Design of magnet and control of the beam emittance for Penning H－ ion source

The design requirement and principle of the deflection magnet for Magnetron and Penning H^－ ion source are discussed. It is proved that there exists a maximum emittance for the beam that may be transformed by the magnet into a state with equal Twiss parameters of α_r=α_y and β_r=β_y, which is the requisite condition to get a minimum emittance at the entrance of RFQ after transporting by a LEBT with solenoids. For this maximum emittance, the corresponding magnetic field gradient index is 1.