Steady improved confinement in FTU high field plasmas sustained by deep pellet injection

Frigione, D.; Giovannozzi, E.; Gormezano, C.; Poli, F. M.; Romanelli, M.; Tudisco, O.; Crisanti, F.; Esposito, B.; Gabellieri, L.; Garzotti, L.; Leigheb, M.; Pacella, D.; Alladio, F.; Angelini, B.; Apicella, M. L.; Apruzzese, G.; Barbato, Emanuele; Bertalot, L.; Bertocchi, A.; Bracco, G.; Buceti, G.; Buratti, P.; Cardinali, A.; Cascino, S.; Castaldo, C.; Centioli, C.; Cesario, R.; Chuilon, P.; Cocilovo, V.; Angelis, R. De; Benedetti, Miriam; Marco, F. De; Gatti, G.; Gravanti, F.; Grolli, M.; Iannone, F.; Kroegler, H.; Maddaluno, G.; Maffia, G.; Marinucci, M.; Mazzitelli, G.; Micozzi, P.; Mirizzi, F.; Panaccione, L.; Panella, M.; Papitto, P.; Pericoli‐Ridolfini, V.; Petrov, A. A.; Pieroni, L.; Podda, S.; Pulcella, G.; Ravera, G.; Righetti, Giulia; Romanelli, Francesco; Santini, F.; Sassi, Mohamed; Segrè, S. E.; Smeulders, P.; Stermini, E.; Tartoni, N.; Tilia, B.; Trevisanutto, Paolo E.; Tuccillo, A. A.; Vitale, V.; Vlad, G.; Vershkov, V.A.; Zanza, V.; Zerbini, M.; Zonca, F.

doi:10.1088/0029-5515/41/11/310

Cited by 24 publications

(13 citation statements)

References 8 publications

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“…Figure 1 highlights that in LLL-FTU plasmas the core electron density increases together with the amount of injected gas, resulting in the peaking of the electron density profile. The density peaking factor 5 achieved in these discharges is around 2 which is similar to those obtained in FTU pellet injection experiments [15,16]. In [16] it was shown that pellet injected discharges reaching densities above the threshold for the saturated ohmic confinement (SOC) scaling were recovering the Neo-Alcator scaling with density.…”

Section: Lll-ftu Reference Dischargesupporting

confidence: 80%

Linear microstability analysis of a low-Z impurity doped tokamak plasma

Romanelli¹,

Szepesi²,

Peeters³

et al. 2011

Nucl. Fusion

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Improved electron and deuterium energy and particle confinement in the presence of low-Z impurities have been observed in many tokamaks under various experimental conditions. Peaked electron density profiles have been obtained in the Frascati Tokamak Upgrade (FTU) ohmic plasmas where a high concentration of lithium has been detected following the installation of a Liquid Lithium Limiter (LLL). This paper presents the results of a gyrokinetic study on the effects of lithium and other low-Z impurities on the linear stability of deuterium and electron temperature driven modes and their associated fluxes for plasma parameters such as those found in the core of LLL-FTU plasmas. Simulations show that a lithium concentration in excess of n Li/n e = 15%, as estimated in the initial phase of a reference FTU discharge, is found to have a strong stabilizing effect on the TEM and high-frequency ETG modes. A significant stabilization of the electron driven modes can still be observed when the lithium concentration is reduced to 3%. In the presence of a significant impurity concentration (n Li/n e = 3–15%) the long wavelength ITG modes drive an inward electron and deuterium flux and outward lithium flux. This process may lead eventually to an increased electron and deuterium density peaking and a reduced Z eff (lithium density below n Li/n e = 1%).

