K. J. McCollam
A5001501083- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Plasma Diagnostics and Applications
- Solar and Space Plasma Dynamics
- Superconducting Materials and Applications
- Laser-Plasma Interactions and Diagnostics
- Particle accelerators and beam dynamics
- Magnetic Field Sensors Techniques
- Geomagnetism and Paleomagnetism Studies
- Fusion materials and technologies
- Astro and Planetary Science
- Laser-induced spectroscopy and plasma
- Atomic and Subatomic Physics Research
- Magnetic Properties and Applications
- Spacecraft and Cryogenic Technologies
- Nuclear reactor physics and engineering
- Silicon Carbide Semiconductor Technologies
- Nuclear Physics and Applications
- Atomic and Molecular Physics
- Natural Language Processing Techniques
- Advanced DC-DC Converters
- Theoretical and Computational Physics
- Characterization and Applications of Magnetic Nanoparticles
- Magnetic Bearings and Levitation Dynamics
- Dust and Plasma Wave Phenomena
University of Wisconsin–Madison
2015-2024
National Institutes for Quantum Science and Technology
2021
Princeton Plasma Physics Laboratory
2021
Kyushu University
2021
Edgewood College
2021
The University of Tokyo
2021
University of Washington
2001-2002
Energetics (United States)
2001
Energy confinement comparable with tokamak quality is achieved in the Madison Symmetric Torus (MST) reversed field pinch (RFP) at a high beta and low toroidal magnetic field. Magnetic fluctuations normally present RFP are reduced via parallel current drive outer region of plasma. In response, electron temperature nearly triples doubles. The time increases ten-fold (to ∼10 ms), which L- H-mode scaling values for same plasma current, density, heating power, size shape. Runaway evidenced by...
With the exploration of MA plasma current regime in up to 0.5 s long discharges, RFX-mod has opened new and very promising perspectives for reversed field pinch (RFP) magnetic configuration, made significant progress understanding improving confinement controlling stability. A big leap with respect previous knowledge expectations on RFP physics performance been by since last 2006 IAEA Fusion Energy Conference. self-organized helical equilibrium experimentally achieved (the Single Helical...
The Sun, being an active star, undergoes eruptions of magnetized plasma that reach the Earth and cause aurorae near poles. These eruptions, called coronal mass ejections (CMEs), send magnetic fields out into space. CMEs planetary orbits are interplanetary (ICMEs) a source geomagnetic storms, which can major damage to our modern electrical systems with limited warning. To study ICME propagation, we devised scaled experiment using Big Red Ball (BRB) containment device at Wisconsin Plasma...
Optimization of machine operation, including plasma position control, density control and especially feedback on multiple magnetohydrodynamic modes, has led RFX-mod to operate reliably at 1.5 MA, the highest current ever achieved a reversed field pinch (RFP). At high low magnetic topology spontaneously self-organizes in an Ohmical helical symmetry, with new axis helically twisting around geometrical torus. The separatrix island disappears leaving wide symmetric thermal structure large...
An overview of recent results from the MST programme on physics important for advancement reversed field pinch (RFP) as well improved understanding toroidal magnetic confinement more generally is reported. Evidence classical ions in RFP provided by analysis impurity and energetic created 1 MW neutral beam injection (NBI). The first appearance energetic-particle-driven modes NBI a plasma described. plasmas robustly access quasi-single-helicity state that has commonalities to stellarator...
This paper summarizes the main achievements of RFX fusion science program in period between 2008 and 2010 IAEA Fusion Energy Conferences. RFX-mod is largest reversed field pinch world, equipped with a system 192 coils for active control MHD stability. The discovery understanding helical states electron internal transport barriers core temperature >1.5 keV significantly advances perspectives configuration. Optimized experiments plasma current up to 1.8 MA have been realized, confirming...
Current-carrying, toroidal laboratory plasmas typically cannot be sustained with an electron density above the empirical Greenwald limit. Presented here are tokamak experiments in Madison Symmetric Torus a up to unprecedented level about 10 times this This is thought made possible part by thick, stabilizing, conductive wall, and high-voltage, feedback-controlled power supply driving plasma current. The radial profile of current flattens around twice limit, without edge collapse routinely...
Measurements and simulations show that plasma relaxation processes in the reversed field pinch drive redistribute both magnetic flux momentum. To examine this process, a new 3D Mach B-dot probe has been constructed. This collects ion saturation currents through six molybdenum electrodes arranged on flattened vertices of an octahedron made boron nitride (BN). The current flows configurable voltage dividers for measurement returns one selectable return equally spaced along 12 cm BN arm. In...
The Helicity Injected Torus [HIT-II: T. Jarboe et al., Phys. Plasmas 5, 1807 (1998)] is a low-aspect-ratio tokamak capable of both inductive (ohmic) and Coaxial Injection (CHI) current drive. HIT-II modest in size (major radius R=0.3 m, minor a=0.2 on-axis toroidal field up to 0.5 T), but has demonstrated 200 kA plasma current, using either CHI or induction separately. loop voltage, boundary flux, equilibrium are controlled by real-time flux feedback system. ohmic plasmas exhibit...
This paper reports the highlights of RFX-mod fusion science programme since last 2010 IAEA Fusion Energy Conference. The focused on two main goals: exploring potential reversed field pinch (RFP) magnetic configuration and contributing to solution key technology problems in roadmap ITER. Active control several plasma parameters has been a tool this endeavour. New upgrades system for active magnetohydrodynamic (MHD) stability are underway will be presented paper. Unique among existing devices,...
