Radiation source and lithographic apparatus

A radiation source fuel droplet stream generator comprising

• a fuel droplet emitter configured to form groups of fuel droplets, each group comprising a first subset of fuel droplets and a second subset of fuel droplets;
• an electrode located close to the formation point of droplets formed by the emitter, and
• a voltage source configured to apply an alternating voltage between the emitter and the electrode
• whereby alternate droplets in the first and second subsets of fuel droplets are given electrical charges of alternating sign.

A radiation source fuel droplet stream generator comprising:

• a fuel droplet emitter configured to form groups of fuel droplets, each group comprising a first subset of fuel droplets and second subset of fuel droplets,
• an electrode, and
• a voltage source configured to apply an alternating voltage between the emitter and the electrode,
• whereby droplets of the first subset of fuel droplets are formed of opposite electrical signs or of the same sign but different magnitudes than droplets of the second subset of fuel droplets, and whereby the first subset of fuel droplets are either accelerated or decelerated towards the electrode promoting coalescence of the first subset of fuel droplets with the second subset of fuel droplets.

A radiation source fuel droplet stream generator comprising:

• a fuel droplet emitter configured to form groups of fuel droplets, each group comprising a first subset of fuel droplets and second subset of fuel droplets,
• an electrode, and
• a modulating voltage source connected to the emitter for controlling the relative speeds of droplets of the first and second subsets of fuel droplets between the emitter and the electrode by providing at least one of (a) droplets of the first subset of fuel droplets have an electrical charge that has opposite polarity to the electrical charge of droplets of the second subset of fuel droplets and (b) droplets of the first subset of fuel droplets having magnitudes of electrical charge that are different than magnitudes of electrical charge of droplets of the second subset of fuel droplets,
• whereby coalescence of smaller droplets of the first and second subsets of fuel droplets into larger droplets is facilitated.

A lithographic apparatus comprising:

• a radiation source configured to produce a radiation beam, the radiation source comprising:
• a fuel droplet emitter configured to form groups of fuel droplets, each group comprising a first subset of fuel droplets and a second subset of fuel droplets,
• an electrode, and
• a modulating voltage source connected to the emitter for controlling the relative speeds of droplets of the first subset of fuel droplets and droplets of the second subset of fuel droplets between the emitter and the electrode by providing at least one of (a) droplets of the first subset of fuel droplets having an electrical charge of opposite polarity to an electrical charge of droplets of the second subset of fuel droplets and (b) droplets of the first subset of fuel droplets having magnitudes of electrical charge that are different than magnitudes of electrical charge of droplets of the second subset of fuel droplets,
• whereby coalescence of smaller droplets of the first and second subsets of fuel droplets into larger droplets is facilitated,
• an illumination system configured to condition a radiation beam,
• a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam,
• a substrate table constructed to hold a substrate, and
• a projection system configured to project the patterned radiation beam onto a target portion of the substrate.