Polywell

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The polywell is a type of nuclear fusion reactor that uses an electric field to heat ions to fusion conditions. It is closely related to the magnetic mirror, the fusor, the biconic cusp and the high beta fusion reactor. A set of electromagnets generates a magnetic field which traps electrons. This creates a negative voltage, which attracts positive ions. As the ions accelerate towards the negative center, their kinetic energy rises. If the ions collide in the center, they can fuse.

The polywell is one of many devices, which use an electric field to heat ions to fusion conditions.[1] This branch of fusion research is known as Inertial electrostatic confinement. The polywell was developed by Robert Bussard, as an improvement over the fusor. His company, EMC2, Inc., developed the initial devices for the U.S. Navy.

Mechanism[edit]

Fusor[edit]

Main article: Fusor
A homemade fusor
Farnsworth–Hirsch fusor during operation in so called "star mode" characterized by "rays" of glowing plasma which appear to emanate from the gaps in the inner grid.

A Farnsworth-Hirsch fusor consists of two wire cages, one inside the other. These are often referred to as grids. This structure is placed inside a vacuum chamber. The outer cage is charged positively against the inner cage. Nuclei are injected as ions into the system. The most common fuel used is ionized deuterium gas. Because the ions are positive they fly towards the negative inner cage. If they miss the inner cage, they will fly right through the center of the device at high speeds. They can fly out the other side of the inner cage. As the ions move outward, they feel a Coulomb force which directs them back towards the center. Over time, a core of ionized gas can form inside the inner cage. They continue to pass back and forth through the core until they strike either the grid or another nucleus. Most strikes with other nuclei do not result in fusion, but occasionally the strikes are sufficiently energetic that fusion results. Grid strikes raise the temperature of the grid and lower the energy of the plasma.

In fusors, the potential well is made with a wire cage. Because most of the ions fall into the cage, fusors suffer from high conduction losses. Hence, no fusor has ever come close to break-even energy output.

This is an illustration of the basic mechanism of fusion in fusors. (1) The fusor contains two concentric wire cages. The cathode is inside the anode. (2) Positive ions are attracted to the inner cathode. They fall down the voltage drop. The electric field does work on the ions heating them to fusion conditions. (3) The ions miss the inner cage. (4) The ions collide in the center and may fuse.[2][3]

Polywell[edit]

A plot of the magnetic field generated by the MaGrid inside a polywell. The null point is marked in red in the center.

The problem with the fusor is that the inner wire cage conducts away too much energy and mass. The solution, suggested by Robert Bussard and Oleg Lavrentiev,[4] was to replace the negative cage with a "virtual cathode" made of a cloud of electrons.

A polywell consists of several parts:[5]

  • A vacuum chamber
  • Inside the chamber, a set of positively charged electromagnet coils are arranged in a polyhedron called the MaGrid. The simplest MaGrid and the most studied so far is the truncated cube, composed of six ring-shaped coils arranged like the six faces of a cube. The six magnetic poles are pointing in the same direction toward the center. The magnetic field vanishes at the center by symmetry, creating a null point.
  • Electron guns facing ring axis. Once inside the MaGrid, the electrons are confined by the magnetic fields. Those gaining enough energy manage to escape through the magnetic cusps, but are retained by the electric field and tend to slow down and return inside the MaGrid along the cusps, away from the grid, avoiding surface contact and losses. Most of electrons are trapped in the middle of the device. The electrons act as a virtual cathode, a negative electric potential well attracting the positive ions.
  • Gas puffers at corner. The cold gas puffed inside the MaGrid ionizes when it reaches the electron cloud. Ions fall down the potential well, building up speed, slamming together and fusing in the center. Ions are electrostatically confined so densely that they increase the fusion rate, releasing more energy.

The magnetic energy density required to confine electrons is far smaller than that required to directly confine ions, as is done in other fusion projects such as ITER.[6][7][8]

Behavior[edit]

This is an illustration of single electron motion inside the polywell. It is based on figures from "Low beta confinement in a polywell modeled with conventional point cusp theories" but is not an exact copy.

