Cold pulse inversion in a helical plasma is observed in the Large Helical Device (LHD) and thus the strong non-local effects are evident in the helical device as well as in tokamaks. A hydrogen pellet or tracer encapsulated solid pellet is injected into the edge of the LHD plasmas. A significant rise of the electron temperature is observed in the central region in response to the edge cooling. Transient analysis indicates a heat flux jump despite the absence of a change in the local temperature gradient. The non-local temperature rise takes place in the low density and high temperature regime just as predicted by the TFTR scaling.

Astract. The change in thermal transport aaoss the L + H transition is studied in detail for those JET high performance H-modes which have a very fast transftion. It is found that in these pulses the transport changes very rapidly (< 4 msecs) over a very large radial region 0.5 < p < 1, and a very large transport barrier is formed. The reasons for the formation of this barrier are discussed.

New features of the space-time evolution of the internal transport barrier (ITB) were highlighted during recent JT-60U reverse shear (RS) experiments. An ITB evolution in RS plasmas is often a combination of the fast time-scale processes and the gradual ones. Fast time-scale processes are the common intrinsic features of JT-60U RS plasmas and are seen as the simultaneous (within a few milliseconds) rise and decay of electron temperature (T e ) on two zones separated by a region without variation of T e . The region without variation of T e is located near the position of the minimum safety factor profile (q min ) for many fast processes. The present robust result is that the region of fast-time-scale improvements of electron heat diffusivity is wide in space (around 0.3 of the minor radius) and well extended to the zone of T e decay.

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 ...

Internal transport barrier (ITB) formation in the positive shear zone of reverse shear (RS) plasmas in the JT-60U tokamak is described as a series of ITB events, which are abrupt in time and wide in space variations of heat diffusivity, observed as the simultaneous rise and decay of the electron temperature T e in two zones. A new source of heat pulse propagation (HPP) is found in RS plasmas. HPP is created by an ITB event. For the last ITB event described in the present paper, the region of strong (∼20 keV s −1 ) T e rise is initially well localized (∼4 cm) in space. Later, a slow diffusive broadening of the rising T e perturbation is seen. Outward HPP is analysed in the region with ∼8 cm width fully located in the positive shear space zone. Values of the electron dynamic heat diffusivity as low as ∼0.1 m 2 s −1 are found. A similar low value of the ion dynamic heat diffusivity (close to the neoclassical value) is obtained for ion HPP. An important consequence of HPP analysis is the absence of electron and ion 'heat pinch' in the ITB region.