Search

The ITER Electron Cyclotron Heating (ECH) system provides 20 MW of microwave power from 24 gyrotron sources. The power is transmitted through evacuated, corrugated waveguide transmission lines. The...

The ITER Electron Cyclotron Heating (ECH) system consists of transmission lines made up of individual sections of evacuated, aluminum, circularly corrugated waveguides. The high-intensity beam of e...

The ITER Electron Cyclotron Heating (ECH) system will produce a high-intensity beam of electromagnetic radiation for plasma heating. A total of 20 MW of power will be transferred from 170 GHz gyrot...

Finite element analysis calculations are performed to determine the temperature profile in sections of the ITER Electron Cyclotron Heating (ECH) transmission line waveguide. Each aluminum, corrugat...

Initial results for high power testing at ORNL of prototype ECH components for ITER will be presented. The US ITER Project Office is responsible for providing the ITER ECH transmission line system. Evacuated 63.5 mm diameter corrugated waveguide will be used and a total of 24 lines are required. Each line is designed to handle 170 GHz power at 2 MW operating in the HE11 mode. The ITER Organization completed a conceptual design of the system and the USIPO has assumed the responsibility for completing the design. A number of prototype components have been procured from industrial suppliers and some testing of vacuum integrity and mechanical alignment have been performed. Techniques for measuring waveguide straightness, ovality, wall thickness, corrugation depth and other parameters for long sections have been developed. Prototype components including a 140° miter bend, 90° miter bends, waveguide switches, arc detectors, polarization rotators, waveguide pumpouts, DC breaks and others have been procured. A prototype waveguide support and cooling system has been designed and is being installed. Work on commissioning a power supply and interim 400 kW 140 GHz gyrotron system is nearly complete and initial testing is underway. Development of a 170 GHz 0.5–1 MW gyrotron is progressing at CPI. Low power testing of some corrugated waveguide components is being performed in collaboration with the ITER low field side reflectometer team. A resonant ring for very high power testing of components at the 2 MW level or higher is planned using a high power grating-type directional coupler and long loop of waveguide. Low power testing and analysis of waveguide components is also being performed at MIT1.

The Advanced Toroidal Facility (ATF) fusion energy experiment at the Oak Ridge National Laboratory requires high-power microwaves for startup and plasma heating. Power from a gyrotron oscillator tube at 53.2 GHz will be used to ionize and heat the plasma by the electron cyclotron heating process. The confining magnetic field of the device is either 0.95 or 1.9 T. The gyrotron tube generates 200 kW in the TE/sub 02/ mode, which is transported in an overmoded 6.35 cm diameter circular waveguide to the ATF vacuum vessel. The launcher consists of a mode-converting Vlasov section, which converts the nonpolarized TE/sub 02/ wave into a linearly polarized narrow beam. The beam reflects off a tilted spherical reflector grating and is focused at the center of the plasma. The launcher design and laboratory measurements are discussed. >

Several electron cyclotron heating (ECH) experiments have been completed on the Advanced Toroidal Facility (ATF) at Oak Ridge National Laboratory (ORNL) under a variety of operating conditions and launch polarizations. ECH power is launched using a polarization‐controlled beam launcher and microwave detectors are used to measure absorption of first‐pass and multiply‐reflected power. Measurements show that first‐pass absorption efficiency at low plasma density is highly dependent on magnetic field, polarization, and plasma conditions. Wave polarization rotation has been detected; it is caused by the large magnetic field shear on ATF. Detector signals indicate that absorption efficiency is relatively high for medium plasma density at either fundamental or second harmonic operation. Plasmas have also been sustained using the third harmonic cyclotron resonance where absorption efficiency is much lower. Gyrotron power modulation and turn‐off experiments have been performed to study power deposition and transport using plasma diagnostics. These experiments show that power absorption is fairly efficient. However, the power deposition profile is rather broad despite the relatively narrow launcher beam. This effect can be attributed to several factors including the broad extent of the resonant surface and the ∼45% of power contained in both low‐level sidelobes outside the launcher beam and in the wrong plasma mode.

