International Topical Meeting on Nuclear Research Applications and Utilization of Accelerators
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AT/P5-18
Development of Quadrupole Focussing Lenses for Drift Tube Linac S. Malhotra1, U. Mahapatra2, P. Singh3, R.K. Choudhury3, S. Bhattacharya4, and G.P. Srivastava4 1Department of Atomic Energy, Mumbai, India Corresponding Author: sanjaym@barc.gov.in A linear accelerator comprising of Radio frequency quadruple (RFQ) and drift tube linac (DTL) is being developed by BARC. The alvarez type post-coupled cw DTL accelerates protons from an energy of 3 MeV to 20 MeV. The drift tube linac is excited in TM010 mode, wherein the particles are accelerated by longitudinal Electric fields at the gap crossings between drift tubes. The particles are subjected to transverse RF defocusing forces at the gap crossings due to the increasing electric fields in the gap. The transverse defocusing is corrected by housing magnetic quadrupole focussing lenses inside the drift tubes. The permanent magnet quadrupoles are placed inside the hermetically sealed drift tubes and provide constant magnetic field gradient in the beam aperture. The drift tubes are mounted concentrically inside the resonating DTL tank and are attached to the tank body with stems. Rare earth permanent magnets have been used to achieve the high field gradient. The drift tube body is subjected to RF heating due to eddy currents and hence the sealed drift tubes are to be cooled from inside. The temperature rise of the drift tube assemblies has to be limited to avoid demagnetization of permanent magnets and also to limit thermal expansion of the tubes. This paper discusses various aspects of magnetic design, selection of magnetic materials and the engineering development involved in the assembly of the drift tubes. |
