In this paper we investigate non-complete Sawtooth reconnection in ASDEX Upgrade tokamak.Such reconnection phenomena are associated with internal m/n=1/1 kink mode which does not vanish after the crash phase (as would be the case for complete reconnection). It is shown that this sawtooth can not be fully described by pure m/n=1/1 mode and that higher harmonics play an important role during the Sawtooth crash phase. We employ the Hamiltonian formalism and reconstructed perturbations to model incomplete Sawtooth reconnection. It is demonstrated that stochastization appears due to excitation of low-order resonances which are present in the corresponding q-profiles inside the 1 q = surface which reflects the key role of the 0 q value.Depending on this value two completely different situations are possible for one and the same mode perturbations: (i) the resonant surfaces are present in q-profile leading to stochasticity and sawtooth crash ( 0 0.7 0.1 q ≈ ± ); (ii) the resonant surfaces are not present which means no stochasticity in the system and no crash event ( 0 0.9 0.05 q ≈ ± ). Accordingly central safety factor value is always less than unity in case of non-complete sawtooth reconnection. Our investigations show that stochastic model agrees well with experimental observations and can be proposed as a promising candidate for explanation of the sawtooth reconnection.
High rotational states of pile and pLi atoms with one or two electrons are calculated in the Born-Oppenheimer approximation, with a precision which allows a systematic study of diabatic effects. The lifetimes of the relevant pea and peeLi states are in the gs range.
Igochine, V.; Boom, J.E.; Classen, I.G.J.; Dumbrajs, O.; Günter, S.; Lackner, K.; Pereverzev, G.; Zohm, H. Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers)Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. The crash phase of the sawteeth in ASDEX Upgrade tokamak ͓Herrmann et al., Fusion Sci. Technol. 44͑3͒, 569 ͑2003͔͒ is investigated in detail in this paper by means of soft x-ray ͑SXR͒ and electron cyclotron emission ͑ECE͒ diagnostics. Analysis of precursor and postcursor ͑1,1͒ modes shows that the crash does not affect the position of the resonant surface q = 1. Our experimental results suggest that sawtooth crash models should contain two ingredients to be consistent with experimental observations: ͑1͒ the ͑1,1͒ mode structure should survive the crash and ͑2͒ the flux changes should be small to preserve the position of the q = 1 surface close to its original location. Detailed structure of the reconnection point was investigated with ECE imaging diagnostic. It is shown that reconnection starts locally. The expelled core is hot which is consistent with SXR tomography results. The observed results can be explained in the framework of a stochastic model.
Electron transport coefficients have been determined in the W7-AS stellarator. The diffusion and convection coefficients were obtained by modulating the gas feed into the plasma and by measuring the propagation of the density perturbation. The experiments were carried out at a variety of plasma densities, heating powers and magnetic fields. The results are summarized in the form of a scaling expression for the diffusion coefficient. Transient inward convection was found in the boundary plasma. This convection plays a minor role in the core plasma except with higher heating power, where outward convection was observed. The results are compared with earlier W7-AS transport results.
The onset of stochastic oscillations in gyrotrons is studied by means of the self-consistent theory describing nonstationary processes. Complicated alternating sequences of regions of stationary, automodulation, and chaotic oscillations are found in the plane of the generalized gyrotron variables: cyclotron resonance mismatch and dimensionless current. The results of the investigations are important in connection with attempts to increase the output power of gyrotrons by raising the current.
The role of stochastization of magnetic field lines is analyzed in fast reconnection phenomena occurring in magnetized fusion plasma during various conditions in the ASDEX Upgrade tokamak. The mapping technique is applied to trace the field lines of toroidally confined plasma where perturbation parameters are expressed in terms of experimental perturbation amplitudes determined from the ASDEX Upgrade tokamak. It is found that fast reconnection observed during amplitude drops of the neoclassical tearing mode instability in the frequently interrupted regime can be related to stochastization. It is also shown that stochastization can explain the fast loss of confinement during the minor disruption. This demonstrates that stochastization can be regarded as a possible cause for different MHD events in ASDEX Upgrade.
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