Total Conductor Length Research Articles

Multiphysics Model of Quench for the ITER Central Solenoid

The ITER Central Solenoid (CS), the backbone of the ITER magnet system, is composed of 6 modules, each made of 40 pancakes, for a total conductor length of about 36 km. More than 4 km of pipes, about 30 bypass or control valves, the heat exchangers and a cold circulator are part of the cryogenic distribution used to maintain the nominal operating conditions (flow and temperature). During the plasma scenario, several loss sources – such as AC losses, heat from supports and structures, joule heating at joints – can affect the magnet stability. A reliable analysis of quench is therefore of great importance to guarantee the safe operation of the CS superconducting coils. In this work, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SuperMagnet</i> code, a state of the art software for the numerical modelling of hydraulic, electrical and thermal phenomena occurring in superconducting magnets, is applied to study the CS and its cryogenic distribution during quench events.

An HTS Model Magnet for MRI Systems Equipped With Electrically Conductive Epoxy Resin for Quench Protection

We have been developing conduction-cooled HTS magnets wound with REBCO-coated conductors for MRI systems, with the aim of developing 9.4 T MRI magnets for whole-body and brain imaging. One of the key technologies to implement the REBCO coil is quench protection and we proposed a quench protection method using electrically conductive epoxy resin. The electrically conductive epoxy resin is attached to the edge of the winding. When the coil voltage rises unintentionally, the excessive current can be automatically bypassed from turn to turn through the electrically conductive epoxy resin. In order to verify the effectiveness of this method with a large-scale coil that has higher stored energy, an HTS MRI model magnet equipped with conductive epoxy resin was designed and fabricated. The magnet has a REBCO multicoil composed of 100 single pancakes whose inner diameters are 500 mm. The total conductor length is 31 km, and the total inductance is 91 H. The central magnetic field is 3 T at 142.7 A, and the size of the homogeneous magnetic field region is 200 mm diameter spherical volume (DSV). This paper presents the design, fabrication of the REBCO multicoil, and test results of the HTS MRI model magnet in a conduction-cooled configuration.

OPTIMASI PERENCANAAN SISTEM PEMBUMIAN PADA RENCANA PEMBANGUNAN GAS INSULATED SUBSTATION 150 KV PECATU

The construction of the Gas Insulated Substation (GIS) 150 kV Pecatu is planned by PT. PLN(Persero) to get electricity needs in the area of Pecatu, Badung Regency, Bali Province. The GasInsulated Substation (GIS) 150 kV Pecatu is located in a hilly area with a texture of limestone rockysoil and the resulting soil type resistance is ? = 263.76 ohm-meter. The results of calculations for thetype of earthing system Plates earth resistance value of 0.95 ohms at a cost of Rp. 4,196,000,000, -(Four Billion One Hundred Ninety Six Million Rupiah), for the type of Mesh earthing system no resultsare obtained &lt;1 ohm and for the Multi Grid-Rod earthing system type the grounding resistance valueis 0.876 ohms at a cost of Rp 3,753,120,000, - (Three Billion Seven Hundred Fifty Three Million OneHundred Twenty Thousand Rupiah). The type of earthing system recommended is a Multi Grid-Rodearthing system with a distance between parallel conductors (D) of 1 meter, depth of conductorplanting as deep as 4 meters above the ground surface, Rod electrode diameter of 0.015 meters, Rodelectrode length of 4 meters and total conductor length of 12500 meters.

Design and Test of a Double Pancake Coil for SMES Application Wound by HTS Roebel Cable

A double pancake coil wound by HTS Roebel cable was designed, fabricated, and tested at 77 K. This coil winding had eight turns with the inner diameter of 340 mm and a total conductor length of 10 m. With ten ReBCO strands, the transposition length of the cable was 300 mm. To avoid delamination of ReBCO strands, this coil was impregnated with paraffin wax by a vacuum impregnation method. For protecting ReBCO strands, protective copper plates (PCP) were inserted and soldered between cable surface and external current terminal. The voltage probes were not directly soldered on strands, but on the PCP instead. The critical current and central flux density of the coil were measured at 77 K. With the criterion of 1 μV/cm, the critical current was 1025 A at 77 K. Finally, the additional resistance and the heat loss at 77 and 20 K caused by adding the PCP were estimated.

