1,721,396 research outputs found
Effects of outer top gas injection on ICRF coupling in ASDEX Upgrade: Towards modelling of ITER gas injection
No full textThe influence of outer top gas injection on the scrape-off layer (SOL) density and ion cyclotron range of frequency (ICRF) coupling has been studied in ASDEX Upgrade (AUG) L-mode plasmas for the first time. The three-dimensional (3D) edge plasma fluid and neutral transport code EMC3-EIRENE is used to simulate the SOL plasma density, and the 3D wave code RAPLICASOL is used to compute the ICRF coupling resistance with the calculated density. Improvements have been made in the EMC3-EIRENE simulations by fitting transport parameters separately for each gas puffing case. It is found that the calculated local density profiles and coupling resistances are in good agreement with the experimental ones. The results indicate that the SOL density increase depends sensitively on the spreading of the injected outer top gas. If more gas enters into the main chamber through the paths near the top of vessel, the SOL density increase will be more toroidally uniform; if more gas chooses the paths closer to the mid-plane, then the SOL density increase will be more local and more significant. Among the various local gas puffing methods, the mid-plane gas valve close to the antenna is still the best option in terms of improving ICRF coupling. Differences between the outer top gas puffing in AUG and the outer top gas puffing in ITER are briefly summarized. Instructive suggestions for ITER and future plans for ITER gas injection simulations are discussed. © 2017 EUROfusion Max Planck Institute for Plasma Physics
Preface to special topic: Advances in radio frequency physics in fusion plasmas
No full textIt has long been recognized that auxiliary plasma heating will be required to achieve the high temperature, high density conditions within a magnetically confined plasma in which a fusion "burn" may be sustained by copious fusion reactions. Consequently, the application of radio and microwave frequency electromagnetic waves to magnetically confined plasma, commonly referred to as RF, has been a major part of the program almost since its inception in the 1950s. These RF waves provide heating, current drive, plasma profile control, and Magnetohydrodynamics (MHD) stabilization. Fusion experiments employ electromagnetic radiation in a wide range of frequencies, from tens of MHz to hundreds of GHz. The fusion devices containing the plasma are typically tori, axisymmetric or non, in which the equilibrium magnetic fields are composed of a strong toroidal magnetic field generated by external coils, and a poloidal field created, at least in the symmetric configurations, by currents flowing in the plasma. The waves are excited in the peripheral regions of the plasma, by specially designed launching structures, and subsequently propagate into the core regions, where resonant wave-plasma interactions produce localized heating or other modification of the local equilibrium profiles. Experimental studies coupled with the development of theoretical models and advanced simulation codes over the past 40+ years have led to an unprecedented understanding of the physics of RF heating and current drive in the core of magnetic fusion devices. Nevertheless, there are serious gaps in our knowledge base that continue to have a negative impact on the success of ongoing experiments and that must be resolved as the program progresses to the next generation devices and ultimately to "demo" and "fusion power plant." A serious gap, at least in the ion cyclotron (IC) range of frequencies and partially in the lower hybrid frequency ranges, is the difficulty in coupling large amount of power to the plasma while minimizing the interaction between the plasma and launching structures. These potentially harmful interactions between the plasma and the vessel and launching structures are challenging: (i) significant and variable loss of power in the edge regions of confined plasmas and surrounding vessel structures adversely affect the core plasma performance and lifetime of a device; (ii) the launcher design is partly "trial and error," with the consequence that launchers may have to be reconfigured after initial tests in a given device, at an additional cost. Over the broader frequency range, another serious gap is a quantitative lack of understanding of the combined effects of nonlinear wave-plasma processes, energetic particle interactions and non-axisymmetric equilibrium effects on determining the overall efficiency of plasma equilibrium and stability profile control techniques using RF waves. This is complicated by a corresponding lack of predictive understanding of the time evolution of transport and stability processes in fusion plasmas. © 2014 AIP Publishing LLC
Study of EAST LH antennas coupling at ENEA-Frascati
No full textspectra are identified. © 2015 AIP Publishing LLC.The two Lower Hybrid (LH) launchers of the EAST tokamak have been analysed using some tools available at ENEA-Frascati research centre. The antennas, working at 2.45 and 4.6 GHz, have been assessed in terms of reflection coefficient and launched power spectrum for several plasma loads differing in the electron density profile. Fitting an experimental profile we derived a set of parameterised realistic density profiles to compute the coupling performances of different spectra, launched by considering different phasing between antenna modules. The sensitivity to the tilt of the magnetic field with respect to the equatorial plane as well as to an additional progressive phasing at the mouth due to the toroidal curvature has been studied too. The most suitable operational conditions for the minimization of reflected power and side lobes in the
Analysis of a flat, dielectric-loaded, ion cyclotron, test antenna by using three electromagnetic codes
No full textThe present work compares the results coming out from the following three Ion Cyclotron antenna tools: HFSS, COMSOL Multiphysics and the TOPICA code. A simplified flat antenna geometry, working at 30 MHz, is used as benchmark. The comparison is carried out with respect to the scattering matrix and the RF potentials, i.e., the line integrals of the electric field along the flux tubes of the equilibrium magnetic field. Various operational configurations characterized by different antenna load clearance are considered. Very good agreement can be observed among the codes for all the simulated configurations in terms of scattering parameters. RF potentials also match as
regards to patterns, trends as well as absolute values
Mode Filters for Oversized Rectangular Waveguides: A Modal Approach
No full textA semi-analytical approach, relying on the mode-matching method and the resonator technique, is proposed. It is conceived to evaluate the performance of mode filters, based on corrugations partially filled with an absorbing material, in the case of oversized rectangular waveguides. The mathematical formulation allows an accurate and fast computation of the scattering parameters, through closed-form expression of the surface integrals and some matrix algebra. The theoretical model is implemented in a code that is benchmarked against a finite-element method to elucidate its advantages with respect to volumetric solvers. After giving an insight on the physical mechanisms ruling the performance of these devices, the modal method is used to run the particle swarm optimization algorithm for different types of devices, taking advantage of the reduced computation time of the developed tool. © 1963-2012 IEEE
Transmitter and HVPS Architectures in the Ion-Cyclotron Radio Frequency System of DTT
No full textThe design choices for the conversion of electrical energy into radio frequency (RF) waves is critically reviewed in this paper to conceive the most suitable architectures for RF transmitters in nuclear fusion. Ion Cyclotron Resonance Heating (ICRH) systems, using RF waves to heat fusion plasmas, present specific and demanding requirements in terms of power supplies that are tackled here with reference to the DTT, a new advanced fusion machine currently under construction. After the selection of the technology for the amplification stages of ICRH transmitters, the electrical specifications of the power supplies are determined on the basis of several parameters such as amplification, efficiency and loading conditions. The study presented in this paper concerns the choice of the most suitable architecture of the high voltage power supplies. It is based on available literature and technical documentation as well as on the calculation of operational points for the high-power amplification stages in mismatching conditions. Several possible solutions have been analyzed but the peculiar needs of ICRH system, such as the high performance in terms of accuracy, stability and fast response, lead to the adoption of unconventional solutions, resulting in a custom design. Finally, some alternatives and improvements are proposed
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