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High-Energy Electron Confinement in a Magnetic Cusp Configuration (Polywell)
http://journals.aps.org/prx/abstract/10.1103/PhysRevX.5.021024[font face=Serif][font size=5]High-Energy Electron Confinement in a Magnetic Cusp Configuration[/font]
[font size=4]Jaeyoung Park, Nicholas A. Krall, Paul E. Sieck, Dustin T. Offermann, Michael Skillicorn, Andrew Sanchez, Kevin Davis, Eric Alderson, and Giovanni Lapenta
Phys. Rev. X 5, 021024 – Published 11 June 2015
Abstract[/font]
[font size=3]We report experimental results validating the concept that plasma confinement is enhanced in a magnetic cusp configuration when ? (plasma pressure/magnetic field pressure) is of order unity. This enhancement is required for a fusion power reactor based on cusp confinement to be feasible. The magnetic cusp configuration possesses a critical advantage: the plasma is stable to large scale perturbations. However, early work indicated that plasma loss rates in a reactor based on a cusp configuration were too large for net power production. Grad and others theorized that at high ? a sharp boundary would form between the plasma and the magnetic field, leading to substantially smaller loss rates. While not able to confirm the details of Grad’s work, the current experiment does validate, for the first time, the conjecture that confinement is substantially improved at high ?. This represents critical progress toward an understanding of the plasma dynamics in a high-? cusp system. We hope that these results will stimulate a renewed interest in the cusp configuration as a fusion confinement candidate. In addition, the enhanced high-energy electron confinement resolves a key impediment to progress of the Polywell fusion concept, which combines a high-? cusp configuration with electrostatic fusion for a compact, power-producing nuclear fusion reactor.
…[/font]
[font size=4]V. CONCLUSIONS[/font]
[font size=3]The present experimental results demonstrate for the first time that high- ? plasma operation can dramatically improve high-energy electron confinement in the magnetic cusp system. The experimental results also show that the enhanced confinement persists even after ? decreases significantly in the cusp, requiring further investigation. This enhanced high-energy electron confinement resolves the key issue of poor electron-beam confinement in the low- ? cusp system that had impeded the progress of the Polywell fusion concept to date. The current plan is to extend the present work with increased electron beam power to sustain the high- ? plasma state and to form an electrostatic well. If the deep potential well can be formed and the scaling of the electron-beam confinement is found to be favorable, as conjectured by Grad and others, it may be possible to construct a compact high- ? fusion power reactor based on the Polywell concept.
…[/font][/font]
[font size=4]Jaeyoung Park, Nicholas A. Krall, Paul E. Sieck, Dustin T. Offermann, Michael Skillicorn, Andrew Sanchez, Kevin Davis, Eric Alderson, and Giovanni Lapenta
Phys. Rev. X 5, 021024 – Published 11 June 2015
Abstract[/font]
[font size=3]We report experimental results validating the concept that plasma confinement is enhanced in a magnetic cusp configuration when ? (plasma pressure/magnetic field pressure) is of order unity. This enhancement is required for a fusion power reactor based on cusp confinement to be feasible. The magnetic cusp configuration possesses a critical advantage: the plasma is stable to large scale perturbations. However, early work indicated that plasma loss rates in a reactor based on a cusp configuration were too large for net power production. Grad and others theorized that at high ? a sharp boundary would form between the plasma and the magnetic field, leading to substantially smaller loss rates. While not able to confirm the details of Grad’s work, the current experiment does validate, for the first time, the conjecture that confinement is substantially improved at high ?. This represents critical progress toward an understanding of the plasma dynamics in a high-? cusp system. We hope that these results will stimulate a renewed interest in the cusp configuration as a fusion confinement candidate. In addition, the enhanced high-energy electron confinement resolves a key impediment to progress of the Polywell fusion concept, which combines a high-? cusp configuration with electrostatic fusion for a compact, power-producing nuclear fusion reactor.