Screening-Current-Induced Magnetic Field of Conduction-Cooled HTS Magnets Wound With REBCO-Coated Conductors

Superconducting magnets for magnetic resonance imaging systems require homogeneous, stable magnetic fields. The homogeneity of the magnetic field is highly dependent on the coils shape and positions. Furthermore, in REBa2 Cu3O7−δ (REBCO) magnets, the screening-current-induced magnetic field, which changes the magnetic field distribution of the magnet, is one of the most critical issues. In the work described here, a small REBCO coil that can generate a magnetic field of over 10 T was fabricated and tested. The small REBCO coil was composed of a stack of 22 single pancake coils whose inner and outer diameters were 50 mm and 130 mm, respectively. The total conductor length was 1.5 km. The small REBCO coil could generate a central magnetic field of 8.27 T at 10 K. A magnetic field of over 10 T was achieved by replacing 12 of the single pancake coils with new ones wound with the latest REBCO-coated conductors. The measured value of the central magnetic field at 10 K was 13.53 T, which was lower than the calculated value of 13.94 T obtained without taking account of the screening-current-induced magnetic field. Furthermore, it was examined whether the current sweep reversal would be effective for 10 T-class magnetic field conditions.

Progress in the Development of Conduction-Cooled REBCO Magnets for Ultrahigh-Field MRI Systems

We started developing REBa 2 Cu 3 O 7-δ (REBCO) magnets for ultrahigh-field magnetic resonance imaging (MRI) systems in 2013. Our final targets are 9.4 T MRI systems for whole-body and brain imaging. In this paper, a conduction-cooled 1.5 T REBCO MRI magnet having a room-temperature bore of 396 mm was fabricated and tested in order to evaluate the magnetic field homogeneity and stability. The magnet was composed of 60 single pancakes whose inner diameter was 500 mm. The total conductor length was 10.3 km, and the total inductance was 12.4 H. The size of the homogeneous magnetic field region was 200 mm diameter spherical volume. The central magnetic field was as high as 1.5 T at 192.7 A, and the current density of single pancakes was 301 A/mm 2 . The magnet was cooled from room temperature to 4.7 K in 55 hours, and the temperature difference among the coils was 0.1 K or less during both initial cooling and excitation. The magnetic field inhomogeneity was 249.7 parts per million (ppm), and the Z 2 coefficient was largest at 579.6 ppm. The main reason for the error magnetic field was dimensional errors in the positions on the z-axis. The magnetic field inhomogeneity was improved to 4.1 ppm by passive shimming using iron pieces. The magnetic field stability was about 2 ppm/h because of a reduction in screening-current induced in the REBCO-coated conductors. Current sweep reversal improved the magnetic field stability from 2 ppm/h to 0.8 ppm/h.

Design of a conduction-cooled 9.4 T REBCO magnet for whole-body MRI systems

A project on the development of REBa2Cu3O7−δ (REBCO) magnets for ultra-high-field magnetic resonance imaging (MRI) was started in 2013. Since REBCO-coated conductors feature high mechanical strength under tensile stress and high critical current density, use of REBCO coils would allow superconducting magnets to be made smaller and lighter than conventional ones. In addition, a conduction-cooled superconducting magnet is simpler to use than one cooled by a liquid helium bath because the operation and maintenance of the cryogenic system become simpler, without the need to handle cryogenic fluid. Superconducting magnets for MRI require homogeneous, stable magnetic fields. The homogeneity of the magnetic field is highly dependent on the coil shape and position. Moreover, in REBCO magnets, the screening-current-induced magnetic field, which changes the magnetic field distribution of the magnet, is one of the critical issues. In order to evaluate the magnetic field homogeneity and the screening-current-induced magnetic field, a 1 T model magnet and some test coils were fabricated. From an evaluation of the 1 T model magnet, it was found that the main reason for magnetic field inhomogeneity was the tolerances in the z-axis positions of the coils, and therefore, it is important to control the gap between the single pancakes. In addition, we have already demonstrated the generation of an 8.27 T central magnetic field at 10 K with a small test coil. The screening-current-induced magnetic field was 0.43 T and was predictable by using an electromagnetic field simulation program. These results were reflected in the design of a conduction-cooled 9.4 T REBCO magnet for whole-body MRI systems. The magnet was composed of six main coils and two active shield coils. The total conductor length was 581 km, and the stored energy was 293 kJ. The field inhomogeneity was 24 ppm peak to peak and 3 ppm volume-root-mean-square (VRMS) for a 500 mm diameter spherical volume (DSV). The axial and radial 5 gauss line locations were less than 5 m and 4.2 m respectively.

