Design and Construction of Septum Magnets at 3-GeV RCS in J-PARC

Abstract

3 GeV RCS (Rapid Cycling Synchrotron) at J-PARC (Japan Proton Accelerator Research Complex) comprises with several magnets of different kinds. These include seven septum magnets for the beam injection and extraction at RCS ring. Design requirements for these magnets often conflicts with efforts to minimize leakage magnetic field. Silicon steel sheets set outside of the septum magnets shield leakage magnetic fields so as to keep proper beam orbits in the ring in most cases. At the beam junction areas for beam injection and extraction, sufficient spacing is not available for installing thick magnetic shields. Vacuum chambers are made by the magnetic stainless steel to reduce the leakage field without a large shield. Results obtained from 3-D field calculations by TOSCA indicate the magnetic leakage field is suppressed down to a few Gauss or less in the present design.All septum magnets and branch structure vacuum chamber made of titanium and magnetic stainless steel are manufactured and assembled successfully. The field measurements of the septum magnets proved that both the strength and also gradient of the magnetic leakage field are diminished.Index Terms-Leakage field, magnetic vacuum chamber, proton synchrotron, septum magnet.

FEM models and Fourier decomposition of three thick septa

“…The field in the region with circulating beam may be reduced to nil by making the vacuum vessel of magnetic material. The models discussed here and [6] show that this should be standard practice in all "C" septa.…”

“…In most accelerators septum magnets are used in injection and extraction [1][2][3][4][5][6][7][8][9]. CEBAF is a recirculating electron accelerator with two linacs and ten arcs [10].…”

Localization of the large-angle foil-scattering beam loss caused by the multiturn charge-exchange injection

“…Based on the measurement results taken in 2006 when the DSEP1 was installed in the RCS [12], it was recognized that the leakage field caused by the DSEP1 was approximately several mT. Therefore, Helmholtz coils that can generate a maximum field of approximately 8.5 mT were prepared as the external magnetic source.…”

Beam commissioning of the 3-GeV rapid cycling synchrotron of the Japan Proton Accelerator Research Complex

“…The beam centers and widths on MWPM's were defined by Gaussian fitting. After the L-3BT beam tuning was fixed, we first roughly adjusted the injection and dump-line orbits, and then performed a series of orbit response matrix measurements such as MWPM3-5 vs injection septa (ISEP1-2 [26,27]), MWPM6-7 vs dump-line septa (DSEP1-2 [26,27]) and MWPM4 vs SB1-4 for the horizontal plane, and MWPM3-5 vs vertical steering magnets (IVSTM1-2) for the vertical plane. The measured response matrices were almost consistent with the calculated ones.…”

“…As shown in Fig. 12, three sets of septum magnets (ESEP1-3 [26,27]) are installed in the extraction area. Figure 13 shows the COD caused by a leakage field from ESEP excited at 181 MeV (open blue circles) or at 3 GeV (closed red circles), which was derived from a difference of COD's observed when turning ESEP on (at 181 MeV or at 3 GeV) and off.…”