Forced Flow Supercritical Helium Research Articles

Hysteresis Loss in Poloidal Coils of the Large Helical Device

Hysteresis loss in poloidal coils of the Large Helical Device (LHD) has been measured during single-pulse operation. The superconductors of the coils are Nb-Ti cable-in-conduit conductors (CICC) cooled by forced-flow supercritical helium. The loss was measured by monitoring the enthalpy increase of the helium coolant between the inlet and outlet. Although the hysteresis loss was extracted by extrapolating several data sets from pulse excitations with different sweep rates, the extrapolated loss was much larger than the estimation using the magnetic hysteresis of the conductor. The anomalous increase in the loss is likely due to inter-strand coupling loss with long time constants from the order of 10 to 1000 s. The calculations show that the additional coupling loss behaves like a hysteresis loss.

The cryogenic system for ITER CC superconducting conductor test facility

This paper describes the cryogenic system of the International Thermonuclear Experimental Reactor (ITER) Correction Coils (CC) test facility, which consists of a 500 W/4.5 K helium refrigerator, a 50 kA superconducting transformer cryostat (STC) and a background field magnet cryostat (BFMC). The 500 W/4.5 K helium refrigerator synchronously produces both the liquid helium (LHe) and supercritical helium (SHe). The background field magnet and the primary coil of the superconducting transformer (PCST) are cooled down by immersing into 4.2 K LHe. The secondary Cable-In-Conduit Conductor (CICC) coil of the superconducting transformer (SCST), superconducting joints and the testing sample of ITER CC are cooled down by forced-flow supercritical helium. During the commissioning experiment, all the superconducting coils were successfully translated into superconducting state. The background field magnet was fully cooled by immersing it into 4.2 K LHe and generated a maximal background magnetic field of 6.96 T; the temperature of transformer coils and current leads was reduced to 4.3 K; the inlet temperature of SHe loop was 5.6 K, which can meet the cooling requirements of CIC-Conductor and joint boxes. It is noted that a novel heat cut-off device for High Temperature Superconducting (HTS) binary current leads was introduced to reduce the heat losses of transformer cryostat.

Conceptual Design of the 45 T Hybrid Magnet at the Nijmegen High Field Magnet Laboratory

A 45 T Hybrid Magnet System is being developed at the Nijmegen High Field Magnet Laboratory as part of the Nijmegen Center for Advanced Spectroscopy. The 45 T Hybrid Magnet System will be used in combination with far-infra-red light produced by a Free Electron Laser under construction directly adjacent to the High Field Magnet Laboratory. The superconducting outsert magnet will consist of three CICC coils wound on a single coil form, using strands. A test program for strand and cable qualification is underway. The CICC will carry 13 kA and the coils will produce 12 T on axis field in a 600 mm warm bore. The nominal operating temperature will be 4.5 K maintained with forced-flow supercritical helium. The insert magnet will produce 33 T at 40 kA in a 32 mm bore consuming 20 MW, and will consist of four coils. The insert magnet will be galvanically and mechanically isolated from the outsert magnet. Complete system availability for users is expected in 2014. In this paper we will report on the conceptual design of the 45 T Hybrid Magnet System.

Analysis of the Helium Behavior Due to AC Losses in the KSTAR Superconducting Coils

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The KSTAR superconducting magnetic coils, which are made of cable in-conduit conductor (CICC), maintain a superconducting state with forced-flow supercritical helium (4.5 K, 5.5 bar). During current changing of the superconducting magnetic coils, AC losses are generated in the CICC due to dI/dt, and the heat generated from the loss is removed by high heat capacity supercritical helium. At the same time, reversed flow of the helium occurs due to a rapid increase of the helium temperature and momentary changing of the pressure inside the CICC. This phenomenon has been detected in all of the poloidal field (PF) coils, especially in the upper (U) and lower (L) PF1<formula formulatype="inline"> <tex Notation="TeX">$\sim$</tex></formula>PF4 coils. The maximum change of the magnetic field in the PF1UL<formula formulatype="inline"><tex Notation="TeX">$\sim$</tex> </formula>PF4UL coils is located near the inlet and outlet of the helium cooling channels, and that of the PF5UL<formula formulatype="inline"><tex Notation="TeX">$\sim$</tex> </formula>7UL coils is located at the center of the cooling channel. The temperature variation at the helium inlet was always measured to have a time delay after each shot. In the PF1 coil tests, it was measured to have a delay of 26 sec. During the first plasma campaign, this phenomenon was more severe in the case of all PF coils operating together than for a single PF operation. In this paper, we investigated the thermal-hydraulics of this phenomenon . </para>

Mechanical Analysis of the Superconducting Outsert for the Series Connected Hybrid Magnets

The NHMFL presently has three series-connected-hybrid (SCH) projects, two of which are entering a construction phase. The design of the SCH outsert magnets is based on a CICC configuration using cable of multi-filamentary Nb3Sn and Cu strands inside a stainless steel jacket cooled by forced flow supercritical helium at 4.5 K. The outsert coil design is presented along with the design criteria for the evaluation of conduit and conductor insulation components. The results of detailed finite element analysis performed for normal, quench and fault load conditions are discussed to ensure the levels of stress and strain in conduit and insulations satisfy the design criteria. The conduit evaluation of fatigue life and fatigue crack growth rate (FCGR) is performed and the results are discussed for a possible cyclic lifetime and a minimum detectable flaw size for the SCH outsert.

