The maximum-J (J is the second adiabatic invariant) capability, i.e., the drift reversal capabili... more The maximum-J (J is the second adiabatic invariant) capability, i.e., the drift reversal capability, is examined in quasi-axisymmetric (QAS) stellarators and quasi-poloidally symmetric (QPS) stellarators as a possible mechanism for turbulent transport suppression. Due to the existence of non-axisymmetry of the magnetic field strength in QAS configurations, a local maximum of J is created to cause the drift reversal. The increase of magnetic shear in finite beta equilibria also has favorable effect in realizing the drift reversal. The radial variation of the uniform magnetic field component plays a crucial role for the drift reversal in a QPS configuration. Thus, the drift reversal capability and its external controllability are demonstrated for QAS and QPS stellarators, by which the impact of magnetic configuration on turbulent transport can be studied in experiments.
The National Compact Stellarator Experiment (NCSX), currently under construction, is a modular qu... more The National Compact Stellarator Experiment (NCSX), currently under construction, is a modular quasi-axisymmetric stellarator designed to study confinement and stability of high-beta plasmas. It has 18 modular coils, 18 planar weak toroidal field coils, and 6 pairs of poloidal field coils. Each type of coil is powered separately, providing a wide range of 3D shape flexibility. This equilibrium flexibility space has been explored to determine the range available, to identify candidate equilibria for early experiments, and to analyze the expected plasma characteristics. Vacuum equilibria, with well formed flux surfaces are found for iota (magnetic rotational transform) ranging from 0.19 to 0.9 and low effective helical ripple < 1%. The effective ripple can be varied by more than a factor of 10, at fixed rotational transform. At low effective ripple, the ripple generated neoclassical transport is predicted to be negligible. At the maximum ripple, the ripple generated transport reduc...
A wide range of MHD stable high ..beta.. plasmas is produced in the Wisconsin Levitated Octupole.... more A wide range of MHD stable high ..beta.. plasmas is produced in the Wisconsin Levitated Octupole. At or near the single fluid regime we obtain, in the bad curvature region, ..beta.. = nk(T/sub e/ + T/sub i/)8..pi../B/sup 2/ approx. = 8%, twice the theoretical single fluid ballooning instability limit of 4%. We also obtain stable plasmas at ..beta.. approx. = 35%, 9 times the theoretical limit, in a regime in which both finite ion gyroradius and gyroviscosity effects are important.
Over the last several years the motional Stark effect (MSE) diagnostic has become the technique o... more Over the last several years the motional Stark effect (MSE) diagnostic has become the technique of choice for determining the q-profile in tokamaks. The success of MSE polarimetry is due to its good temporal and spatial resolution, which combined with its accuracy, has resulted in important contributions towards understanding stability and transport in tokamaks. The MSE diagnostic is also sensitive to radial electric fields. In order to separate the electric field from the poloidal magnetic field, two separate measurements with different sensitivities to the fields are required. This can be done with either two views or with one view that uses both the full energy and half energy components from the neutral beam. On TFTR we have modified the MSE system to add additional channels for the half energy component. In addition, for both the full and half energy channels, several photomultiplier detectors have been replaced with higher quantum efficiency avalanche photodiodes improving the...
Recent development of a steady-state after the transition into the enhanced reverse shear (ERS) m... more Recent development of a steady-state after the transition into the enhanced reverse shear (ERS) mode simplifies transient helium and tritium transport analysis. This regime is characterized by slow changes in the neutron rate, central electron density (n_e(0) = 1 x 10^20 m-3), stored energy, ion and electron temperatures, and Shafranov shift. Transport analysis for both particle species requires small amounts of gas puffed into the plasma. The tritium transport is inferred from the DT neutrons as measured with a multi-channel neutron collimator, and the helium transport is observed with charge exchange recombination spectroscopy (CHERS). The ERS regime has been previously characterized by a large reduction in the electron particle transport inside the reverse shear region.(F. M. Levinton, et al., PRL, Vol. 75, 4417 (1996).) Initial observations indicate that the core particle confinement for tritium and helium is better in ERS plasmas than in plasmas with reverse shear and no transi...
