Directly laser driven and X-radiation driven DT filled capsules differ in the relationship between neutron and X-ray images. Shot N110217, a directly driven DT-filled glass micro-balloon provided the first neutron images at the National Ignition Facility. As seen in implosions on the Omega laser, the neutron image can be enclosed inside time integrated X-ray images. HYDRA simulations show the X-ray image is dominated by emission from the hot glass shell while the neutron image arises from the DT fuel it encloses. In the absence of mix or jetting, X-ray images of a cryogenically layered THD fuel capsule should be dominated by emission from the hydrogen rather than the cooler plastic shell that is separated from the hot core by cold DT fuel. This cool, dense DT, invisible in X-ray emission, shows itself by scattering hot core neutrons. Germanium X-ray emission spectra and Ross pair filtered X-ray energy resolved images suggest that germanium doped plastic emits in the torus shaped hot spot, probably reducing the neutron yield.

Received 28 February 2011DOI:https://doi.org/10.1103/PhysRevLett.106.109903© 2011 American Physical Society

We demonstrate the hohlraum radiation temperature and symmetry required for ignition-scale inertial confinement fusion capsule implosions. Cryogenic gas-filled hohlraums with 2.2 mm-diameter capsules are heated with unprecedented laser energies of 1.2 MJ delivered by 192 ultraviolet laser beams on the National Ignition Facility. Laser backscatter measurements show that these hohlraums absorb 87% to 91% of the incident laser power resulting in peak radiation temperatures of T(RAD)=300 eV and a symmetric implosion to a 100 μm diameter hot core.

The U.S. Department of Energy has embarked on a campaign to conduct credible fusion ignition experiments on the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory in 2010. The target assembly specified for this campaign requires the formation of a deuterium-tritium fuel ice layer in a 2-mm-diam capsule at the center of a 9-mm-long X 5-mm-diam cylinder, called a hohlraum. The ice layer must be formed and maintained at temperatures below 20 K. At laser shot time, the target is positioned at the center of the NIF target chamber, aligned to the laser beams, and held stable to <7-mu m root-mean-square. We have completed the final design of the cryogenic target system and are currently integrating the devices necessary to create, characterize, and position the cryogenic target for ignition experiments.

The Experimental Test Accelerator II (ETA-II) is the first induction linac designed specifically to FEL requirements. It is primarily intended to demonstrate induction accelerator technology for high-average-power, high-brightness electron beams, and will be used to drive a 140 and 250 GHz microwave FEL for plasma heating experiments in the Microwave Tokamak Experiment (MTX) at LLNL. Its features include high-vacuum design which allows the use of an intrinsically bright dispenser cathode, induction cells designed to minimize BBU growth rate, and careful attention to magnetic alignment to minimize radial sweep due to beam corkscrew. The use of magnetic switches allows high-average-power operation. At present ETA-II is being used to drive 140 GHz plasma heating experiments. These experiments require nominal beam parameters of 6 MeV energy, 2 kA current, 20 ns pulse width and a brightness of 1 × 108 A/(m rad)2 at the wiggler with a pulse repetition frequency (prf) of 0.5 Hz. Future 250 GHz experiments require beam parameters of 10 MeV energy, 3 kA current, 50 ns pulse width and a brightness of 1 × 108 A/(m rad)2 with a 5 kHz prf for 0.5 s. In this paper we discuss the present status of ETA-II parameters and the phased development program necessary to satisfy these future requirements.

We describe the modeling, the experimental facility and the initial operating results for ELF-II, an induction-linac-based free-electron laser designed to produce up to 2 GW of peak power at 140 GHz ELF-II is the initial configuration of an FEL system which will eventually produce up to 2 MW of average power at a frequency of 250 GHz, for use in plasma heating experiments in the Microwave Tokamak Experiment.

The Microwave Tokamak Experiment (MTX) is under construction at Lawrence Livermore National Laboratory to investigate the feasibility of intense, pulsed microwave radiation for plasma heating on future ignition tokamaks. A high-average-power free-electron laser (FEL) will use the Experimental Test Accelerator (ETA-II), a linear induction accelerator, in combination with an advanced high-field wiggler, to produce 1-2 MW of power at 1-2-mm wavelengths for periods of up to 0.5 s. The design of the FEL, termed the Intense Microwave Prototype (IMP), is described, along with the status and major issues associated with the experiment

The Intense Microwave Prototype (IMP) is an induction-linac based free electron laser (IFEL) amplifier system that is presently under construction at the Lawrence Livermore National Laboratory (LLNL). It will produce up to 2 MW of average power at 250 GHz for electron cyclotron resonance heating experiments in the Microwave Tokamak Experiment (MTX). The Experimental Test Accelerator-II (ETA-II) will provide the electron beam. ETA-II is designed to produce an electron beam with a current of 3 kA at an energy of 10 MeV and a brightness of over 108 A/(m rad)2. In addition, it is designed to produce 70-ns-FWHM pulses at a repetition rate of 5 kHz. The high magnetic field and wide tunability capabilities required for the FEL will be provided by a permanent magnet-laced electromagnetic wiggler with a 10-cm period and an overall length of 5.5 m. We present the physics design and expected performance of the FEL, along with a description of the experiment and of the phased development to high average power.