Magnetic mirror and cusp confinement[edit]

Almost all simulations and experiments with polywells involved low-beta plasma regimes (where β < 1).[9] In such configurations, the plasma pressure is weak compared to the magnetic pressure. The electron recirculation and losses occur through the magnetic cusps. The electron cloud in the center is confined by cusp confinement, as an improvement over the simpler magnetic mirror confinement in biconic cusp experiments.[10]

The biconic cusp consists of two opposed ring-shaped electromagnetic coils, spaced apart the diameter of the ring. The losses in this mirror device come from two point cusps, each located at the center of the rings; and one linear equatorial cusp between the rings.[11]

The truncated cube polywell is an improvement over this design because it moves the magnets closer together, thus narrowing the problematic line cusps, while still preserving the internal volume of the reactor. The MaGrid has six point cusps, each located in the middle of the rings; and two highly modified line cusps, linking the eight corner cusps located at cube vertices. The key is that these two line cusps are much narrower than the single line cusp in the traditional magnetic mirror machines, so the net losses are less. The two line cusps losses are similar to or lower than the six face-centered point cusps.[12]

Wiffle-Ball confinement[edit]

In 1955, Harold Grad theorized that a high-beta configuration coupled with a cusped magnetic field would dramatically improve plasma confinement.[13] Following this idea, Bussard repeatedly claimed that at β = 1 the central electron cloud would become diamagnetic and would push the magnetic field lines back, out from the center; almost closing the cusps through which electrons can escape, increasing the number of electrons being trapped inside.

WiffleBall confinement in a Polywell: magnetic field lines are expelled and cusps narrowed inside MaGrid due to the high-beta diamagnetic cloud of electrons in the center.

Cusped confinement was explored theoretically [14] and experimentally.[15] However, most cusped experiments failed and disappeared from national programs by 1980. Bussard later called this type of confinement the Wiffle-Ball. This analogy was used to describe electron trapping inside the field. Marbles can be trapped inside a Wiffle ball, a hollow, perforated sphere; if marbles are put inside, they can roll and sometimes escape through the holes in the sphere. The magnetic topology of a high-beta polywell acts similarly with electrons.

Evolution of magnetic topology inside a Polywell from magnetic mirror to WiffleBall confinement. B = constant and I = variable.

For many decades, cusped confinement never behaved experimentally as was predicted. Sharply bent fields were even used by Lawrence Livermore National Laboratory in a series of magnetic mirror machines from the late sixties to mid eighties. After investing hundreds of millions into the program, the machines still leaked plasma at the field ends. Many scientists shifted focus onto looping the fields making the tokamak. it was thought the cusped confinement effect did not even exist. Until June 2014, when EMC2 published a preprint[16] provide strong evidence that the effect is real.

According to Bussard, typical cusp leakage rate is such that an electron makes 5 to 8 passes before escaping through a cusp in a standard mirror confinement biconic cusp; 10 to 60 passes in a polywell under mirror confinement (at low-beta) that he called cusp confinement; and several thousand passes in Wiffle-Ball confinement (high Beta).[17][18]

In February 2013, Lockheed Martin Skunk Works announced a new compact fusion machine, the high beta fusion reactor, closely related to the biconic cusp and the polywell, and working at β = 1.[19]

Particles motion[edit]

Inside the MaGrid, single electrons travel straight through the null point, due to their infinite gyroradius in regions of no magnetic field. Next, as they head towards the MaGrid, they experience a Lorentz force which causes them to corkscrew tighter and tighter along the denser magnetic field lines.[9][20] Their gyroradius shrinks and when they hit a dense magnetic field they can be reflected using the magnetic mirror effect.[21][22][23] Electron trapping has been measured in polywells with Langmuir probes.[8][24][25]

A visualization of the electron flow in a polywell has been made in 3D simulations by Indrek Mare.[26]

The polywell attempts to confine the ions and electrons through two different means, borrowed from fusors and magnetic mirrors. The electrons are easier to confine magnetically because they have so much less mass than the ions.[27] The machine confines ions using an electric field in the same way a fusor confines the ions: in the polywell, the ions are attracted to the negative cloud in the center. In the fusor, they are attracted to a negative wire cage in the center.

Electron recirculation and thermalization[edit]

The space between the MaGrid and the vacuum chamber must be sufficient for the electron recirculation through all cusps of the machine, so that cusp electron flow is not a loss mechanism to structures.[28][29]

According to Bussard, the plasma is nonthermal in the sense that it does not reach Maxwellian thermalization statistics; and not that ions and electrons have different average temperatures. Questions have been raised about the ability of the polywell to maintain a quasi-monoenergetic energy distributions among the ion and electron populations, which are driven by the continuous injection of new electrons in order to recover from their loss to structures, and because an excess of electrons is needed to maintain the negative potential well.[5]

If the electrons lifetime is too long in the polywell, electrons could become thermalized, and develop high energy loss distributions. But this has been proven not to be the case, because the potential wells for the ions and the electrons are in opposite directions, so the Coulomb collisions varies so greatly across the system:

  • at the edge, ions are slow whereas electrons are fast with a small Coulomb cross-section;
  • at the center, ions are fast whereas electrons are slow with a high cross-section, but they occupy a small volume for a short fractional time of their transit life in the system.