Measured impurity poloidal rotation, v_theta, in TFTR reversed shear plasmas has been shown to di... more Measured impurity poloidal rotation, v_theta, in TFTR reversed shear plasmas has been shown to differ significantly from neoclassically predicted values of v_theta.(R. E. Bell, F. M. Levinton, S. H. Batha, et al.), Phys. Rev. Lett., to be published The core v_theta is found to be offset in the ion diamagnetic direction, with respect to neoclassical v_theta, yielding a positive core radial electric field, E_r. Er is determined spectroscopically using the radial force balance equation, E_r=nablap/(eZn)+v_phiB_theta-v_thetaB_phi. A similar offset is found for v_theta in TFTR supershot plasmas. The sign of v_theta and in some cases the sign of Er are reversed compared to neoclassical predictions. For supershot plasmas with balanced beam injection, the core Er was also positive and dominated by the positive -v_thetaB_phi term. Dynamic changes in v_theta and Er were observed during pellet injection, helium gas puffing, and changes in the direction of neutral beam injection. The magnitude ...
We are modifying the GTC(Z. Lin, W. M. Tang, and W. W. Lee, Phys. Plasmas) 2(8) 2975 (1995). delt... more We are modifying the GTC(Z. Lin, W. M. Tang, and W. W. Lee, Phys. Plasmas) 2(8) 2975 (1995). delta f general geometry particle simulation code to include a self-consistent neoclassical radial electric field. This will provide a new capability for kinetic, global, neoclassical calculations with self-consistent radial potential for stellarators, and for tokamaks with shaped flux surfaces. The potential is calculated from the neoclassical particle flux,(W.X. Wang et al.), Phys. Rev. Lett. 87(5) 5002 (2001). obtained with low noise from variations of the parallel and perpendicular pressures on a flux surface.(J.L.V. Lewandowski et al.), Phys. Plasmas 8(6) 2849 (2001). Kinetic calculations of the toroidal flow damping rate in stellarators address the efficacy of neutral beam injection in driving sheared flows to suppress turbulence. The results for tokamaks will be compared with standard neoclassical theory in steep gradient regimes. Simulations of HSX plasmas for comparison with direct ...
The instability growth rates on the tokamak fusion test reactors are commented upon. Comments by ... more The instability growth rates on the tokamak fusion test reactors are commented upon. Comments by Nordman and Weiland 1,3,4 on mode stability and transport are discussed. (AIP)
Real-time language constructs in the REBEL/BASIC language are described as implemented on the PDP... more Real-time language constructs in the REBEL/BASIC language are described as implemented on the PDP-11/LSI-11 series of computers at LLL. The currently implemented ideas are documented. A general discussion of the underlying concepts and features is followed by a detailed description of each of the REBEL/BASIC statements. This manual is designed to serve as both a learning and a reference manual for the real-time features. (RWR)
... been presented. The full set of transport equations has been implemented, allowing for the se... more ... been presented. The full set of transport equations has been implemented, allowing for the self-consistent simulation of the SOL and target deposition. Calculations indicate that the ... Sci. Technol.47 (2005) 172. [7] AH Reiman, Computer Phys. Comm. 43 (1986) 157. ...
The q profile plays a key role for plasma equilibrium and theories of magnetohydrodynamic instabi... more The q profile plays a key role for plasma equilibrium and theories of magnetohydrodynamic instabilities. With the development of the motional Stark effect (MSE) diagnostic, accurate q(r,t) profiles have been measured and utilized for equilibrium and stability analysis. Improvements to the MSE diagnostic on TFTR include a new method for calibrating the system and increasing the number of sightlines from 12 to 21 channels. A technique that uses the known poloidal field at the edge of the plasma is utilized to calibrate each sightline. The major radius is moved over the course of a discharge such that the plasma edge covers each sightline radius. Then with several discharges at various plasma currents each channel is independently calibrated. This method has been compared to our earlier calibration technique using neutral beam injection into a gas filled torus and some differences in the calibration have been found that have been attributed to differences in the excitation and l mixing...