Performance Tests of Superconducting Combined Function Magnets in the First Full-Scale Prototype Cryostat for the J-PARC Neutrino Beam Line

The first full-scale prototype magnet system assembled with the cryostat for the J-PARC proton beam line of neutrino experiment was successfully developed and tested. Two superconducting combined function magnets have been installed into the cryostat. The magnets were successfully cooled down to 4.5 K by forced flow supercritical helium and excited up to the current of 7345 A which is the nominal current of 50 GeV proton beam. The spot heater quench test showed that the quench characteristics in the supercritical helium were very similar to that in the liquid helium at 4.2 K, 1 atm. The quench protection scheme with both cold diodes and quench protection heaters was tested, and it has been verified that the magnet can be protected with safe margin.

Cryogenics in EAST

The EAST superconducting tokamak, an advanced steady-state plasma physics experimental device, is now being built at Institute of Plasma Physics, Chinese Academy of Sciences (CASIPP). All of toroidal field (TF) magnets and poloidal field (PF) magnets made of NbTi/Cu CICC are cooled with forced flow supercritical helium at 3.8 K. The cryogenic system of EAST consists of a 2 kW/4 K helium refrigerator and a helium distribution system for the cooling of PF and TF coils, structures, thermal shields, buslines and the current leads. The assembling and the installation of the 2 kW/4 K refrigerator were finished at the end of 2004 and the refrigerator has been commissioned successfully in July, 2005. The installation of the cryogenic distribution system will be finished at the end of 2005. This paper presents the design of the cryogenic system, the present states of the construction and the test results of the helium refrigerator.

Superconducting Magnet System at the 50 GeV Proton Beam Line for the J-PARC Neutrino Experiment

A neutrino oscillation experiment using the J-PARC 50 GeV 0.75 MW proton beam is planned as a successor to the K2K project currently being operated at KEK. A superconducting magnet system is required for the arc section of the primary proton beam line to be within the space available at the site. A system with 28 combined function magnets is proposed to simplify the system and optimize the cost. The required fields for the magnets are 2.6 T dipole and 19 T/m quadrupole. The magnets are also required to have a large aperture, 173.4 mm diameter, to accommodate the large beam emittance. The magnets will be protected by cold diodes and cooled by forced flow supercritical helium produced by a 4.5 K, 2/spl sim/2.5 kW refrigerator. This paper reports the system overview and the design status.

Cryogenic System for the Superconducting Tokamak HT-7U

HT-7U is a fully superconducting tokamak. All of the toroidal field and poloidal field superconducting magnets are made of NbTi superconductor and are designed to operate at 3.8 K in the steady-state operation mode. The magnet system will be cooled with forced-flow supercritical helium to this temperature level with an equivalent refrigeration capacity of ~2 kW/4.4 K. To satisfy this requirement, a helium refrigerator is designed to be able to provide the cooling power at 3.5, 4.5, and 80 K for the coils, supports, and thermal shields. The refrigerator can also produce liquid helium for the cooling of the current leads. This paper describes the cryogenic system of HT-7U, the refrigeration process and helium plant, and the forced-flow cooling requirement of the superconducting magnets.

Construction of a 2 kW /4 K Helium Refrigerator for HT-7U

Superconducting magnets of toroidal field (TF) and poloidal field (PF) of HT-7U tokamak are all made of NbTi/Cu Cable-in-Conduit Conductor (CICC), and cooled with a forced flow supercritical helium of 3.8 K. A helium refrigerator with an equivalent capacity of 2 kW/4 K will be constructed. This paper presents the design of the helium refrigerator process, the thermodynamics of the refrigeration cycle and the refrigerator equipments.

