Pellet fuelling

Plasma and Fusion Research

2011

A three-dimensional observation of the solid hydrogen pellet ablation has been performed by using a fast stereo imaging camera to investigate the pellet ablation dynamics. The initial velocity component of the injected pellet is maintained during ablation in a hot plasma, and the pellet penetrates to the core plasma. On the other hand, it has been observed that part of high density pellet plasmoid, which is formed around the pellet substance by ablating hydrogen pellet, intermittently breaks away from the pellet ablating position and the breakaway plasmoid is transported across a confinement field. The breakaway plasmoid recurrently develops at the rate of about 100 times per millisecond and it is non-diffusively transported approximately 0.1 m during its several 10 µs lifetime in the opposite direction to the pellet motion, namely, toward the low magnetic field side. This observation gives a reasonable explanation for the difference between the pellet ablation position and the effective particle deposition profile.

Section: Introductionmentioning

confidence: 99%

Observation of Cross-Field Transport of Pellet Plasmoid in LHD

Plasma and Fusion Research

2011

“…In fact, pellet injection has extended the operational regime to higher densities while maintaining favorable confinement properties. 1,2 On the other hand, obvious degradation of the fueling efficiency is observed in high-temperature plasmas under highpower heating conditions. 3 The fact that the pellet massdeposition profile is skewed toward the edge when compared to the measured pellet penetration depth 2,4 and the pellet ablatant promptly drifts towards the low-magnetic-field direction, 5,6 have been confirmed in several experiments.…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional observation system for pellet ablation traveling in the high-temperature plasmas

Review of Scientific Instruments

2005

In order to investigate the ablation of a solid hydrogen pellet, which is injected into a high-temperature plasma with high speed ͑ϳ1 km/s͒ for the plasma refueling, a three-dimensional observation system using a fast camera has been developed. A stereo method has been employed to obtain the three-dimensional information of the pellet ablation. A pair of the stereo images, which have been taken from different locations, has been focused onto a single fast camera by using a bifurcated fiber scope to ensure the simultaneity of both images. The projection matrix, which is used for stereo reconstruction, is calibrated by taking images of a model plane of known coordinates from the actual camera positions. The measuring error of the stereo observation is within 2% in the depth direction.

“…The 1-D spherically symmetric hydrodynamic model of the expansion in the ablation cloud is then solved in the model. Only the thermal electron as mono-energetic incident particles is regarded in pellet ablation since plasma electrons dominate the cloud heating and ionization, consequently the ablation of the pellet in the model [1]. By assuming the continuous loss of mono-energetic electrons in the ablation cloud, the energydependent loss function L(E), which is a semi-empirical formula [16], is defined as dE/dr = ρ cloud L(E)/m, where m and ρ cloud are the average molecular mass and the mass density of the cloud, respectively.…”

Section: The Ngs Ablation Modelmentioning

confidence: 99%

“…The injection of cryogenic solid pellets, which is an alternative approach to fueling, has been attracting interest because of its advantage of deeper and more efficient fueling than gas puffing (see Review Paper [1]). Many experiments support the promise of pellet injection due to its direct fueling into the plasma core region beyond the scrap-off layer of a fusion reactor.…”

Section: Introductionmentioning

confidence: 99%

Observation of the Effect of Energetic Ions on Pellet Ablation in the Large Helical Device

Hoshino

Plasma and Fusion Research

et al. 2006

Ablation of a solid hydrogen pellet in hot plasmas was investigated in the Large Helical Device (LHD). The penetration depth of the injected pellets in the experiment was compared to a theoretical model employing ablation due to the heat flux of fast ions as well as thermal electrons. Shallower penetration than that predicted based on the model considering only electrons was observed in LHD plasmas in the presence of highly energetic (up to 180 keV) fast ions due to neutral beam injection (NBI). This discrepancy can be quantified by the contribution of fast ions in terms of the stored energy of fast ions. The ablation model calculation taking into consideration the effect of thermal electrons and fast ions agrees with the experimental results obtained by LHD. Scaling which includes the fast-ion effect on penetration depth in LHD was compared with the wider multi-experiment database (IPADBASE) [L.R. Baylor et al., Nucl. Fusion 37, 445 (1997)].