The maximum-J (J is the second adiabatic invariant) capability, i.e., the drift reversal capabili... more The maximum-J (J is the second adiabatic invariant) capability, i.e., the drift reversal capability, is examined in quasi-axisymmetric (QAS) stellarators and quasi-poloidally symmetric (QPS) stellarators as a possible mechanism for turbulent transport suppression. Due to the existence of non-axisymmetry of the magnetic field strength in QAS configurations, a local maximum of J is created to cause the drift reversal. The increase of magnetic shear in finite beta equilibria also has favorable effect in realizing the drift reversal. The radial variation of the uniform magnetic field component plays a crucial role for the drift reversal in a QPS configuration. Thus, the drift reversal capability and its external controllability are demonstrated for QAS and QPS stellarators, by which the impact of magnetic configuration on turbulent transport can be studied in experiments.
The National Compact Stellarator Experiment (NCSX), currently under construction, is a modular qu... more The National Compact Stellarator Experiment (NCSX), currently under construction, is a modular quasi-axisymmetric stellarator designed to study confinement and stability of high-beta plasmas. It has 18 modular coils, 18 planar weak toroidal field coils, and 6 pairs of poloidal field coils. Each type of coil is powered separately, providing a wide range of 3D shape flexibility. This equilibrium flexibility space has been explored to determine the range available, to identify candidate equilibria for early experiments, and to analyze the expected plasma characteristics. Vacuum equilibria, with well formed flux surfaces are found for iota (magnetic rotational transform) ranging from 0.19 to 0.9 and low effective helical ripple < 1%. The effective ripple can be varied by more than a factor of 10, at fixed rotational transform. At low effective ripple, the ripple generated neoclassical transport is predicted to be negligible. At the maximum ripple, the ripple generated transport reduc...
A wide range of MHD stable high ..beta.. plasmas is produced in the Wisconsin Levitated Octupole.... more A wide range of MHD stable high ..beta.. plasmas is produced in the Wisconsin Levitated Octupole. At or near the single fluid regime we obtain, in the bad curvature region, ..beta.. = nk(T/sub e/ + T/sub i/)8..pi../B/sup 2/ approx. = 8%, twice the theoretical single fluid ballooning instability limit of 4%. We also obtain stable plasmas at ..beta.. approx. = 35%, 9 times the theoretical limit, in a regime in which both finite ion gyroradius and gyroviscosity effects are important.
Over the last several years the motional Stark effect (MSE) diagnostic has become the technique o... more Over the last several years the motional Stark effect (MSE) diagnostic has become the technique of choice for determining the q-profile in tokamaks. The success of MSE polarimetry is due to its good temporal and spatial resolution, which combined with its accuracy, has resulted in important contributions towards understanding stability and transport in tokamaks. The MSE diagnostic is also sensitive to radial electric fields. In order to separate the electric field from the poloidal magnetic field, two separate measurements with different sensitivities to the fields are required. This can be done with either two views or with one view that uses both the full energy and half energy components from the neutral beam. On TFTR we have modified the MSE system to add additional channels for the half energy component. In addition, for both the full and half energy channels, several photomultiplier detectors have been replaced with higher quantum efficiency avalanche photodiodes improving the...
Recent development of a steady-state after the transition into the enhanced reverse shear (ERS) m... more Recent development of a steady-state after the transition into the enhanced reverse shear (ERS) mode simplifies transient helium and tritium transport analysis. This regime is characterized by slow changes in the neutron rate, central electron density (n_e(0) = 1 x 10^20 m-3), stored energy, ion and electron temperatures, and Shafranov shift. Transport analysis for both particle species requires small amounts of gas puffed into the plasma. The tritium transport is inferred from the DT neutrons as measured with a multi-channel neutron collimator, and the helium transport is observed with charge exchange recombination spectroscopy (CHERS). The ERS regime has been previously characterized by a large reduction in the electron particle transport inside the reverse shear region.(F. M. Levinton, et al., PRL, Vol. 75, 4417 (1996).) Initial observations indicate that the core particle confinement for tritium and helium is better in ERS plasmas than in plasmas with reverse shear and no transi...
