The National Ignition Facility (NIF) will contain the world’s most powerful laser. NIF requires more than 1500 precisely timed trigger pulses to control the timing of laser and diagnostic equipment. The Integrated Timing System applies new concepts to generate and deliver triggers at preprogrammed times to equipment throughout the laser and target areas of the facility. Trigger pulses during the last 2 seconds of a shot cycle are required to have a jitter of less than 20 ps (rms) and a wander of less than 100 ps (max). Also, the Timing System allows simultaneous, independent use by multiple clients by partitioning the system hardware into subsets that are controlled via independent software keys. The hardware necessary to implement the Integrated Timing System is commercially available.

A new 250-GHz, two-frequency microwave interferometer system has been developed to diagnose divertor plasmas on DIII-D. This diagnostic will measure the line-averaged density across both the inner and outer, lower divertor legs. With a cutoff density of over 7×1014 cm−3, temporal measurements of edge localized modes (ELMs) and plasma detachment are expected. The outer-leg system will use a double-pass method while the inner-leg system will be single pass. Two special three-dimensional (3D) carbon composite tiles are used, one to protect the microwave antennas mounted directly under the strike point and the other as the outer-leg reflecting surface. Performance, design constraints, and the thermal-mechanical design of the 3D carbon composite tiles are discussed.

The authors describe the installation and operation of the 400 kW 140 GHz gyrotron used for plasma heating on the Microwave Tokamak Experiment (MTX). The gyrotron system comprises a high-voltage (80 kV) modulated power supply, a multistation CAMAC computer control, a 5 T superconducting magnet, a series of conventional copper magnets, a circulating fluorinert (FC75) window cooling system, a circulating oil cooling system, a water cooling system, and microwave frequency and power diagnostics. The microwave power measured at the MTX tokamak input is typically 200 kW for a gyrotron output of approximately 400 kW. Losses in the system arise from power in modes other than the desired TE 15,2 mode, transport losses in the Vlasov sidelobes, small waveguide losses to the Vlasov, and small losses in the quasi-optical beamline. Individual MTX shots with the gyrotron have shown a stored energy increase of 1 kJ in the plasma in high density plasmas, and central electron temperature increases of up to 800 eV have been obtained. Even larger temperature increases have been observed recently in low density plasmas

The MTX (Microwave Tokamak Experiment) experiment diagnostic capabilities were upgraded, with the addition of five new diagnostics. A second beamline was added on the existing Michelson ECE waveguide to accommodate the new polychromator. This provides four orders of magnitude higher time resolution (1-2 μs) than the Michelson, with an improved spectral resolution (5 GHz) using up to nine separate channels. A four-channel ECE microwave receiver system using both an inside and an outside horn placed on the inner tokamak makes it possible to measure the hot electron emission generated from gyrotron and FEL (free-electron-laser) heating. A 15-channel interferometer on MTX was upgraded with the addition of polarimetry to provide measurements of the poloidal magnetic field. This upgrade uses a technique that determines the Faraday rotation by measuring the phase of a rapidly rotating polarization ellipse. The high-speed rotating optics (>60 K rpm) used to produce this state of polarization is reviewed. A two-channel O-mode reflectometer spanning 75-105 GHz is being added to measure the movements of the cutoff layer. By varying the frequency of this diagnostic, one can measure fluctuations deep within the plasma. A particle probe diagnostic currently under construction will measure the FEL electric field strength inside the tokamak plasma

In the microwave tokamak experiment (MTX) program, we are concentrating on experiments using intense, free-electron laser (FEL) generated microwave pulses. In initial FEL experiments, several diagnostic instruments were operated during injection of microwave pulses with peak powers to 0.2 GW at durations of 10 ns. Fixed and spatially scanning microwave detectors and receivers and a 48-element calorimeter on the inside wall of MTX diagnosed the GW-level FEL microwave pulses. With these diagnostics, linear-wave absorption and efficiencies of transmission through the quasi-optical transport system were studied. In addition, several radially resolved measurements of plasma density, temperature, and emission were made during FEL injection and were used in the analysis of microwave absorption data. A timing system, slaved to the FEL pulse arrival time, is capable of accuracy to a few nanoseconds in order to allow measurement of heating effects on the time scale of a single FEL pulse.

Techniques for measuring the power and frequency of the Electron Laser Facility (ELF)-II free-electron laser (FEL) used for plasma heating experiments on the Microwave Tokamak Experiment (MTX) have been developed. A multichannel 140-GHz receiver capable of measuring FEL power levels from 10 mW to 0.1 mu W within an accuracy of +or-1 dB and with a 50-dB dynamic range and a 2-ns response time has been designed. By using calibrated attenuators, it is possible to measure power levels from 10 GW to 0.1 mu W. The microwave output of the FEL in a microwave load tank is sampled by using WR-8 or WR-28 stub waveguide antennas. Microwave turning mirrors are used to guide the microwave beam down an evacuated beam tube to the MTX. Stub, WR-8, fundamental-mode waveguide antennas are used for beam detection on the microwave turning mirrors.< >

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.

The electron laser facility (ELF) at LLNL has been used to generate high peak powers at 140 GHz, extending the operating range of the device from previous experiments at 35 GHz. With 30 W of input signal, an exponential gain of 21 dB/m and a saturated output power of over 50 MW were measured. Numerical tapering studies indicate that space charge effects at 3.5 MeV were sufficiently large to affect trapping efficiency. Broadband spontaneous emission was observed over a wide range of wiggler fields at frequencies corresponding to FEL resonance. Over 150 MW of spontaneous power was measured near 94 GHz. The results are in good agreement with particle simulation codes.