Characteristics of Magnetic Focusing and Chromaticity Correction System for TARN

TARN is designed by a separated function F¿D¿ lattice. Its main magnet system consists of eight dipole and sixteen quadrupole magnets. The relatively lower injection energy of TARN (ß ¿ 0.134) leads to large transverse coupling impedance and the relatively smaller intensity limit from transverse coherent instability (6 × 108 ions/pulse). In order to surmount the instability by Landau damping, a chromaticity control system with twelve sextupole magnets are designed and fabricated. The field properties of all the magnets are measured precisely before alignment and the result is taken into account by the calculation with the computer code SYNCH. The closed orbit is obtained by iteration and the nonlinear elements such as sextupole magnets are linearized in the neighbourhood of the closed orbit. The work line is also experimentally studied by an RF knock-out method. The chromaticities of TARN without correction sextupole magnets were measured at -1.59 and -0.47 in horizontal and vertical directions, respectively.