Omega Volume VII-System Description, Operation Manual

Page: 5 / 40

S-AD-M-005
Chapter 1: System Overview
January 2006—Page 3 of 35
focused on integrated experiments and developing an improved understanding of physics issues related
to fast ignition (such as the laser-to-electron coupling efficiency and electron-beam propagation in high-
conductivity plasmas), benchmarking theoretical models and defining the requirements for full-scale fast
ignition on the NIF. A deliverable of this research is to observe significant ion heating (more than one
thousand electron volts) and the concomitant increased neutron production in integrated fast-ignition
experiments on OMEGA.
(c)
Long-pulse experiments in the OMEGA EP target chamber
When operated in long-pulse mode, the four beams will be used primarily for planar-target
experiments in OMEGA EP’s baseline configuration. The long-pulse beams are frequency converted
from 1
~
to 3
~
to improve their coupling efficiency to the target. Frequency conversion occurs before
final transport to eliminate unconverted light before the beams enter the chamber. They are arrayed
at near-normal incidence (23º). It will be possible to extend current OMEGA HED experiments to
higher laser energies and longer pulse lengths. Alternatively, one or two of the beams can be used in
compressed-pulse mode to produce short bursts of hard x rays and/or energetic protons for diagnosing
targets driven by the long-pulse beams. These beams can radiograph targets along and/or perpendicular
to target normal. The OMEGA EP chamber could eventually accommodate experiments in the indirect-
drive configuration with half-hohlraums (hohlraums illuminated from one side), using up to four beams
of variable pulse lengths. For this purpose, the outer cone of beam ports at 48º relative to the hohlraum
axis allow the beams to be incident at an optimum angle for coupling to the hohlraum walls. The 48º
beam cone and options such as frequency converting the beams to 2
~
provide additional experimental
flexibility. Only the 23º UV beams are included in the OMEGA EP baseline design.
(d)
Fast-ignition relevant experiments in the OMEGA EP target chamber
The OMEGA EP configuration will permit experiments using various combinations of short-
and long-pulse laser beams to be carried out in the new target chamber, allowing many aspects of high-
intensity and HED physics to be studied. One or two of the new beams will be compressed and will
interact with solid targets or with plasmas produced by two or three long-pulse beams. This will allow
studies of laser and electron beam propagation in plasmas with ignition-scale conductivities. OMEGA
EP is designed to support planar cryogenic target experiments using the OMEGA planar cryogenic target
positioner (not in the baseline).
(e)
High-intensity laser–matter interaction experiments in the OMEGA EP target chamber
The compressed petawatt laser beam can be propagated into the OMEGA EP target chamber,
allowing high-intensity laser–matter interaction experiments with intensities in excess of 10
20
W/cm
2
.
1.1.1 High-Power, High-Energy, and Proton-Beam Radiography
The probing of high-energy-density (HED) matter with penetrating x rays or energetic particles
has evolved over the last two decades as the principal technique for measuring the evolution of HED
targets. A large fraction of the HED physics experiments on OMEGA (and on Nova prior to its shutdown)
use drive beams to illuminate a backlighting target, producing x rays to radiograph the primary target.
Thousands of HED backlighting experiments have been performed in the last decade on these and other
facilities, despite the absence of dedicated backlighting laser beams.