An EUV 
light source apparatus and method are disclosed, which may comprise a 
pulsed laser providing 
laser pulses at a selected pulse repetition rate focused at a desired target ignition site; a target formation 
system providing discrete targets at a selected interval coordinated with the 
laser pulse repetition rate; a target 
steering system intermediate the target formation 
system and the desired target ignition site; and a target 
tracking system providing information about the movement of target between the target formation 
system and the target 
steering system, enabling the target 
steering system to direct the target to the desired target ignition site. The target 
tracking system may provide information enabling the creation of a 
laser firing 
control signal, and may comprise a droplet 
detector comprising a 
collimated light source directed to intersect a point on a projected delivery path of the target, having a respective oppositely disposed 
light detector detecting the passage of the target through the respective point, or a 
detector comprising a 
linear array of a plurality of photo-sensitive elements aligned to a coordinate axis, the light from the 
light source intersecting a projected delivery path of the target, at least one of the which may comprise a plane-intercept detection device. The droplet detectors may comprise a plurality of droplet detectors each operating at a different light frequency, or a camera having a 
field of view and a two dimensional array of pixels imaging the 
field of view. The apparatus and method may comprise an electrostatic 
plasma containment apparatus providing an electric 
plasma confinement field at or near a target ignition site at the time of ignition, with the target 
tracking system providing a 
signal enabling control of the electrostatic 
plasma containment apparatus. The apparatus and method may comprise a vessel having and intermediate wall with a low pressure trap allowing passage of EUV light and maintaining a 
differential pressure across the low pressure trap. The apparatus and method may comprise a magnetic 
plasma confinement mechanism creating a 
magnetic field in the vicinity of the target ignition site to confine the plasma to the target ignition site, which may be pulsed and may be controlled using outputs from the target tracking system.