Real-time fast ferrite ICRF tuning system on the Alcator C-Mod tokamak

Lin, Y.; Binus, A.; Wukitch, S.J.

doi:10.1016/j.fusengdes.2008.08.044

Cited by 26 publications

(11 citation statements)

References 25 publications

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“…There are generally two kinds of power loss mechanisms, dubbed as dynamic loss, which can happen at any RF power level, and nonlinear loss, which only happens at very high RF power intensity. [19] In the previous study [4], we found the evidence of non-linear power loss in the ferrite tuners during high power operation during the first implementation of the tuners without Stub-3, where the circulating RF power inside the tuners was very high. After several iterations of optimization, especially with the careful design and installation of Stub-3, the circulating power in the ferrite tuners at the same net power to the antennas has been significantly lowered.…”

Section: Figure 6 Time Traces During An Edge Localized Mode (Elm) (Amentioning

confidence: 76%

“…As a result, if plasma loading changes rapidly or varies in a large range, the transmitter would be mismatched. Many groups have studied and implemented matching systems that can be used in real-time, including frequency modulation on JET [1], dielectric liquid stubs on EAST [2] and LHD [3], ferrite tuners on Alcator C-Mod [4], EAST [5] and KSTAR [6]. In this paper, we report the recent progress on the implementation and performance of real time fast matching system using ferrite tuners on the Alcator C-Mod tokamak.…”

Section: Introductionmentioning

confidence: 99%

“…In Ref. [4], we reported the successful implementation of a prototypical fast ferrite tuning (FFT) system on the E-port antenna, commissioned in 2009. The real-time matching system included two ferrite tuners and a real-time control computer that was incorporated into the plasma control system.…”

Section: Introductionmentioning

confidence: 99%

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ICRF antenna matching systems with ferrite tuners for the Alcator C-Mod tokamak

Lin

Binus

Wukitch

et al. 2015

Fusion Engineering and Design

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Real-time fast ferrite tuning (FFT) has been successfully implemented on the ICRF antennas on Alcator C-Mod. The former prototypical FFT system on the E-port 2-strap antenna has been upgraded using new ferrite tuners. A new FFT system with two ferrite tuners and one fixedlength stub has been installed on the transmission line of the D-port 2-strap antenna. These two systems are able to achieve and maintain the reflected power to the transmitters to less than 1% in real time under almost all plasma conditions and help ensure reliable high power operation of the antennas. The loading insensitivity feature vs. plasma conditions of the innovative fieldaligned (FA) 4-strap antenna on the J-port allows us to significantly improve the matching by installing a carefully designed stub on each of the two transmission lines. The reduction of the RF voltages in the transmission lines has enabled the J-port FA antenna to deliver 3.7 MW RF power to plasmas out of 4 MW source power. The matching on the J-port antenna can be further improved by adding a single ferrite tuner under real-time control on each transmission line and this scheme will be implemented in the near future.

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Section: Figure 6 Time Traces During An Edge Localized Mode (Elm) (Amentioning

confidence: 76%

Section: Introductionmentioning

confidence: 99%

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ICRF antenna matching systems with ferrite tuners for the Alcator C-Mod tokamak

Lin

Binus

Wukitch

et al. 2015

Fusion Engineering and Design

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“…[4,5] The coil currents of the tuners, and thus the electrical length of the tuners, are controlled by a Linux-server based real-time controller. During a plasma discharge, the controller reads the RF power information from the three directional couplers (DC1, DC2 and DC3) as shown in Fig.…”

Section: Design and Performance Of The Fast Ferrite Tuning Systemmentioning

confidence: 99%

ICRF antenna matching system with ferrite tuners for the Alcator C-Mod tokamak

Lin¹,

Binus²,

Wukitch³

et al. 2015

AIP Conference Proceedings

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Study and design of the ion cyclotron resonance heating system for the stellarator Wendelstein 7-X Physics of Plasmas 21, 061514 (2014) Abstract. Real-time fast ferrite tuning (FFT) has been successfully implemented on the ICRF antennas on Alcator C-Mod. The former prototypical FFT system on the E-port 2-strap antenna has been upgraded using new ferrite tuners that have been designed specifically for the operational parameters of the Alcator C-Mod ICRF system (~ 80 MHz). Another similar FFT system, with two ferrite tuners and one fixed-length stub, has been installed on the transmission line of the D-port 2-strap antenna. These two systems share a Linux-server-based real-time controller. These FFT systems are able to achieve and maintain the reflected power to the transmitters to less than 1% in real time during the plasma discharges under almost all plasma conditions, and help ensure reliable high power operation of the antennas. The innovative field-aligned (FA) 4-strap antenna on J-port has been found to have an interesting feature of loading insensitivity vs. plasma conditions. This feature allows us to significantly improve the matching for the FA J-port antenna by installing carefully designed stubs on the two transmission lines. The reduction of the RF voltages in the transmission lines has enabled the FA J-port antenna to deliver 3.7 MW RF power to plasmas out of the 4 MW source power in high performance I-mode plasmas.

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“…Stub tuning networks have been used to reduce power reflected from the plasma on many fusion experiments in the ion cyclotron range of frequencies (<∼ 100 MHz) [1,2] but have not yet been deployed at higher frequencies. A double stub matching network with electronically controlled tuning stubs is under development for the lower hybrid current drive (LHCD) system on Alcator C-Mod [3,4].…”

Section: Introductionmentioning

confidence: 99%

Analysis of double stub tuner control stability in a phased array antenna with strong cross-coupling

Wallace

Hillairet

Koert

et al. 2014

Fusion Engineering and Design

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Active stub tuning with a fast ferrite tuner (FFT) has greatly increased the effectiveness of fusion ion cyclotron range of frequency (ICRF) systems (50-100 MHz) by allowing for the antenna system to respond dynamically to changes in the plasma load impedance such as during the L-H transition or edge localized modes (ELMs). A high power waveguide double-stub tuner is under development for use with the Alcator C-Mod lower hybrid current drive (LHCD) system at 4.6 GHz. The amplitude and relative phase shift between adjacent columns of an LHCD antenna are critical for control of the launched n || spectrum. Adding a double-stub tuning network will perturb the phase and amplitude of the forward wave particularly if the unmatched reflection coefficient is high. This effect can be compensated by adjusting the phase of the low power microwave drive for each klystron amplifier. Crosscoupling of the reflected power between columns of the launcher must also be considered. The problem is simulated by cascading a scattering matrix for the plasma provided by a linear coupling model with the measured launcher scattering matrix and that of the FFTs. The solution is advanced in an iterative manner similar to the time-dependent behavior of the real system. System performance is presented under a range of edge density conditions from under-dense to over-dense and a range of launched n || . Simulations predict power reflection coefficients (Γ 2 ) of less than 1% with no contamination of the n || spectrum. Instability of the FFT tuning network can be problematic for certain plasma conditions and relative phasings, but reducing the control gain of the FFT network stabilizes the system.

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Real-time fast ferrite ICRF tuning system on the Alcator C-Mod tokamak

Cited by 26 publications

References 25 publications

ICRF antenna matching systems with ferrite tuners for the Alcator C-Mod tokamak

ICRF antenna matching systems with ferrite tuners for the Alcator C-Mod tokamak

ICRF antenna matching system with ferrite tuners for the Alcator C-Mod tokamak

Analysis of double stub tuner control stability in a phased array antenna with strong cross-coupling

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