TJ-II:PelletFuelling: Difference between revisions
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Since the start of pellet injector operation, 0.66, 0.76 and 1 mm (the latter for NBI only) diameter pellets (containing ≤8x10^18, ≤1.6x10^19, and ≤4x10^19 H particles, respectively) have been successfully injected into ECRH, ECRH & NBI, and NBI-only heated plasmas created using the 100_44_64 configuration. Although the result has been significantly increased electron densities, it is found that fuelling efficiency (ratio of deposited particles to injected particles) varies from ~30% in ECRH plasmas to ~80% for high-density NBI-heated plasmas. | Since the start of pellet injector operation, 0.66, 0.76 and 1 mm (the latter for NBI only) diameter pellets (containing ≤8x10^18, ≤1.6x10^19, and ≤4x10^19 H particles, respectively) have been successfully injected into ECRH, ECRH & NBI, and NBI-only heated plasmas created using the 100_44_64 configuration. Although the result has been significantly increased electron densities, it is found that fuelling efficiency (ratio of deposited particles to injected particles) varies from ~30% in ECRH plasmas to ~80% for high-density NBI-heated plasmas. | ||
In all cases, pellet ablation is monitored across the plasma radius using photodiodes, and a fast camera. Furthermore, using multiple Thomson Scattering profiles, it has been possible to study particle diffusion, deposition and confinement. However, fast radial drift that leads to large particle losses, and hence low efficiency, remains to be evaluated. | In all cases, pellet ablation is monitored across the plasma radius using photodiodes, and a fast camera. Furthermore, using multiple Thomson Scattering profiles, it has been possible to study particle diffusion, deposition and confinement. However, fast radial drift that leads to large particle losses, and hence low efficiency, remains to be evaluated. In addition, using the Doppler Reflectometer, which is sensitive to a local density perturbation, it may be possible to study the plasmoid that extends toroidally out from the neutral cloud surrounding an ablated pellet along magnetic field lines. if successfull this will be important for studying pellet particle deposition in stellarator devices. | ||
In the first instance, it is intended to broaden the current pellet fuelling database by performing injections into a broad range of magnetic configurations in order to determine efficiencies, as well as pellet penetration, ablation processes, particle drift and diffusion, plus the possible role of magnetic islands and magnetic well/hill. In parallel, is intended to determine if it is possible to increase fuelling efficiency by firstly injecting a small pellet to pre-cool the outer plasma core | In the first instance, it is intended to broaden the current pellet fuelling database by performing injections into a broad range of magnetic configurations in order to determine efficiencies, as well as pellet penetration, ablation processes, particle drift and diffusion, plus the possible role of magnetic islands and magnetic well/hill. In parallel, is intended to determine if it is possible to increase fuelling efficiency by firstly injecting a small pellet (or using a gas puff) to pre-cool the outer plasma core just prior to injecting a fuelling pellet (here Δt ≤ 1 ms). The TJ-II pellet injector is unique for undertaking this study as up to 4 pellets can be injected simultaneously. | ||
== If applicable, International or National funding project or entity == | == If applicable, International or National funding project or entity == | ||