This variation is sufficient to prevent energy spreading in the electron population before the electrons are lost by collisions with walls. Similarly, for ion-ion and electron-ion collisions before ions can fuse vary so greatly across the system that fusion reaction rates dominate the tendency to energy exchange and spreading.

Since the electrons are slower in the center where fusion reactions occur, the Bremsstrahlung is less in this core region. This is why Bremsstrahlung may be less that predicted by Rider.[30] As of 2014, whether the electrons are thermalized and the plasma is thermal or not remains to be demonstrated experimentally.

Considerations for net power[edit]

Fuel type[edit]

This is a plot of the cross section of different fusion reactions.

Nuclear fusion refers to reactions in which lighter nuclei are combined to become heavier nuclei. This process changes mass into energy which may be captured to provide fusion power. Many types of atoms can be fused. The probability of a fusion reaction occurring is controlled by the cross section of the fuel,[31] which is in turn a function of its temperature. The easiest nuclei to fuse are deuterium and tritium, and their fusion occurs when the ions have a temperature of at least 4 keV (kiloelectronvolts) or about 45 million Kelvin. The polywell would achieve this by accelerating an ion with a charge of 1 down a 4,000 volt electric field. The high cost, short half-life and radioactivity of tritium made it difficult to be used by Bussard's team. The second easiest reaction is to fuse deuterium with itself. Because of its low cost, deuterium is commonly used by Fusor amateurs, and Bussard's polywell experiments were performed using this fuel. Any fusion reaction using deuterium or tritium will produce a fast neutron and is therefore radioactive. Bussard's goal was to fuse boron-11 with protons; this is a fusion reaction which is aneutronic (does not produce neutrons). An advantage of p-11B as a fusion fuel is that the primary reactor output would be energetic alpha particles, which can be directly converted to electricity at high efficiency (>90%) using suitably engineered collectors.

Lawson criterion[edit]

At such conditions, the atoms are ionized and make a plasma. The energy generated by fusion, inside a hot plasma cloud can be found with the following equation.[32]

P_\text{fusion} = n_A n_B \langle \sigma v_{A,B} \rangle E_\text{fusion}

where:

  • P_\text{fusion} is the fusion power density (energy per time per volume),
  • n is the number density of species A or B (particles per volume),
  • \langle \sigma v_{A,B} \rangle is the product of the collision cross-section σ (which depends on the relative velocity) and the relative velocity of the two species v, averaged over all the particle velocities in the system.

This equation shows that energy varies with the temperature, density, speed of collision, and fuel used. To reach net power, fusion reactions have to occur fast enough to make up for energy losses. Any power plant using fusion will hold in this hot cloud. Plasma clouds lose energy through conduction and radiation.[32] Conduction is when ions, electrons or neutrals touch a surface and leak out. Energy is lost with the particle. Radiation is when energy leaves the cloud as light. Radiation increases as the temperature rises. To get net power from fusion, you must overcome these losses. This leads to an equation for power output (where: η is machine efficiency).

P_\text{out} = \eta_\text{capture}\left(P_\text{fusion} - P_\text{conduction} - P_\text{radiation}\right)

John Lawson used this equation to estimate some conditions for net power [32] based on a Maxwellian cloud.[32] This is the Lawson criterion.

However, the Lawson criterion could not be used for a Polywell if Bussard's conjecture about the plasma being nonthermal is proven to be right. John D. Lawson himself stated in his founding report (p. 4, part 5):[32] "It is of course easy to postulate systems in which the velocity distribution of the particle is not Maxwellian. These systems are outside the scope of this report." But he also rules-out the possibility of a nonthermal plasma to ignite: "Nothing may be gained by using a system in which electrons are at a lower temperature [than ions]. The energy loss in such a system by transfer to the electrons will always be greater than the energy which would be radiated by the electrons if they were are the [same] temperature."

