I. Bogdanov, S. Kozub, V. Pokrovsky, L. Shirshov, Investigations concerned with development of SC dipole for the SIS 300 accelerator I. Bogdanov, S. Kozub, V. Pokrovsky, L. Shirshov, P. Shcherbakov, V. Sytnik, L. Tkachenko, V. Zubko, Institute for High Energy Physics (IHEP), Protvino, Moscow region, Russia, G. Moritz, J. Kaugerts, Gesellschaft für Schwerionenforschung (GSI), Darmstadt, Germany
Main parameters of the SC-dipole for the SIS-300 Magnetic field 6 T Field ramp rate 1 T/s GSI trapezoid field cycle 1,6 – 6 - 1,6 T Full coil aperture diameter 100 mm Effective magnetic length 2900 mm
The main problems During the UNK project, superconducting dipoles have been developed and produced in a pilot industrial batch of 25 magnets. The operating field of the dipoles was 5.11 T, at 0.11 T/s ramp rate. Improvements of the present UNK dipole design will be considered to extend the operating range of the dipoles to 6 T, with ramp rates of 1 T/s. To design and choice of new current carrying element both wire and cable. To select of new material for iron yoke. To choice of magnet geometry (2D and 3D) of computer simulation To minimaze of total AC-losses and their components in the coil and iron yoke.
Steel choice. Two candidate steels 2212 and M250-50A were chosen for analysis of the influence of these steels on field quality, as well as on heat loss in the iron yoke during magnet pulsed operation. Steel 2212 is better, from the viewpoint of field quality, but full hysteresis losses in iron (for 1-m dipole) of this steel is 44.8 [J/m] and 24.8 [J/m] for M250-50A.
Characteristics of SC-cable Cable consists of 36 strands with 100-mm (16.8º) transposition pitch and has core made with 25-μm thick stainless steel. Strands in the cable are covered by 0.5-μm thick stabrite coating. The cable has three layers all-polyimide film insulation, having 0.125-μm and 0.098-μm radial and azimuthal thickness after the coil assembly Strand (0.825-mm diameter) consists 3.5-μm filaments of Nb47%Ti alloy, enclosed in a Cu matrix; 5-mm filament twist pitch; Cu/superconductor ratio is 1.4; critical current density is Jc = 2700 A/mm2 (at 5 T, 4.2 K).
Adjacent resistance Ra in 36-strand cored cable Preliminary heat treatment Curing regimes Ra, 200C, 2 hours 220C, 10 min 46 120C, 2 hours 109 83 200C, 4 hours 16.7 118
Measurements of Rc Measurements of Rc were performed on the small pieces of SC cable. Side ridge of cable were cut. Current flowed across cable through the area of 1312 mm2 (~120 crossover joints). Pressure applied to this area at 4.2 K was varied from 0 to 90 MPa. Above 20 MPa the pressure dependence of Rc have gentle dip. For the cables exposed by 4 hour heat treatment The crossover resistance Rc at 50 Mpa and 4.2 K (operating condition) was equal 450 and 120 m for polyimide or epoxy adhesive gluing regimes correspondingly.
Tests of Straight and Bent Superconducting Dipoles According to the technical requirements the SIS300 dipole length is close to 2900 mm and the particle orbit radius is about 50 m. These numbers determine a value of the orbit sagitta inside the magnet of 22.5 mm. A model superconducting dipole, manufactured for the UNK project, was chosen for study of the influence of bending effects on magnet characteristics. The straight collared coil of this model magnet was tested, then bent with a 50 m curvature radius, and then retested.
Magnet training before and after bending After bending, the dipole began to retrain. The maximum critical current reached during training of the dipole did not decrease after its bending. Bending of the collared dipole coil (50 m curvature radius) did not produce turn-to-turn shorts and did not decrease ground insulation resistance.
The results of SC-dipole test before and after magnet bending Ramp rate dependences of the straight and bent dipoles before (I) and after (II) 1000 cycles of 0 – 5 T – 0 with 1000-A/s current ramp rate. Test results showed similar characteristics, both in training and in ramp rate dependence, as well as in field quality of the straight and bent coils.
Model SC-dipole Magnet for the SIS 300 General view of cross section Main parameters of the model SC-dipole are: 100-mm coil aperture; 86-mm mechanical aperture and 80-mm useful aperture (good field region). Length of the magnet is 1 m. The magnet has 6-T central magnetic field with 1 T/s operating field ramp rate. Operating current of 6.615 kA gives 6-T central field with real magnetic permeability in the iron yoke.
AC losses in the 1-m model SC-dipole Hysteresis in the SC-coil 42.7 [J/m] Matrix losses in the SC-wire 13.9 [J/m] Cable losses 11.4 [J/m] Hysteresis losses in the iron (using measured specific losses in steel M250-50) 24.8 [J/m] Total AC-losses in the SC-coil and iron yoke 92.8 [J/m]
CONCLUSION Magnetic properties of tree types of cold rolled thin sheet of electrical Si steels have been measured at room and 4.2 K temperatures. For the iron yoke of the SIS-300 dipole was choice steel type M250-50A. The contact resistances (Ra and Rc ) of SC-cable were measured that permitted to calculate AC-losses of SIS300 dipole. Bending of the collared dipole coil (50 m curvature radius) did not produce turn-to-turn shorts. Training and ramp rate dependence of the straight and bent dipoles are similar. AC-losses were practically unchanged, after dipole bending. The magnetic, thermal and mechanical calculations of the SIS300 dipole was carried out. The next step consists of manufacture and test 1-meter SC dipole model with the parameters of the last developed design.
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