…[/font]
[font size=4]V. CONCLUSIONS[/font]
[font size=3]The present experimental results demonstrate for the first time that high- ? plasma operation can dramatically improve high-energy electron confinement in the magnetic cusp system. The experimental results also show that the enhanced confinement persists even after ? decreases significantly in the cusp, requiring further investigation. This enhanced high-energy electron confinement resolves the key issue of poor electron-beam confinement in the low- ? cusp system that had impeded the progress of the Polywell fusion concept to date. The current plan is to extend the present work with increased electron beam power to sustain the high- ? plasma state and to form an electrostatic well. If the deep potential well can be formed and the scaling of the electron-beam confinement is found to be favorable, as conjectured by Grad and others, it may be possible to construct a compact high- ? fusion power reactor based on the Polywell concept.
…[/font][/font]
http://arstechnica.com/science/2015/06/magnetic-mirror-holds-promise-for-fusion/
[font face=Serif][font size=5]Magnetic mirror holds promise for fusion[/font]
[font size=4]In a Polywell design, a high-density plasma excludes magnetic field, traps itself.[/font]
by Chris Lee - Jun 22, 2015 4:00pm EDT
[font size=3]Once upon a time, I worked at a research institute that was, for the most part, devoted to nuclear fusion. Although I was never involved myself, two things impressed me about the research. The first was the pure difficulty facing researchers: there are material, plasma physics, and control system issues that are enormously challenging. And, yet, progress is made—I am now, and will forever be, impressed by the achievements that I saw during my short stay among the fusion researchers.
…
The Polywell concept, instead, tries to create a magnetic box to confine the plasma in place, which reduces the turbulence and solves many control problems. However, a true box is simply not possible. This is because the force applied by a magnetic field depends on the direction of motion of a charged particle, which causes the electrons and ions to travel in a corkscrew motion around magnetic field lines. At each corner of the magnetic field box, the magnetic field lines point outward away from the center of the box, so the plasma can spiral out of the box. The upshot is that the harder you squeeze, the quicker the plasma leaks out, leaving you with a low beta plasma.
To help overcome this, additional high energy electrons are injected into the plasma. The electrons create a large negative potential that draws the ions to the center of the box, slowing their escape. Nevertheless, even with the electrostatic draw slowing ion escape, the magnetic field still wins in the end, because the electrons are also driven to spiral along magnetic field lines.
But researchers quickly realized that if the plasma was dense enough—in other words, if it had a high beta—it would exclude the magnetic field lines, creating a sharp boundary between the plasma and the magnetic field. The sharp boundary acts like a mirror for charged particles, vastly slowing their rate of ion escape. This unfortunately creates a chicken and egg scenario: if you have a high beta plasma, a Polywell design will keep it confined at high beta. But first, you must have a high beta plasma.
…[/font][/font]
[font size=4]In a Polywell design, a high-density plasma excludes magnetic field, traps itself.[/font]
by Chris Lee - Jun 22, 2015 4:00pm EDT
[font size=3]Once upon a time, I worked at a research institute that was, for the most part, devoted to nuclear fusion. Although I was never involved myself, two things impressed me about the research. The first was the pure difficulty facing researchers: there are material, plasma physics, and control system issues that are enormously challenging. And, yet, progress is made—I am now, and will forever be, impressed by the achievements that I saw during my short stay among the fusion researchers.
…
The Polywell concept, instead, tries to create a magnetic box to confine the plasma in place, which reduces the turbulence and solves many control problems. However, a true box is simply not possible. This is because the force applied by a magnetic field depends on the direction of motion of a charged particle, which causes the electrons and ions to travel in a corkscrew motion around magnetic field lines. At each corner of the magnetic field box, the magnetic field lines point outward away from the center of the box, so the plasma can spiral out of the box. The upshot is that the harder you squeeze, the quicker the plasma leaks out, leaving you with a low beta plasma.
To help overcome this, additional high energy electrons are injected into the plasma. The electrons create a large negative potential that draws the ions to the center of the box, slowing their escape. Nevertheless, even with the electrostatic draw slowing ion escape, the magnetic field still wins in the end, because the electrons are also driven to spiral along magnetic field lines.
But researchers quickly realized that if the plasma was dense enough—in other words, if it had a high beta—it would exclude the magnetic field lines, creating a sharp boundary between the plasma and the magnetic field. The sharp boundary acts like a mirror for charged particles, vastly slowing their rate of ion escape. This unfortunately creates a chicken and egg scenario: if you have a high beta plasma, a Polywell design will keep it confined at high beta. But first, you must have a high beta plasma.
…[/font][/font]