Criticism[edit]

In his thesis[33] and his 1995 publication,[30] MIT doctoral student Todd Rider had calculated that X-ray radiation losses with this fuel will exceed fusion power production by at least 20%. Rider modeled the system using the following assumptions:

  • The plasma was quasineutral. Therefore positives and negatives were equally mixed together.[30]
  • The fuel was evenly mixed throughout the volume.[30]
  • The plasma was isotropic, meaning that its behavior was the same in any given direction.[30]
  • The plasma had a uniform energy and temperature throughout the cloud.[30]
  • The plasma was an unstructured Gaussian sphere, with a strongly converged dense central core. The core represented a small (~1%) part of the total volume.[30] In a later 1995 paper, William Nevins at LANL argued against this assumption. He argued that the particles would build up angular momentum, causing the dense core to degrade.[34] The loss of density inside the core would reduce fusion rates.
  • The potential well was broad and flat.[30]

Based on these assumptions, Rider used general equations[35] to estimate the rates of different physical effects. These included, but were not limited to, the loss of ions to up-scattering, the ion thermalization rate, the energy loss due to X-ray radiation and the fusion rate.[30] His conclusions were that the device suffered from "fundamental flaws".[30]

By contrast, Bussard has argued[18] that the plasma inside the polywell has different structure, temperature distribution and well profile. These characteristics have not been fully measured and are central to the device's feasibility. Based on this his calculations indicate that the bremsstrahlung losses would be much smaller.[36][37] According to Bussard the high speed and therefore low cross section for Coulomb collisions of the ions in the core makes thermalizing collisions very unlikely, while the low speed at the rim means that thermalization there has almost no impact on ion velocity in the core.[38][39] Bussard calculated that a polywell reactor with a radius of 1.5 meters would produce net power fusing deuterium.[40]

Other studies also disproved some of assumptions made by Rider and Nevins, arguing the real fusion rate and the associated recirculating power (needed to overcome the thermalizing effect and sustain the non-Maxwellian ion profile) could be estimated only with a self-consistent collisional treatment of the ion distribution function, lacking in Rider's work.[41]

Energy capture[edit]

It has been proposed that energy may be extracted in polywells using heat capture or, in the case of aneutronic fusion like D-3He or p-11B, direct energy conversion, though that scheme will have general challenges. The energetic alpha particles (up to a few MeV) generated by the aneutronic fusion reaction would exit the MaGrid through the six axial cusps as cones (spread ion beams). Direct conversion collectors inside the vacuum chamber would convert the kinetic energy of the positively charged alpha particles to a high-voltage direct current. If the alpha particles can slow down enough before they contact the collector plates, a very high conversion efficiency (over 90%) is expected.[42]

History[edit]

In the late 1960s there were several investigations of polyhedral magnetic fields as a possibility to confine a fusion plasma.[43][44] The first proposal to combine this magnetic configuration with an electrostatic potential well in order to improve electron confinement was made by Oleg Lavrentiev in 1975.[4] The idea was picked up by Robert Bussard in 1983, a link acknowledged in the references cited by his 1989 patent application,[12] though in 2006 he appears to claim to have re-discovered the idea independently.[45]

HEPS[edit]

Research was funded first by the Defense Threat Reduction Agency beginning in 1987 and later by DARPA.[24]:32:30 This funding resulted in a first machine known as the high energy power source (HEPS) experiment. This was built by Directed Technologies Inc in San Diego.[46] This machine was a large (190 cm across) machine, where the rings were placed outside of the vacuum chamber.[24]:32:33 This machine performed poorly because the magnetic fields sent electrons into the walls, driving up conduction losses. At the time, these losses were thought to be due to poor electron injection.[46] The United States Navy began providing low-level funding to the project in 1992.[47] Results from the HEPS program were published by Nicholas Krall in 1994.[46]

Bussard, who had been an advocate for Tokamak research, became the advocate for this concept, so that the idea is now indelibly associated with his name. In 1995 he sent a letter to the United States Congress stating that he had only supported Tokamaks in order to get fusion research sponsored by the government, but he now believed that there are better alternatives to Tokamaks.

EMC2, Inc.[edit]

Robert Bussard founded Energy/Matter Conversion Corporation, Inc. (aka EMC2) in 1985[12][24] and after the HEPS program ended, the company took on the research. Successive machines were made, starting from WB-1 to WB-8. The company won an SBIR I grant in 1992–93 and an SBIR II grant in 1994–95, both from the US Navy.[45] In 1993, it received a grant from the Electric Power Research Institute to examine the use of this machine in power production.[45] In 1994, The company received small grants from NASA and LANL.[45] Starting in 1999, the company was primarily funded by the US Navy.[45]

