Experimental Measurements of the Ion Cyclotron Antennas' Coupling and RF Characteristics

Hoffman, D. J.; Baity, F. W.; Becraft, W.R.; Caughman, J. B. O.; Owens, T.L.

doi:10.13182/fst85-a40079

Cited by 9 publications

(4 citation statements)

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“…Crucially, the Conjugate-T approach doesn't require dedicated bulky infrastructure allowing a compact design. The idea of using the matching scheme where resistive loads are present in both branches of tuneable parallel resonant circuit (figure 2(a)) emerged in the 1980s when Resonant Double Loop (RDL) ICRH launcher design was proposed [34]. The focus of the RDL design was a compact high-power main-port antenna directly matched to the generator output impedance Z 0 within the tokamak vacuum boundary, minimizing voltages at the vacuum feedthroughs and reducing power losses in the mismatched part of the system.…”

Section: Application Of the Conjugate-t Principle In The Icrh Systemsmentioning

confidence: 99%

Design and operations of a load-tolerant external conjugate-T matching system for the A2 ICRH antennas at JET

Monakhov¹,

Graham²,

Blackman³

et al. 2013

Nucl. Fusion

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A load-tolerant External Conjugate-T (ECT) impedance matching system for two A2 Ion Cyclotron Resonance Heating (ICRH) antennas has been successfully put into operation at JET. The system allows continuous injection of the RF power into plasma in the presence of strong antenna loading perturbations caused by Edge Localized Modes (ELMs). Reliable ECT performance has been demonstrated under a variety of antenna loading conditions including H-mode plasmas with Radial Outer Gaps (ROG) in the range of 4-14 cm. The high resilience to ELMs predicted during the circuit simulations has been fully confirmed experimentally. Dedicated arc detection techniques and real-time matching algorithms have been developed as a part of the ECT project. The new Advanced Wave Amplitude Comparison System (AWACS) has proven highly efficient in detection of arcs both between and during ELMs. The ECT system has allowed the delivery of up to 4 MW of RF power without trips into plasmas with Type-I ELMs. Together with the 3dB system and the ITER-Like Antenna (ILA), the ECT has brought the total RF power coupled to ELMy plasma to over 8 MW, considerably enhancing JET research capabilities. This paper provides an overview of the key design features of the ECT system and summarizes the main experimental results achieved so far. PACS: 52.55.Fa, 52.50.Qt, 28.52.Cx It is noteworthy that the ICRH&CD phenomena and consequently the performance of the RF heating systems are quite sensitive to the parameters of both bulk and Scape-Off Layer (SOL) plasma. In this respect JET has an advantageous position among the existing tokamaks: large-scale plasmas with significant antenna-plasma distances, variety of operational regimes including H-mode and advanced scenarios, the all-metal first wall and the RF power capabilities comparable with ITER offer the best opportunities for the assessment of reactor-relevant aspects of the ICRH physics and technology [8][9][10][11].Since 1994 JET has been equipped with four identical A2 antennas each comprising an array of four straps [12]; new compact ITER-Like Antenna (ILA) was installed in the tokamak main port in 2008 [10]. The RF plant at JET has convenient modular design [13] capable of energizing the antennas at different frequencies with controllable strap phasing and launched power.The practical implementation of the ICRH technique in tokamaks faces significant challenges. Among other factors, the success of the method depends on efficient and reliable operation of the RF plant delivering multi-MW power levels to phased antenna straps in the presence of small and variable plasma load [14,15]. The main difficulty in meeting this requirement stems from the fact that only a fraction of the RF power reaching the ICRH antenna is radiated into plasma while the rest is reflected back to the RF plant. In order to prevent this power from damaging expensive generator tubes, dedicated tuneable elements are introduced in the transmission lines which make the returning power circulate in a resonant circuit outside the generator...

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Section: Application Of the Conjugate-t Principle In The Icrh Systemsmentioning

confidence: 99%

Design and operations of a load-tolerant external conjugate-T matching system for the A2 ICRH antennas at JET

Monakhov¹,

Graham²,

Blackman³

et al. 2013

Nucl. Fusion

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“…The parameters for the modified antenna (Antenna II) are compared with those of Antenna I in Table I. The electrical properties of the compact loop antenna differ somewhat from those of standard loop antennas because of the resonant configuration used [12]. An equivalent lumped circuit model for the ORNL antenna is shown in Fig.…”

Section: Nfecuum Variable Capacitormentioning

confidence: 99%

“…To couple ICRF at high power densities into compact devices such as CIT, it will be necessary to maximize the voltage and current levels achievable in antenna structures without incurring RF breakdown or impurity effects. The maximum power level achievable with a resonant antenna can be written [12] as:…”

Section: Technology Implicationsmentioning

confidence: 99%

“…To assess the coupling of compact launchers to divertor plasmas, a prototype compact loop antenna [10][11][12][13] has been installed on the DJJJ.-D tokamak. As described in Section 2, the antenna is recessed in a single midplane port on DUJ-D and it features frequency tunability and internal impedance matching by means of a variable capacitor.…”

Section: Introductionmentioning

confidence: 99%

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Coupling of fast waves in the ion cyclotron range of frequencies to H-mode plasmas in DIII-D

et al. 1990

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Measurements of low power (≃ 1 mW) antenna loading are used to study the coupling of a compact loop antenna structure to plasmas in the divertor configuration in DIII-D heated by neutral beam injection (NBI) or electron cyclotron heating (ECH). When a transition to the H-mode regime occurs during NBI, the antenna loading resistance drops by approximately a factor of two. This coupling decrease is due to a steepening of the edge density profile near the separatrix, accompanied by a reduction in edge density in the scrape-off layer. During edge localized modes, the opposite effects occur, and the antenna coupling increases transiently. The loading measurements are compared with theoretical calculations which take into account the measured density profiles as well as the conducting side-walls of the recessed antenna housing. Absolute agreement between the theoretical and the experimental results is obtained, including the correct dependence on the density, antenna position, RF frequency and antenna geometry. The theoretical interpretation of the results is discussed, together with the technological implications for future high power experiments.

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A 3D Analysis of maxwell's equations for cavities of arbitrary shape

Whealton

Chen

Raridon

et al. 1988

Journal of Computational Physics

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Experimental Measurements of the Ion Cyclotron Antennas' Coupling and RF Characteristics

Cited by 9 publications

References 0 publications

Design and operations of a load-tolerant external conjugate-T matching system for the A2 ICRH antennas at JET

Design and operations of a load-tolerant external conjugate-T matching system for the A2 ICRH antennas at JET

Coupling of fast waves in the ion cyclotron range of frequencies to H-mode plasmas in DIII-D

A 3D Analysis of maxwell's equations for cavities of arbitrary shape

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