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.

Overmoded corrugated waveguide is efficient at transmitting power over a large frequency bandwidth. This operational flexibility becomes important in multi-frequency systems. For 50-mm diameter aluminum corrugated waveguide nominally designed for the ITER 170 GHz ECH system, the theoretical ohmic loss of the HE11 mode is around 0.3e-3 dB/m. In a possible dual-frequency system at ITER, the theoretical loss in the same waveguide increases to a manageable 0.8e-3 dB/m at 104 GHz. As examples of other wideband components, General Atomics has built several pairs of 63.5-mm diameter waveguide polarizers for the TCV tokamak's ECH transmission line that are designed to operate for 1 MW at frequencies ranging from 82.6 to 118 GHz. In addition, polarizers have been designed for ITER's 50-mm diameter transmission line. A computer code that calculates both the required mirror rotation angles and the ohmic losses predicts that these polarizers will function effectively at both 170 GHz and 104 GHz. A new class of wideband waveguide switches with rotary actuators have been supplied for the 82.6-126 GHz transmission lines at TCV, further emphasizing the broadband capabilities of corrugated waveguide components.

This paper provides an overview of high power components for the application of Electron Cyclotron Heating transmission lines, and broadband devices for Electron Cyclotron Emission detection systems. The unique fabrication and assembly challenges are discussed, particularly in the context of ITER. The ITER ECH system will require robust, vacuum-compatible components such as polarizers, dummy loads, and switches that are sufficiently cooled to withstand 1 MW for 3,600 seconds. These elements, along with overmoded corrugated waveguide, are necessary to form transmission lines with efficiencies of 90%, and 90% transmitted HE11 mode purity. Recent high power test results are summarized and scaled from the 63.5 mm internal diameter design to the 50 mm diameter version that will be used for ITER. Elements designed for Electron Cyclotron Emission detection and reflectometry systems are discussed, such as frequency filters and polarization rotators. The large frequency operating range of corrugated waveguide is exploited for such applications. The application of additive manufacturing technology towards both low and high power components is considered as a promising new area of development.

DIII-D research is addressing critical challenges in preparation for ITER and the next generation of fusion devices through focusing on plasma physics fundamentals that underpin key fusion goals, understanding the interaction of disparate core and boundary plasma physics, and developing integrated scenarios for achieving high performance fusion regimes. Fundamental investigations into fusion energy science find that anomalous dissipation of runaway electrons (RE) that arise following a disruption is likely due to interactions with RE-driven kinetic instabilities, some of which have been directly observed, opening a new avenue for RE energy dissipation using naturally excited waves. Dimensionless parameter scaling of intrinsic rotation and gyrokinetic simulations give a predicted ITER rotation profile with significant turbulence stabilization. Coherence imaging spectroscopy confirms near sonic flow throughout the divertor towards the target, which may account for the convection-dominated parallel heat flux. Core-boundary integration studies show that the small angle slot divertor achieves detachment at lower density and extends plasma cooling across the divertor target plate, which is essential for controlling heat flux and erosion. The Super H-mode regime has been extended to high plasma current (2.0 MA) and density to achieve very high pedestal pressures (similar to 30 kPa) and stored energy (3.2 MJ) with H-98y2 approximate to 1.6-2.4. In scenario work, the ITER baseline Q = 10 scenario with zero injected torque is found to have a fusion gain metric beta(TE) independent of current between q(95) = 2.8-3.7, and a lower limit of pedestal rotation for RMP ELM suppression has been found. In the wide pedestal QH-mode regime that exhibits improved performance and no ELMs, the start-up counter torque has been eliminated so that the entire discharge uses approximate to 0 injected torque and the operating space is more ITER-relevant. Finally, the high-beta(N) (<= 3.8) hybrid scenario has been extended to the high-density levels necessary for radiating divertor operation, achieving similar to 40% divertor heat flux reduction using either argon or neon with P-tot up to 15 MW.

