D.A. Rasmussen

A lower hybrid current drive system for ITER

A 20 MW/5 GHz lower hybrid current drive (LHCD) system was initially due to be commissioned and used for the second mission of ITER, i.e. the Q = 5 steady state target. Though not part of the currently planned procurement phase, it is now under consideration for an earlier delivery. In this paper, both physics and technology conceptual designs are reviewed. Furthermore, an appropriate work plan is also developed. This work plan for design, R&D, procurement and installation of a 20 MW LHCD system on ITER follows the ITER Scientific and Technical Advisory Committee (STAC) T13-05 task instructions. It gives more details on the various scientific and technical implications of the system, without presuming on any work or procurement sharing amongst the possible ITER partners(b). This document does not commit the Institutions or Domestic Agencies of the various authors in that respect.

Pellet fuelling and control of burning plasmas in ITER

Pellet injection from the inner wall is planned for use in ITER as the primary core fuelling system since gas fuelling is expected to be highly inefficient in burning plasmas. Tests of the inner wall guide tube have shown that 5 mm pellets with up to 300 m s−1 speeds can survive intact and provide the necessary core fuelling rate. Modelling and extrapolation of the inner wall pellet injection experiments from present days smaller tokamaks leads to the prediction that this method will provide efficient core fuelling beyond the pedestal region. Using pellets for triggering of frequent small edge localized modes is an attractive additional benefit that the pellet injection system can provide. A description of the ITER pellet injection systems capabilities for fuelling and ELM triggering is presented and performance expectations and fusion power control aspects are discussed.

Loss Estimate for ITER ECH Transmission Line Including Multimode Propagation

Abstract The ITER electron cyclotron heating (ECH) transmission lines (TLs) are 63.5-mm-diam corrugated waveguides that will each carry 1 MW of power at 170 GHz. The TL is defined here as the corrugated waveguide system connecting the gyrotron mirror optics unit (MOU) to the entrance of the ECH launcher and includes miter bends and other corrugated waveguide components. The losses on the ITER TL have been calculated for four possible cases corresponding to having HE11 mode purity at the input of the TL of 100, 97, 90, and 80%. The losses due to coupling, ohmic, and mode conversion loss are evaluated in detail using a numerical code and analytical approaches. Estimates of the calorimetric loss on the line show that the output power is reduced by about 5, ±1% because of ohmic loss in each of the four cases. Estimates of the mode conversion loss show that the fraction of output power in the HE11 mode is ~3% smaller than the fraction of input power in the HE11 mode. High output mode purity therefore can be achieved only with significantly higher input mode purity. Combining both ohmic and mode conversion loss, the efficiency of the TL from the gyrotron MOU to the ECH launcher can be roughly estimated in theory as 92% times the fraction of input power in the HE11 mode.

Pellet fuelling, ELM pacing and disruption mitigation technology development for ITER

Plasma fuelling with pellet injection, pacing of edge localized modes (ELMs) by small frequent pellets and disruption mitigation with gas jets or injected solid material are some of the most important technological capabilities needed for successful operation of ITER. Tools are being developed at the Oak Ridge National Laboratory that can be employed on ITER to provide the necessary core pellet fuelling and the mitigation of ELMs and disruptions. Here we present progress on the development of the technology to provide reliable high throughput inner wall pellet fuelling, pellet ELM pacing with high frequency small pellets and disruption mitigation with gas jets and shattered pellets. Examples of how these tools can be employed on ITER are discussed.

THE EC H&CD TRANSMISSION LINE FOR ITER

Abstract The transmission line (TL) subsystem associated with the ITER electron cyclotron heating and current drive system has reached the conceptual design maturity. At this stage the responsibility of finalizing the design has been transferred from the ITER Organization to the U.S. Domestic Agency. The purpose of the TL is to transmit the microwaves generated by the 170-GHz gyrotrons installed in the radio-frequency building to the launchers located in one equatorial and four upper tokamak ports. Each TL consists of evacuated HE11 waveguides, direct-current breaks, power monitors, mitre bends, polarizers, switches, loads, and pumping sections and will have a typical length that ranges from 100 to 160 m. Overall transmission efficiency could be as high as 92% depending on the specific path between a given gyrotron and launcher. All components are required to be 2-MW compatible, and their layout and organization have been optimized for simplifying the maintenance accessibility and monitoring the primary tritium barrier integrity. Two different TL layouts are at the moment under study, to accommodate the two alternative options for the European sources: four 2-MW units or eight 1-MW units. In this paper the actual design is presented and the technical requirements are discussed.