Current feeder system for the KSTAR device

The current feeder system consisting of superconducting (SC) bus-lines, SC bus-line interface terminal, and current leads is used as the current transmission system for the KSTAR SC coils. The current lead system consists of 11 pairs of vapor-cooled leads for the PF coils and a pair of leads for the TF coils. The PF coils are operated at full currents only during a portion of the entire time. The heat loads of current leads in idle mode, when it carries no current, depend quite strongly on the using material. We have measured the heat load and temperature profile when the overload current was charged in 200 A optimum brass lead. Also, the current feeder system requires a long bus-line that must supply a large amount of current from a current lead to SC coils. We have designed a SC bus-line with NbTi cable-in-conduit conductor (CICC) to reduce Joule heating loss. The CICC is cooled with forced-flow supercritical helium (SHe). The bus-line requires higher reliability and safety than those of the SC coils of the KSTAR. The KSTAR bus-line has been designed to have an independent vacuum space and consist of SHe return and 60 K thermal shield line for shielding. To connect the bus-line with a cryostat of the KSTAR and current lead box, we have developed a prototype SC bus-line interface terminal.

Development of forced flow cooled current leads for fusion magnets

During the past 15 years, the Institut für Technische Physik of the Forschungszentrum Karlsruhe, Germany, has developed current leads cooled by forced-flow supercritical helium in the current range from 20 to 80 kA. The design is based on a separation of the current carrying part and the heat exchanger part as well as the presence of the so-called superconductor inserts made of Nb 3Sn wires inside the conductor in the heat exchanger area which allows the operation of the current lead at minimum helium mass flow in a wide current range. The paper describes the design and construction of the current leads as well as operation results obtained during various tests performed in the coil test facility TOSKA at the Forschungszentrum Karlsruhe.

ＩＴＥＲ‐ＣＳモデル・コイルとＣＳインサート・コイルの実験結果 ＣＳモデル・コイルとＣＳインサート・コイルの初期冷凍・定常熱負荷・昇温特性

In International Thermonuclear Experimental Reactor (ITER) Engineering Design Activities, the Central Solenoid Model Coil (CSMC) and the CS Insert Coil (CSIC) have been fabricated, and installed into the ITER CSMC test facility at Naka Fusion Establishment, Japan Atomic Energy Research Institute (JAERI). The CSMC and CSIC conductors are applied to the cable-in-conduit conductors cooled by forced-flow supercritical helium (SHe) at 4.5K. There are 48 parallel cooling channels for the CSMC, the CSIC and the structures. In the CSMC experiment, the cool-down and the warm-up were finished successfully. The cool-down time was within 480 hours. The steady head load without coil current was measured and evaluated.

The test facility for the KSTAR superconducting magnets at SAIT

SSTF (Samsung Superconductor Test Facility) has been built with the primary goal of testing the KSTAR TF (Toroidal Field) and PF (Poloidal Field) magnets as well as CICC (Cable-in-Conduit Conductor) and superconducting strands in the most relevant manner. The facility is located at SAIT (Samsung Advanced Institute of Technology) near the KSTAR project home site. Two helium liquefiers of 120 liter/hr capacity have been utilized as refrigerators demonstrating simultaneous double mode operation of refrigeration and liquefaction. A forced flow supercritical helium cooling circuit allows the test facility to be operated at temperatures down to 4.5 K. Other major SSTF components are a large vacuum vessel (6 m diameter and 7.3 m height) with liquid nitrogen temperature shield, data acquisition and control system with EPICS (Experimental Physics and Industrial Control System), current leads, and 50 kA modular power supply with fast dump quench protection circuitry. SSTF has been used for the first test-phase of KSTAR CICC sample. The current status of SSTF as the KSTAR magnet test facility for components and qualification test is presented in detail.

Current measurements of the individual strands in CICC magnet

Non-uniform current distribution in CICC (cable-in-conduit conductor) is one of the major concerns for developing a successful magnet system. The three-strand CICC magnet has been constructed in KAIST (Korea Advanced Institute of Science and Technology) for the study of current nonuniformity. The magnet is equipped with a forced flow supercritical helium system at variable temperature to simulate the various thermohydraulic conditions of superconducting Tokamak. Each strand of the magnet has its own shunt resistor to measure the current it carries during the DC and AC operations. This paper describes an experimental apparatus and some current measurement results of the individual CICC strands. The unbalanced current distribution has been obtained directly from the shunt resistor voltage data. The surface contact resistance of the superconducting strands was small enough to allow current redistribution inside the conduit rather than at the terminal joints of the magnet.

