Modeling of Drift Displacement of the Pellet Ablated Material for Outboard Side Injection in Large Helical Device

Matsuyama, Akinobu; Koechl, F.; Pégouriè, B.; Sakamoto, R.; Motojima, G.; Yamada, H.

doi:10.1585/pfr.7.1303006

Cited by 9 publications

(17 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The corresponding drift-damping factor is then obtained by replacing the poloidal connection length ∼πqR ax in equation ( 7) by half the toroidal period in helical configurations, i.e. ∼πR ax /M [14,27], yielding…”

Section: Poloidal Current Connection Rozhansky Et Almentioning

confidence: 99%

“…in NBI-heated plasmas [26], the effect of fast ions was taken into account in both ablation and homogenization calculations. In an earlier paper [27], the comparison of HPI2 predictions with mass deposition measurements for LFS launched pellets was reported. Here, we present a more detailed description of the drift model and newly consider HFS launched pellets.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Modelling of the pellet deposition profile and ∇B-induced drift displacement in non-axisymmetric configurations

Matsuyama¹,

Koechl²,

Pégouriè³

et al. 2012

Nucl. Fusion

View full text Add to dashboard Cite

Drift displacement during density homogenization is modelled for hydrogen pellets injected into the Large Helical Device (LHD). The pellet ablation and deposition profiles are simulated for neutral-beam injection heated plasmas and are shown to reproduce well the main characteristics of the observed drift displacement for both low-field side and high-field side (HFS) injected pellets. The model describes the parallel expansion of ionized ablated pellet particle cloudlets (plasmoid) in non-axisymmetric magnetic configurations and the associated evolution of the plasmoid drift acceleration force exerted by the average magnetic field gradient over the plasmoid length. It is shown that, during the ablation and early homogenization phases, plasmoids are strongly accelerated towards the inverse direction of the local magnetic field gradient. In the case of the LHD, its direction and magnitude depend mainly on the pellet launching location with respect to the external helical coils. While such an initial drift—induced near the ablation region—is efficiently damped by plasmoid internal currents as soon as the plasmoid length becomes comparable to a toroidal connection length, a weak drift acceleration force is maintained over the whole homogenization time, whose direction depends on whether the confining magnetic field possesses a magnetic well or hill structure. Simulations show that, in a strong magnetic hill configuration like the LHD, this small but long-term drift becomes significant and results in a radially outward displacement of the mass deposition even for pellets injected from the HFS.

show abstract

Section: Poloidal Current Connection Rozhansky Et Almentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Modelling of the pellet deposition profile and ∇B-induced drift displacement in non-axisymmetric configurations

Matsuyama¹,

Koechl²,

Pégouriè³

et al. 2012

Nucl. Fusion

View full text Add to dashboard Cite

show abstract

“…During the initial short drift phase, acceleration of the plasmoid, in opposite directions for electrons and ions, is induced. The time evolution of its drift velocity can be written, for non-axisymmetric devices, as [31], where p is the pressure, n is the density, m i is the ion mass, and the subscripts 0 and ∞ refer to cloud and background plasma, respectively. For the TJ-II, the cross-field gradient scale-length, L B = B ∞ /∇ ⊥ B ∞ , is close to 1 m −1 on the LFS of the plasma centre, thus V d is directed towards the plasma outer edge (see fig.…”

Section: -Experimentmentioning

confidence: 99%

“…It is considered that the most efficient for non-axisymmetric devices is Rozhansky's effect. It is accounted for by adding the drift-dampening factor, A[L 0 ], to the δV d /δt term [31,32]. The combined PI/TESPEL experimental set-up means that the crossfield gradient scale-lengths, L B = B ∞ /∇ ⊥ B ∞ , are almost identical for flight paths through the plasma.…”

Section: -Experimentmentioning

confidence: 99%

“…The combined PI/TESPEL experimental set-up means that the crossfield gradient scale-lengths, L B = B ∞ /∇ ⊥ B ∞ , are almost identical for flight paths through the plasma. Thus, assuming that the background plasma and cloud pressures are equal, or similar, for both, and that A[L 0 ] is independent of the pellet type [31], then the ion mass (m i = 1 amu for a hydrogen atom and 12 amu for a carbon atom) is the only parameter that can explain differences in plasmoid drift and hence deposition profiles and efficiency. Hence, this significantly larger TESPEL ion mass during the initial stage of plasmoid acceleration may explain both the significant difference in deposited pellet electrons and the radial positions of the deposition profiles.…”

Section: -Experimentmentioning

confidence: 99%

See 1 more Smart Citation

Comparison of cryogenic (hydrogen) and TESPEL (polystyrene) pellet particle deposition in a magnetically confined plasma

McCarthy¹,

Tamura²,

Combs³

et al. 2017

EPL

View full text Add to dashboard Cite

A cryogenic pellet injector (PI) and tracer encapsulated solid pellet (TESPEL) injector system has been operated in combination on the stellarator TJ-II. This unique arrangement has been created by piggy-backing a TESPEL injector onto the backend of a pipe-gun–type PI. The combined injector provides a powerful new tool for comparing ablation and penetration of polystyrene TESPEL pellets and solid hydrogen pellets, as well as for contrasting subsequent pellet particle deposition and plasma perturbation under analogous plasma conditions. For instance, a significantly larger increase in plasma line-averaged electron density, and electron content, is observed after a TESPEL pellet injection compared with an equivalent cryogenic pellet injection. Moreover, for these injections from the low-magnetic-field side of the plasma cross-section, TESPEL pellets deposit electrons deeper into the plasma core than cryogenic pellets. Finally, the physics behind these observations and possible implications for pellet injection studies are discussed.

show abstract

Pellet fuelling requirements to allow self-burning on a helical-type fusion reactor

Sakamoto¹,

Miyazawa²,

Yamada³

et al. 2012

Nucl. Fusion

View full text Add to dashboard Cite

Pellet refuelling conditions to sustain a self-burning plasma have been investigated by extrapolating the confinement property of the LHD plasma, which appears to be governed by a gyro-Bohm-type confinement property. The power balance of the burning plasma is calculated taking into account the profile change with pellet deposition and subsequent density relaxation. A self-burning plasma is achieved within the scope of conventional pellet injection technology. However, a very small burn-up rate of 0.18% is predicted. Higher velocity pellet injection is effective in improving the burn-up rate by deepening particle deposition, whereas deep fuelling leads to undesirable fluctuation of the fusion output.

show abstract

Modeling of Drift Displacement of the Pellet Ablated Material for Outboard Side Injection in Large Helical Device

Cited by 9 publications

References 12 publications

Modelling of the pellet deposition profile and ∇B-induced drift displacement in non-axisymmetric configurations

Modelling of the pellet deposition profile and ∇B-induced drift displacement in non-axisymmetric configurations

Comparison of cryogenic (hydrogen) and TESPEL (polystyrene) pellet particle deposition in a magnetically confined plasma

Pellet fuelling requirements to allow self-burning on a helical-type fusion reactor

Contact Info

Product

Resources

About