TJ-II:Large pellet injection into NBI-heated plasmas of tJ-II
Experimental campaign
2019 Autumn
Proposal title
Large Pellet Injection into TJ-II NBI plasmas
Name and affiliation of proponent
K. J. McCarthy, Ciemat
Details of contact person at LNF
K. J. McCarthy, Ciemat
Description of the activity
Since initial pellet injections into TJ-II, the majority of successfully deposited small and medium-sized pellets (0.42, 0.6 & 0.7 mm) have been injected into ECRH plasmas while a smaller, but significant, number of similar pellets have been injected into NBI heated plasmas. Although these injection resulted in increased electron densities, fuelling efficiency (deposited particles/injected particles) was always less than ~40% in ECRH plasmas and ≤80% for NBI-heated plasmas.[1] It was found that rapid outwards radial drifting of the cloud attached to an ablating pellet leads to large particle losses.[2] Since these losses are most severe for particles ablated close to the plasma outer edge (injection side), the deeper penetration achieved for the lower temperature NBI-heated plasmas resulted in improved efficiency.
In contrast, only a few of the largest available pellets (1 mm) have been injected into TJ-II, these being injected into NBI-heated plasmas during injector commissioning. An analysis of Thomson Scattering profiles recorded just after these injections shows that core densities, with rather steep profiles, and temperatures reached values of ~5x10^19 m^-3 and 200 eV, respectively. Such plasmas are reminiscent of Super Dense Core plasmas (high central densities, improved confinement and high β) achieved in the LHD after pellet injection.[3] It is intended here to explore the density limit with pellet injection in NBI-heated plasmas of TJ-II. For this 1 mm diameter pellets will be injected into plasmas having peaked density profiles with line-averaged densities above 1.5x10^19 m^-3 and flat central temperature profiles with Te(0) ≥250 eV.
International or National funding project or entity
MICINN: FIS2019-89326-R EUROfusion: WP1
Description of required resources
Required resources: Diagnostics: TS, microwave interferometer, plasma current measurements. Fast-frame camera with fibre-optic bundle. Plasma Density: >1.5x1019 m-3 Configurations: Configurations about 100_44_64. Heating: NBI heating. Plasma Duration: ≥200 ms. PI Checks: We will require some time at 9 am to check out and condition the PI. Other considerations: Frequent access to the TJ-II experimental hall. Days: 2. Dates when unavailable: K. J. McCarthy will be unavailable from 4th to 15th of October (NIFS) and from 25rd to 29th of November (LATINfusion). N. Pandero will be unavailable from 28th Oct to 8th Nov & 18th Nov to 29th Nov.
Preferred dates and degree of flexibility
Preferred dates: (03-12-2019 to 19-12-2019)