Measurement and analysis of<i>Z</i><sub>eff</sub>in EAST tokamak

Chen, Yingjie; Wu, Zhenwei; Gao, Wei; Zhang, Ling; Jie, Yinxian; Zhang, Jizong; Zang, Qing; Huang, Juan; Zuo, Guizhong; Zhao, Junyu

doi:10.1088/0741-3335/56/10/105006

Cited by 27 publications

(15 citation statements)

References 39 publications

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“…(H or D as main ion, so Z i =1), which models the generally observed decreasing trend with density [34]. The constant ζ mostly depends on the wall conditions for an ohmic device.…”

Section: Tokamak and Rfpmentioning

confidence: 74%

“…The FTU geometry (a=0.28m, R 0 =0.935m), and Ψ tok =1.9, h AUX =0, are then set in (14). A constant radial profile is taken for Z eff (apart the very edge where the measurement is less reliable, reconstructions in different devices both tokamak, stellarator and RFP support this assumption [32][33][34][35][36]), alongside the scaling As far as DL in auxiliary heated tokamak is concerned, NBI-heated L-mode discharges performed in Textor-94 support a Greenwald-scaling modified by the additional dependence P tot 0.44 for both edge and line-average densities [37]. Given the nearly identical exponent for P tot predicted by (14) (h AUX =1), the present model seems compatible with these results, even though a more detailed comparison is prevented by the lack of information on the current drive and P Ohm in [37].…”

Section: )mentioning

confidence: 99%

Section: Tokamak and Rfpmentioning

confidence: 99%

“…( 2) We take a radially constant Z eff : Z eff (0) = Z eff,* = Z eff . Apart the very edge where the estimate is less reliable, reconstructions in different devices, either tokamak, stellarator or RFP [33][34][35][36][37], do not evidence strong radial variations for this quantity. Therefore, one gets:…”

Section: Comparison With Tokamak and Rfp Experimentsmentioning

confidence: 99%

“…According to analyses made on EAST [35], for pure ohmic heating ζ is a constant depending on the wall conditions only. Use of ( 20) is justified, since the FTU experiments realized a significant variation of n e in clean machine conditions.…”

Section: Ftu Ohmic Experimentsmentioning

confidence: 99%

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A unified model of density limit in fusion plasmas

et al. 2017

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A limit for the edge density, ruled by radiation losses from light impurities, is established by a minimal cylindrical magneto-thermal equilibrium model. For ohmic tokamak and reversed field pinch the limit scales linearly with the plasma current, as the empirical Greenwald limit. The auxiliary heating adds a further dependence, scaling with the 0.4 power, in agreement with Lmode tokamak experiments. For a pure externally heated configuration the limit takes on a Sudolike form, depending mainly on the input power, and is compatible with recent Stellarator scalings.A discharge-terminating density limit (DL) is found in all the magnetic confinement fusion devices [1]. One of the main interpretative branches invokes impurity radiation losses, which scale with the square of the density. The consequent cooling of the plasma can become critical at high density, giving rise to a variety of instabilities, both thermal [2][3][4][5][6][7][8], and MHD [9][10][11][12][13]. Given the rich phenomenology, DL seems elusive of an explanation based on a single mechanism. This letter presents a complementary approach to the problem, analysing, in cylindrical geometry, the feasibility of a magneto-thermal equilibrium with realistic temperature profile, rather than addressing specific instabilities. Such a study provides a unified interpretation of the phenomenon, given that a DL ruled by light impurities radiation (experiments show that any significant contamination by heavy impurities is just detrimental towards the achievement of high densities [1]), quantitatively consistent with experimental scalings, emerges naturally for all the magnetic configurations. In particular, we found a Greenwald-like scaling [1] for tokamak and reversed field pinch (RFP), and a Sudo-like scaling [14,15] for a pure externally heated configuration, taken as approximation of the stellarator. We are aware that this analysis cannot 2 exhaust the topic, since some instability mechanism is necessary to describe the dynamical route to the plasma termination. Consequently, we speak of an 'equilibrium DL' and not of the DL in the ultimate sense. This work has been inspired by analyses of the ohmic tokamak presented in[16] (section 7.8) and in [17] (section 8). The differences rely in a more general approach, besides a more accurate treatment of the profile dependent terms.We introduce a minimal cylindrical equilibrium model (each quantity depending on the radial coordinate r only), analytically treated with a formalism able to unify the configurations with an applied electric field, namely the tokamak, both ohmic and with additional heating, and the RFP, considered as purely ohmic. Basically, we will take integral relations from the heat transport equation, in some way similar to those carried out in [18] apart for the simpler geometry, and combine them with Ohm's law at r=0 (on-axis). Ohm's law is replaced by a suitable scaling for the energy confinement time in the case of pure auxiliary heating. [ ]Here, T is the electron temperature and K an effec...

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“…(H or D as main ion, so Z i =1), which models the generally observed decreasing trend with density [34]. The constant ζ mostly depends on the wall conditions for an ohmic device.…”

Section: Tokamak and Rfpmentioning

confidence: 74%