Plasma edge density and lower hybrid current drive in JET (Joint European Torus)

Cesario, R.; Amicucci, L.; Castaldo, C.; Kempenaars, M.; Jachmich, S.; Mailloux, J.; Tudisco, O.; Galli, Alessandro; Křivská, A.; Contributors, Jet‐Efda

doi:10.1088/0741-3335/53/8/085011

Cited by 59 publications

(63 citation statements)

References 23 publications

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“…Indeed, these eff ects (of the order of 1 % ) are generally insuffi cient to explain the observed lack of LH power penetration in JET, in which the much higher core electron temperature ( T e0 ≈ 6 keV), compared with that in FTU, results in LH power that is mostly deposited during the fi rst radial pass 13,15 . It is more likely in both cases that the PI produces strong single-pass wave damping at the edge, thus having a dominant role 15 .…”

Section: Discussionmentioning

confidence: 99%

“…In ITER, useful conditions should be produced to avoid the launched n Խ Խ spectrum from being strongly broadened as it propagates through the cold layer of the plasma edge, which would prevent the LH wave penetration into the plasma core 35 . Recent experiments at JET indicate that this undesirable condition can actually occur 15 , but the related FTU results show how the problem can be solved.…”

Section: Discussionmentioning

confidence: 99%

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Current drive at plasma densities required for thermonuclear reactors

Cesario¹,

Amicucci²,

Cardinali³

et al. 2010

Nat Commun

135

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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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Current drive at plasma densities required for thermonuclear reactors

Cesario¹,

Amicucci²,

Cardinali³

et al. 2010

Nat Commun

135

140

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show abstract

“…Regardless of the coupling types, ion cyclotron parametric decay is found to be dominant over ion sound parametric decay in C-Mod edge plasmas due to relatively higher edge density as compared to other tokamaks such as FTU [9] and JET [17]. Figure 6(a) shows the homogeneous growth rate (γ) as a function of the normalized real frequency of the ion mode (ω/ω ci ) at the LFS based on measured density and temperature profiles of high density USN plasmas ( Figure 5 (a)) when θ = 90 • .…”

Section: Experimental Results and Pdi Analysismentioning

confidence: 95%

Characterization of onset of parametric decay instability of lower hybrid waves

Baek

Bonoli

Parker

et al. 2014

AIP Conference Proceedings

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Abstract. The goal of the lower hybrid current drive (LHCD) program on Alcator C-Mod is to develop and optimize ITERrelevant steady-state plasmas by controlling the current density profile. Using a 4x16 waveguide array, over 1 MW of LH power at 4.6 GHz has been successfully coupled to the plasmas. However, current drive efficiency precipitously drops as the line averaged density (n e ) increases above 10 20 m −3 . Previous numerical work shows that the observed loss of current drive efficiency in high density plasmas stems from the interactions of LH waves with edge/scrape-off layer (SOL) plasmas [Wallace et al., Physics of Plasmas 19, 062505 (2012)]. Recent observations of parametric decay instability (PDI) suggest that non-linear effects should be also taken into account to fully characterize the parasitic loss mechanisms [Baek et al., Plasma Phys. Control Fusion 55, 052001 (2013)]. In particular, magnetic configuration dependent ion cyclotron PDIs are observed using the probes near n e ≈ 1.2 × 10 20 m −3 . In upper single null plasmas, ion cyclotron PDI is excited near the low field side separatrix with no apparent indications of pump depletion. The observed ion cyclotron PDI becomes weaker in inner wall limited plasmas, which exhibit enhanced current drive effects. In lower single null plasmas, the dominant ion cyclotron PDI is excited near the high field side (HFS) separatrix. In this case, the onset of PDI is correlated with the decrease in pump power, indicating that pump wave power propagates to the HFS and is absorbed locally near the HFS separatrix. Comparing the observed spectra with the homogeneous growth rate calculation indicates that the observed ion cyclotron instability is excited near the plasma periphery. The incident pump power density is high enough to overcome the collisional homogeneous threshold. For C-Mod plasma parameters, the growth rate of ion sound quasi-modes is found to be typically smaller by an order of magnitude than that of ion cyclotron quasi-modes. When considering the convective threshold near the plasma edge, convective growth due to parallel coupling rather than perpendicular coupling is likely to be responsible for the observed strength of the sidebands.To demonstrate the improved LHCD efficiency in high density plasmas, an additional launcher has been designed. In conjunction with the existing launcher, this new launcher will allow access to an ITER-like high single pass absorption regime, replicating the J LH (r) expected in ITER. The predictions from the time domain discharge scenarios, in which the two launchers are used, will be also presented.

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“…Recent high density experiments on FTU have shown that LH wave's efficiency is recovered and measured spectral broadening of launched wave reduced, by increasing peripheral temperature 11 as expected by the theory that predicts a reduced effect of parametric instability. 25 Different mechanisms can concur in preventing LH wave penetration at high density, for example, collisional absorption (CA), 26 PI, 11,25,27 scattering from density fluctuations (SDF), [28][29][30] and so on. The broadening of the LH power spectra 31 vs. the parallel refractive index N//, produced by PI, results in spurious LH power absorption at the edge, via Landau damping.…”

Section: Optimization Of Lhcd In Eastmentioning

confidence: 99%

Lower hybrid current drive and ion cyclotron range of frequencies heating experiments in H-mode plasmas in Experimental Advanced Superconducting Tokomak

et al. 2014

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An ion cyclotron range of frequencies (ICRF) system with power up to 6.0 MW and a lower hybrid current drive (LHCD) system up to 4 MW have been applied for heating and current drive experiments in Experimental Advanced Superconducting Tokomak (EAST). Significant progress has been made with ICRF heating and LHCD for realizing the H-mode plasma operation in EAST. During 2010 and 2012 experimental campaigns, ICRF heating experiments were carried out at the fixed frequency of 27MHz, achieving effective ions and electrons heating with the H minority heating (H-MH) mode. The H-MH mode produced good plasma performance, and realized H-mode using ICRF power alone in 2012. In 2010, H-modes were generated and sustained by LHCD alone, where lithium coating and gas puffing near the mouth of the LH launcher were applied to improve the LHCD power coupling and penetration into the core plasmas of H-modes. In 2012, the combination of LHCD and ICRH power extended the H-mode duration up to over 30 s. H-modes with various types of edge localized modes (ELMs) have been achieved with HIPB98(y, 2) ranging from 0.7 to over unity. A brief overview of LHCD and ICRF Heating experiment and their application in achieving H-mode operation during these two campaigns will be presented.

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Plasma edge density and lower hybrid current drive in JET (Joint European Torus)

Cited by 59 publications

References 23 publications

Current drive at plasma densities required for thermonuclear reactors

Current drive at plasma densities required for thermonuclear reactors

Characterization of onset of parametric decay instability of lower hybrid waves

Lower hybrid current drive and ion cyclotron range of frequencies heating experiments in H-mode plasmas in Experimental Advanced Superconducting Tokomak

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