The results of high power testing of new water-cooled ECH waveguide components for ITER are presented. The components are a precision-coupled 4.2 m waveguide assembly, a short expansion joint, and water-cooled waveguide for gyrotron commissioning. The testing was conducted at the QST Naka Fusion Institute using gyrotron pulses of 450 kW at 170 GHz for 300 s. Analysis shows that the power absorbed per unit length for the various waveguide components are dependent on location in the transmission line with respect to high order mode generators, such as miter bends. Additionally, larger-than-expected reflections from the load led to high absorption levels in the transmission line.

Waveguide miter bends with grooved mirrors are used to alter the polarization in oversized waveguides. The grooves increase the ohmic loss on the mirrors, and this increase is a function of the incident and output polarizations. In this paper, theoretical calculations of ohmic loss are compared with other available theory and experimental data. The optimum orientation and location of the polarizer miter bends for the lowest maximum ohmic loss is determined from the theory. Then the capability of polarizer miter bends to handle the heat loading at ITER is evaluated, using theoretical calculations of the ohmic loss and ANSYS modeling of the mirror cooling.

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 2 MW cw requirement for ITER EC transmission lines has led GA to design a number of new and modified components, namely power monitors and polarizers to meet this requirement. In addition, the ITER transmission lines may require sliding joints or bellows to accommodate the thermal expansion of the lines and/or vessel motion. The ex-vessel sections of the EC launchers require double seal waveguides, miter bends and possibly double seal sliding joints to assure tritium retention in this region. GA has developed designs for many of these components and some of them have already been tested at high power at the JAEA RF Test Stand. Thermal analyses of the standard GA power monitor miter bend show that our standard design is suitable for 1 MW cw operation when the H-field is in the plane of the miter bend. For 2 MW cw operation a modified design, which also requires H-plane orientation, has been developed and a prototype has been fabricated and is ready for testing. For long pulse/cw operation, a 2 MW calorimetric miter bend with thermally isolated mirror has been designed and a prototype has been fabricated. Since the mirror is thermally isolated, calorimetry on the mirror cooling water can provide a measure of absorbed power. Such a miter bend, when made in a double seal version, could be useful for monitoring total power at the end of an EC transmission line just before the in-vessel section of an EC launcher. A mode analyzer using an all metal water-cooled beam splitter is being developed for use in measuring in real time the HE11 and higher order mode content or total power in EC transmission lines. Such a high power diagnostic can be very useful in optimizing the alignment of the MOU output into a transmission line and in monitoring the HE 11 mode purity at various locations in a transmission line. Prior to making a 63.5 mm 170 GHz version suitable for use on ITER, several prototype 31.75 mm 110 GHz versions have been fabricated and tested at DIII-D. A 170 GHz version is now being fabricated. This paper addresses the performance characteristics, design features and test results for the new and modified components being developed to assure low loss transmission and acceptable component stresses for 2 MW cw operation.

Testing of prototypical ITER electron cyclotron heating transmission line components at representative ITER conditions has been carried out at the JAEA RF Test Stand (RFTS). Many 240 second pulses of ~600 kW 170 GHz power were transmitted reliably through these components. Based on these tests, it appears that the ITER requirement for 2 MW cw operation with high transmission efficiency is achievable. GA components tested in 2008 included polarizer miter bends, waveguides, very low diffraction loss miter bends (LDLMBs), and a dc break. Components tested in 2010 include an expansion section and polarizer miter bends with improved grooved mirrors. The tests showed that improvement in the polarizer mirror cooling is needed to support 2 MW operation. Measurements of the dc break showed that the temperature increase of the outer surface of the ceramic insulator was less than 10°C. The LDLMB tests showed that mirror losses were close to the theoretical prediction. Due to lower diffraction, losses in waveguides adjacent to the LDLMBs were much less than in those next to standard miter bends.

