B. Felker

Generation of high power 140 GHz microwaves with an FEL for the MTX experiment

We have used the improved ETA-II linear induction accelerator (ETA-III) and the IMP steady-state wiggler to generate high power (1-2 GW) microwaves at 140 GHz. The FEL was used in an amplifier configuration with a gyrotron driver. Improved control of energy sweep and computerized magnetic alignment in ETA-III resulted in small beam corkscrew motion (<1.5 mm) at 6 Mev, 2.5 kA. Reduction of wiggler errors (<0.2%), improved electron beam matching, and tapered wiggler operation resulted in peak microwave power (single-pulse) of up to 2 GW. These pulses were transported to the MTX tokamak for microwave absorption experiments. In addition, the FEL was run in a burst mode, generating 50-pulse bursts of microwaves; these results are discussed elsewhere.<<ETX>>

Burst mode FEL with the ETA-III induction linac

Pulses of 140 GHz microwaves have been produced at a 2 kHz rate using the ETA-III induction linac and IMP wiggler. The accelerator was run in bursts of up to 50 pulses at 6 MeV and greater than 2 kA peak current. A feedback timing control system was used to synchronize acceleration voltage pulses with the electron beam, resulting in sufficient reduction of the corkscrew and energy sweep for efficient FEL operation. Peak microwave power for short bursts was in the range 0.5-1.1 GW, which is comparable to the single-pulse peak power of 0.75-2 GW. FEL bursts of more than 25 pulses were obtained.<<ETX>>

TPX superconducting tokamak magnet system 1995 design and status overview

The TPX magnet preliminary design effort is summarized. Key results and accomplishments during preliminary design and supporting R&D are discussed, including conductor development, quench detection, TF and PF magnet design, conductor bending and forming, reaction heat treating, helium stubs, and winding pack insulation.

IMP, a free electron laser amplifier for plasma heating in the Microwave Tokamak Experiment☆

Abstract 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.

X-ray imaging in an environment with high-neutron background on National Ignition Facility

X-ray imaging instruments will operate in a harsh ionizing radiation background environment on implosion experiments at the National Ignition Facility. These backgrounds consist of mostly neutrons and gamma rays produced by inelastic scattering of neutrons. Imaging systems based on x-ray framing cameras with film and CCDs have been designed to operate in such harsh neutron-induced background environments. Some imaging components were placed inside a shielded enclosure that reduced exposures to neutrons and gamma rays. Modeling of the signal and noise of the x-ray imaging system is presented.

The 27.3 meter neutron time-of-flight system for the National Ignition Facility

One of the scientific goals of the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory, Livermore CA, is to obtain thermonuclear ignition by compressing 2.2 mm diameter capsules filed with deuterium and tritium to densities approaching 1000 g/cm3 and temperatures in excess of 4 keV. Thefusion reaction d + t → n + a results in a 14.03 MeV neutron providing a source of diagnostic particles to characterize the implosion. The spectrum of neutrons emanating from the assembly may be used to infer the fusion yield, plasma ion temperature, and fuel areal density, all key diagnostic quantities of implosion quality. The neutron time-of-flight (nToF) system co-located along the Neutron Imaging System line-of-site, (NIToF), is a set of 4 scintillation detectors located approximately 27.3 m from the implosion source. Neutron spectral information is inferred using arrival time at the detector. The NIToF system is described below, including the hardware elements, calibration data, analysis methods, and an example of its basic performance characteristics.

Design and implementation of high magnification framing camera for NIF ARIANE Light

Gated X-Ray imagers have been used on many ICF experiments around the world for time resolved imaging of the target implosions. ARIANE (Active Readout In A Neutron Environment) has been developed for use in the National Ignition Facility and has been deployed in multiple phases. Phase 1 (complete) known as ARIANE Ultra Light (Alignment proof of concept), Phase 2a known as ARIANE Light (complete) (X-ray gated detector with electronic recording), Phase 2b (complete) (X-ray gated detector with film recording) and Phase 3 known as ARIANE Heavy which is currently under development. The ARIANE diagnostic is comprised of the following subsystems: pinhole imaging system, filtering, detector head, detector head electronics, control electronics, CCD, and film recording systems. The phased approach allows incremental increases in tolerance to neutron yield. Phase 2a and 2b have been fielded successfully and captured gated implosion images on CCD and film at neutron yields up to 7 x 1014. As the yields in the NIF increase Phase 3 will be a longer term solution incorporating an indirect optical path, hardened advanced detectors and significant (tons) of shielding. Design and Initial commissioning data for Phase 1-2b are presented here.

Microwave transport system for the MTX

The design and construction, as well as the initial operation, of the Microwave Transmission System is presented. The system consists of containment vessels, mirror boxes, mirrors, an alignment system, two turbomolecular pump vacuum stations, and a microwave source. Pulses of 50-ns-length and of 6-MeV electrons pass through a free electron laser (FEL) wiggler. A 300-W, 140-GHz extended interaction oscillator (EIO) supplies the seed signal for amplification in the wiggler. The electron beam is dumped and the microwave beam is quasi-optically transmitted 90 ft by six aluminum mirrors through an evacuated tube. Three of the mirrors are elliptical paraboloids and the others are flat. A seventh mirror is rotated into the microwave beam to divert it into a load tank. The transport vacuum vessel is a 20-in-diameter stainless steel tube with bellows and mirror boxes at each mirror. Two vacuums systems at each end of the transport tube allow a base pressure of 10/sup -7/ torr to be attained by 7000 L/s of turbomolecular pumping. At each mirror, at the MTX vessel, and at the two ends of the wiggler waveguide are He-Ne laser detectors used for vacuum alignment. The major components, their requirements, system requirements, and the initial operation of the system and its performance are described.<<ETX>>

Radiation induced noise in x-ray imagers for high-yield inertial confinement fusion experiments

The large fluence of 14-MeV neutrons produced in high-yield inertial confinement fusion (ICF) experiments creates a variety of backgrounds in x-ray imagers viewing the implosion. Secondary charged particles produce background light by Cherenkov emission, phosphor screen excitation and possibly scintillation in the optical components of the imager. In addition, radiation induced optical absorption may lead to attenuation of the signal. Noise is also produced directly in the image recorder itself (CCD or film) via energy deposition by electrons and heavy charged particles such as protons and alphas. We will present results from CCD background measurements and compare them to Monte Carlo calculations. In addition we show measurements of luminescence and long-term darkening for some of the glasses employed in imagers.

140 GHz microwave FEL experiments using ELF-II☆

Abstract 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.