In this paper, we present an overview of the development of two high power traveling wave antennas (TWAs) termed the “comb-line” and the “finline” for launching fast and slow waves in plasmas. The comb-line antenna which has been deployed at the DIII-D National Fusion Facility tokamak can couple megawatt (MW) level RF power into the tokamak plasma with $\sim$ 2% reflected power and $\sim$ 2% dissipated power per array element at its design frequency, 476 MHz. A prototype of the finline antenna which has been designed to launch lower hybrid slow waves at 4.6 GHz, has reflection coefficient below 10% with 1.8 dB insertion loss.

The ECRH (Electron Cyclotron Resonance Heating) system was used in the EAST (Experimental Advanced Superconducting Tokamak) experiments for several years, and some good experimental results have been obtained. However, the performance of the gyrotrons is degraded and the ability to stabilize output RF (Radio Frequency) power is reduced. Two single-frequency 140 GHz gyrotrons are planned to be repaired in order to improve the performance of the gyrotrons. At the same time, some internal components of the gyrotrons (such as collectors, electron guns, mode conversion mirrors) will be upgraded to make the gyrotrons have the output capability of 0.6 MW/1 MW at 105 GHz/140 GHz. The MOUs (Matching Optical Units), transmission lines, the low voltage power supplies, the measurement and control system, and the water-cooling system also need to be modified for the dual-frequency operation of the new gyrotrons. The retrofitted design of the EAST ECRH system using dual-frequency gyrotrons is discussed in the paper. The upgraded ECRH system will be used for future EAST experiments to explore the range of low q(95) and high beta(N), to study the steady-state operation mode for the future nuclear fusion power plants.

Technology developed in the pursuit of fusion energy has had an impact in many other industries. The requirements being met by advanced microwave and millimeter wave components for fusion applications can open up whole new areas in emerging industries. For plasma heating, microwave components such as waveguide, switches, and polarizers, are being built which can withstand megawatts of sustained power at frequencies up to 170 GHz. In microwave-based diagnostics for fusion systems, enormous frequency bandwidths such as 35-170 GHz are possible for transmission lines at very high propagation efficiency (< 1% loss over 100 m). The techniques and materials being developed for these systems are transferrable to other microwave-based applications.

A mechanism for driving current off-axis in high beta tokamaks using fast electromagnetic waves, called Helicons, will be experimentally tested in the DIII-D tokamak. This method is calculated to be more efficient than current drive using electron cyclotron waves or neutral beam injection, and it may be well suited to reactor-like configurations [1], [2]. A low power (100W) 476MHz “combline” antenna, consisting of 12 inductively coupled, electrostatically shielded, modular resonators [3], was recently installed in DIII-D. Initial operation showed that the plasma operating conditions were achieved under which helicon waves can be launched. Plasma operations also showed that the location of the antenna has not reduced the performance of, or introduced excessive impurities into, the discharges produced in DIII-D.

A long pulse electron cyclotron resonance heating (ECRH) system has been developed to meet the requirements of steady-state operation for the EAST superconducting tokamak, and the first EC wave was successfully injected into plasma during the 2015 spring campaign. The system is mainly composed of four 140 GHz gyrotron systems, 4 ITER-Like transmission lines, 4 independent channel launchers and corresponding power supplies, a water cooling, control & inter-lock system etc. Each gyrotron is expected to deliver a maximum power of 1 MW and be operated at 100-1000 s pulse lengths. The No.1 and No.2 gyrotron systems have been installed. In the initial commissioning, a series of parameters of 1 MW 1 s, 900 kW 10 s, 800 kW 95 s and 650 kW 753 s have been demonstrated successfully on the No.1 gyrotron system based on calorimetric dummy load measurements. Significant plasma heating and MHD instability suppression effects were observed in EAST experiments. In addition, high confinement (H-mode) discharges triggered by ECRH were obtained.

Additive manufacturing technology has made significant advances in terms of materials, tolerances, and surface finishes. The technique is becoming more common in science and industry. Since it has proven effective in constructing small parts with fine features, 3D printing is well suited for improving upon the manufacturing processes of millimeter-wave components. This paper explores the approach specifically applied to waveguide components produced using two different additive manufacturing approaches. One is a metal 3D printing process called Direct Metal Laser Sintering (DMLS). The other is high resolution stereolithography with metallic plating. Several millimeter-wave corrugated horns were "printed" in an aluminum alloy (AlSi10Mg) using DMLS, as well using Nickel-plated stereolithography. The testing of the components' electrical performance in terms of losses and radiation patterns at 100 GHz and 170 GHz is promising. Work is also being done to fabricate parts via additive manufacturing techniques in-house at General Atomics.

The gyrotron installation on the DIII-D tokamak has been in operation at the second harmonic of the electron cyclotron resonance since the mid-1990s. Prior to that a large installation of ten 60 GHz tubes was operated at the fundamental resonance. The system has been upgraded regularly and is an everyday tool for experiments on DIII-D.

Two miter bends are described for monitoring the power transmitted in an oversized corrugated waveguide. One has an array of holes in its mirror that couples a small fraction of the incident power to a rectangular waveguide directly machined into the mirror. Millimeter-wave detectors on the outputs of this miter bend can respond very rapidly to the transmitted power, but the coupling is sensitive to the mode purity in the oversized waveguide. The other miter bend monitors the power by measuring the rise in temperature of the cooling water passing through the mirror. The mirror is well isolated from the miter bend housing to prevent heat from neighboring waveguides from reaching the mirror. The measurement requires about 200 s to reach steady state, but it is relatively insensitive to mode purity. The measurement does require knowledge of the input polarization.Thermo-mechanical analyses of the miter bends indicate that they are capable of reliable operation with 1.5 MW transmitted through them. High-power long-pulse 170 GHz tests of these miter bends at the Japan Atomic Energy Agency (JAEA) are described. (C) 2015 Elsevier B.V. All rights reserved.

The electron cyclotron heating and current drive (ECH/ECCD) gyrotron complex on the DIII-D tokamak is being upgraded with the addition of new gyrotrons. The transmitted power monitoring in the high power millimeter wave transmission system will be upgraded with new rf power monitors sensitive to the wave polarization and mode content. The speed of the real time steering antenna is being increased using a new control system.

Microfabrication techniques are commonly used to build circuits for millimeter-wave and THz vacuum electron devices. A cost effective solution is becoming available, at least for building prototype circuits intended for cold-testing. Rapid prototyping machines such as 3D printers have advanced to the point that their resolution is below the wavelength of many microwave circuits. This paper reviews the application of this quickly-advancing technology towards waveguide components of vacuum electron devices. The authors use a rapid prototype technique called Direct Metal Laser Sintering (DMLS) to “print” sample 35 GHz circuits in metal. Circuits in two different materials (aluminum and chromium cobalt) are printed and cold-tested. The test data shows good agreement with simulation.