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1 DISCHARGE CHAMBER GAS REPLENISHMENT SYSTEM BACKGROUND [0001] Photolithography is a process by which semiconductor circuitry is patterned on a 5 substrate such as a silicon wafer. A photolithography radiation source provides DUV radiation (radiation having wavelengths in a range of about 100 nanometers (nm) to about 400 nm) used to expose a photoresist on the wafer. Often, the radiation source is a laser source and the radiation is a pulsed laser beam. The radiation beam is passed through a beam delivery unit, then through or reflected by a reticle or a mask, and then projected onto a silicon wafer coated with photoresist. In this way, a chip design is 10 patterned onto a photoresist that is then etched and cleaned. [0002] Many systems that produce a beam of DUV laser radiation do so by creating discharges produced in a discharge region between electrodes in a discharge chamber. More precisely, the DUV discharge chamber has a pair of electrodes (a pair being comprised of one anode and one cathode) arranged to generate plasma discharges from a lasing gas (generally a gas mixture) when a high voltage 15 is applied across the electrodes. The discharge is pulsed at a repetition rate of, for example, 6 kHz (6000 times per second), and thus produces a train or burst of DUV radiation emission pulses. [0003] During a discharge the lasing gas in the discharge region between the electrodes becomes depleted of one or more components. Thus the DUV discharge chamber typically includes at least one cross flow blower to establish a flow of gas through the discharge region. The gas flow replaces 20 the depleted gas in the discharge region with fresh gas from elsewhere in the discharge chamber in preparation for the next discharge event. [0004] Cross flow blowers are inefficient and the motor for the cross flow blower can consume a substantial amount of energy while driving a flow of gas in the discharge chamber. The amount of energy can constitute a non-negligible fraction of the total energy used by the overall DUV laser system 25 in discharge production. In addition, demands for increased production will necessitate the use of increased pulse repetition rates. This will reduce the time between pulses, and so the time permitted to clear the spent gas from the discharge region between pulses. Thus the clearance speed will need to be increased. This would cause a cross flow blower to consume even more power. [0005] It would be advantageous to improve the process of replenishing gas in the discharge 30 region of a DUV laser source without unduly increasing energy consumption. It is in this context that the need for the subject matter of the present disclosure arises. DETAILED DESCRIPTION [0006] Various embodiments are now described with reference to the drawings, wherein like 35 reference numerals are used to refer to like elements throughout. In the following description, specific details are set forth in order to promote a thorough understanding of one or more embodiments. It may 2 be evident in some or all instances, however, that variations of any described embodiment can be implemented without departing from the teachings provided by this disclosure. In other...