High Plasma Density Lower-Hybrid Current Drive in the FTU Tokamak

Pericoli‐Ridolfini, V.; Barbato, Emanuele; Cirant, S.; Kroegler, H.; Panaccione, L.; Podda, S.; Alladio, F.; Angelini, B.; Apicella, M. L.; Apruzzese, G.; Bertalot, L.; Bertocchi, A.; Borra, M.; Bracco, G.; Bruschi, A.; Buceti, G.; Buratti, P.; Cardinali, A.; Centioli, C.; Cesario, R.; Ciattaglia, S.; Cocilovo, V.; Crisanti, F.; Angelis, R. De; Marco, F. De; Esposito, B.; Frigione, D.; Gabellieri, L.; Gatti, G.; Giovannozzi, E.; Gourlan, C.; Granucci, G.; Gravanti, F.; Grolli, M.; Imparato, A.; Leigheb, M.; Lovisetto, L.; Maffia, G.; Maddaluno, G.; Marinucci, M.; Mazzitelli, G.; Micozzi, P.; Mirizzi, F.; Nowak, S.; Orsitto, F.; Pacella, D.; Panella, M.; Pieroni, L.; Righetti, Giulia; Romanelli, Francesco; Santini, F.; Sassi, Mohamed; Segrè, S. E.; Simonetto, A.; Sozzi, C.; Sternini, E.; Tudisco, O.; Vitale, V.; Vlad, G.; Tartoni, N.; Tilia, B.; Tuccillo, A. A.; Zanza, V.; Zerbini, M.; Zonca, F.

doi:10.1103/physrevlett.82.93

Cited by 51 publications

(16 citation statements)

References 16 publications

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“…In the Joint European Torus (JET), signatures of LH wave penetration into the plasma core disappear at plasma edge densities in the range of n e_0.8 ≈ 0.3 × 10 20 m − 3 (and n e0 ≈ 0.5 × 10 20 m − 3 ), signifi cantly lower than those necessary for ITER 13 -15 . In previous experiments at Frascati Tokamak Upgrade (FTU) 23 , LH wave penetration occurred only up to a line-averaged density of n e_av ≈ 1.3 × 10 20 m − 3 and edge density of n e_0.8 ≈ 0.4 × 10 20 m − 3 , still too low to be ITER relevant 24 . Similarly, in Alcator C-Mod, the LHCD was not seen at n e_av ≥ 1.5 × 10 20 m − 3 and was weaker than expected at n e_av ≥ 0.8 -1.0 × 10 20 m − 3 (depending on the choice of other plasma parameters) 14 .…”

mentioning

confidence: 99%

Current drive at plasma densities required for thermonuclear reactors

Cesario¹,

Amicucci²,

Cardinali³

et al. 2010

Nat Commun

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136

140

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Progress in thermonuclear fusion energy research based on deuterium plasmas magnetically confi ned in toroidal tokamak devices requires the development of effi cient current drive methods. Previous experiments have shown that plasma current can be driven effectively by externally launched radio frequency power coupled to lower hybrid plasma waves. However, at the high plasma densities required for fusion power plants, the coupled radio frequency power does not penetrate into the plasma core, possibly because of strong wave interactions with the plasma edge. Here we show experiments performed on FTU (Frascati Tokamak Upgrade) based on theoretical predictions that nonlinear interactions diminish when the peripheral plasma electron temperature is high, allowing signifi cant wave penetration at high density. The results show that the coupled radio frequency power can penetrate into high-density plasmas due to weaker plasma edge effects, thus extending the effective range of lower hybrid current drive towards the domain relevant for fusion reactors.

