Electrostatic focusing and RFQ (radio frequency quadrupole) matching system for a low-energy H- beam

摘要

Abstract: The conceptual design of an electrostatic quadrupole (ESQ) system for focusing and matching a 30 mA, 35 kV H$+$MIN$/ beam into a radio frequency quadrupole (RFQ) accelerator has been developed. The design procedure involves two steps. First, a linear beam optics code which solves the K-V envelope equations is used to design a lens system based on a hard-edge focusing function. The beam envelope, in conjunction with the lens parameters, should satisfy several constraints concerning electric breakdown, image forces, spherical and chromatic aberrations. Next, a practical lens design is developed. The field gradient is calculated numerically with a 3-D Laplace solver and the fringe-field integrals are evaluated to obtain the nonlinear forces up to the third order. The results from the Laplace solver generate input to a modified PARMILA code, and the beam propagation and emittance growth in the system are evaluated. Preliminary analysis shows an emittance growth of about 50%. Design of the apparatus and experimental plans are discussed.!