Michael E Mauel | Columbia University (original) (raw)
Uploads
Papers by Michael E Mauel
ABSTRACT LDX studies plasma confined by the field of a magnetic dipole. The plasma profiles are d... more ABSTRACT LDX studies plasma confined by the field of a magnetic dipole. The plasma profiles are distinctly different when the superconducting dipole is mechanically supported and when it is magnetically levitated. When supported, profiles are determined by particle losses to the supports, leading to flat density profiles. By contrast, when the dipole is levitated, parallel losses are eliminated, a thermal electron population is formed and turbulent radial ExB driven transport creates ``stationary'' profiles. Interferometry shows that the density profile is centrally peaked during levitation. Equilibrium calculations with the measured density profile and edge temperature imply a centrally peaked temperature profile. The condition for marginal MHD stability, δ(pV^γ)=0, relates the polytropic index of the turbulent transport, γ, to the peakedness of the pressure profile. We estimate the value of γ by developing the magnetic reconstructions and examining both soft X-ray and visible spectra.
Physics of Fluids, 1986
ABSTRACT
Physics of Fluids, 1988
ABSTRACT
The feedback system for uc(hbt-ep) uses a two-phase set of discrete saddle coils with small toroi... more The feedback system for uc(hbt-ep) uses a two-phase set of discrete saddle coils with small toroidal extent (12^circ per phase) to produce a rotating magnetic perturbation resonant with the 2/1 mode. A quadrature m=2 mode diagnostic is developed from a set of poloidal Mirnov probes. A digital signal-processing (DSP) computer combines the probe signals to obtain mode phase and amplitude
Closed and open loop control techniques were applied to growing m/n=2/1 rotating islands in wall ... more Closed and open loop control techniques were applied to growing m/n=2/1 rotating islands in wall stabilized plasmas in the HBT-EP tokamak. The approach taken by HBT-EP combines an adjustable segmented conducting wall (which slows the growth or stabilizes ideal external kinks) with a number of small (6° wide) saddle coils located between the gaps of the conducting wall. In this
The feedback system for HBT-EP consists of four discrete saddle coil pairs, two high-power amplif... more The feedback system for HBT-EP consists of four discrete saddle coil pairs, two high-power amplifiers, and signals derived from magnetic and soft X-ray diagnostics. The four compact saddle coil pairs are mounted to approximate two-phase, m=2, n=1 helical windings. A digital signal-processing (DSP) system is used to test various feedback techniques. The DSP hardware is based on the Analog Devices
Frequency modulated resonant magnetic perturbations (RMPs) have been successful in controlling th... more Frequency modulated resonant magnetic perturbations (RMPs) have been successful in controlling the rotation velocity of m/n = 2/1 MHD modes in the HBT-EP tokamak. The RMPs are generated by a compact, four coil, two phase saddle coil set imposing a rotating perturbation on only 3.3 % of the plasma surface. The frequency of naturally occurring modes (f = 7 kHz)
We report the design, fabrication, and installation of an inboard launch RF antenna for beta enha... more We report the design, fabrication, and installation of an inboard launch RF antenna for beta enhancement and (2) an active feedback system for the resistive wall mode (RWM). These systems are collaborations between Columbia University, PPPL, and LANL. The ICRF antenna has been designed and fabricated by PPPL in order to launch up to 200 kW in the mode-conversion regime
The interaction of rotating magnetic islands with tokamak plasmas creates two types of perturbati... more The interaction of rotating magnetic islands with tokamak plasmas creates two types of perturbations: first, rotating density and/or temperature fluctuations, and second, changes in the plasma ion fluid velocity. The HBT-EP tokamak offers a unique opportunity to study the motion of these plasma perturbations using Mach probes. Mach probes can measure the perturbation velocities at a normalized minor radius of
Measurements of radial and azimuthal mode structures of plasma waves excited by both the hot elec... more Measurements of radial and azimuthal mode structures of plasma waves excited by both the hot electron interchange (HEI) instability and by a broad-band antenna with m = 3 symmetry located at one of the magnetic poles of CTX(H. P. Warren and M. E. Mauel, Phys. Plasmas), 2 (1995) 4185. are presented. The hot electron population, produced via electron cyclotron heating,
Interchange instabilities excited by energetic electrons trapped by a magnetic dipole nonlinearly... more Interchange instabilities excited by energetic electrons trapped by a magnetic dipole nonlinearly saturate with complex spectral characteristics. Since low-frequency interchange instabilities preserve the electron's first and second adiabatic invariant, the wave-particle interaction is described with a two-dimensional phase-space that is directly observable. Electron flux modulations together with numerical simulation illustrate rotating "phase-space holes" that move inward as the mode rotation
