Glen Wurden | Los Alamos National Laboratory (original) (raw)

Papers by Glen Wurden

Review of Scientific Instruments, 2004

Magnetic pickup coils and single turn flux loops are installed on the FRX-L device. The combinati... more Magnetic pickup coils and single turn flux loops are installed on the FRX-L device. The combination of the two measurements provides the excluded flux radius that approximates the separatrix radius of the field-reversed configuration (FRC) plasma. Arrays of similar probes are used to map out local magnetic field dynamics beyond both ends of the theta-coil confinement region to help understand the effects of cusp locations on flux trapping during the FRC formation process. Details on the probe design and system calibrations are presented. The overall system calibration of excluded flux radius measurement is examined by replacing FRC plasma with a known radius aluminum conductor cylinder.

Proceedings of 1994 IEEE 21st International Conference on Plasma Sciences (ICOPS)

During a major disruption in a tokamak, electrons can be accelerated to 10’s of MeV energies [1],... more During a major disruption in a tokamak, electrons can be accelerated to 10’s of MeV energies [1], and they can cause serious damage to the tokamak armor and vessel walls. These “runaway electrons” can quickly build up to a significant fraction of the original toroidal plasma current before they are eventually lost. For ITER, if runaways cannot be prevented and eliminated, they are expected to be a serious threat to machine operation. Not only would repeated water leaks (caused by runaways deeply damaging the armor) be a major inconvenience and cost, but they could essentially preclude getting administrative permissions to introduce tritium into ITER, which would prevent the study of burning DT plasmas. Therefore it is imperative that we gain an increased understanding of runaway electron dynamics, including generation and loss mechanisms in present-day tokamaks. We describe a proposal to build and field a powerful new diagnostic tool, called Laser Inverse Compton Scattering (LICS), ...

Physics of Plasmas, 2019

Wendelstein 7-X is the first comprehensively optimized stellarator aiming at good confinement wit... more Wendelstein 7-X is the first comprehensively optimized stellarator aiming at good confinement with plasma parameters relevant to a future stellarator power plant. Plasma operation started in 2015 using a limiter configuration. After installing an uncooled magnetic island divertor, extending the energy limit from 4 to 80 MJ, operation continued in 2017. For this phase, the electron cyclotron resonance heating (ECRH) capability was extended to 7 MW, and hydrogen pellet injection was implemented. The enhancements resulted in the highest triple product (6.5 Â 10 19 keV m À3 s) achieved in a stellarator until now. Plasma conditions [T e (0) % T i (0) % 3.8 keV, s E > 200 ms] already were in the stellarator reactor-relevant ion-root plasma transport regime. Stable operation above the 2nd harmonic ECRH X-mode cutoff was demonstrated, which is instrumental for achieving high plasma densities in Wendelstein 7-X. Further important developments include the confirmation of low intrinsic error fields, the observation of current-drive induced instabilities, and first fast ion heating and confinement experiments. The efficacy of the magnetic island divertor was instrumental in achieving high performance in Wendelstein 7-X. Symmetrization of the heat loads between the ten divertor modules could be achieved by external resonant magnetic fields. Full divertor power detachment facilitated the extension of high power plasmas significantly beyond the energy limit of 80 MJ.

Nuclear Fusion, 2019

The optimized superconducting stellarator device Wendelstein 7-X (with major radius , minor radiu... more The optimized superconducting stellarator device Wendelstein 7-X (with major radius , minor radius , and plasma volume) restarted operation after the assembly of a graphite heat shield and 10 inertially cooled island divertor modules. This paper reports on the results from the first high-performance plasma operation. Glow discharge conditioning and ECRH conditioning discharges in helium turned out to be important for density and edge radiation control. Plasma densities of with central electron temperatures were routinely achieved with hydrogen gas fueling, frequently terminated by a radiative collapse. In a first stage, plasma densities up to were reached with hydrogen pellet injection and helium gas fueling. Here, the ions are indirectly heated, and at a central density of a temperature of with was transiently accomplished, which corresponds to with a peak diamagnetic energy of and volume-averaged normalized plasma pressure . The routine access to high plasma densities was opened w...

