Bulletin of the American Physical Society
56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014; New Orleans, Louisiana
Session NO3: MHD, Energetic Particles, Heating and Current Drive |
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Chair: Eric Gillman, Naval Research Laboratory Room: Salon D |
Wednesday, October 29, 2014 9:30AM - 9:42AM |
NO3.00001: Effects of stochastic field lines on the pressure driven MHD instabilities in the Large Helical Device Satoshi Ohdachi, Kiyomasa Watanabe, Satoru Sakakibara, Yasuhiro Suzuki, Hayato Tsuchiya, TingFeng Ming, XiaoDi Du In the Large Helical Device (LHD), the plasma is surrounded by the so-called magnetic stochastic region, where the Kolmogorov length of the magnetic field lines is very short, from several tens of meters and to thousands meters. Finite pressure gradient are formed in this region and MHD instabilities localized in this region is observed since the edge region of the LHD is always unstable against the pressure driven mode. Therefore, the saturation level of the instabilities is the key issue in order to evaluate the risk of this kind of MHD instabilities. The saturation level depends on the pressure gradient and on the magnetic Reynolds number; there results are similar to the MHD mode in the closed magnetic surface region. The saturation level in the stochastic region is affected also by the stocasticity itself. Parameter dependence of the saturation level of the MHD activities in the region is discussed in detail. [Preview Abstract] |
Wednesday, October 29, 2014 9:42AM - 9:54AM |
NO3.00002: Peeling-off modes at tokamak plasma edge Linjin Zheng, M. Furukawa It is pointed out that there is a current jump between the edge plasma inside the last closed flux surface and the scrape-off layer and the current jump can lead the external kink modes to convert to the tearing modes, due to the current interchange effects. This mode conversion is proved by deriving the extended Rutherford equation. The magnetic reconnection in the presence of tearing modes subsequently causes the tokamak edge plasma to be peeled off to link to the diverters. In particular, the peeling or peeling-ballooning modes can become the ``peeling-off" modes in this sense. This phenomenon indicates that the tokamak edge confinement can be worse than the expectation based on the conventional kink mode picture. [Preview Abstract] |
Wednesday, October 29, 2014 9:54AM - 10:06AM |
NO3.00003: Seed islands driven by turbulence and NTM dynamics M. Muraglia, O. Agullo, A. Poye, S. Benkadda, W. Horton, N. Dubuit, X. Garbet, A. Sen Magnetic reconnection is an issue for tokamak plasmas. Growing magnetic islands expel energetic particles from the plasma core leading to high energy fluxes in the SOL and may cause damage to the plasma facing components. The islands grow from seeds from the bootstrap current effects that oppose the negative delta-prime producing nonlinear island growth. Experimentally, the onset of NTM is quantified in terms of the beta parameter and the sawtooth period. Indeed, in experiments, (3;2) NTM magnetic islands are often triggered by sawtooth precursors. However (2;1) magnetic islands can appear without noticeable MHD event and the seed islands origin for the NTM growth is still an open question. Macroscale MHD instabilities (magnetic islands) coexist with micro-scale turbulent fluctuations and zonal flows which impact island dynamics. Nonlinear simulations show that the nonlinear beating of the fastest growing small-scale ballooning interchange modes on a low order rational surface drive a magnetic islands located on the same surface [1]. The island size is found to be controlled by the turbulence level and modifies the NTM threshold and dynamics. [1] M. Muraglia et al, Phys. Rev. Lett., 107, 095003 (2011) [Preview Abstract] |
Wednesday, October 29, 2014 10:06AM - 10:18AM |
NO3.00004: ABSTRACT MOVED TO JO3.00005 |
Wednesday, October 29, 2014 10:18AM - 10:30AM |
NO3.00005: Instability of the ion-ion hybrid Alfv\'{e}n resonator in the presence of superthermal alpha-particles W.A. Farmer, G.J. Morales A previous theoretical study has suggested that the ion hybrid wave (or shear Alfv\'{e}n wave) will be unstable in a burning plasma environment due to fusion-born alpha particles [1]. It was concluded that instability occurs for a band of frequencies near the ion-ion hybrid frequency in a homogeneous D-T plasma. In a tokamak, the periodic variation in the strength of the magnetic field along a field--line causes the ion-ion hybrid frequency to vary between the outboard and inboard sides of the device. Because the shear Alfv\'{e}n wave predominantly propagates along a field-line and experiences a parallel cut-off at the ion-ion hybrid frequency, this instability can lead to excitation of the ion-ion hybrid Alfv\'{e}n resonator. Recent experiments [2] in the linear device LAPD at UCLA have demonstrated the existence of such a resonator in a magnetic mirror configuration through excitation by an antenna. In this study, instability of the shear Alfv\'{e}n wave in the magnetic topology of a tokamak due to energetic alpha particles is considered [3]. \\[4pt] [1] C. N. Lashmore-Davies and D. A. Russell. Phys. Plasmas \textbf{4}, 369 (1997).\\[0pt] [2] S. T. Vincena, et al., Phys. Plasmas \textbf{20}, 012111 (2013).\\[0pt] [3] W. A. Farmer and G. J. Morales, Phys. Plasmas \textbf{21}, 062507 (2014). [Preview Abstract] |
Wednesday, October 29, 2014 10:30AM - 10:42AM |