One early design was WB-1, which had six conventional magnets in a cube. This device was 10 cm across.[45] This was followed by WB-2, which used coils of wires to generate the magnetic field. Each electromagnet had a square cross section, which created problems. The magnetic fields drove electrons into the metal rings raising conduction losses and affects electron trapping. This design also suffered from "funny cusp" losses at the joints between magnets. The WB-6 machine attempted to address these problems, by using circular rings and spacing them some distance apart.[24] The next device, PXL-1, was built in 1996 and 1997. This machine was 26 cm across and used flatter rings to generate the field.[45] From 1998 to 2005 the company built a succession of six machines: WB-3, MPG-1,2, WB-4, PZLx-1, MPG-4 and WB-5. All of these reactors were six magnet designs built as a cube or truncated cube. They ranged from 3 to 40 cm in radius.[45]

Despite initial difficulties in spherical electron confinement, at the time of the 2005 research project's termination, Bussard reported a fusion rate of 109 per second running D-D fusion reactions at only 12.5 kV (based on detecting a total of nine neutrons in five tests,[18][48] giving a wide confidence interval). He stated that the fusion rate achieved by WB-6 was roughly 100,000 times greater than what Farnsworth achieved at similar well depth and drive conditions.[49][50] By comparison, researchers at the University of Wisconsin–Madison reported a neutron rate of up to 5×109 per second at voltages of 120 kV with an electrostatic fusor without magnetic fields.[51]

Bussard asserted, by using superconductor coils, the only significant energy loss channel is through electron losses proportional to the surface area. He also stated that the density would scale with the square of the field (constant beta conditions), and the maximum attainable magnetic field would scale with the radius (technological constraints). Under those conditions, the fusion power produced would scale with the seventh power of the radius, and the energy gain would scale with the fifth power. While Bussard did not publicly document the physical reasoning underlying this estimate,[52] if true, it would enable a model only ten times larger to be useful as a fusion power plant.[18]

WB-6[edit]

Funding became tighter and tighter. According to Bussard, "The funds were clearly needed for the more important War in Iraq."[50] An extra $900k of Office of Naval Research funding allowed the program to continue long enough to reach WB-6 testing in November 2005. The WB-6 machine had rings with circular cross sections that space apart at the joints. This reduced the metal surface area unprotected by magnetic fields. These changes dramatically improved system performance, leading to more electron recirculation and better confinement of electrons, in a progressively tighter core. This machine produced a fusion rate of 109 per second. This is based on a total of nine neutrons in five tests, giving a wide confidence interval.[18][48] Drive voltage on the WB-6 tests was about 12.5 kV, with a resulting potential well depth of about 10 kV.[18] Thus deuterium ions could have a maximum of 10 keV of kinetic energy in the center. By comparison, a Fusor running deuterium fusion at 10 kV would produce a fusion rate difficult to detect at all. Robert L. Hirsch reported a fusion rate this high only by driving his machine with a 150 kV drop between the inside and outside cages.[53] Hirsch also used deuterium and tritium, a much easier fuel to fuse, because it has a higher nuclear cross section.

While the pulses of operation in WB-6 were sub-milliseconds, Bussard felt the conditions should represent steady state as far as the physics are concerned. A last-minute test of WB-6 ended prematurely when the insulation on one of the hand-wound electromagnets burned through, destroying the device.

Efforts to restart funding[edit]

With no more funding during 2006, the project was stalled. This ended an 11 year embargo on publication and publicizing which the US Navy had in place from 1994 and 2005 [54] The company's military-owned equipment was transferred to SpaceDev, which also hired three of the team's researchers.[50] After the transfer, Bussard tried to attract new investors, giving talks trying to raise interest in his design. He gave a talk at Google headquarters entitled, "Should Google Go Nuclear?"[24] He also presented and published an overview of the work at the 57th International Astronautical Congress in October 2006.[18] He presented at an internal Yahoo! Tech Talk on April 10, 2007.[55] and spoke on the internet talk radio show The Space Show on May 8, 2007. Bussard had plans for a WB-8 machine which was a higher-order polyhedron, with 12 electromagnets. However, this design was not used in the actual WB-8 machine.

