High Power Septum Magnet with a Conductive Septum Coil Holder

Abstract

A pulse septum magnet is designed and fabricated to have a high magnetic field intensity with thin septum width. The magnetic field is 1.75 T with a septum width of 2.3 mm. The applied current waveform is one cycle sinusoidal wave and the peak current is 13, 500 A.
In our magnet, a conductive (made of copper) septum coil holder is used to overcome the difficulties of high power septum magnet, such as the heat loss at the thin septum coil, the degradation of the field uniformity in the magnet and the leakage flux outside the magnet.
The heat loss at the septum coil is effectively removed by tightening up the septum coil to the coil holder with thin stainless steel bands. The temperature rise of the septum coil is only 20 centigrade at normal operation.
The degradation of the field uniformity and the leakage flux are suppressed by an eddy current, which is induced in the coil holder.
The pulse magnetic field distribution of the septum magnet is measured by a pick-up loop and the results show that the good field region, where the field homogeneity is less than ±0.1%, is 7.5 mm which is twice as large as the septum magnet without the eddy current in the coil holder. As for a leakage flux, the field intensity is only 14 G at 10 mm outside the magnet which is also reduced to 1/10 by the eddy current in the coil holder.
The high energy beam extraction experiments are also perfomed and the beam monitors, which are placed down stream of the beam transport line, show that the beam can be stably extracted by the septum magnet.