Design and optimization of a HTS insert for solenoid magnets

With the availability of High-Temperature Superconducting (HTS) prototype cables, based on high-performance REBCO Coated Conductor (CC) tapes, new designs can now be made for large bore high-field inserts in superconducting solenoids, thus extending the magnet operating point to higher magnetic fields. In this work, as an alternative approach to the standard trial-and-error design process, an optimization procedure for a HTS grading section design is proposed, including parametric electro-magnetic and structural analyses, using the ANSYS software coupled with a numerically-efficient optimization algorithm. This HTS grading section is designed to be inserted into a 12T large bore Low-Temperature Superconducting (LTS) solenoid (diameter about 1m) to increase the field up to a maximum value of at least 17T. The optimization variables taken into consideration are the number of turns and layers and the circle-in-square jacket inner diameter in order to minimize the total needed conductor length to achieve a peak field of at least 17T, while guaranteeing the structural integrity and manufacturing constraints. By means of the optimization, an optimal 360m total conductor length was found, achieving 17.2T with an operating current of 22.4kA and a coil comprised of 18×12 turns, shortened of about 20% with respect to the best initial candidate architectural design. The optimal HTS insert has a bore compatible with manufacturing constraints (inner bore radius larger than 30cm). A scaled HTS insert for validation purposes, with a reduced conductor length, to be tested in an advanced experimental facility currently under construction, is also mentioned.

Testing of stacked pancake coils for a cryogen-free 25 T superconducting magnet

A cryogen-free 25-T superconducting magnet with a 52-mm room temperature bore consists of an 11-T REBa 2 Cu 3 O 7-δ (REBCO) insert coil and outer 14-T lowtemperature superconducting (LTS) coils. The REBCO insert coil is composed of a stack of 56 single pancake coils. The inner and outer diameters of the REBCO insert coil are 102 and 263 mm, respectively, and the total conductor length is about 14 km. The REBCO insert coil is cooled by circulating helium gas using both single-stage and two-stage Gifford-McMahon cryocoolers, and the LTS coils are cooled by two Gifford-McMahon/Joule-Thomson cryocoolers. The maximum hoop stress of the REBCO insert coil was estimated to be 387 MPa when the central magnetic field was 25 T. If thermal runaway occurs in a conduction-cooled system, the REBCO coils will almost certainly be burned out. Therefore, the coil should have no damaged area in the winding because a damaged area would generate heat locally, eventually resulting in thermal runaway. In order to avoid the degradation of the coil due to thermal stress, the coil was divided into all winding parts in the radial direction. In practice, the coil was divided by inserting a polyimide tape coated with a fluorine resin, which has low adhesive strength, into the epoxy resin at every turn. Before fabricating and testing the actual REBCO insert coil, two kinds of coils were fabricated and tested in order to evaluate the validity of the winding method. Two stacked pancake coils wound with REBCO-coated conductors were fabricated and tested in liquid helium with a 4-T background magnetic field in order to evaluate whether the coil could withstand the hoop stress of over 387 MPa. Moreover, we fabricated and tested a demonstration coil which was composed of a stack of four single pancake coils with the same size as the pancake coils used for the REBCO insert coil in order to evaluate whether the coil could withstand the thermal stress and the electromagnetic force.

Design of a REBCO Insert Coil for a Cryogen-Free 25-T Superconducting Magnet

A cryogen-free 25-T superconducting magnet with a 52-mm room-temperature bore consisting of an 11.5-T REBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-δ</sub> (REBCO) insert coil and outer 14-T low-temperature superconducting (LTS) coils is currently under development. The REBCO insert coil is composed of a stack of 68 single pancake coils. The inner and outer diameters of the REBCO insert coil are 102 and 276 mm, respectively; and the total conductor length is 17.6 km. The maximum hoop stress of the REBCO insert coil was estimated to be 455 MPa when the central magnetic field was 25.5 T. The REBCO insert coil is cooled by circulating helium gas using both single- and two-stage GM cryocoolers, and the LTS coils are cooled by Gifford–McMahon/Joule–Thomson cryocoolers. If thermal runaway occurs in a conduction-cooled system, the REBCO coil will almost certainly be burned out. Therefore, it is important to avoid thermal runaway of the REBCO insert coil under all operating conditions and protected operations. As operating conditions of the REBCO insert coil, quenching of the LTS coils should be assumed in the severest situation, since the current of the REBCO insert coil will increase after the LTS coils quench. From the results of quench analysis of the LTS coils and circuit simulations, it was confirmed that thermal runaway can be avoided by setting the intermediate potential of the REBCO coil to the ground potential and by using an external dump resistance of 11 Ω.