Bussard believed that the WB-6 machine had demonstrated itself to the degree and that no intermediate-scale models would be needed, and noted, "We are probably the only people on the planet who know how to make a real net power clean fusion system"[49] He proposed to rebuild WB-6 more robustly to verify its performance. After publishing the results, he planned to convene a conference of experts in the field in an attempt to get them behind his design. The first step in that plan was to design and build two more small scale designs (WB-7 and WB-8) to determine which full scale machine would be best. He wrote "The only small scale machine work remaining, which can yet give further improvements in performance, is test of one or two WB-6-scale devices but with "square" or polygonal coils aligned approximately (but slightly offset on the main faces) along the edges of the vertices of the polyhedron. If this is built around a truncated dodecahedron, near-optimum performance is expected; about 3–5 times better than WB-6." [18] Robert W. Bussard died in October 6, 2007 from multiple myeloma at the age of 79.[56]

In 2007, Stephen Chu, Nobel laureate and former United States Secretary of Energy, answered a question about polywell at a tech talk at Google. He said: "So far, there's not enough information so [that] I can give an evaluation of the probability that it might work or not...But I'm trying to get more information."[57]

Bridge funding 2007–09[edit]

Reassembling team[edit]

In August 2007, EMC2 received a $1.8M U.S. Navy contract to continue the reactor development.[58] Before Bussard's death in October, 2007,[59] Dolly Gray, who co-founded EMC2 with Bussard and served as its president and CEO, helped assemble the small team of scientists in Santa Fe to carry on his work. The group was led by Richard Nebel and included Princeton trained physicist Jaeyoung Park. Both physicists were on leave from the Los Alamos National Laboratory (LANL). The group also included Mike Wray, the physicist who ran the key 2005 tests; and Kevin Wray, who is the computer specialist for the operation.

WB-7[edit]

A more robust version of the WB-6 fusion device, was constructed at a machine shop in San Diego and shipped to Santa Fe to the EMC2 testing facility. The device was termed WB-7 and like prior ones, was designed by engineer Mike Skillicorn. This machine has a design similar to WB-6. WB-7, achieved "1st plasma" in early January, 2008.[60][61] In August 2008, the team finished the first phase of their experiment and submitted the results to a peer review board. Based on this review, federal funders agreed the team should proceed to the next phase. Nebel has said "we have had some success", referring to the team's effort to reproduce the promising results obtained by Bussard. "It's kind of a mix", Nebel reported. "We're generally happy with what we've been getting out of it, and we've learned a tremendous amount" he also said.[62]

FY 2009 work[edit]

In September 2008 the Naval Air Warfare Center, Weapons Division, China Lake, California publicly pre-solicited a contract for research on an Electrostatic "Wiffle Ball" Fusion Device.[63] In October 2008 the US Navy publicly pre-solicited two more contracts[64][65] also targeted toward EMC2 as preferred supplier. These two tasks were to develop better instrumentation and to develop an ion injection gun.[66][67] In December 2008, following many months of review by the expert review panel of the submission of the final WB-7 results, Richard Nebel commented that "There's nothing in [the research] that suggests this will not work", but "That's a very different statement from saying that it will work."[68]

In January 2009 the Naval Air Warfare Center pre-solicited another contract for "modification and testing of plasma wiffleball 7"[69] which appears to be funding to install the instrumentation developed in a prior contract, install a new design for the connector (joint) between coils, and operate the WB-7 with the modifications. The modified unit is now called WB-7.1. This pre-solicitation started as a $200k contract but the final award was for $300k.

In April 2009, the DoD published a plan to provide Polywell a further $2 million in funding as part of the American Recovery and Reinvestment Act of 2009. The citation in the legislation was labelled as Plasma Fusion (Polywell) – Demonstrate fusion plasma confinement system for shore and shipboard applications; Joint OSD/USN project.[70] The citation occurs 166 pages into the document, and suggests development of the device for 'Domestic Energy Supply / Distribution'.

Contract with United States Navy[edit]

In September 2009, the Recovery Act funded the Navy in the amount of $7.86M to construct and test a WB-8.[71] The Navy contract has an option for an additional $4.46M for "...based on the results of WB8 testing, and the availability of government funds the contractor shall develop a WB machine (WB8.1) which incorporates the knowledge and improvements gained in WB8. It is expected that higher ion drive capabilities will be added, and that a "PB11" reaction will be demonstrated".[71] This device increase the magnetic field strength eightfold over WB-6. The US Department of Defense announced this award as required by law. The announcement stated that the funding was provided for "research, analysis, development, and testing in support of the Plan Plasma Fusion (Polywell) Project. Efforts under this Recovery Act award will validate the basic physics of the Plasma Fusion (Polywell) concept, as well as provide the Navy with data for potential applications of polywell fusion." [72] The contract [71] had delivery dates for specific tasks. These were:

  • Completion of the WB-8 machine by April 30, 2010.
  • Completion of device testing by April 30, 2011
  • Completion of an optional second machine WB-8.1 by October 31, 2011.
  • Completion of WB-8.1 machine testing by October 31, 2012.
FY 2010 work[edit]

