TOPLHA: an accurate and efficient numerical tool for analysis and design of LH antennas

This paper presents a self-consistent, integral-equation approach for the analysis of plasma-facing lower hybrid (LH) launchers; the geometry of the waveguide grill structure can be completely arbitrary, including the non-planar mouth of the grill. This work is based on the theoretical approach and code implementation of the TOPICA code, of which it shares the modular structure and constitutes the extension into the LH range. Code results are validated against the literature results and simulations from similar code

On the rehydration of organic layered double hydroxides to form low-ordered carbon/LDH nanocomposites

Low-ordered carbon/layered double hydroxide (LDH) nanocomposites were prepared by rehydration of the oxides produced by calcination of an organic LDH. While the memory effect is a widely recognized effect on oxides produced by inorganic LDH, it is unprecedented from the calcination/rehydration of organic ones. Different temperatures (400, 600, and 1100 °C) were tested on the basis of thermogravimetric data. Water, instead of a carbonate solution, was used for the rehydration, with CO2 available from water itself and/or air to induce a slower process with an easier and better intercalation of the carbonaceous species. The samples were characterized by X-ray powder diffraction (XRPD), infrared in reflection mode (IR), and Raman spectroscopies and scanning electron microscopy (SEM). XRPD indicated the presence of carbonate LDH, and of residuals of unreacted oxides. IR confirmed that the prevailing anion is carbonate, coming from the water used for the rehydration and/or air. Raman data indicated the presence of low-ordered carbonaceous species moieties and SEM and XRPD the absence of separated bulky graphitic sheets, suggesting an intimate mixing of the low ordered carbonaceous phase with reconstructed LDH. Organic LDH gave better memory effect after calcination at 400 °C. Conversely, the carbonaceous species are observed after rehydration of the sample calcined at 600 °C with a reduced memory effect, demonstrating the interference of the carbonaceous phase with LDH reconstruction and the bonding with LDH layers to form a low-ordered carbon/LDH nanocomposite

The tunable resonant IC antenna concept and its design for DTT experiment

The intrinsic poor loading of Ion Cyclotron (IC) plasma-facing antennas makes the use of Tuning and Matching Systems (TMSs) a necessity. The antenna plus TMS is a resonant system; in the TMS and access lines high voltages (tens of kV) must be accounted for in the unavoidable unmatched part of the feeding lines. In this work, we propose and test an innovative type of IC launcher; it is based on achieving resonance of the self-standing antenna, i.e. without the TMS. A mechanical full-metal tuning mechanism is described and demonstrated to allow wide-band operation. A systematic analysis of possible antenna topologies has led to identifying a structure that can allow good impedance matching along with compliance with maximum electric field constraints. Most of the design is carried out using a simplified plasma and a commercial analysis tool and then validated with a realistic plasma using TOPICA code

Progress and verification of DTT ICRF antenna simulation using COMSOL

In this paper we present the extension of a full-wave FEM model (COMSOL®+MATLAB®) - initially developed to compute the electromagnetic field in presence of the anisotropic inhomogeneous plasma of the Electron Cyclotron Resonance Ion Sources (ECRISs) [1] – to the Ion Cyclotron Range of Frequency (ICRF). The model - based on the full non-uniform dielectric tensor in "cold plasma" approximation - has been employed to study antenna geometries of increasing complexity. Various antenna types have been analyzed, starting from single flat strap up to the two straps of an antenna option considered for the Divertor Tokamak Test facility (DTT) [2]. The results have been compared, cross-checked and validated with a simpler COMSOL-based tool [3] and with the TOPICA code [4]

Preliminary analysis of the ICRF launcher for DTT

The paper reports the preliminary analysis of different typologies of ICRH launchers for chosing the most efficient solution for the ICRH system of the Divertor Tokamak Test facility (DTT), designed by the Italian DTT Limited Liability Consortium (S.C. a r.l.). In its final configuration this system will couple to the DTT plasma a nominal power of 6 MW in the 60 – 90 MHz frequency range by means of four launchers. This very preliminary analysis has been done with the ANSYS HFSS code

Improved measurements of ICRF antenna input impedance at ASDEX Upgrade during ICRF coupling studies

A new set of diagnostics has been implemented on ASDEX Upgrade to measure the input impedance of the ICRF antennas, in the form of a voltage and current probe pair installed on each feeding line of every antenna. Besides allowing the measurement of the reflection coefficient Γ of each antenna port, the probes have two advantages: first, they are located close to the antenna ports (∼3 m) and thus the measurements are not affected by the uncertainties due to the transmission and matching network; second, they are independent of matching conditions. These diagnostics have been used to study the behavior of the ASDEX Upgrade antennas while changing the plasma shape (low to high triangularity) and applying magnetic perturbations (MPs) via saddle coils. Scans in the separatrix position Rsep were also performed. Upper triangularity δo was increased from 0.1 to 0.3 (with the lower triangularity δu kept roughly constant at 0.45) and significant decreases in |Γ| (up to ∼30%, markedly improving antenna coupling) and moderate changes in phase (up to ∼5°) of Γ on each feeding line were observed approximately at δo ≥ 0.29. During MPs (in ∼0.5 s pulses with a coil current of 1 kA), a smaller response was observed: 6% - 7% in |Γ|, with changes in phase of ∼5° apparently due to Rsep scans only. As |Γ| is usually in the range 0.8 - 0.9, this still leads to a significant increase in possible coupled power. Numerical simulations of the antenna behavior were carried out using the FELICE code; the simulation results are in qualitative agreement with experimental measurements. The results presented here complement the studies on the influence of gas injection and MPs on the ICRF antenna performance presented in [4]

The ICRF antenna of DTT: Design status and perspectives

The basis of design for the Ion Cyclotron Range of Frequency (ICRF) antennas of the Divertor Tokamak Test facility (DTT) is defined and the most suitable design solutions abiding by such requirements are shown. DTT will be equipped with one, two or three ICRF modules – the final choice to be taken during the first years of operations – and each module will have two antennas. Each antenna has to reliably couple a radiofrequency (RF) power ≥1.5 MW in the range 60÷90 MHz to the single-null, 6 T, 5.5 MA, DTT scenario and allow for remote (dis)assembling and maintenance operations of its plasma-facing components. Most documented antenna concepts are considered and a large set of alternatives, based on toroidal arrays of two, three or four straps with different shapes and constraints, is quantitatively assessed in terms of RF performances. Two most promising candidates are identified: the one, selected to access a detailed design phase, relies on traditional radiating elements, the other is an innovative concept requiring some R&D

Characterizations and first plasma operation of the WEST load-resilient actively cooled ICRF launchers

The paper discusses the characterization of the three high power steady-state and load-resilient ICRF launchers of WEST before their installation in the tokamak. These launchers have been characterized and validated in low-power experiments (milliwatt range) as well as in experiments at the nominal RF voltages and currents in the TITAN vacuum chamber (~30 kV and 915 A peak). The successful commissioning of two of the launchers during the WEST C3 campaign at ~1 MW power level is illustrated. Manual and real-time controlled impedance-matching of the launchers are discussed, as well as the validation of their load-resilience. Furthermore, several redundant and complementary protection systems have been validated and are reviewed in the paper