Nuclear Fusion, 2017

In the first campaign Wendelstein 7-X was operated with five poloidal graphite limiters installed... more In the first campaign Wendelstein 7-X was operated with five poloidal graphite limiters installed stellarator symmetrically. In an ideal situation the power losses would be equally distributed between the limiters. The limiter shape was designed to smoothly distribute the heat flux over two strike lines. Vertically the strike lines are not uniform because of different connection lengths. In this paper it is demonstrated both numerically and experimentally that the heat flux distribution can be significantly changed by non-resonant n = 1 perturbation field of the order of 10 −4. Numerical studies are performed with field line tracing. In experiments perturbation fields are excited with five error field trim coils. The limiters are diagnosed with infrared cameras, neutral gas pressure gauges, thermocouples and spectroscopic diagnostics. Experimental results are qualitatively consistent with the simulations. With a suitable choice of the phase and amplitude of the perturbation a more symmetric plasma-limiter interaction can be potentially achieved. These results are also of interest for the later W7-X divertor operation.

Journal of Fusion Energy, 2015

In this community white paper, we describe an approach to achieving fusion which employs a hybrid... more In this community white paper, we describe an approach to achieving fusion which employs a hybrid of elements from the traditional magnetic and inertial fusion concepts, called magneto-inertial fusion (MIF). The status of MIF research in North America at multiple institutions is summarized including recent progress, research opportunities, and future plans.

28th IAEA Fusion Energy Conference (FEC 2020), 2020

Plasma Physics and Controlled Fusion, 2021

In the Wendelstein 7-X stellarator, the main locations of particle sources are expected to be the... more In the Wendelstein 7-X stellarator, the main locations of particle sources are expected to be the carbon divertors, baffles and graphite heat shield first wall. In this paper, the heat shield is implemented in EMC3-EIRENE to understand the expected areas and magnitudes of the recycling flux to this component. It is found that in the simulation the heat shield is not a significant source of recycling neutrals. The areas of simulated recycling flux are shown to correlate well with footprints of plasma-wetting seen in post-experimental campaign in-vessel inspection photos. EMC3-EIRENE reconstruction of line-integrated H-alpha measurements at the heat shield indicate that the majority of emission does not come from local recycling neutrals. Rather, the H-alpha signals at the heat shield are dominated by ionization of neutrals which have leaked from the divertor/baffle region into the midplane. The magnitude of the H-alpha line emission from the synthetic reconstruction is consistent wit...

2016 IEEE International Conference on Plasma Science (ICOPS), 2016

Summary form only given. A collaborative research effort was launched in 2000 between the Air For... more Summary form only given. A collaborative research effort was launched in 2000 between the Air Force Research Laboratory and Los Alamos National Laboratory to investigate the formation of high density field-reversed configuration (FRC) plasmas for the purpose of then adiabatically compressing them to a high energy density (HED) state. The goal of the experimental system developed through this collaboration was to enable a low-cost approach to achieving thermonuclear fusion of the target plasma, which would then facilitate magneto-inertial fusion studies, laboratory astrophysical studies, and numerous other basic research studies connected with HED plasmas. This system was assembled at the Shiva Star facility at the Air Force Research Laboratory and referred to as the Field-Reversed Configuration Heating Experiment (FRCHX). The target FRC plasma is formed in the experiment through a reversed-field theta pinch that uses four to five capacitor banks. Once formed, the FRC is translated a...

Review of Scientific Instruments, 2018

Nature Physics, 2018

In the version of this Article originally published, the superscript 6 indicating equally contrib... more In the version of this Article originally published, the superscript 6 indicating equally contributing authors was missing from M. Buzzi. This has now been corrected.

