Escaping and transport barrier due to ergodic magnetic limiters in tokamaks with reversed magnetic shear

Silva, Elton C. da; Roberto, Marisa; Portela, Jefferson S. E.; Caldas, Iberê L.; Viana, Ricardo L.

doi:10.1088/0029-5515/46/4/s11

Cited by 6 publications

(5 citation statements)

References 37 publications

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“…A least square power fit to the results shows that the percentage deviation varies as N −10 p , where k = 2π/N p . From this analysis, we conclude that the average size of magnetic asymmetries introduced by symplectic discretization in the DIII-D map in natural canonical coordinates is extremely fast, σ scales as k 10 . This means that if we choose sufficiently small k (or sufficiently large N p ), the oscillations in the equilibrium poloidal flux (or the noise in the Hamiltonian) can be made considerably small in the DIII-D.…”

Section: Stochastic Broadening From Toroidal Asymmetries Introduced B...mentioning

confidence: 84%

“…The reason for this is that here the new approach is used for the DIII-D, and more details of how the new approach is applied are given, so that if other researchers wish to apply the new approach to the exact magnetic geometries of the ITER [5], the ASDEX UG [6], or other divertor tokamak, they can readily do so. Construction of symplectic mappings for integration of magnetic field lines in tokamaks is an important and active area of present day fusion science research; see [1,[5][6][7][8][9][10][11][12][13][14][15] and [17][18][19][20][21][22][23][24][25][26] in [1].…”

Section: Introductionmentioning

confidence: 99%

“…We repeat this for three different values of k, k = 2π/72, 2π/36 and 2π/18. After each iteration, we calculate the poloidal flux χ n = χ EGF (ψ n , θ n ), using equation (10). The subscript n denotes the iteration of the map.…”

Section: Stochastic Broadening From Toroidal Asymmetries Introduced B...mentioning

confidence: 99%

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An area-preserving mapping in natural canonical coordinates for magnetic field line trajectories in the DIII-D tokamak

Punjabi

2009

Nucl. Fusion

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The new approach of integrating magnetic field line trajectories in natural canonical coordinates (Punjabi and Ali 2008 Phys. Plasmas 15 122502) in divertor tokamaks is used for the DIII-D tokamak (Luxon and Davis1985 Fusion Technol. 8 441). The equilibrium EFIT data (Evans et al 2004 Phys. Rev. Lett. 92 235003, Lao et al 2005 Fusion Sci. Technol. 48 968) for the DIII-D tokamak shot 115467 at 3000 ms is used to construct the equilibrium generating function (EGF) for the DIII-D in natural canonical coordinates. The EGF gives quite an accurate representation of the closed and open equilibrium magnetic surfaces near the separatrix, the separatrix, the position of the X-point and the poloidal magnetic flux inside the ideal separatrix in the DIII-D. The equilibrium safety factor q from the EGF is somewhat smaller than the DIII-D EFIT q profile. The equilibrium safety factor is calculated from EGF as described in the previous paper (Punjabi and Ali 2008 Phys. Plasmas 15 122502). Here the safety factor for the open surfaces in the DIII-D is calculated. A canonical transformation is used to construct a symplectic mapping for magnetic field line trajectories in the DIII-D in natural canonical coordinates. The map is explored in more detail in this work, and is used to calculate field line trajectories in the DIII-D tokamak. The continuous analogue of the map does not distort the DIII-D magnetic surfaces in different toroidal planes between successive iterations of the map. The map parameter k can represent effects of magnetic asymmetries in the DIII-D. These effects in the DIII-D are illustrated. The DIII-D map is then used to calculate stochastic broadening of the ideal separatrix from the topological noise and field errors, the low mn, the high mn and peeling–ballooning magnetic perturbations in the DIII-D. The width of the stochastic layer scales as 1/2 power of amplitude with a maximum deviation of 6% from the Boozer–Rechester scaling (Boozer and Rechester 1978 Phys. Fluids 21 682). The loss of poloidal flux scales linearly with the amplitude of perturbation with a maximum deviation of 10% from linearity. Perturbations with higher mode numbers result in higher stochasticity. The higher the complexity and coupling in the equilibrium magnetic geometry, the closer is the scaling to the Boozer–Rechester scaling of width. The comparison of the EGF for the simple map (Punjabi et al 1992 Phys. Rev. Lett. 69 3322) with that of the DIII-D shows that the more complex the magnetic geometry and the more coupling of modes in equilibrium, the more robust or resilient is the system against the chaos-inducing, symmetry-breaking perturbations.

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Section: Stochastic Broadening From Toroidal Asymmetries Introduced B...mentioning

confidence: 84%

Section: Introductionmentioning

confidence: 99%

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An area-preserving mapping in natural canonical coordinates for magnetic field line trajectories in the DIII-D tokamak

Punjabi

2009

Nucl. Fusion

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“…A recent work has shown that the connection lengths are comparable to the electron collisional mean free path for tokamaks with divertors [10]. In our work, we are going to study the patterns produced by the escaping chaotic field line near the tokamak wall [11,12] for an equilibrium with reversed magnetic shear perturbed by an ergodic magnetic limiter. The escaping of the field line is analyzed for a range of control parameters and the connections lengths are calculated and compared to the electron collisional mean free path in order to estimate the relevance of the field line transport.…”

Section: Introductionmentioning

confidence: 98%

Magnetic Field Line Escape: Comparison with Mean Free Path

Martins

Roberto

Caldas

et al. 2011

J. Phys.: Conf. Ser.

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In the present work, we determine the fraction of magnetic field lines that reach the tokamak wall leaving the plasma surrounded by a chaotic layer created by resonant perturbations at the plasma edge. The chaotic layer arises in a scenario where an integrable magnetic field with reversed magnetic shear is perturbed by an ergodic magnetic limiter. For each considered line, we calculate its connection length, i.e. the number of toroidal turns that the field lines complete before reaching the wall. We represent the results in the poloidal section in which the initial coordinates are chosen. We also estimate the radial profile of the fraction of field lines, for different temperatures, whose connection lengths are smaller than the electron collisional mean free path.

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“…Our goal in this work is to present a particular solution for this wave Hamiltonian model that prevents the breaking of the RT, even if we add as many waves as we want in the perturbation. This is an important fact since the creation of barriers in Hamiltonian systems has been considered an important subject in several areas of physics especially in plasma confinement in tokamaks [2,7,12,13].…”

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confidence: 99%