大型ヘリカル装置の超伝導システム 大型ヘリカル装置の低温システム ヘリウム液化冷凍装置

A large-scale helium refrigerator/liquefier has been developed to provide reliable and safe operation for the Large Helical Device (LHD). The refrigerator is required to satisfy four different types of cooling methods: forced-flow supercritical helium, a pool boiling method, two-phase helium flow and forced-flow low-temperature (40-80K) helium gas. The forced-flow supercritical helium is widely used in modern large-scale superconducting magnets. This method requires a much more complex refrigeration system than does pool boiling because of the circulation of low-temperature helium within a very long cooling path. The overall refrigeration system is fairly complicated because of these multi-refrigeration requirements. As a matter of fact, it is not likely to find this type of refrigeration plant in the world. The helium refrigerator has a total refrigeration capacity of 5.65kW at 4.4K and 20.6kW at 80K and 650l/h liquefaction. The refrigerator was designed to have high processing efficiency since the construction expense is much less than the operating cost. In order to achieve this, the refrigerator has two precooling cycles (300 to 80K and 80 to 20K) and has two turboexpanders running in parallel with different temperature levels at the cold end. To achieve a high mass flow rate in a low-temperature regime, eight screw-type compressors are operated at room temperature. There are two compressor groups, group A and group B, to reduce the overall work load. Each group consists of 1st and 2nd stage compression processes. The total mass flow rate becomes 960g/s at 1.864MPa. This article reviews the basic chracteristics of a 10kW class helium refrigerator/liquefier and a simple refrigeration cycle.

Ramp-rate limitation experiments using a hybrid superconducting cable

Ramp-rate limitation experiments were done in a new facility at the MIT (Massachusetts Institute of Technology) Plasma Fusion Center. The features of this new facility include (1) a superconducting pulse coil that can superimpose high ramp-down rates, up to 25 T s −1, (2 T in 80 ms) at a background field up to 5 T, (2) new power supplies that can supply high rates of dl dt and dB dt to the sample under test and (3) a forced-flow supercritical helium system for cooling CICCs (Cable-In-Conduit Conductors). This paper discusses the results of the ramp-rate limitation experiments on a 27-strand hybrid Nb 3Sn cable. The cable was tested under field ramps of up to 2.5 T s −1 with various operating currents. It did not quench with dB dt , field and average strand currents that were simultaneously above the operating range of TPX-PF (Tokamak Physics Experiment Poloidal Field) coils. Further ramp-rate limitation experiments revealed that the tested 27-strand hybrid cable has very high transient stability at ramped fields, extending out to average strand currents that are nearly triple the TPX-PF operating current.

Cooling of small SMES system with forced flow supercritical helium

Technische Universität München (Lehrstuhl für Elektrische Maschinen) is currently constructing a small superconducting magnetic energy storage (SMES) system. Six coils, forming a torus, store 1.4 MJ of energy at 1360 A maximum current. Simulations show that the fastest charge/discharge cycle time that can be realized is 1.5 s. The coils are cooled indirectly by supercritical helium in a closed forced flow circuit. To obtain low cable temperatures even at high superconductor losses the helium is recooled with intermediate heat exchangers by boil-off from two pools of liquid helium. This paper discusses the plant's capability in different load cycles with respect to the refrigeration capacity, where the superconductor losses and the coil and helium temperatures are calculated. In addition, the pressure rise in the cooling tube during coil quench is investigated.

Test of a forced-flow cooled 30 kA/23 kV current lead for the POLO model coil

A 30 kA/23 kV current lead cooled by forced-flow supercritical helium has been developed at KfK. It allows position independent installation and well controlled operation which would be advantageous for operation of all kind of superconducting forced-flow cooled magnets. The design of the lead is described in this paper. The main feature is the insertion of Nb/sub 3/Sn wires inside the conductor of the heat exchanger allowing the operation at minimum mass flow in a wide current range. Measurement results are presented for steady-state operation up to 30 kA, for short time operation up to 50 kA, for pulsed operation up to /spl plusmn/1000 A at 10 Hz, and for simulation of loss of mass flow. A high-voltage test up to 28 kV DC has been done. The mass flow rate normalized to current is about 0.055 g/(s-kA) for 15 to 30 kA proving the effectiveness of the Nb/sub 3/Sn inserts. Comparison to numerical calculations shows good agreement allowing extrapolation for the design of leads for currents up to 80 kA for ITER model coil tests in the TOSKA test facility at KfK.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Present status of design and manufacture of the superconducting magnets for the Large Helical Device

The Large Helical Device (LHD) is a nuclear fusion experimental device with superconducting magnets. Manufacture of the cryostat, the inner vertical coils, and the helical-coil winding machine are now being carried out. Designs for constructing two helical coils and two other pairs of poloidal coils are in progress. The outside diameter of the torus-shaped cryostat is 13.5 m. There are two operational stages for the LHD. Phase I and Phase II. The helical coils will have a magnetic energy of 1.6 GJ and an overall current density of 53 A/mm/sup 2/ in Phase II. The rated current is 13.0 kA in Phase I, and the maximum magnetic field in the helical coil winding in Phase I was calculated to be 6.9 T. Three pairs of poloidal coils are cooled by forced-flow supercritical helium because of the necessity of having no metal coil vessel. The rated current of one inner vertical (IV) poloidal coil is 20.8 kA, and its stored energy is 80 MJ. The maximum magnetic field of the two IV coils was calculated to be 5.8 T. The type of superconductor for the IV coils is a cable-in-conduit conductor.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>