IEEE International Conference on Plasma Science

It has been shown that typically one-third of the input power is accounted for by radiation as me... more It has been shown that typically one-third of the input power is accounted for by radiation as measured by bolometers. This radiated power fraction has been varied from 0.15 to 0.95 in impurity injection experiments with the global β and τE values maintained to within a factor of two. This implies that the nonradiative confinement varied by a factor of five or more while the total confinement remained roughly the same. The fraction of the input power absorbed by fluctuations in the discharge is typically 0.2 to 0.3 in ZT-40M and correlates with the ion heating. Ion energy losses are dominated by recycling. Electrons are heated ohmically, and collisional coupling to the ions is relatively weak. Electron energy transport is dominated by a small number of energetic electrons moving along field lines to the edge. The field line wandering implied by this interpretation is consistent with the level of magnetic field fluctuation measured in the edge plasma

Physics of Fluids B: Plasma Physics, 1991

This paper documents the effects on confinement of introducing discrete limiters into the edge pl... more This paper documents the effects on confinement of introducing discrete limiters into the edge plasma of the ZT-40M reversed-field pinch (RFP) [Fusion Technol. 8, 157 1 (1985) 1. RFP confinement is not significantly degraded by appropriately designed single limiters inserted to a sufficient depth for effective local vacuum vessel wall protection. Inserting limiters too deeply into the plasma results in excess limiter heating, and a consequent increase in the impurity content of the plasma. Under these conditions the plasma loop voltage increases. The heating of the limiters is observed to be asymmetric, with the majority of the heat flux in ZT40M being attributable to suprathermal electrons [ Tsupra-2-3 X T, (0) ] reaching the edge moving almost unidirectionally along magnetic-field lines.

Fusion Technology, 1985

The present status of research on the ZT-40M Reversed-Field Pinch (RFP) will be described. RFP di... more The present status of research on the ZT-40M Reversed-Field Pinch (RFP) will be described. RFP discharges have been sustained for times (27 ms) >> the classical resistive diffusion time, implying the existence of a flux-sustainment mechanism (''dynamo''). This mechanism opens the possibility for a steady-state RFP reactor utilizing a unique form of non-inductive current drive. T /sub e/ > 500 eV has been obtained for 400 kA discharges with ⁻n /sub e/ about 4 x 10¹⁹ m⁻³. Total energy confinement time /tau/ /sub E/ has reached 0.7 ms with a Lawson parameter of 5 x 10¹⁶ m⁻³s for discharges with ⁻n /sub e/ = 8 x 10¹⁹ m⁻³ and T /sub e/ = 330 eV at a plasma current of 330 kA and 0.33 T total confining field at the wall. Reactor-like ..beta..theta about 10-20% is routinely obtained for plasma currents from 60-400 kA (..beta.. about ..beta..theta/2). Scaling of ⁻n /sub e/ /tau/ /sub E/ about I /sup 2.2+or-0.4/ is found, more than adequate for a compact RFP reactor.

Review of Scientific Instruments, 2004

Magnetic pickup coils and single turn flux loops are installed on the FRX-L device. The combinati... more Magnetic pickup coils and single turn flux loops are installed on the FRX-L device. The combination of the two measurements provides the excluded flux radius that approximates the separatrix radius of the field-reversed configuration (FRC) plasma. Arrays of similar probes are used to map out local magnetic field dynamics beyond both ends of the theta-coil confinement region to help understand the effects of cusp locations on flux trapping during the FRC formation process. Details on the probe design and system calibrations are presented. The overall system calibration of excluded flux radius measurement is examined by replacing FRC plasma with a known radius aluminum conductor cylinder.