The team's progress was reported on the Recovery Act Tracking site in the form of quarterly reports.[73]

  • The first quarterly report stated: "The main focus of this quarter was the design, procurement and construction of equipment for the new WB-8 Polywell device. Theoretical work was also initiated to build the computational tools required to analyze and understand the data from WB-8."[73]
  • The second quarterly report stated: "on budget, on schedule for new lab test facility. Primary focus has been construction, procurement and relocation of personnel and chamber." (Slightly different format to award number so on a different page.)
  • The fourth quarterly report stated: "WB8 is fully under construction, progress made on Theoretical modeling of the Polywell. 2 full-time physicists hired. (On the original page)." [73] The location of work was also updated to San Diego. Confirmation of a lab move to San Diego was provided by an on-site visit.[74]
FY 2011 work[edit]

A series of quarterly reports on the Recovery Act site followed the team's progress:[73]

  • The first quarter report stated: "WB-8 device construction is completed. The first plasma was generated successfully on Nov. 1, 2010." [73] The report listed Jaeyoung Park as the Company Officer.
  • The second quarter report stated: "the WB-8 device operates as designed and it is generating positive results. EMC2 is planning to conduct comprehensive experiments on WB-8 in the next 9–12 months based on the current contract funding schedule." [73]
  • The third quarter report stated: "As of 2Q/2011, the WB-8 device has demonstrated excellent plasma confinement properties. EMC2 is conducting high power pulsed experiments on WB-8 to test the Wiffle-Ball plasma scaling law on plasma energy and confinement."[73] As of 3Q/2011, the WB-8 device had generated over 500 high power plasma shots. EMC2 is conducting tests on Wiffle-Ball plasma scaling law on plasma heating and confinement.[75]
  • The fourth quarter report of 2011 stated that the modification of the electron injectors increased the plasma heating. The higher plasma density in WB-8 prompted the need for higher heating power. They planned to operate WB-8 in high beta regime with the modified electron injectors during the first quarter of 2012.[76]

In 2011, Jaeyoung Park became President of Energy Matter Conversion Corporation.[77] In a May 2011 interview, Park commented that "This machine [WB8] should be able to generate 1,000 times more nuclear activity than WB-7, with about eight times more magnetic field.... We'll call that a good success."[78]

FY 2012 work[edit]

As of August 15, 2012, the Navy had agreed to fund EMC2 with an additional $5.3 million over 2 years to work on the problem of pumping electrons into the whiffleball. They plan to integrate a pulsed power supply to support the electron guns (100+A, 10kV). WB-8 has been operating at 0.8 Tesla. The review of the work produced the recommendations to continue and expand the effort,[79] stating: "The experimental results to date were consistent with the underlying theoretical framework of the polywell fusion concept and, in the opinion of the committee, merited continuation and expansion."[80]

FY 2014 work[edit]

In June 2014, EMC2 demonstrated for the first time that the electron cloud becomes diamagnetic in the center of a magnetic cusp configuration when beta is high, resolving an earlier conjecture.[13][16] Whether the electrons are thermalized and the plasma is thermal or not remains to be demonstrated experimentally.

After $12 to $20 million received from the U.S. Navy, EMC2 is now attempting to raise money in the private sector. CEO Jaeyoung Park gave a talk about their latest cusp-confinement experiments at UC Irvine.[81] EMC2 is planning a three-year, $30 million commercial research program to prove the Polywell can work as a nuclear fusion power generator.[82]

Other projects[edit]

Prometheus Fusion Perfection[edit]

Mark Suppes, a web developer, built his own polywell in a warehouse in Brooklyn, New York. He was the first amateur in the world to detect electron trapping using a Langmuir probe inside a polywell. He presented at the 2012 LIFT conference and the 2012 WIRED conference.[83] The project officially ended in July 2013, while the blog would remain online indefinitely.[84]

University of Sydney[edit]

The University of Sydney in Australia have been conducting studies and experiments with polywell devices. To date, they have published four papers in Physics of Plasmas on this topic, one in 2010,[85] one in late 2011,[9] and two in 2013.[20][27] They also published one PhD thesis[25] on the subject and presented their work at IEC Fusion conferences.[86][87]

