Performance of the Scattering Matrix Arc Detection System on the JET ITER-like ICRF antenna

Vrancken, M.; Lerche, E.; Blackman, T.; Durodié, F.; Evrard, M.; Graham, M.; Jacquet, Philippe; Kaye, A.; Mayoral, M.‐L.; Nightingale, M.; Ongena, J.; Eester, D. Van; Schoor, M. Van

doi:10.1016/j.fusengdes.2011.02.056

Cited by 9 publications

(6 citation statements)

References 4 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The installation of in-vessel sensors complicates the antenna-vacuum interfaces and the complexity of the sensor in situ calibration contributes to difficulties with the circuit control and analysis. Finally, the expectations of enhanced electrical strength of the antenna with in-vessel matching appear to be burdened by a new challenging problem related to the electrical vacuum breakdown at the T-junction [40] which requires development of sophisticated dedicated arc-detection techniques [41].…”

Section: Generatormentioning

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

Self Cite

View full text Add to dashboard Cite

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...

show abstract

Section: Generatormentioning

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

Self Cite

View full text Add to dashboard Cite

show abstract

“…Most objectives of the ILA have been demonstrated; matching of an array of closely packed straps, ELM resilience using internal conjugate-T matching, arc detection using Scattering Matrix and Sub-Harmonic Arc Detection (SMAD & SHAD) systems [88,89] and operation at ITER-relevant power densities (up to 6.2 MW m −2 on L-mode, 4.1 MW m −2 on H-mode) and RF voltages (42 kV, also on ELMy H-mode plasmas). No evidence of increased impurity production has been found at these power densities which are up to 6 times higher than hitherto achieved on JET [85].…”

Section: Iter-relevant Icrh Studiesmentioning

confidence: 99%

Overview of JET results

Paméla

Ongena²,

Contributors³

2011

Nucl. Fusion

View full text Add to dashboard Cite

Since the last IAEA Conference JET has been in operation for one year with a programmatic focus on the qualification of ITER operating scenarios, the consolidation of ITER design choices and preparation for plasma operation with the ITER-like wall presently being installed in JET. Good progress has been achieved, including stationary ELMy H-mode operation at 4.5 MA. The high confinement hybrid scenario has been extended to high triangularity, lower ρ * and to pulse lengths comparable to the resistive time. The steady-state scenario has also been extended to lower ρ * and ν * and optimized to simultaneously achieve, under stationary conditions, ITER-like values of all other relevant normalized parameters. A dedicated helium campaign has allowed key aspects of plasma control and H-mode operation for the ITER non-activated phase to be evaluated. Effective sawtooth control by fast ions has been demonstrated with 3 He minority ICRH, a scenario with negligible minority current drive. Edge localized mode (ELM) control studies using external n = 1 and n = 2 perturbation fields have found a resonance effect in ELM frequency for specific q 95 values. Complete ELM suppression has, however, not been observed, even with an edge Chirikov parameter larger than 1. Pellet ELM pacing has been demonstrated and the minimum pellet size needed to trigger an ELM has been estimated. For both natural and mitigated ELMs a broadening of the divertor ELM-wetted area with increasing ELM size has been found. In disruption studies with massive gas injection up to 50% of the thermal energy could be radiated before, and 20% during, the thermal quench. Halo currents could be reduced by 60% and, using argon/deuterium and neon/deuterium gas mixtures, runaway electron generation could be avoided. Most objectives of the ITER-like ICRH antenna have been demonstrated; matching with closely packed straps, ELM resilience, scattering matrix arc detection and operation at high power density (6.2 MW m −2) and antenna strap voltages (42 kV). Coupling measurements are in very good agreement with TOPICA modelling.

show abstract

“…Two different arc detection systems have been validated on JET H-mode plasmas; the Scattering Matrix Arc Detection (SMAD) system [23][24][25] and the Sub-Harmonic Arc Detection (SHAD) system [26]. SMAD, which can identify arcs also in low-impedance areas of the antenna by comparing measured probe voltages and directional coupler signals to those calculated using an RF model, was successfully commissioned and proved capable of protecting the antenna from arcs also during ELMy H-mode operation [25]. After tuning the system sensitivity SHAD also proved to be efficient and should offer an extra level of protection.…”

Section: Performance On Jet Plasmamentioning

confidence: 99%