Transient transport phenomena induced by cold pulses in W7-AS

Walter, H.; Stroth, U.; Bleuel, J.; Burhenn, R.; Geist, T.; Giannone, L.; Hartfuß, H. J.; Koponen, J.; Ledl, L.; Pereverzev, G.; Team, W As

doi:10.1088/0741-3335/40/9/009

Cited by 17 publications

(9 citation statements)

References 8 publications

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“…The similarities in the nonlocal T e rise between tokamaks and LHD may suggest that the sign of the magnetic shear does not play an important role in this phenomenon. It must be noted here that the comparison between LHD and Wendelstein 7-AS ͑W7-AS͒ stellarator, in which the nonlocal T e rise has not been observed, 14 indicates that the magnetic shear itself and/or the existence of the rational values of the rotational transform at the plasma edge could be a crucial part of the nonlocal T e rise. Further investigation on this matter will be performed on LHD.…”

Section: -3mentioning

confidence: 72%

Observation of core electron temperature rise in response to an edge cooling in toroidal helical plasmas

et al. 2005

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The first observation of a significant rise of core electron temperature in response to edge cooling in a helical plasma has been made on the Large Helical Device ͓O. Motojima et al., Phys. Plasmas 6, 1843 ͑1999͔͒. When the phenomenon occurs, the electron heat diffusivity in the core region is reduced abruptly without changing local parameters in the region of interest. Therefore the phenomenon can be regarded as a so-called "nonlocal" electron temperature rise observed so far only in many tokamaks. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.2131047͔The clarification of electron heat transport in magnetically confined plasmas is still an important issue, since the performance of a probable fusion reactor should be determined by electron heating as a result of the interaction between electrons and alpha particles as a fusion reaction product. In order to promote a better understanding of the electron heat transport, the electron heat transport analysis for both transient and steady state has been carried out diligently in many tokamaks 1-3 and helical systems. [4][5][6] One of the significant issues found in these studies is a "nonlocal transport phenomenon" observed in perturbation experiments on many tokamaks 7-12 and a few helical systems. 4 In particular, a rise of the core electron temperature T e invoked by the rapid cooling of the edge plasma has been observed in various tokamaks with both ohmically heated plasmas and plasmas with an auxiliary heating, such as electron cyclotron heating ͑ECH͒, at a sufficiently low density ͑e.g., Ref. 13͒. The amplitude reversal of the cold pulse propagation in the core plasma cannot be explained even by the model based on the assumption that heat flux has a strong nonlinear dependence on temperature and its gradient. In addition there seem to be no changes in the thermodynamic forces, such as those due to the temperature gradient and/or the density gradient, in the core plasma at the onset of the core T e rise. Consequently, the core T e rise invoked by the edge cooling is considered to result from a nonlocality in the electron heat transport. On the contrary, such a core T e rise in response to the edge cooling has not been observed so far in helical systems.14 Recently, to rationalize the so-called "nonlocal" T e rise, some physics-based transport models including a critical gradient scale length, such as the ion temperature gradient ͑ITG͒ model, have been set up and tested.2,15 It should be noted that despite being dependent on local variables, the ITG-based model shows a nonlocal response to small changes in the profiles as a result of a slight deviation from near marginality. The ITG-based model with strongest stiffness 16 can reproduce some of the same qualitative characteristics observed in carbon laser blow-off experiments in the Texas Experimental Tokamak ͑TEXT͒.13 The magnitude and response time of the core T e rise, however, are still in quantitative disagreement with those predicted by the strongest stiff ITG-based model. 15 Moreover, it is an open ...

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Section: -3mentioning

confidence: 72%

Observation of core electron temperature rise in response to an edge cooling in toroidal helical plasmas

et al. 2005

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“…Figure 5 The similarities in the nonlocal T e rise between tokamaks and LHD suggest that the sign of the magnetic shear does not play an important role in this phenomenon. The core T e rise in response to the edge cooling has not been observed in the lowshear W7-AS stellarator [35], which allows the exclusion of rational values of the rotational transform at the plasma edge. Thus the comparison between LHD and W7-AS indicates that the magnetic shear itself and/or the existence of the rational values of the rotational transform at the edge region could be a crucial part of the nonlocal T e rise.…”

Section: Characteristics Of Nonlocal T E Rise In Lhd Plasmasmentioning

confidence: 97%

Impact of nonlocal electron heat transport on the high temperature plasmas of LHD

et al. 2007

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Edge cooling experiments with a tracer-encapsulated solid pellet in the Large Helical Device (LHD) show a significant rise of core electron temperature (the maximum rise is around 1 keV) as well as in many tokamaks. This experimental result indicates the possible presence of the nonlocality of electron heat transport in plasmas where turbulence as a cause of anomalous transport is dominated. The nonlocal electron temperature rise in the LHD takes place in almost the same parametric domain (e.g. in a low density) as in the tokamaks. Meanwhile, the experimental results of LHD show some new aspects of nonlocal electron temperature rise, for example the delay of the nonlocal rise of core electron temperature relative to the pellet penetration time increases with the increase in collisionality in the core plasma and the decrease in electron temperature gradient scale length in the outer region of the plasma.

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“…In addition to impurity transport, preliminary measurements of heat transport of the LBI cold pulse are presented. The study of cold pulse propagation, using either laser blow-off or pellet injection, has shown that electron energy transport has a localized character in the W7-AS stellarator [6] and the RFP reversed-pinch [7], which is in contrast to the LHD stellarator [8] and to tokamaks such as TEXT [9] and JET [10] which exhibit non-local behaviours. In the TJ-II cold pulse propagation was previously studied using nitrogen puffing [11].…”

Section: Introductionmentioning

confidence: 99%

Transport studies using laser blow-off injection of low-Z trace impurities injected into the TJ-II stellarator

Zurro¹,

Hollmann

Baciero³

et al. 2011

Nucl. Fusion

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Laser blow-off of low-Z (boron and carbon) material is used to study parallel and radial impurity ion transport, as well as radial heat transport, in the TJ-II stellarator. Toroidal transport is found to be, consistent with entrainment in edge toroidal rotation. Radial/poloidal transport and loss to the plasma edge is seen to be slower (about 5 ms) and is clearly seen to be slower for carbon than for boron, consistent with collisional (neoclassical) cross-field transport. Radial heat transport is observed to be quite rapid (0.1 ms time scale).

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Transient transport phenomena induced by cold pulses in W7-AS

Cited by 17 publications

References 8 publications

Observation of core electron temperature rise in response to an edge cooling in toroidal helical plasmas

Observation of core electron temperature rise in response to an edge cooling in toroidal helical plasmas

Impact of nonlocal electron heat transport on the high temperature plasmas of LHD

Transport studies using laser blow-off injection of low-Z trace impurities injected into the TJ-II stellarator

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