Magnets and Power Supply System of Jhf 50-gev Main Ring

The JHF 50-GeV main ring, very high-intensity proton synchrotron, for the JHF project has been designed.[1][2] The main ring consists of 96 bending magnets, 176 quadrupole magnets, 48 sextupole magnets and 176 steering magnets. The bending magnet is of a modified window frame type, whose maximum field is 1.9 T. Field gradient of the quadrupole magnet is 20 T/m in peak and the bore radius is 63 mm. The total active power of bending and quadrupole magnets is estimated to be about 100 MW in peak. The recent progress of design studies of the magnets and the power supply system are described in this paper. The preliminary results of R&D study of the bending magnet, being now in progress, is also reported. 1 JHF MAIN RING MAGNETS The principal parameters of the bending magnet and quadrupole magnet are summarized in Table 1. Table 1. Main Parameters of JHF 50-GeV Main Ring Magnets Bending Magnet Magnetic Rigidity 12.76 170 Tm Field 0.143 T (for 3 GeV) 1.9 T (for 50 GeV) Useful Aperture (horizontal) 112 mm Gap Height 106 mm Length 5.85 m Quadrupole Magnet (8 families) Max. Field Gradient 20 T/m Aperture 126 mmφ Length 2 m and 1.5 m The bending magnet has been designed to have the maximum field of 1.9 T. It was revised from the old design whose maximum field is 1.8 T [3], to make the magnet shorter. The electric resistance and inductance are estimated to be 40 m-ohm and 100 mH, respectively. The maximum ampere-turn is 92800 AT for the field strength of 1.9 T. The total weight is about 30 tons/magnet. The quadrupole magnet, the sextupole magnet and the steering magnet have been also designed.[2] 2 R&D STUDY OF THE BENDING MAGNET 2.1 Bending Magnet for R&D Study A short-size R&D bending magnet based on the original design, whose maximum field is 1.8 T, was constructed to study about field quality, end plate effect, problem of mechanical structure, and so on. It has the cross section of actual size and the length of about 1.7 m (nearly 1/4 of actual size). Figure 1 shows the cross sectional view of the R&D bending magnet. Fig. 1. Cross sectional view of the R&D bending magnet The core material is 0.5 mm thick laminated silicon steel, 50RM600. The maximum ampere-turn is 84630 AT for the magnetic field of 1.8 T. The gap height of 106 mm is the same as that of the design of 1.9 T. In order to investgate a cut shape of the magnet end, the magnet ends are cut with step shapes, approximating to a Rogowski curve and a B-constant curve. Rogowski curve and B-constant curve are described as follows: z/d = 1+(2/π)exp(πx/2d), and z/d = cosh(x/d), respectively. Here d is the half length of the gap and x is the position of the logitudinal direction. 2.2 Preliminary Results of Field Measurement The field structure of the R&D bending magnet has been studied within the field range of up to 6 kG, because of the limitation of a DC power supply. The relative field strength is measured with a gauss meter equipped with a Hall probe, and an absolute value of the field is monitored with an NMR probe. The Hall probe is positioned threedimensionally with the accuracy of 10 μm by a newly developed moving stand. The measured field distribution in radial direction is shown in Fig.2, together with the result calculated with the program Poisson. The field strength of 1.43 kG is corresponding to the injection energy of the JHF 50-GeV main ring. -0.3 -0.2 -0.1 0 0.1 -80 -60 -40 -20 0 20 40 60 80 B (%) I=355.1A, Bo=1430.01 Gauss B (%) I=1499.1A, Bo=6028.98 Gauss Calculated Result with Poisson (I=1500.0A, Bo=6035.03 Gauss) d B /B o (% ) Radial Position (mm) (98-3) Fig.2. Radial distribution of field strength As seen in the figure, the field deviation of less than 0.05% is obtained in the radial region of +60 mm. On the other hand, there is a slight difference between the measurement and the calculation results, whose cause is now under investigation.