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Section: Lll-ftu Reference Dischargesupporting

confidence: 80%

Linear microstability analysis of a low-Z impurity doped tokamak plasma

Romanelli¹,

Szepesi²,

Peeters³

et al. 2011

Nucl. Fusion

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“…The injection of solid pellets of frozen fuel in a wide velocity range (50-3000 m s −1 ) has proven to be an efficient method for raising the density of tokamak plasmas. The peaked density profiles thus obtained are often associated with improved core energy confinement, which has been observed on several machines [1][2][3][4][5][6]. In general, the particle deposition due to the pellet injection has a combined effect both on the electron density and on the plasma current density profile.…”

Section: Introductionmentioning

confidence: 91%

Pellet injection and high density ITB formation in JET advanced tokamak plasmas

et al. 2007

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High density Internal Transport Barriers (ITB) with peaked density profiles have been produced at JET by optimising the pellet fuelling, heating power, current drive and plasma start-up. The scenario was developed with moderate momentum input and comparable ion and electron temperatures. Both features aim at matching the conditions envisaged for a burning plasma regime. Current and density profiles, which both appear to influence transport barrier formation, were independently controlled. The optimisation recipe included early Lower Hybrid Current Drive (LHCD) followed by an Ohmic or Neutral Beam heated pellet fuelling gap. The internal transport barrier was then formed at the start of a high power additionally heated phase. Typical plasmas were at a toroidal field of 3T and plasma current of 2MA, corresponding to a peripheral safety factor q 95 ≈5. Particle and energy transport were analysed by a 1.5 dimensional code including a pellet ablation module and a criterion for the barrier formation. Results of turbulence simulations with global electrostatic and electromagnetic fluid codes and a description of the observed magnetohydrodynamic instabilities are also reported.

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“…Two pellet injectors are currently available on FTU: a horizontal injector for low-field side fuelling, shooting 3 mm in diameter cylindrical deuterium pellets (10 21 particles) at a maximum speed of 1.3 km s −1 , and a vertical injector located at the same toroidal position injecting deuterium pellets of the same size from the high-field side and at a reduced speed of 500 m s −1 . Pellet penetration depends on the temperature of the target: in the experiments analysed here pellets have been injected on plasma targets with a central temperature in the range 1.5-2.0 keV and the ablation is found to occur at about one-third of the plasma minor radius [4,5] (r/a ∼ 0.3, which in these plasmas corresponds approximately to the position of the q = 1 resonant surface). Pellet-fuelled discharges, which exhibit enhanced confinement above the ITER97-L scaling, qualitatively recover the linear dependence of τ E on the lineaveraged density (neo-Alcator type scaling τ E = kn e q 1.42 , and k = 7.1); this effect was also shown in [3] with the inclusion of post-pellet enhanced τ E in discharges at various currents.…”

Section: Confinement In Gas-fuelled and Pellet-fuelled Ohmic Dischargesmentioning

confidence: 99%

Confinement and turbulence study in the Frascati Tokamak Upgrade high field and high density plasmas

et al. 2006

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The Frascati Tokamak Upgrade (FTU) is a high field and high density device which allows one to study confinement and transport at plasma parameters generally not accessible to other tokamaks and is relevant to next generation experiments (ITER). In this paper we study the effect of different density, temperature and q profiles on confinement and transport in various types of plasmas including ohmic, externally heated and pellet-fuelled discharges. Peaking of the electron density profile in pellet-fuelled discharges has been found to enhance the energy confinement time on FTU to values as high as 120 ms at densities of the order of those expected in ITER. Experiments designed to further improve confinement by injecting pellets at higher densities show the existence of a second threshold for saturation of confinement when the local electron heat conductivity corresponds to the same order of the local ion neoclassical conductivity in the region of maximum temperature gradient. Reflectometry measurements show turbulence suppression in pellet-injected discharges (as predicted by microstability analysis) and give insights to the change in turbulence in electron internal transport barrier plasmas. Finally, particle transport has been studied in experiments with full LH current drive.

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Steady improved confinement in FTU high field plasmas sustained by deep pellet injection

Cited by 24 publications

References 8 publications

Linear microstability analysis of a low-Z impurity doped tokamak plasma

Linear microstability analysis of a low-Z impurity doped tokamak plasma

Pellet injection and high density ITB formation in JET advanced tokamak plasmas

Confinement and turbulence study in the Frascati Tokamak Upgrade high field and high density plasmas

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