Proceedings of 1994 IEEE 21st International Conference on Plasma Sciences (ICOPS)

During a major disruption in a tokamak, electrons can be accelerated to 10’s of MeV energies [1],... more During a major disruption in a tokamak, electrons can be accelerated to 10’s of MeV energies [1], and they can cause serious damage to the tokamak armor and vessel walls. These “runaway electrons” can quickly build up to a significant fraction of the original toroidal plasma current before they are eventually lost. For ITER, if runaways cannot be prevented and eliminated, they are expected to be a serious threat to machine operation. Not only would repeated water leaks (caused by runaways deeply damaging the armor) be a major inconvenience and cost, but they could essentially preclude getting administrative permissions to introduce tritium into ITER, which would prevent the study of burning DT plasmas. Therefore it is imperative that we gain an increased understanding of runaway electron dynamics, including generation and loss mechanisms in present-day tokamaks. We describe a proposal to build and field a powerful new diagnostic tool, called Laser Inverse Compton Scattering (LICS), ...

Physics of Plasmas, 2019

Wendelstein 7-X is the first comprehensively optimized stellarator aiming at good confinement wit... more Wendelstein 7-X is the first comprehensively optimized stellarator aiming at good confinement with plasma parameters relevant to a future stellarator power plant. Plasma operation started in 2015 using a limiter configuration. After installing an uncooled magnetic island divertor, extending the energy limit from 4 to 80 MJ, operation continued in 2017. For this phase, the electron cyclotron resonance heating (ECRH) capability was extended to 7 MW, and hydrogen pellet injection was implemented. The enhancements resulted in the highest triple product (6.5 Â 10 19 keV m À3 s) achieved in a stellarator until now. Plasma conditions [T e (0) % T i (0) % 3.8 keV, s E > 200 ms] already were in the stellarator reactor-relevant ion-root plasma transport regime. Stable operation above the 2nd harmonic ECRH X-mode cutoff was demonstrated, which is instrumental for achieving high plasma densities in Wendelstein 7-X. Further important developments include the confirmation of low intrinsic error fields, the observation of current-drive induced instabilities, and first fast ion heating and confinement experiments. The efficacy of the magnetic island divertor was instrumental in achieving high performance in Wendelstein 7-X. Symmetrization of the heat loads between the ten divertor modules could be achieved by external resonant magnetic fields. Full divertor power detachment facilitated the extension of high power plasmas significantly beyond the energy limit of 80 MJ.

Nuclear Fusion, 2019

The optimized superconducting stellarator device Wendelstein 7-X (with major radius , minor radiu... more The optimized superconducting stellarator device Wendelstein 7-X (with major radius , minor radius , and plasma volume) restarted operation after the assembly of a graphite heat shield and 10 inertially cooled island divertor modules. This paper reports on the results from the first high-performance plasma operation. Glow discharge conditioning and ECRH conditioning discharges in helium turned out to be important for density and edge radiation control. Plasma densities of with central electron temperatures were routinely achieved with hydrogen gas fueling, frequently terminated by a radiative collapse. In a first stage, plasma densities up to were reached with hydrogen pellet injection and helium gas fueling. Here, the ions are indirectly heated, and at a central density of a temperature of with was transiently accomplished, which corresponds to with a peak diamagnetic energy of and volume-averaged normalized plasma pressure . The routine access to high plasma densities was opened w...

Nuclear Fusion, 2017

In the first campaign Wendelstein 7-X was operated with five poloidal graphite limiters installed... more In the first campaign Wendelstein 7-X was operated with five poloidal graphite limiters installed stellarator symmetrically. In an ideal situation the power losses would be equally distributed between the limiters. The limiter shape was designed to smoothly distribute the heat flux over two strike lines. Vertically the strike lines are not uniform because of different connection lengths. In this paper it is demonstrated both numerically and experimentally that the heat flux distribution can be significantly changed by non-resonant n = 1 perturbation field of the order of 10 −4. Numerical studies are performed with field line tracing. In experiments perturbation fields are excited with five error field trim coils. The limiters are diagnosed with infrared cameras, neutral gas pressure gauges, thermocouples and spectroscopic diagnostics. Experimental results are qualitatively consistent with the simulations. With a suitable choice of the phase and amplitude of the perturbation a more symmetric plasma-limiter interaction can be potentially achieved. These results are also of interest for the later W7-X divertor operation.

