by a Cryocooler for High Field Magnet
Choi, Y.S.,Painter, T.A.,Kim, D.L.,Yang, H.S.,Lee, B.S. IEEE 2009 IEEE transactions on applied superconductivity Vol.19 No.3
<P>The semi-retractable current lead cooled by a cryocooler is designed for a high field superconducting magnet system. The semi-retractable current lead is composed of a normal metal element, conducting the current from room temperature to an intermediate temperature, and an HTS element, conducting the current down to liquid helium temperature. An HTS element and the joint between the normal metal and HTS element are connected to a two-stage cryocooler. The intermediate joint carries current through a strip of louvered material. After charging the normal metal element is disengaged from the HTS element without breaking vacuum in the insulating space. The semi-retractable current lead is fabricated and assembled with a two-stage cryocooler for feasibility test. The adaptability and reliability of the lead are tested during engage and disengage performance. The electrical contact resistance is also measured in the intermediate joint with respect to the vacuum level and temperature has been measured.</P>
Conduction-Cooled Superconducting Magnet for Material Control Application
Yeon Suk Choi,Dong Lak Kim,Byoung Seob Lee,Hyung Suk Yang,Painter, T.A. IEEE 2009 IEEE transactions on applied superconductivity Vol.19 No.3
<P>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.</P>