DIII-D has four neutral beamlines (NB). Each of these beamlines has two ion sources, each of which injects up to 2.5 MW for 3 s. These beamlines intersect the vacuum vessel at an angle of 19.5 deg off from radial, enabling current drive in the same direction as the plasma current (co-injection). In 2004, one of these beamlines (210 deg) was rotated to provide counter-injection (opposite of plasma current). A different beamline (150 deg) has been modified to have the capability to provide off-axis neutral beam current drive. The goal of the off-axis injection is to have the center of the ion sources aimed at a position 40 cm below the geometric center of the plasma. To achieve this off-axis injection, the beamline requires a mechanical lifting system that can elevate the beamline up to 16.5 deg from horizontal. The beamline also requires more strongly vertically focused ion sources (in order to pass the beam through a reduced effective aperture) as well as modified internal components. Additionally, the design of the new internal components incorporated modifications to allow for the doubling of ion source pulse lengths without the need for active cooling. This paper discusses the various beamline system design requirements for off-axis injection, as well as the results from the actual commissioning of the beamline. Overviews of the design and performance of mechanical lifting system (hydraulics and controls), focused ion sources, flexible beamline support systems (vacuum, cryogenic, power and water cooling), and internal beamline collimators are included. Additionally, the in-vessel monitoring and shine-through protection requirements are discussed. The actual data obtained during beamline commissioning and during normal physics operations is also presented.

The ITER Electron Cyclotron Heating and Current Drive (ECH&CD) transmission line components will need to be suitable for 1-2 MW CW operation. The high heat loads compared to existing transmission lines will require enhanced cooling and, for some components, new or modified designs. Testing at representative ITER conditions of key components has been carried out at the JAEA 170 GHz gyrotron test stand at Naka. Preliminary test results and a discussion of new ITER-relevant components are presented.

Initial testing on the Japan Atomic Energy Agency Gyrotron Test Stand of ITER-relevant TL components, has shown reasonable efficiencies, but identified that trapped modes between closely located miter bends, as well as mode conversion at miter bends can lead to excessive heating of the connecting waveguides. General Atomics has designed, built, and will test components to address this issue as well as ITER relevant components that have not been tested at the levels of 1 MW, 170 GHz, for extended pulse lengths. Some of the components that will be tested are ultra low loss miter bends, dc breaks, polarizers, power monitors, bellows, waveguide switches, waveguide cooling clamps, etc. Details of the components and test results will be presented.

The availability of high power, (-1 MW) long pulse length (effectively cw), high frequency, (>lo0 GHz) gyrotrons has opened the opportunity for enhanced scientific results on magnetic confinement devices for fusion research worldwide. This has led to successful experiments on electron cyclotron heating, electron cyclotron current drive, non-inductive tokamak operation, tokamak energy transport, suppression of instabilities and advanced profile control leading to enhanced performance. The key development in the gyrotron community that has led to the realization of high power long pulse gyrotrons is the availability of edge cooled synthetic diamond gyrotron output windows, which have low loss and excellent thermal and mechanical properties. In addition to the emergence of reliable high power gyrotrons, ancillary equipment for efficient microwave transmission over distances of hundreds of meters, polarization control, diagnostics, and flexible launch geometry have all been developed and proven in regular service. ... GENERAL ATOMICS REPORT GA-A24118 1ll MATURING ECRF TECHNOLOGY FOR PLASMA CONTROL R. W. CALLIS, et al.

The performance requirement of 1 (possibly 2) MW cw at 170 GHz for ITER Electron Cyclotron Heating and Current Drive transmission line components is much more demanding than the 1 MW 10 s performance, generally at 110 GHz, that has been demonstrated on present devices. The high ITER heat loads will require enhanced cooling and, for some components, new or modified designs. Before component designs are finalized, testing at ITER conditions is strongly advisable.

The performance requirement of 1 (possibly 2) MW cw at 170 GHz for ITER electron cyclotron heating & current drive transmission line components is much more demanding than the 1 MW, 5 to 10 s performance, generally at 110 GHz, that has been demonstrated on present devices. The high ITER heat loads will require enhanced cooling and, for some components, new or modified designs. In addition to thermal management issues, the components must be designed to have very low losses in order to meet the ITER transmission line efficiency requirements. Testing at representative ITER conditions of some components has been initiated at the JAEA 170 GHz gyrotron test stand at Naka, Japan. In addition, testing of a complete prototype ITER transmission line is planned in order to validate the designs for use on ITER. The design changes that are being made for the various components to assure low loss transmission and acceptable component temperatures are presented.