Two new magnetic dipole experiments are discussed in the context of understanding the confinement... more Two new magnetic dipole experiments are discussed in the context of understanding the confinement and stability of high-temperature plasma. The Levitated Dipole Experiment (LDX) is a new device that will enable the first study of the properties of a high-temperature plasma confined by a dipole for many collision times. LDX consists of a large, high-field, superconducting coil magnetically levitated within
We present results using the VALEN code that model present and proposed experiments to actively c... more We present results using the VALEN code that model present and proposed experiments to actively control the RWM mode in the HBT-EP tokamak. The HBT-EP active feedback system consists of thirty flux loop sensors and thirty control coils mounted behind resistive wall segments in poloidal arrays spaced toroidally at five locations. Each sensor/control-coil pair is connected to an independent feedback
The goal of the HBT-EP experiment is to demonstrate the feasibility of a high-beta tokamak stabil... more The goal of the HBT-EP experiment is to demonstrate the feasibility of a high-beta tokamak stabilized by a combination of a close-fitting conducting wall, plasma rotation, and active feedback. The specific approach taken in HBT-EP incorporates: (1) a segmented adjustable conducting wall to eliminate ideal-MHD time scale external kink instabilities; (2) a modular saddle-coil set which applies rotating magnetic perturbations
Active feedback control of the resistive wall mode (RWM) has been achieved and RWM induced disrup... more Active feedback control of the resistive wall mode (RWM) has been achieved and RWM induced disruptions have been suppressed with an in-vessel array of 30 sensor-loop and control-coil pairs each of which is connected through an independent feedback circuit in a 'smart shell' configuration, capable of suppressing up to 95% of the mode radial flux through the resistive wall. This
Control of long-wavelength MHD instabilities using conducting walls and external magnetic perturb... more Control of long-wavelength MHD instabilities using conducting walls and external magnetic perturbations has been shown to be a promising route to improved performance of magnetic fusion devices. The control physics issues of optimized feedback and sensor coil layout and geometry are crucial to maximizing the efficacy of MHD instability control for fusion systems. To experimentally address these issues, we have
Control of long wavelength magnetohydrodynamic (MHD) kink instabilities using conducting walls an... more Control of long wavelength magnetohydrodynamic (MHD) kink instabilities using conducting walls and external magnetic perturbations has been shown to be a promising route to improved performance of magnetic fusion devices. Experiments on the HBT-EP tokamak have demonstrated the dependence of the growth rate of kink instabilities on the wall conductivity as well as its stabilization by active feedback. The control
Accurate knowledge of current profile parameters and safety factor profile is essential in the as... more Accurate knowledge of current profile parameters and safety factor profile is essential in the assessment of tokamak plasma equilibrium and stability. In HBT-EP a movable, high spatial resolution Hall probe sensor array has been built to measure the azimuthal magnetic field and its fluctuations at the edge of plasma. The new array consists of 20 Hall probe sensors spaced 4
The goal of the HBT-EP experiment is to show the feasibility of a high-beta tokamak stabilized by... more The goal of the HBT-EP experiment is to show the feasibility of a high-beta tokamak stabilized by a combination of a close-fitting conducting wall, plasma rotation, and active feedback. The HBT-EP approach incorporates: (1) a segmented adjustable conducting wall to eliminate fast external kink instabilities, and (2) modular saddle-coil sets to apply magnetic perturbations to control and study slowly growing
ABSTRACT LDX studies plasma confined by the field of a magnetic dipole. The plasma profiles are d... more ABSTRACT LDX studies plasma confined by the field of a magnetic dipole. The plasma profiles are distinctly different when the superconducting dipole is mechanically supported and when it is magnetically levitated. When supported, profiles are determined by particle losses to the supports, leading to flat density profiles. By contrast, when the dipole is levitated, parallel losses are eliminated, a thermal electron population is formed and turbulent radial ExB driven transport creates ``stationary'' profiles. Interferometry shows that the density profile is centrally peaked during levitation. Equilibrium calculations with the measured density profile and edge temperature imply a centrally peaked temperature profile. The condition for marginal MHD stability, δ(pV^γ)=0, relates the polytropic index of the turbulent transport, γ, to the peakedness of the pressure profile. We estimate the value of γ by developing the magnetic reconstructions and examining both soft X-ray and visible spectra.