Measured impurity poloidal rotation, v_theta, in TFTR reversed shear plasmas has been shown to di... more Measured impurity poloidal rotation, v_theta, in TFTR reversed shear plasmas has been shown to differ significantly from neoclassically predicted values of v_theta.(R. E. Bell, F. M. Levinton, S. H. Batha, et al.), Phys. Rev. Lett., to be published The core v_theta is found to be offset in the ion diamagnetic direction, with respect to neoclassical v_theta, yielding a positive core radial electric field, E_r. Er is determined spectroscopically using the radial force balance equation, E_r=nablap/(eZn)+v_phiB_theta-v_thetaB_phi. A similar offset is found for v_theta in TFTR supershot plasmas. The sign of v_theta and in some cases the sign of Er are reversed compared to neoclassical predictions. For supershot plasmas with balanced beam injection, the core Er was also positive and dominated by the positive -v_thetaB_phi term. Dynamic changes in v_theta and Er were observed during pellet injection, helium gas puffing, and changes in the direction of neutral beam injection. The magnitude ...
We are modifying the GTC(Z. Lin, W. M. Tang, and W. W. Lee, Phys. Plasmas) 2(8) 2975 (1995). delt... more We are modifying the GTC(Z. Lin, W. M. Tang, and W. W. Lee, Phys. Plasmas) 2(8) 2975 (1995). delta f general geometry particle simulation code to include a self-consistent neoclassical radial electric field. This will provide a new capability for kinetic, global, neoclassical calculations with self-consistent radial potential for stellarators, and for tokamaks with shaped flux surfaces. The potential is calculated from the neoclassical particle flux,(W.X. Wang et al.), Phys. Rev. Lett. 87(5) 5002 (2001). obtained with low noise from variations of the parallel and perpendicular pressures on a flux surface.(J.L.V. Lewandowski et al.), Phys. Plasmas 8(6) 2849 (2001). Kinetic calculations of the toroidal flow damping rate in stellarators address the efficacy of neutral beam injection in driving sheared flows to suppress turbulence. The results for tokamaks will be compared with standard neoclassical theory in steep gradient regimes. Simulations of HSX plasmas for comparison with direct ...
The instability growth rates on the tokamak fusion test reactors are commented upon. Comments by ... more The instability growth rates on the tokamak fusion test reactors are commented upon. Comments by Nordman and Weiland 1,3,4 on mode stability and transport are discussed. (AIP)
Real-time language constructs in the REBEL/BASIC language are described as implemented on the PDP... more Real-time language constructs in the REBEL/BASIC language are described as implemented on the PDP-11/LSI-11 series of computers at LLL. The currently implemented ideas are documented. A general discussion of the underlying concepts and features is followed by a detailed description of each of the REBEL/BASIC statements. This manual is designed to serve as both a learning and a reference manual for the real-time features. (RWR)
... been presented. The full set of transport equations has been implemented, allowing for the se... more ... been presented. The full set of transport equations has been implemented, allowing for the self-consistent simulation of the SOL and target deposition. Calculations indicate that the ... Sci. Technol.47 (2005) 172. [7] AH Reiman, Computer Phys. Comm. 43 (1986) 157. ...
The q profile plays a key role for plasma equilibrium and theories of magnetohydrodynamic instabi... more The q profile plays a key role for plasma equilibrium and theories of magnetohydrodynamic instabilities. With the development of the motional Stark effect (MSE) diagnostic, accurate q(r,t) profiles have been measured and utilized for equilibrium and stability analysis. Improvements to the MSE diagnostic on TFTR include a new method for calibrating the system and increasing the number of sightlines from 12 to 21 channels. A technique that uses the known poloidal field at the edge of the plasma is utilized to calibrate each sightline. The major radius is moved over the course of a discharge such that the plasma edge covers each sightline radius. Then with several discharges at various plasma currents each channel is independently calibrated. This method has been compared to our earlier calibration technique using neutral beam injection into a gas filled torus and some differences in the calibration have been found that have been attributed to differences in the excitation and l mixing...
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