A large bore pulsed quadrupole magnet for transport of high current beams at low energies

We present the design of a large bore pulsed quadrupole magnet for transport of a high current, space charge-dominated heavy ion beam in a neutralized beam focussing experiment using four magnets. The design is current dominated, with solid circular cross-section insulated copper conductors located within a circular laminated iron core. The design produces a field of 0.96 T at the maximum beam envelope of 12 cm. The magnet has a short length relative to its bore, and a small number of turns in order to minimize inductance, thus allowing high currents at modest voltage. A conductor diameter is chosen to minimize the combination of resistive and eddy current losses in the magnet coils, within limits of existing fabrication equipment. Higher order multipole field components sum to 0.06% B₂ @ 10 cm radius. Coils are fabricated using a wind/stretch technique to produce straight and accurately located conductor runs while preserving the integrity of the polymer insulation. Coils are wound in a "single layer/double pancake" style to place all conductor runs at the same radius, yet avoid "stranded" conductors at the poles. The beamtube is a separate composite stainless steel/fiberglass epoxy beam tube for the entire magnetic transport line. This minimizes eddy current losses in the vacuum system, both in the midsection of the magnets and at the magnet ends, where thick flanges would normally be present