The invention relates to a method and apparatus that can improve the lifetime and performance of an ion source in a cyclotron. According to one embodiment, the invention comprises an ion source tube for sustaining a plasma discharge therein. The ion source tube comprises a slit opening along a side of the ion source tube, wherein the slit opening has a width less than 0.29 mm. The ion source tube also comprises an end opening in an end of the ion source tube. The end opening is smaller than an inner diameter of the ion source tube and is displaced by 0 1.5 mm from a central axis of the ion source tube toward the slit opening. The plasma column is displaced 0.2 to 0.5 mm relative the slit opening. The ion source tube comprises a cavity that accommodates the plasma discharge. The invention also relates to a method for making an ion source tube.