NO3.00006: Local wave particle resonant interaction causing energetic particle prompt loss in DIII-D plasmas Ruibin Zhang, Guoyong Fu, Roscoe White A new resonance mechanism is introduced to explain the observed first-orbit prompt beam ion losses induced by RSAE in the D3D tokamak [1]. Because of large banana width and localized radial structure, some trapped beam ions can only interact with RSAE on the inner legs of their banana orbits. A beam ion can interact resonantly with the RSAE when the mode phase is nearly constant within the local interaction region. We identify this strong local wave particle interaction as local resonance. The local resonance condition is determined by the local poloidal and toroidal velocity of beam ions and can be written as $<-m\dot\theta+n\dot\phi>_{gc}-\omega=0$, where $<>$ denotes local time average within the interaction region and $_{gc}$ stands for guiding center coordinates. A full orbit test particle code FOST confirms the local resonance theory. Both the linear scaling with the mode amplitude and the frequency of the loss signals detected by FILD on D3D as well as the measured fast ion radial kick size can be well explained by this local resonance theory and simulation. \\[4pt] [1] X. Chen, et al, Phys.Rev.Lett. 110,065004(2013). [Preview Abstract] |
Wednesday, October 29, 2014 10:42AM - 10:54AM |
NO3.00007: Control of energetic particle driven modes in MAST David Keeling, Tom Barrett, Clive Challis, Nick Hawkes, Owen Jones, Ken McClements, Alex Meakins, Joe Milnes, Marco Cecconello, Iwona Klimek, Mikhail Turnyanskiy Core MHD is known to redistribute fast ions originating from Neutral Beam Injection (NBI). Theory suggests that these modes are driven by gradients in the fast ion distribution, providing the possibility for instability control by optimisation of the fast ion pressure profile to suppress these modes and prevent the redistribution or loss of the fast ions themselves. Experiments on MAST have demonstrated this approach by vertically displacing the plasma to achieve off-axis NBI fast ion injection [Turnyanskiy M. \textit{et al} 2013 Nucl Fusion \textbf{53} 053016] or by changing plasma density or NBI power to vary the magnitude of the fast ion pressure [Keeling DL \textit{et al} submitted to Nucl Fusion]. Measurements using various fast-ion diagnostics show large redistribution in the absence of mitigating effects [Cecconello M \textit{et al} submitted to Plasma Phys Control Fusion] whilst measurements and comparisons with modelling have confirmed the suppression of redistribution by appropriate optimisations of the fast ion pressure. These results have led to design options for MAST-Upgrade to allow access to a wide range of plasma parameters without significant fast ion redistribution. [Preview Abstract] |
Wednesday, October 29, 2014 10:54AM - 11:06AM |
NO3.00008: Evolution of the radial electric field in high-Te ECH heated plasmas on LHD Novimir Pablant, Manfred Bitter, Luis F. Delgado Aparicio, Andreas Dinklage, David Gates, Motoshi Goto, Takeshi Ido, Kenneth H. Hill, Shin Kubo, Shigeru Morita, Kenichi Nagaoka, Tetsutarou Oishi, Shinsuke Satake, Hiromi Takahashi, Masayuki Yokoyama A detailed study is presented on the evolution of the radial electric field (Er) under a range of densities and injected ECH powers on the Large Helical Device (LHD). These plasmas focused on high-electron temperature ECH heated plasmas which exhibit a transition of Er from the ion-root to the electron-root when either the density is reduced or the ECH power is increased. Measurements of poloidal rotation were achieved using the X-Ray Imaging Crystal Spectrometer (XICS) and are compared with neo-classical predictions of the radial electric field using the GSRAKE and FORTEC-3D codes. This study is based on a series of experiments on LHD which used fast modulation of the gyrotrons on LHD to produce a detailed power scan with a constant power deposition profile. This is a novel application of this technique to LHD, and has provided the most detailed study to date on dependence of the radial electric field on the injected power. Detailed scans of the density at constant injected power were also made, allowing a separation of the power and density dependence. [Preview Abstract] |
Wednesday, October 29, 2014 11:06AM - 11:18AM |
NO3.00009: Transport equations for lower hybrid waves in a turbulent plasma J.T. Mendonca, W. Horton, R.M.O. Galvao, Y. Elskens Injection and control of intense lower hybrid (LH) wave spectra is required to achieve steady state tokamak operation in the new WEST tokamak at CEA France. The tungsten [W] environment [E] steadytstate [S] tokamak [T] has two high-power [20MW] lower hybrid antennas launching 3.7 GHz polarized waves for steady fusion-grade plasmas control. The wave propagation and scattering is described in by ray equations in the presence of the drift wave turbulence. Theory for the wave transport equations for propagation of the wave momentum and energy densities are derived from the Wigner function method of QM. The limits of the diffraction and scattering for ray transport theory are established. Comparisons are made between the wave propagation in WEST and ITER tokamaks. [Preview Abstract] |
Wednesday, October 29, 2014 11:18AM - 11:30AM |
NO3.00010: Global particle simulation of lower hybrid waves in fusion plasmas Jian Bao, Zhihong Lin, Animesh Kuley, Zhixin Lu, Zhixuan Wang Global particle simulations of the lower hybrid (LH) waves have been carried out based on the first principle, which use the fully kinetic ion/ drift kinetic electron model with a realistic electron-to-ion mass ratio. The LH wave frequency, mode structure, and electron Landau damping from the electrostatic simulations agree very well with the analytic theory. Linear simulation of the propagation of a LH wave-packet in the toroidal geometry shows that the wave propagates faster in the high field side than the low field side, in agreement with a ray tracing calculation. This poloidal asymmetry arises from the non-conservation of the poloidal mode number due to the non-uniform magnetic field. In contrast, the poloidal mode number is conserved in the cylindrical geometry with the uniform magnetic field. Furthermore, an electromagnetic particle simulation model is developed to study the accessibility of LH waves based on the first principle, the dispersion relations of the slow and fast waves in LH frequency range are well benchmarked. The mode-conversion between slow and fast waves is observed, which is consistent with the theory. [Preview Abstract] |
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