Analytic fluid theory of beam spiraling in high-intensity cyclotrons

Using a two-dimensional fluid description, we investigate the nonlinear radial-longitudinal dynamics of intense beams in isochronous cyclotrons in the nonrelativistic limit. With a multiscale analysis separating the time scale associated with the betatron motion and the slower time scale associated with space-charge effects, we show that the longitudinal-radial vortex motion can be understood in the frame moving with the charged beam as the nonlinear advection of the beam by the E×B velocity field, where E is the electric field due to the space charge and B is the external magnetic field. This interpretation provides simple explanations for the stability of round beams and for the development of spiral halos in elongated beams. By numerically solving the nonlinear advection equation for the beam density, we find that it is also in quantitative agreement with results obtained in particle-in-cell simulations

Progress report on the construction of the Northeast Proton Therapy Center (NPTC) equipment

The IBA proton therapy system selected by the Massachusetts General Hospital (MGH) to equip its new NPTC is presently under construction and test. This paper presents a progress report on the equipment construction. The cyclotron, as well as the rest of the equipment, are being progressively installed in the NPTC building. The acceptance tests of the whole system are foreseen for the end of 1997.Anglai