Design of YBCO Insert Coil for a Cryogen-Free 22 T Superconducting Magnet

A YBCO insert coil has been developed for upgrading a cryogen-free 18 T superconducting magnet installed in the High Field Laboratory for Superconducting Materials (HFLSM) at Tohoku University to a 22 T superconducting magnet. The YBCO insert coil is designed to generate 6.5 T at 200 A in 15.5 T outer LTS coils. The YBCO insert coil is composed of a stack of 50 single pancake coils wound with YBCO-coated conductors (0.23 mm × 4 mm). The inner and outer diameters of the YBCO insert coil are 96 mm and 178 mm, respectively, and the total conductor length is about 3 km. The maximum hoop stress of the YBCO insert coil was estimated to be 310 MPa when the central magnetic field was 22 T. The magnet system is cooled by a GM/JT cryocooler and two single-stage GM cryocoolers. Thermal runaway may cause burnout of the YBCO insert coil, and therefore, it is important to calculate the voltage-current characteristics of the coil from the superconducting properties of the YBCO-coated conductors. The coil should have no damaged area in the windings because a damaged area would generate heat locally, eventually resulting in thermal runaway. Therefore, a demonstration coil with almost the same size as the pancake coils used for the YBCO insert coil was fabricated and tested in conduction cooling conditions in order to evaluate whether the coil could withstand the thermal stresses and electromagnetic force.

Progress in the Development of a Superconducting 32 T Magnet With REBCO High Field Coils

The design and development of a 32 T, 32 mm cold bore superconducting magnet with high field REBCO inner coils are underway at the NHMFL. The two nested REBCO coils that form the high field section are dry wound, with uninsulated conductor and insulated stainless steel cowind reinforcement. Active quench protection uses distributed protection heaters. As part of the development activity, prototype coils of the two REBCO coils with full scale radial dimensions and final design features, but with reduced axial length are being constructed. The first of these prototype coils was tested in a 15 T resistive background field magnet. The coil has inner and outer winding diameters of 40 mm and 140 mm, respectively, and consists of six double pancakes with a total conductor length of roughly 900 m. The construction of this prototype coil is described, including the protection heaters. Coil test results are reported including coil critical current, coil ramping characteristics, thermal stability, joint, and terminal resistance with field cycling. The corresponding operating stress in the windings is calculated. Importantly, the performance characteristics of the protection heaters will be measured including activation time.

Limiting GPR in a two-layer soil model via genetic algorithms

In this paper, an optimum grounding grid that provides the conditions of GPR< E touch and minimum cost in the structures of two-layer soil model is designed and the length of total conductor and the quantity of ground rod are calculated via Genetic Algorithms (GA). A new approach is presented for the calculation of total conductor length. At the same time, the subject regarding in which layer the ground conductors and rods that form the grounding grid in a substation are to be placed in two-layer soil is analysed using GA. With this as the goal, the depth of optimum grid burial is determined. Our study is compared with the design study for a two-layer soil model in the literature. As a result, the high performance of optimum grid design that is achieved using GA is emphasized by varied applications.

Design Concepts of Optimized MRI Magnet

This paper describes a simple technique to design compact air core magnets for magnetic resonance imaging (MRI). The optimum geometry is obtained by a combination of analytical and numerical methods. The technique emphasizes achieving the required field homogeneity with a shorter magnet having a minimum amount of ampere turns. The code calculates the total inductance of the set of coils, total conductor length, force, and maximum field on each coil. The code also calculates the allowable geometrical tolerance to achieve the field uniformity. The code is flexible and can be used for various geometries. Here, we present three different cases to demonstrate the efficiency of the code. First, we present the design details of a 1.5 m long 1.5 T actively shielded magnet, where the stray field is reduced to less than 4 gauss outside the sphere of radius 3.65 m using a pair of shielded coils. A total of four pairs of coils provide a field uniform to within 5.2 parts per million (ppm) within a sphere of 50 cm diameter. Calculated values of all the higher order moments lie within a few ppm. Second, we describe optimized geometry of unshielded 1.5 T symmetric magnets having three pairs of coils. Third, we optimize the geometry of a 1.2 m long 1 T asymmetric magnet having five coils. Here, the good field region starts at 20 cm from one of the edges of the magnet, providing the attending physician better accessibility to the patient. But the ampere turns and computation time required are quite large compared to a symmetric magnet.