Journal of Fusion Energy, 2015

In this community white paper, we describe an approach to achieving fusion which employs a hybrid... more In this community white paper, we describe an approach to achieving fusion which employs a hybrid of elements from the traditional magnetic and inertial fusion concepts, called magneto-inertial fusion (MIF). The status of MIF research in North America at multiple institutions is summarized including recent progress, research opportunities, and future plans.

28th IAEA Fusion Energy Conference (FEC 2020), 2020

Plasma Physics and Controlled Fusion, 2021

In the Wendelstein 7-X stellarator, the main locations of particle sources are expected to be the... more In the Wendelstein 7-X stellarator, the main locations of particle sources are expected to be the carbon divertors, baffles and graphite heat shield first wall. In this paper, the heat shield is implemented in EMC3-EIRENE to understand the expected areas and magnitudes of the recycling flux to this component. It is found that in the simulation the heat shield is not a significant source of recycling neutrals. The areas of simulated recycling flux are shown to correlate well with footprints of plasma-wetting seen in post-experimental campaign in-vessel inspection photos. EMC3-EIRENE reconstruction of line-integrated H-alpha measurements at the heat shield indicate that the majority of emission does not come from local recycling neutrals. Rather, the H-alpha signals at the heat shield are dominated by ionization of neutrals which have leaked from the divertor/baffle region into the midplane. The magnitude of the H-alpha line emission from the synthetic reconstruction is consistent wit...

2016 IEEE International Conference on Plasma Science (ICOPS), 2016

Summary form only given. A collaborative research effort was launched in 2000 between the Air For... more Summary form only given. A collaborative research effort was launched in 2000 between the Air Force Research Laboratory and Los Alamos National Laboratory to investigate the formation of high density field-reversed configuration (FRC) plasmas for the purpose of then adiabatically compressing them to a high energy density (HED) state. The goal of the experimental system developed through this collaboration was to enable a low-cost approach to achieving thermonuclear fusion of the target plasma, which would then facilitate magneto-inertial fusion studies, laboratory astrophysical studies, and numerous other basic research studies connected with HED plasmas. This system was assembled at the Shiva Star facility at the Air Force Research Laboratory and referred to as the Field-Reversed Configuration Heating Experiment (FRCHX). The target FRC plasma is formed in the experiment through a reversed-field theta pinch that uses four to five capacitor banks. Once formed, the FRC is translated a...

Review of Scientific Instruments, 2018

Nature Physics, 2018

In the version of this Article originally published, the superscript 6 indicating equally contrib... more In the version of this Article originally published, the superscript 6 indicating equally contributing authors was missing from M. Buzzi. This has now been corrected.

IEEE International Conference on Plasma Science

It has been shown that typically one-third of the input power is accounted for by radiation as me... more It has been shown that typically one-third of the input power is accounted for by radiation as measured by bolometers. This radiated power fraction has been varied from 0.15 to 0.95 in impurity injection experiments with the global β and τE values maintained to within a factor of two. This implies that the nonradiative confinement varied by a factor of five or more while the total confinement remained roughly the same. The fraction of the input power absorbed by fluctuations in the discharge is typically 0.2 to 0.3 in ZT-40M and correlates with the ion heating. Ion energy losses are dominated by recycling. Electrons are heated ohmically, and collisional coupling to the ions is relatively weak. Electron energy transport is dominated by a small number of energetic electrons moving along field lines to the edge. The field line wandering implied by this interpretation is consistent with the level of magnetic field fluctuation measured in the edge plasma

Physics of Fluids B: Plasma Physics, 1991

This paper documents the effects on confinement of introducing discrete limiters into the edge pl... more This paper documents the effects on confinement of introducing discrete limiters into the edge plasma of the ZT-40M reversed-field pinch (RFP) [Fusion Technol. 8, 157 1 (1985) 1. RFP confinement is not significantly degraded by appropriately designed single limiters inserted to a sufficient depth for effective local vacuum vessel wall protection. Inserting limiters too deeply into the plasma results in excess limiter heating, and a consequent increase in the impurity content of the plasma. Under these conditions the plasma loop voltage increases. The heating of the limiters is observed to be asymmetric, with the majority of the heat flux in ZT40M being attributable to suprathermal electrons [ Tsupra-2-3 X T, (0) ] reaching the edge moving almost unidirectionally along magnetic-field lines.