Techniques for cleaning and conditioning the vacuum vessel of the Advanced Toroidal Facility (ATF) and its internal components are described. The vacuum vessel cleaning technique combines baking to 150 °C and glow discharges with hydrogen gas. Chromium gettering is used to further condition the system. The major internal components are the anodized aluminum baffles in the Thomson scattering system, a graphite‐shielded ICRF antenna, two graphite limiters, and a diagnostic graphite plate. Three independent heating systems are used to bake some of the major components of the system. The major characteristics used for assessing cleanliness and conditioning progress are the maximum pressure attained during bakeout, the results of gas analysis, and revelant plasma parameters (e.g., time to radiative decay). Details of the various cleaning and conditioning procedures and results are presented.

Experiments were conducted in the ELMO Bumpy Torus (EBT) from 1973 until 1984. A number of papers have been published concerning various aspects of experiments during the final two years of operation. The paper summarizes the final experimental conclusions and discusses those issues which remain unresolved. The main conclusions are as follows: (1) measurements of the width of the hot electron rings showed them to be wider than previously suspected, diluting their diamagnetism and negating their ability to locally reverse the magnetic field gradient; (2) two-dimensional plots of the plasma potential revealed open potential contours in the C-mode and closed potential contours near the plasma centre in the T-mode; (3) an in–out asymmetry in the plasma potential was always observed, giving rise to electric fields which drove convective plasma loss.

A system for launching 53.2-GHz electron cyclotron heating (ECH) power is being installed on the Advanced Toroidal Facility (ATF) fusion experiment at Oak Ridge National Laboratory. The launcher provides a narrow linearly polarized beam. The plane of polarization is easily rotated. Measurements indicate that the launcher will have a -20 dB beam width of 15 cm at the plasma center and polarization purity of >97%. The ATF (1) requires 53.2-GHz microwave power for ECH plasma ionization and heating; this power is generated by a 200-kW cw gyrotron. Theoretical ray tracing studies have shown almost complete first-pass power absorption is possible if the power is within the saddle point in the proper polarization (2). Therefore, a narrow-beam-width launcher with adjustable polarization is being developed. In ATF the confining magnetic field can operate continuously at 1 T or in long pulses at 2 T. Either second harmonic or fundamental ECH absorption occurs, depending on the field strength, and it is of interest to operate experiments using both values. With perpendicular propagation and low-field-side launch, the ECH power must be in the extraordinary mode (X-mode, Erf perpendicular to Bo) for second harmonic (co = 2 wee) or in the ordinary mode (0-mode, Enr parallel to Bo) for fundamental (o) = c),) operation. The magnetic field in ATF is formed primarily by helical windings, which produce a shear in the plane of the field along a radial chord. This shear may cause polarization rotation of the ECH wave as it travels through the outer plasma regions because of the unequal 0- and X-mode phase velocities at higher plasma density (similar to Faraday rotation). The ECH resonance zone is a 10-cm-wide saddle point near the plasma center.

The Advanced Toroidal Facility (ATF) [Fusion Technol. 10, 179 (1986)] is the world’s largest stellarator. It was designed and built to demonstrate high beta, steady‐state operation in a toroidal confinement system. During its final operating period ATF achieved pulse lengths of over one hour (4667 s). The objectives of these experiments were (1) investigation of plasma performance at times that are long compared to the plasma/wall equilibrium time; (2) determination of plasma control and wall conditioning techniques; and (3) adaptation of plasma diagnostic and data acquisition systems to long‐pulse operation. Other experiments have also extended earlier studies of dimensionless‐parameter plasma confinement scaling. By employing two discrete electron cyclotron heating (ECH) frequencies (28 and 35 GHz), and by simultaneously modulating the ECH power, magnetic field, and plasma density, it has been possible to maintain fixed plasma beta and collisionality while modulating the normalized gyroradius.