Development of impedance matching technologies for ICRF antenna arrays

Pinsker, R. I.

doi:10.1088/0741-3335/40/8a/015

Cited by 36 publications

(29 citation statements)

References 33 publications

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“…The first 'monster' crash at 1.97 s triggers an H mode transition (evidenced by the characteristic reduction in D α light). Since the antenna is operated at a fixed peak voltage, the reduced antenna loading [17,36] causes an immediate reduction in coupled RF power. Meanwhile, the plasma density begins to increase in response to the improved particle confinement.…”

Section: Enhanced Sawtooth Stabilitymentioning

confidence: 99%

High harmonic ion cyclotron heating in DIII-D: Beam ion absorption and sawtooth stabilization

et al. 1999

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Abstract. Combined neutral beam injection and fast wave heating at the fourth cyclotron harmonic produce an energetic deuterium beam ion tail in the DIII-D tokamak. When the concentration of thermal hydrogen exceeds ∼5%, the beam ion absorption is suppressed in favour of second harmonic hydrogen absorption. As theoretically expected, the beam absorption increases with beam ion gyroradius; also, central absorption at the fifth harmonic is weaker than central absorption at the fourth harmonic. For central heating at the fourth harmonic, an energetic, perpendicular, beam population forms inside the q = 1 surface. The beam ion tail transiently stabilizes the sawtooth instability but destabilizes toroidicity induced Alfvén eigenmodes (TAEs). Saturation of the central heating correlates with the onset of the TAEs. Continued expansion of the q = 1 radius eventually precipitates a sawtooth crash; complete magnetic reconnection is observed.

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Section: Enhanced Sawtooth Stabilitymentioning

confidence: 99%

High harmonic ion cyclotron heating in DIII-D: Beam ion absorption and sawtooth stabilization

et al. 1999

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“…Stub tuners have been used extensively for impedance matching of ion cyclotron range of frequency (ICRF) antennas [15], but this technique has not been applied to LH antennas. A double stub tuner can be used to match any reflection coefficient outside the "forbidden region" (a circle on the Smith Chart centered on the real axis and tangent to the Γ = 1 circle) [16].…”

Section: High Power Fast Ferrite Stub Tunermentioning

confidence: 99%

Advances in lower hybrid current drive technology on Alcator C-Mod

et al. 2013

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Abstract. Lower Hybrid Current Drive is an attractive option for non-inductive tokamak operation due to its high current drive efficiency and ability to drive current off axis. The parameters of the Alcator C-Mod LHCD system (f 0 = 4.6 GHz, B φ 5.5 T, n e 10 20 m −3 ) are similar to the proposed LHCD system on ITER. This paper will describe improvements in LHCD technology on C-Mod designed to increase single-pass absorption at high n e , extend pulse length (to > 3 s), and increase power delivered to the plasma by reducing reflection coefficients. Modeling of LH wave propagation indicates that the loss of LHCD efficiency at highern e can be mitigated by enhancing the single pass power absorption. To this end, an off mid-plane launcher has been designed combining the 4-way poloidal splitting concept of the current LH antenna on C-Mod with a toroidal bi-junction. The four rows of the launcher are located above the mid-plane in order to exploit the poloidal upshift of n || as rays propagate from the antenna into the plasma. The maximum LHCD pulse length was previously restricted to 0.5 s to prevent boiling of the klystron collector coolant. The Transmitter Protection System (TPS) was redesigned to model the coolant temperature in real time and shut off the klystron beam if the coolant is close to boiling. The TPS upgrade has been installed and operated on C-Mod for pulses up to 4.5 s into dummy loads and 1.0 s into the plasma. A new moveable local LH launcher protection limiter was designed to reduce reflection coefficients across a wide range of launcher positions while still providing effective protection from plasma heat flux. Initial high power (P net ∼ 700 kW) results show that lower reflection coefficients are achievable with the new limiter configuration as compared to the old configuration. Rapid degradation of power handling after boronization of the plasma facing surfaces, which does not occur with the fixed position limiters, highlights the need for the local protection limiter to provide sufficient protection from contamination during boronization.Advances in lower hybrid current drive technology on Alcator C-Mod 2 PACS numbers: 52.35. Hr, 52.50.Sw, 52.55.Wq Advances in lower hybrid current drive technology on Alcator C-Mod 3

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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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Development of impedance matching technologies for ICRF antenna arrays

Cited by 36 publications

References 33 publications

High harmonic ion cyclotron heating in DIII-D: Beam ion absorption and sawtooth stabilization

High harmonic ion cyclotron heating in DIII-D: Beam ion absorption and sawtooth stabilization

Advances in lower hybrid current drive technology on Alcator C-Mod

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

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