The Tenth Anniversary of OMEGA EP
Ten years ago, OMEGA EP (extended performance), one of two kilojoule-class laser systems at the University of Rochester’s Laboratory for Laser Energetics, went into operation. Commisioning of OMEGA EP, built directly adjacent to the OMEGA laser, was completed in April 2008. It supports a wide variety of target-irradiation conditions including pulses having multikilojoule energies, picosecond pulse widths, near-petawatt powers, and ultrahigh intensities of ~1020 W/cm2. The laser beams can be delivered to the 60-beam OMEGA target chamber, or, alternatively, to the independent OMEGA EP target chamber. The co-location of the petawatt capability of the OMEGA EP laser with the well-established compression OMEGA laser offers a unique platform to experimentally verify laboratory ignition-relevant design models. The short-pulse and long-pulse systems operating jointly can interrogate high-temperatures and materials in high-energy-density (HED) regimes of greater than one million atmospheres of pressure.
The OMEGA EP Laser System, operating at a base wavelength of 1053 nm (IR), consists of four beamlines of which two have picosecond pulse capability. For pulse widths of 10 ps or greater, the on-target energy can be as high as 2600 J. When the pulse width is between 1 and 10 ps, the on-target energy is reduced, scaling as a function of the pulse width. This is because of damage thresholds of the optical coatings at the output of the system. For pulse widths less than 1 ps, the system is capable of producing ~0.7 PW (500 J/0.7 ps) of optical power on target. The focal spot of the short-pulse beams encloses 80% of the energy in a 16-µm-radius spot, producing on-target intensities of greater than 7 × 1019 W/cm2.
In addition to the short-pulse capability in two of the beamlines, all four OMEGA EP beamlines have a long-pulse capability with pulses ranging from 0.1 to 10 ns. These pulses are used to produce plasmas for interaction experiments with the short-pulse beams and for nanosecond, high-energy-density experiments in the OMEGA EP target chamber. The nanosecond pulses are generated and delivered in essentially the same manner as those on OMEGA, including wavelength conversion from the base wavelength to 351 nm (UV). The long-pulse, on-target UV energies are again limited by the damage thresholds of the optical coatings but can reach 1250 J per beam for 1-ns pulses and 5000 J per beam for 10-ns pulses.
Radiography and other extreme-field experiments drive the mission for OMEGA EP. This system provides ultrahigh intensities for advanced x-ray and proton-beam radiography of compressed targets. Radiography is an important technique used in inertial confinement fusion (ICF) experiments for capturing a snapshot of targets as they are being driven by the laser. An intense laser pulse illuminates a block of material located near the target and generates a short burst of x rays or protons which, like a dental x-ray, produces a radiograph of the target. OMEGA EP’s very high intensities produce x-ray sources that can overcome the radiation emitted by the target driven by the OMEGA laser. In addition, x rays with very high photon energies can be produced that permit backlighting targets compressed to high density. The pulse widths described earlier provide for a short duration of the x-ray burst that sets the temporal resolution of the images that are collected. This is very important in capturing clear (not blurry) images of objects moving at very high velocity. High-energy protons can be produced in addition to x rays, offering the opportunity to probe a compressed target’s ionization state and electromagnetic fields in and around the target.
OMEGA EP shown firing its four beamlines and bathed in its own light
OMEGA and OMEGA EP are the two laser facilities made available to U.S. academic institutions through the National Laser Users’ Facility (NLUF). Through the NLUF OMEGA and OMEGA EP are accessible to conduct basic research experiments in ICF, high-energy-density physics, and other laser–matter interactions. They also provide research experience to maintain a corps of scientists specially trained to meet the nation’s future needs in these areas of science and technology. In contrast to other major ICF/high-energy-density science (HEDS) facilities, external users lead more than 60% of experiments executed at LLE. The large number of shots, state-of-the-art facilities, and university setting provide an attractive environment for training and education. Over the last two decades, LLE has fostered and enabled excellence in research and student education on OMEGA and OMEGA EP by 40 Universities. These users include MIT; University of Michigan; SUNY Geneseo; Princeton University; UC San Diego; Stanford University; Syracuse University; University of Arizona; University of Florida; UC Berkeley; University of Nevada, Reno; UC Davis; Howard University; and others.
Over the next five years, a focus on innovation in laser science and technology at LLE, driven by program needs and emerging national priorities, will include:
- Laser generation, manipulation, and control
- ultrahigh-peak-power lasers
- fourth-generation ICF/HEDS lasers
- Optical materials
- efficient, damage-resistant optics
- gratings, broadband optics, “polarization smoothing,” plasma mirrors
- development of novel radiation sources (betatron x rays, deep UV, THz, electrons) for HEDS research
Plans are underway for an intermediate-scale pulsed-power facility mated with OMEGA EP. Coupling an advanced pulsed-power driver to the four beams of OMEGA EP will uniquely expand the parameter space for Stockpile Stewardship Program (SSP)-relevant research.
Celebrating its 10th anniversary, OMEGA EP continues to nimbly and powerfully contribute to the Laboratory’s five-fold mission:
- To conduct implosion experiments and basic physics experiments in support of the National Inertial Confinement Fusion (ICF) program
- To conduct research and development in advanced technology related to high-energy-density phenomena.
- To operate the National Laser Users’ Facility
- To develop new laser and materials technologies
- To provide graduate and undergraduate education in electro-optics, high-power lasers, high-energy-density physics, plasma physics, and nuclear fusion technology