Status and plans for TFTR

AbstractRecent research on TFTR has emphasized optimization of performance in deuterium plasmas, transport studies and studies of energetic ion and fusion product physics in preparation for the D-T experiments that will commence in July of 1993. TFTR has achieved full hardware design parameters, and the best TFTR discharges in deuterium are projected to QDT of 0.3 to 0.5.The physics phenomena that will be studied during the D-T phase will include: tritium particle confinement and fueling, ICRF heating with tritium, species scaling with tritium, collective alpha-particle instabilities, alpha heating of the plasma and helium ash buildup. It is important for the fusion program that these physics issues be addressed to identify regimes of benign alpha behavior, and to develop techniques to actively stabilize or control instabilities driver by collective alpha effects.

Density fluctuation measurements in ATF using correlation reflectometry

A two-frequency correlation reflectometer has been operated on the Advanced Toroidal Facility (ATF) to measure plasma electron density fluctuations. This reflectometer uses quadrature phase detection to permit true phase measurement of the reflected microwave signal (probing beam). By measuring the phase fluctuations in the reflected probing beam, the amplitude of the density fluctuations can be estimated. Simultaneous two-frequency operation makes it possible to measure the coherence between fluctuations at two radially separated cut-off layers, from which the radial correlation lengths and wavenumbers can be estimated. This reflectometer has been used to study the density fluctuations in the edge gradient region of low density ATF plasmas produced by electron cyclotron heating. These studies have revealed globally coherent turbulence with a radial correlation length of up to approximately 5 cm, a radial wavenumber kr ≈ 0 cm-1 and a poloidal wavenumber kθ ≈ 1 cm-1. The rms amplitude of the fluctuations reaches a maximum of ≈ 5% at the plasma edge (ρ = 1, where ρ is the flux surface normalized radius) and decreases with decreasing radius to a level of 1%. Simultaneous measurements of the fluctuations with the reflectometer, the heavy ion beam probe and the fast reciprocating Langmuir probe provide consistent results. A comparison of the measurements with simplistic mixing length estimates, ne/ne = 1/kθLn or ne/ne = 1/krLn, shows that these estimates are too high by factors of two to more than 100, while a comparison with a more detailed estimate for the pressure gradient driven resistive interchange turbulence yields reasonable agreement with the experimentally measured fluctuation characteristics

Direct to digital holography for semiconductor wafer defect detection and review

A method for recording true holograms directly to a digital video medium in a single image has been invented. This technology makes the amplitude and phase for every pixel of the target object wave available. Since phase is proportional wavelength, this makes high-resolution metrology an implicit part of the holographic recording. Measurements of phase can be made to one hundredth or even one thousandth of a wavelength, so the technology is attractive for dining defects on semiconductor wafers, where feature sizes are now smaller than the wavelength of even deep UV light.

Direct To Digital Holography For High Aspect Ratio Inspection of Semiconductor Wafers

Direct to Digital Holography (DDH) has been developed as a semiconductor wafer inspection tool and in particular as a tool for seeing defects in high aspect ratio (HAR) structures on semiconductor wafers and also for seeing partial‐height defects. While the tool works very well for general wafer inspection, it has unusual capabilities for high aspect ratio inspection (HARI) and for detecting thin residual film defects (partial height defects). Inspection of HAR structures is rated as one of the highest unmet priorities of the member companies of International SEMATECH, and finding residual thin film defects (in some cases called “stringers”) is also a very difficult challenge. The capabilities that make DDH unusually sensitive include: 1) the capture of the whole wave—both the classical amplitude captured by traditional optical systems, and the phase of the wave, with phase potentially measured to ∼1/1000’th of a wavelength or ∼2 to 3 Angstroms for a deep ultra‐violet (DUV) laser; 2) heterodyne detection—...

Three dimensional modelling of ICRF launchers for fusion devices

The three dimensional (3-D) nature of antennas for fusion applications in the ion cyclotron range of frequencies (ICRF) requires accurate modelling to design and analyse new antennas. In this article, analysis and design tools for radiofrequency (RF) antennas are successfully benchmarked with experiment, and the 3-D physics of the launched waves is explored. The systematic analysis combines measured density profiles from a reflectometer system, transmission line circuit modelling, detailed 3-D magnetostatics modelling and a new 3-D electromagnetic antenna model including plasma. This analysis gives very good agreement with measured loading data from the Tokamak Fusion Test Reactor (TFTR) Bay-M antenna, thus demonstrating the validity of the analysis for the design of new RF antennas. The 3-D modelling is contrasted with 2-D models, and significant deficiencies are found in the latter. The 2-D models are in error by as much as a factor of 2 in real and reactive loading, even after they are corrected for the most obvious 3-D effects. Three dimensional effects play the most significant role at low parallel wavenumbers, where the launched power spectrum can be quite different from the predictions of 2-D models. Three dimensional effects should not be ignored for many RF designs, especially those intended for fast wave current drive.