Physics of Fluids, 1986
ABSTRACT
Physics of Fluids, 1988
ABSTRACT
The feedback system for uc(hbt-ep) uses a two-phase set of discrete saddle coils with small toroi... more The feedback system for uc(hbt-ep) uses a two-phase set of discrete saddle coils with small toroidal extent (12^circ per phase) to produce a rotating magnetic perturbation resonant with the 2/1 mode. A quadrature m=2 mode diagnostic is developed from a set of poloidal Mirnov probes. A digital signal-processing (DSP) computer combines the probe signals to obtain mode phase and amplitude
Closed and open loop control techniques were applied to growing m/n=2/1 rotating islands in wall ... more Closed and open loop control techniques were applied to growing m/n=2/1 rotating islands in wall stabilized plasmas in the HBT-EP tokamak. The approach taken by HBT-EP combines an adjustable segmented conducting wall (which slows the growth or stabilizes ideal external kinks) with a number of small (6° wide) saddle coils located between the gaps of the conducting wall. In this
The feedback system for HBT-EP consists of four discrete saddle coil pairs, two high-power amplif... more The feedback system for HBT-EP consists of four discrete saddle coil pairs, two high-power amplifiers, and signals derived from magnetic and soft X-ray diagnostics. The four compact saddle coil pairs are mounted to approximate two-phase, m=2, n=1 helical windings. A digital signal-processing (DSP) system is used to test various feedback techniques. The DSP hardware is based on the Analog Devices
Frequency modulated resonant magnetic perturbations (RMPs) have been successful in controlling th... more Frequency modulated resonant magnetic perturbations (RMPs) have been successful in controlling the rotation velocity of m/n = 2/1 MHD modes in the HBT-EP tokamak. The RMPs are generated by a compact, four coil, two phase saddle coil set imposing a rotating perturbation on only 3.3 % of the plasma surface. The frequency of naturally occurring modes (f = 7 kHz)
We report the design, fabrication, and installation of an inboard launch RF antenna for beta enha... more We report the design, fabrication, and installation of an inboard launch RF antenna for beta enhancement and (2) an active feedback system for the resistive wall mode (RWM). These systems are collaborations between Columbia University, PPPL, and LANL. The ICRF antenna has been designed and fabricated by PPPL in order to launch up to 200 kW in the mode-conversion regime
The interaction of rotating magnetic islands with tokamak plasmas creates two types of perturbati... more The interaction of rotating magnetic islands with tokamak plasmas creates two types of perturbations: first, rotating density and/or temperature fluctuations, and second, changes in the plasma ion fluid velocity. The HBT-EP tokamak offers a unique opportunity to study the motion of these plasma perturbations using Mach probes. Mach probes can measure the perturbation velocities at a normalized minor radius of
Measurements of radial and azimuthal mode structures of plasma waves excited by both the hot elec... more Measurements of radial and azimuthal mode structures of plasma waves excited by both the hot electron interchange (HEI) instability and by a broad-band antenna with m = 3 symmetry located at one of the magnetic poles of CTX(H. P. Warren and M. E. Mauel, Phys. Plasmas), 2 (1995) 4185. are presented. The hot electron population, produced via electron cyclotron heating,
Interchange instabilities excited by energetic electrons trapped by a magnetic dipole nonlinearly... more Interchange instabilities excited by energetic electrons trapped by a magnetic dipole nonlinearly saturate with complex spectral characteristics. Since low-frequency interchange instabilities preserve the electron's first and second adiabatic invariant, the wave-particle interaction is described with a two-dimensional phase-space that is directly observable. Electron flux modulations together with numerical simulation illustrate rotating "phase-space holes" that move inward as the mode rotation
