Low energy beam transport in a periodic focusing quadrupole channel

In the FOM MEQALAC (Multiple Electrostatic Quadrupole Array Linear Accelerator) experiment the Low Energy Beam Transport section (LEBT) transports the four 40 keV He+ beams from the ion source to the RF accelerator. The transport section consists of an array of four parallel channels each made up of 34 electrostatic quadrupole singlet lenses. The first five lenses are excited independently to match the cylindrically symmetric beams extracted from the source to the acceptance of the periodic focusing quadrupole channel. Typical beam losses are of the order of 15%. The authors report measurements of currents and emittances of DC and bunched beams performed behind the ion source, matching section and LEBT section. The injection energy of the He+ ion beamlets is 40 keV. The current per beamlet is 7, 10 and 14 mA. Typical (RMS) emittance values are 10-30 π mm mrad. The phase advance per cell μ0 is varied between 400 and 1150