A compact flexible pellet injector for the TJ-II stellarator

McCarthy, K. J.; Combs, S. K.; Baylor, L. R.; Caughman, J. B. O.; Fehling, D. T.; Foust, C. R.; McGill, J. M.; Carmona, J. M.; Rasmussen, D. A.

doi:10.1063/1.2955706

Cited by 7 publications

(2 citation statements)

References 11 publications

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“…A four-pellet pipe-gun type pellet injector system is operated on TJ-II [28]. It is fitted with a cryogenic refrigerator system for in situ pellet formation (hydrogen is used), fast propellant valves for pellet acceleration, in-line diagnostics to determine pellet velocity (light emitting/sensitive diode) and mass (inline microwave resonance cavity), plus straight delivery lines (resulting in little or no mass loss due to friction) that deliver pellets to the plasma outer edge.…”

Section: Pellet Injection Set-upmentioning

confidence: 99%

The interpretation of magnetic activity associated with pellet injections into plasmas created in the stellarator TJ-II

McCarthy¹,

Ascasíbar²,

Tamura³

et al. 2021

Nucl. Fusion

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Pellet injection into magnetic confinement plasma is widely employed for plasma fuelling and impurity transport studies. While post-injection effects include changes in density and temperature, several short-lived effects have been identified during and immediately after pellet ablation, e.g. pre-cooling of the plasma core or a strong reduction in fluctuations. Here, transitory effects observed in magnetic signals during and immediately after the injection of fuel and tracer encapsulated solid pellets into microwave and neutral beam heated plasma in the stellarator TJ-II are reported. One effect is the excitation of a clear, short-lived, magnetic instability during the ablation phase of a cryogenic pellet. Another effect is a brief reduction in broadband magnetic fluctuations immediately after an injection while a third effect is frequency jumps of already excited Alfvén eigenmodes (AE) when neutral beam heating is employed. The interpretation of these effects is facilitated by signals from 2 recently installed toroidal arrays of magnetic coils that follow the helicity of this device along one of its quadrants. It is concluded that interactions between outward drifting pellet particles and a low-order rational surface lead to the magnetic instability, that pellet-induced plasma cooling induces a transitory reduction in broadband magnetic fluctuations and that plasma mass density changes dominate jumps in AE frequencies.

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Section: Pellet Injection Set-upmentioning

confidence: 99%

The interpretation of magnetic activity associated with pellet injections into plasmas created in the stellarator TJ-II

McCarthy¹,

Ascasíbar²,

Tamura³

et al. 2021

Nucl. Fusion

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“…For instance, the pellet injection system in the large helical device (LHD) [11] extends its operational regime with good energy confinement [12]. More recently, a four-barrel compact pellet injector has entered operation in the stellarator TJ-II [13,14]. In Wendelstein 7-X, in operation since December 2015 [15], a pellet blower gun is expected to be available during the second (OP1.2) phase of operation in order to fuel the core of plasmas heated using electron cyclotron resonance heating (ECH).…”

Section: Introductionmentioning

confidence: 99%

Particle transport after pellet injection in the TJ-II stellarator

Velasco¹,

McCarthy²,

Panadero³

et al. 2016

Plasma Phys. Control. Fusion

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We study radial particle transport in stellarator plasmas using cryogenic pellet injection. By means of perturbative experiments, we estimate the experimental particle flux and compare it with neoclassical simulations. Experimental evidence is obtained of the fact that core depletion in helical devices can be slowed-down even by pellets that do not reach the core region. This phenomenon is well captured by neoclassical predictions with DKES and FORTEC-3D.

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