Two new magnetic dipole experiments are discussed in the context of understanding the confinement... more Two new magnetic dipole experiments are discussed in the context of understanding the confinement and stability of high-temperature plasma. The Levitated Dipole Experiment (LDX) is a new device that will enable the first study of the properties of a high-temperature plasma confined by a dipole for many collision times. LDX consists of a large, high-field, superconducting coil magnetically levitated within
We present results using the VALEN code that model present and proposed experiments to actively c... more We present results using the VALEN code that model present and proposed experiments to actively control the RWM mode in the HBT-EP tokamak. The HBT-EP active feedback system consists of thirty flux loop sensors and thirty control coils mounted behind resistive wall segments in poloidal arrays spaced toroidally at five locations. Each sensor/control-coil pair is connected to an independent feedback
The goal of the HBT-EP experiment is to demonstrate the feasibility of a high-beta tokamak stabil... more The goal of the HBT-EP experiment is to demonstrate the feasibility of a high-beta tokamak stabilized by a combination of a close-fitting conducting wall, plasma rotation, and active feedback. The specific approach taken in HBT-EP incorporates: (1) a segmented adjustable conducting wall to eliminate ideal-MHD time scale external kink instabilities; (2) a modular saddle-coil set which applies rotating magnetic perturbations
Active feedback control of the resistive wall mode (RWM) has been achieved and RWM induced disrup... more Active feedback control of the resistive wall mode (RWM) has been achieved and RWM induced disruptions have been suppressed with an in-vessel array of 30 sensor-loop and control-coil pairs each of which is connected through an independent feedback circuit in a 'smart shell' configuration, capable of suppressing up to 95% of the mode radial flux through the resistive wall. This
Control of long-wavelength MHD instabilities using conducting walls and external magnetic perturb... more Control of long-wavelength MHD instabilities using conducting walls and external magnetic perturbations has been shown to be a promising route to improved performance of magnetic fusion devices. The control physics issues of optimized feedback and sensor coil layout and geometry are crucial to maximizing the efficacy of MHD instability control for fusion systems. To experimentally address these issues, we have
Control of long wavelength magnetohydrodynamic (MHD) kink instabilities using conducting walls an... more Control of long wavelength magnetohydrodynamic (MHD) kink instabilities using conducting walls and external magnetic perturbations has been shown to be a promising route to improved performance of magnetic fusion devices. Experiments on the HBT-EP tokamak have demonstrated the dependence of the growth rate of kink instabilities on the wall conductivity as well as its stabilization by active feedback. The control
Accurate knowledge of current profile parameters and safety factor profile is essential in the as... more Accurate knowledge of current profile parameters and safety factor profile is essential in the assessment of tokamak plasma equilibrium and stability. In HBT-EP a movable, high spatial resolution Hall probe sensor array has been built to measure the azimuthal magnetic field and its fluctuations at the edge of plasma. The new array consists of 20 Hall probe sensors spaced 4
The goal of the HBT-EP experiment is to show the feasibility of a high-beta tokamak stabilized by... more The goal of the HBT-EP experiment is to show the feasibility of a high-beta tokamak stabilized by a combination of a close-fitting conducting wall, plasma rotation, and active feedback. The HBT-EP approach incorporates: (1) a segmented adjustable conducting wall to eliminate fast external kink instabilities, and (2) modular saddle-coil sets to apply magnetic perturbations to control and study slowly growing