Fusion Technology, 1985

The present status of research on the ZT-40M Reversed-Field Pinch (RFP) will be described. RFP di... more The present status of research on the ZT-40M Reversed-Field Pinch (RFP) will be described. RFP discharges have been sustained for times (27 ms) >> the classical resistive diffusion time, implying the existence of a flux-sustainment mechanism (''dynamo''). This mechanism opens the possibility for a steady-state RFP reactor utilizing a unique form of non-inductive current drive. T /sub e/ > 500 eV has been obtained for 400 kA discharges with ⁻n /sub e/ about 4 x 10¹⁹ m⁻³. Total energy confinement time /tau/ /sub E/ has reached 0.7 ms with a Lawson parameter of 5 x 10¹⁶ m⁻³s for discharges with ⁻n /sub e/ = 8 x 10¹⁹ m⁻³ and T /sub e/ = 330 eV at a plasma current of 330 kA and 0.33 T total confining field at the wall. Reactor-like ..beta..theta about 10-20% is routinely obtained for plasma currents from 60-400 kA (..beta.. about ..beta..theta/2). Scaling of ⁻n /sub e/ /tau/ /sub E/ about I /sup 2.2+or-0.4/ is found, more than adequate for a compact RFP reactor.

G. A. Wurden Los Alamos National Laboratory Workshop: MFE Roadmapping in the ITER Era Princeto... more G. A. Wurden
Los Alamos National Laboratory
Workshop: MFE Roadmapping in the ITER Era
Princeton, NJ
Sept. 9, 2011
LA-UR-11-11465

ITER (and someday DEMO) will operate subject to multiple physics and engineering constraints, and to be successful they must satisfy many constraints simultaneously. One of the most serious issues a large tokamak will face is controlling 100’s of MJ of plasma energy that can be quickly released in the event of a disruption, whether due to burning plasma issues, or more everyday tokamak physics. The number of full energy disruptions that an armor system in a large tokamak can survive is very small, due to the opposing engineering constraints of rapid heat removal in steady-state, versus designing survivability to transient events. Multimegaampere beams of runaway electrons (created by the avalanche effect after a disruption) hitting thin armor tiles will prevent achieving the desired science or energy missions, if not eliminated. A coordinated global effort to avoid, control, and mitigate tokamak disruptions must be developed with the highest priority. The timing for this effort must be now, before ITER begins operation, as a key element of prudent risk management in a global MFE program. Supported by DOE Contract DE-AC52-06-NA25396

LANL Fusion Energy Sciences Research G. A. Wurden Fusion Power Associates Meeting Washington DC D... more LANL Fusion Energy Sciences Research
G. A. Wurden
Fusion Power Associates Meeting
Washington DC
Dec. 11, 2013
LA-UR-13-29463

G. A. Wurden, with C. Grabowski, J. H. Degnan, D. J. Amdahl, M. Domonkos, E. L. Ruden, W. M. Whi... more G. A. Wurden,
with C. Grabowski, J. H. Degnan, D. J. Amdahl, M. Domonkos, E. L. Ruden, W. M. White, M. H. Frese, S. D. Frese, J. F. Camacho, S. K. Coffey, M. Kostora, J. McCullough, W. Sommars, B. Bauer, S. R. Fuelling, K. Yates, A. G. Lynn

Exploratory Plasma Research 2013 Workshop
Feb. 12-16, 2013
LA-UR-13-20795