UA-25427628-1

Power Amplifier - Prometheus:

The main amplifier of our system is a KrF power amplifier. Its name is Prometheus. Prometheus was designed and built in Los Alamos during star wars era. After life and politics were normalized Prometheus was taken apart and than it was rebuilt in our laboratory for KrF excimer amplifier. You can read detailed History and Description below. For a long time Prometheus has been our power amplifier. Its preionizer is a powerful x-ray gun; its main ionizer system works with high voltages. Prometheus has two amplifier volumes (tubes) but both tubes belong to one gas reservoir.

Prometheus uses also DA amplification technique but here beam is aligned in on-axis geometry. In other words, preamplified and beam expanded laser pulse goes through Prometheus’ tubes one-one time following on-axis scheme. Behind Prometheus main laser beam parameters are:

  • pulse energy: 350-450 mJ
  • pulse duration: ~ 200 fs
  • wavelength: 248.5 nm
  • beam size: ~ 10 cm (4 inches) in diameter

Prometheus shot 1
Prometheus shot 2

History and Description:
Prometheus is one of two identical amplifiers delivered to both Los Alamos and UIC in the spring of 1988 by Beta Development Corporation under Gary Loda (now deceased). The device consists of two main discharge cavities (10cm x 10cm x 2.5m long) that share a common x-ray pre-ionizer that operates at 150 kV. Originally, each main discharge electrode was driven by a two-stage saturable core compressor with the main voltage step-up achieved by a 6.33:1 Stangenes autotransformer. The prime energy store is at 25 - 30 kV and switched to each discharge side (called North and South) by a North and South bank of six Thyratrons. This design architecture was chosen by the manufacturer as a way to achieve ~ 1 Hz or more repetition rate operation and results in a final fast rising voltage pulse of 150 – 180 kV on the main discharge anodes. At Los Alamos and UIC the discharge cavities were utilized in a folded series configuration except that Los Alamos used a XeCl based gas mixture at 3 atm and UIC uses a KrF based gas mixture at about 1.6 to 1.7 atm.
Shortly after installation at Los Alamos, the South amplifier experienced poor performance as evidenced by low measured small-signal laser gain in the South laser cavity. Chuck Tallman (now retired from Los Alamos) was called upon to investigate the pulsed power operation of the device. Two main changes were made to the x-ray pre-ionizer: (1) the smooth conical epoxy bushing that had evidence of flashover was machined with grooves, and (2) x-ray masks were utilized in an attempt to control the area for main energy disposition in the laser cavity. The first of these changes is present in the UIC amplifier but as for the second change, I was unable to ascertain whether any x-ray masks are incorporated at UIC. Generally, positive improvement changes made at Los Alamos were incorporated immediately into the UIC device that was operating in parallel under the direction of Keith Boyer (retired from Los Alamos and now affiliated with the UIC effort).