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mentioning

confidence: 99%

Current drive at plasma densities required for thermonuclear reactors

Cesario¹,

Amicucci²,

Cardinali³

et al. 2010

Nat Commun

Self Cite

136

140

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show abstract

“…Prior investigation of LHCD at such high densities was conducted in circular, limited tokamaks such as Alcator C [24] and FTU [25,18,19]. Although the experiments on C-Mod show no dependence on elongation, the difference between limited and diverted plasmas is significant and this may explain the unexpectedly low density limit encountered for diverted discharges in C-Mod.…”

Section: Discussionmentioning

confidence: 92%

“…These results show a clear difference in the phenomenology of LHCD as a function of density between diverted and limited configurations. Prior investigation of LHCD at such high densities was conducted in circular, limited tokamaks such as Alcator C [24] and FTU [19,20,25]. Although the experiments on C-Mod show no dependence on elongation, the difference between limited and diverted plasmas is significant and this may explain the unexpectedly small fast electron population at high density for diverted discharges in C-Mod.…”

Section: Discussionmentioning

confidence: 99%

Lower hybrid current drive at high density in Alcator C-Mod

et al. 2011

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Abstract. Experimental observations of lower hybrid current drive (LHCD) at high density on the Alcator C-Mod tokamak are presented in this paper. Bremsstrahlung emission from relativistic fast electrons in the core plasma drops suddenly above line averaged densities of 10 20 m −3 (ω/ω LH ∼ 3) in single null discharges with large (> 10 mm) plasma-inner wall gaps, well below the density limit previously observed on limited tokamaks (ω/ω LH ∼ 2). Modeling and experimental evidence suggest that the absence of LHCD driven fast electrons at high density may be due to parasitic collisional absorption in the scrape off layer. Experiments show that the population of fast electrons produced by LHCD at high density (n e > 10 20 m −3 ) can be increased significantly by operating with a plasma-inner wall gap of less than ∼ 5 mm with the strongest non-thermal emission in inner-wall limited plasmas. A change in plasma topology from single to double null produces a modest increase in non-thermal emission at high density. Increasing the electron temperature in the periphery of the plasma (0.8 > r/a > 1.0) also results in a modest increase in non-thermal electron emission above the density limit. Ray tracing/Fokker-Planck simulations of these discharges predict the observed sensitivity to plasma position when the effects of collisional absorption in the SOL are included in the model.

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“…The value of n ||crit is evaluated based on the line averaged density and on axis magnetic field. According to results from FTU [13], accessibility should only be an issue…”

Section: A Hard X-ray Bremsstrahlungmentioning

confidence: 99%

Absorption of lower hybrid waves in the scrape off layer of a diverted tokamak

Wallace¹,

Parker²,

Bonoli³

et al. 2010

Physics of Plasmas

131

126

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The goal of the Lower Hybrid Current Drive (LHCD) system on the Alcator C-Mod tokamak is to investigate current profile control under plasma conditions relevant to future devices such as ITER and DEMO. Experimental observations of an LHCD "density limit" for C-Mod are presented in this paper. Bremsstrahlung emission from relativistic fast electrons in the core plasma drops suddenly above line averaged densities of 10 20 m −3 (ω/ω LH ∼3-4), well below the density limit previously observed on other experiments (ω/ω LH ∼ 2). Electric currents flowing through the scrape off layer (SOL) between the inner and outer divertors increase dramatically across the same density range that the core bremsstrahlung emission drops precipitously. These experimental x-ray data are compared to both conventional modeling, which gives poor agreement with experiment above the density limit, and a model including collisional absorption in the SOL, which dramatically improves agreement with experiment above the observed density limit. These results show that strong absorption of LH waves in the SOL is possible on a high density tokamak and the SOL must be included in simulations of LHCD at high density.

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High Plasma Density Lower-Hybrid Current Drive in the FTU Tokamak

Cited by 51 publications

References 16 publications

Current drive at plasma densities required for thermonuclear reactors

Current drive at plasma densities required for thermonuclear reactors

Lower hybrid current drive at high density in Alcator C-Mod

Absorption of lower hybrid waves in the scrape off layer of a diverted tokamak

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