An overview of recent results from the MST reversed field pinch programme is presented. With neutral beam injection, bursty energetic particle (EP) modes are observed. The profiles magnetic and density fluctuations associated with these EP measured using a far infrared interferometer–polarimeter. Equilibrium reconstructions quasi-single-helicity 3D helical state provided by V3FIT code that now incorporates several MST's advanced diagnostics. orientation structure controlled new resonant...
Oscillating-field current drive (OFCD) is a steady-state magnetic helicity injection method to net toroidal in plasma by applying oscillating poloidal and loop voltages. OFCD added standard induction produce about 10% of the total Madison symmetric torus. The dependence on phase between two applied voltages measured. Maximum does not occur at maximum rate. Effects fluctuations dissipated power are shown.
To aid in diagnosis of 3D equilibria the Madison Symmetric Torus, it has become necessary to control orientation equilibria. In reversed field pinch experiments a transition equilibrium is common with sufficiently large plasma current (and Lundquist number). Diagnosis this state hampered by fact that helical structure stationary but an varies shot-to-shot. A resonant magnetic perturbation (RMP) technique been developed vary controllably and optimized minimize wall interaction due its use....
This paper explores the behavior of runaway electrons in tokamak plasmas at low electron density, plasma current, and magnetic field using experimental data from Madison Symmetric Torus (MST) computational NIMROD nonlinear resistive 3D MHD code. Density thresholds for onset suppression are determined experimentally steady plasmas, with a population electrons, resonant perturbations different poloidal mode numbers applied. Poloidal number m = 3 suppress while 1 have little effect. difference...
Internal fluctuation measurements with Faraday-effect polarimetry in the DIII-D tokamak reveal onset of a tearing mode toroidal number n = 3 well before it is detected by sensing coils external to plasma. This appears 2, 1 modes and first internal at lower value ideal-wall kink beta limit than indicated time detection coils. When detected, linear resistive stability parameter, Δ′, indicates marginal continues do so until later when amplitude begins increasing linearly time—together...
This paper presents the development of an all-in-one probe to simultaneously measure all components generalized Ohm’s law in reversed-field pinch plasmas and tokamaks. The polyhedral configuration Mach is achieved through specific arrangement, angle, depth collimator channel apertures drilled into surface a hollow boron nitride cylinder encasing it. includes central assess ion velocity field three dimensions. Initial tests at RELAX Madison Symmetric Torus machines have confirmed probe’s...
Confinement in the reversed field pinch (RFP) has been shown to increase strongly with current profile control. The MST RFP can operate two regimes: standard regime a naturally occurring density profile, robust reconnection and dynamo activity; improved confinement strong reduction reconnection, transport. New results plasmas include observation of two-fluid Hall effect dynamo, determination that m = 0 edge resonant mode is nonlinearly driven, tearing modes lock wall via eddy currents shell....
Generation and sustainment of the reversed field pinch (RFP) magnetic configuration normally relies on dynamo activity. The externally applied electric tends to drive equilibrium away from relaxed, minimum energy state which is roughly described by a flat normalized parallel current density profile at marginal stability tearing modes. Correlated fluctuations velocity create broadens profile, supplying necessary edge drive. These pervasive are also responsible for destruction flux surfaces,...
The Helicity Injected Torus (HIT-II) (Jarboe T R 1998 Phys. Plasmas 5 1807) is operated with either cathode or anode central column (CC) during coaxial helicity injection (CHI). CC polarity has a strong effect on tokamak behaviour. For operation, the magnetic profile inferred from surface data to be more relaxed, and n = 1 mode stronger slowly rotating than for operation. Mode toroidal rotation follows applied E×B direction. Ion spin-up in core consistent electromotive action. Apparently,...
The Helicity Injected Torus programme has made progress in understanding relaxation and helicity injection current drive. conserving MHD activity during the inductive (ohmic) ramp demonstrates profile flattening needed for coaxial (CHI). Results from cathode anode central column CHI pulses are consistent with electron locking model of drive a pure n = 1 mode. Finally, low density CHI, compatible ohmic operation, been achieved. Some enhancement discharges application heating is shown.
Tokamak plasmas often exhibit self-organizing behavior in which internal modes shape the toroidal current density profile, a common example being sawtooth instability. However, such has not been studied detail for edge safety factor below 2 due to disruptive kink instabilities that typically prevent operation this regime. Now, steady tokamak with an down 0.8 have created Madison Symmetric Torus, where disruptions are prevented thick, conductive wall and feedback power supply sustains plasma...
A high-resolution quartz ultraviolet spectrometer based on a single compact 16-channel multianode photomultiplier tube (MAPMT) has been developed and tested coaxial helicity injection ohmic transformer current drive plasmas generated the Helicity Injected Torus at University of Washington. The use MAPMT allows simple design with high light collection resolution for an ion Doppler shift diagnostic. quality low cost make it uniquely attractive university scale plasma experiments. impurity...
Oscillating-field current drive (OFCD) is a proposed method of steady-state toroidal plasma sustainment in which ac poloidal and loop voltages are applied to produce dc current. OFCD added standard, inductively sustained reversed-field pinch plasmas the Madison Symmetric Torus [R. N. Dexter et al., Fusion Technol. 19, 131 (1991)]. Equilibrium profiles fluctuations during single cycle measured analyzed for different relative phases between two off. For leading most current, energy confinement...
The modification of the shear Alfvén spectrum due to a core resonant magnetic island is used explain Alfvénic activity observed on Madison symmetric torus (MST) reversed-field pinch during neutral beam injection. Theoretical studies show that continua in provide gap which bursts reside. Numerical simulations using new code called SIESTAlfvén have identified as first observation an island-induced eigenmode (IAE) RFP. IAE arises from helical coupling harmonics island.