An emitting capillary discharge light source is modified by means to provide for constant, capillary discharge chamber diameter despite interior surface erosion during operation of the light source in order to maintain capillary bore size. The emissions are generated within the capillary discharge chamber and discharged from its outlet. The emission also carries debris generated from within the capillary discharge chamber by erosion of its inner walls reducing its initial inner diameter. The debris is deleterious to the mirrors and other components positioned in the emission stream whereas the erosion distorts the plasma beam. This increase in the initial inner diameter of the discharge chamber leads rapidly to poor imaging of the light stream. By keeping the inner bore diameter of the capillary discharge chamber constant, i.e., 110%, and preferably 105%, of the initial inner bore diameter, the imaging problem is overcome
