Improvement of high-current large-volume discharge with profiled hollow-cathode electrodes

Filamentary discharge at the electrode of high-power copper vapor lasers prevents stable operation when the buffer gas (Ne) pressures exceeds 30 torr. Experimental evidence indicates that the discharge constriction starts in the cathode fall region. The volumetric power deposition at the cathode fall is estimated to be ~130 MW/cm³ at 40 torr during a peak discharge current of 2.5 KA. This highly pressure-dependent (α P^7/3) large thermal loading at cathode fall is likely to initiate thermal instability as pressure increases. This discharge instability can be mitigated by taking advantage of the hollow-cathode effect even for pressures exceeding 100 torr. We have designed a large-area electrode with many hollow-cathode grooves spreading over the uniform-field-profile area of the electrode for enhanced electron emission. This unique design lowers the cathode-fall voltage, and as a consequence, reduces the thermal loading at the cathode fall. With this profiled, hollow-cathode electrode, we have successfully extended stable discharge from ~30 to ~100 torr. We believe this profiled electrode design with multiple hollow-cathode grooves will expand hollow-cathode electrodes to many applications that require high-current large-volume discharge at elevated pressures