Cryocooled Bi-2212/Ag solenoid magnet system generating 8 T in 50 mm room temperature bore; design and preliminary test

The combination of Bi-2212/Ag conductors and cryocooler is becoming a promising candidate for cryogen free magnet systems because of the rapid progress in conductor fabrication and cryocooler engineering. We started a new project to develop a cryocooled Bi-2212 magnet system generating 8 T in 50 mm room temperature bore. In this project, the system is designed to be composed of two magnets of solenoid winding by using ROSAT (Rotation-Symmetric Arranged Tape-in-tube) wires and to be operated at 10 K with 30 W refrigeration capacity (two GM cryocoolers of 15 W at 10 K). Inner and outer magnets are designed to generate 3.8 T and 4.2 T at 10 K with operating coil current density of 80 and 100 A/mm/sup 2/, respectively. The dimensions of the inner and the outer magnets are 80 mm (bore)/spl times/169 mm (outer diameter)/spl times/203 mm (height) (total conductor length, 0.8 km) and 178 mm/spl times/260 mm/spl times/230 mm (total conductor length, 2.3 km), respectively. We finished the fabrication and a preliminary test of the inner magnet. The whole system and a full operation test will be completed in near future. In this paper, we report the details of system design and the test results of the inner magnet.

Development of long length Bi-based/Ag tapes and experimental magnets

Long lengths of multifilamentary superconducting (BiPb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10/ (Bi-2223)/Ag tapes up to 250 m made with "powder-in-tube" (PIT) process have been successfully prepared on a laboratory scale. Reproducible critical current density of between 12,000-18,000 A/cm/sup 2/ in the long length tapes have been achieved using the optimal reduction in flat-rolling procedure and standard flat-rolling method as the intermediate deformation between sintering periods. Several coils have been fabricated from sections of the long length tape, using the co-wound react-and-wind (R&W) procedure for double pancake-shaped coils and wind-and-react (W&R) procedure for solenoidal pancake shaped coils. Each coil was fabricated by co-wounding three tapes on 30 mm-diameter mandrel. An experimental magnet was designed and constructed by stacking together coils. Dimensions and parameters of this magnet are as follows: height, 105 mm; winding ID, 32 mm; OD, 120 mm; total number of turns, 1068. Total conductor length in the magnet was /spl sim/870 m. The coils were connected in series and then tested at 77 K. The field constant at mid-plane of the magnet, determined by introducing a Hall probe in the bore of the magnet, was /spl sim/105 Gs/A and it generated 0.24 T magnetic field at 77 K. A detailed investigation of the J/sub c/-B properties and J/sub c/-strain characteristic of the Bi-2223 tapes as designing parameters and properties of the test magnet have been carried out.

Design, fabrication and properties of 1 T (4.2 K) Bi-2223 high- superconducting prototype magnet

Ag-sheathed monofilamentary Bi-2223 high-temperature superconducting tapes were fabricated using the `powder-in-tube' (PIT) method with powders of (x = 0, 0.14, 0.24) chemical composition. The highest critical current density and the shortest time for Bi-2223 phase completion were found in tapes with x = 0.24. The x = 0.24 composition tapes with a reproducible critical current density of between and for short samples, with averages of for 4 m long tapes and for 100 m long tapes at 77 K in the self-field, have been produced using the conventional PIT method. A test magnet was designed and constructed by stacking together eight pancake coils. Each pancake coil was made by the react-and-wind technique with three co-wound tapes on an 18 mm diameter mandrel. Dimensions and parameters of this magnet are as follows: height, 46 mm; winding inner diameter, 18 mm; winding outer diameter, 56 mm; total number of turns, 290. Total conductor length in the magnet was m. The coils were connected in series and then tested at 4.2 K and 77 K. The field constant at mid-plane of the magnet, determined by introducing a Hall probe into the bore of the magnet, was 29 G s and the magnet could generate a 0.12 T magnetic field at 77 K, and 1.07 T at 4.2 K. Eight pancake coils were stacked in a testing magnet using the two coils in parallel connection and four double-coils in series connection method; this makes it possible to use a mix of good and less good tapes and to use fully the critical current of each tape. A detailed investigation of the -B properties and -strain characteristic of the Bi-2223 tapes as design parameters and properties of the test magnet has been carried out.

Ramp rate experiments on a Nb/sub 3/Sn CICC wind-and-react magnet

The central solenoid of ITER is designed to operate at 13 T, 0.5-1 T/s, 5.8 K. There is an experimental evidence that reduced performances in variable field, not explained by AC loss, could occur in CIC conductors. Such ramp rate limitations have to be well understood in order to be avoided in the ITER conductors. The ENEA Nb/sub 3/Sn solenoid is a 1 m OD, 0.6 m ID coil, made of a CIC conductor which is a factor 8 smaller than the ITER full size cable. The total conductor length, 750 m, is ITER relevant. An experimental setup has been assembled, allowing ramp rate and DC tests on the ENEA coil up to 8 T, 2-4 T/s, 12 K. Main objectives of the program are experimental data on ramp rate limitation, pulsed current distribution in the s/c cable, limiting currents and global AC loss. This paper reports the results of the measurements carried out up to now.