The May 2010 paper discussed experimental work, testing a small device for its ability to capture electrons. The paper posited that the machine had an ideal magnetic field strength which maximized its ability to catch electrons. The paper analyzed magnetic confinement in the polywell using analytical solutions as well as simulations. The work linked the magnetic confinement in the polywell to magnetic mirror theory.[21] This research was presented at the 12th US-Japan Workshop on Inertial Electrostatic Confinement Fusion,[88] and summarized by John Santarius of the University of Wisconsin [89] The 2011 work uses Particle-in-cell simulations to model particle motion in polywells with a small electron population. Electrons behaved in a similar manner to particles in the biconic cusp.[22]

The first 2013 paper, measured a negative voltage inside a 4 inch aluminum polywell.[27] This was performed using pairs of biased Langmuir probes. Several tests were undertaken that included: measuring an internal beam of electrons, comparing the machine with and without a magnetic field, measuring the voltage at different locations and comparing voltage changes to the magnetic and electric field strength.[27]

Iranian Nuclear Science and Technology Research Institute[edit]

In November 2012, Trend News Agency reported that the Atomic Energy Organization of Iran had allocated "$8 million"[90] to inertial electrostatic confinement research and about half had been spent. The funded group published a paper in the Journal of Fusion Energy, which stated that particle-in-cell simulations of a polywell had been conducted. The study suggested that well depths and ion focus control can be achieved by variations of field strength, and referenced older research with traditional fusors. The group had run a fusor in continuous mode at -140 kV and 70 mA of current, with D-D fuel, producing 2×107 neutrons per second.[91]

University of Wisconsin[edit]

Carl Sovinec and his graduate student have performed Vlasov–Poisson, particle-in-cell simulation work on the polywell. This was funded through the National Defense Science and Engineering Graduate Fellowship and was presented at the 2013 American Physical Society conference.[92]

Convergent Scientific, Inc.[edit]

Convergent Scientific, Inc. (CSI) is an American company founded in December 2010 and based in Huntington Beach, California.[93] Their first polywell design, the Model 1, has been tested on steady-state operations from January to late summer 2012. The MaGrid was made of a unique diamond shaped hollow wire, into which an electric current and a liquid coolant are flowing.[94][95][96] They now has an effort to build a small-scale polywell fusing deuterium.[97][98] The company filed several patents[99][100][101] and in the Fall of 2013, did a series of web-based investor pitches.[102] The presentations mention encountering plasma instabilities including the Diocotron, two stream and Weibel instabilities. The company wants to make and sell Nitrogen-13 for PET scans.[103]

Radiant Matter Research[edit]

Radiant Matter[104] is an organization in the Netherlands which has built a number of fusors and has plans to build a polywell.

References in literature[edit]

The polywell has been referenced in two novels: "A Green Sun" by Charles Gray[105] and a "To Fly From Folly" by William Flint.

See also[edit]

References[edit]

  1. ^ Miley, George H.; Murali, S. Krupakar (8 January 2014). Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications. New York, Heidelberg, Dordrecht, London: Springer Science+Business Media. doi:10.1007/978-1-4614-9338-9. ISBN 978-1-4614-9337-2. 
  2. ^ Thorson, Timothy A. (1996). Ion flow and fusion reactivity characterization of a spherically convergent ion focus (Thesis). University of Wisconsin-Madison. OCLC 615996599. 
  3. ^ Thorson, T. A.; Durst, R. D.; Fonck, R. J.; Sontag, A. C. (1998). "Fusion reactivity characterization of a spherically convergent ion focus". Nuclear Fusion 38 (4): 495. doi:10.1088/0029-5515/38/4/302.  edit
  4. ^ a b Lavrent'ev, O. A (4–7 March 1974). "Electrostatic and Electromagnetic High-Temperature Plasma Traps". Conference on Electrostatic and Electromagnetic Confinement of Plasmas and the Phenomenology of Relativistic Electron BeamsAnnals of the New York Academy of Sciences 251 (New York City: New York Academy of Sciences, published 8 May 1975): 152–178. "as cited by Todd H. Rider in "A general critique of inertial-electrostatic confinement fusion systems", Phys. Plasmas 2 (6), June 1995. Rider specifically stated that Bussard has revived an idea originally suggested by Lavrent'ev." 
  5. ^ a b US patent 5160695, Bussard, Robert W., "Method and apparatus for creating and controlling nuclear fusion reactions", issued 1992-11-03, assigned to Qed, Inc. 
  6. ^ Bussard, Robert W. (March 1991). "Some Physics Considerations of Magnetic Inertial Electrostatic Confinement: A New Concept for Spherical Converging Flow Fusion" (PDF). Fusion Science and Technology (American Nuclear Society) 19 (2): 273–293. 
  7. ^ Krall, Nicholas A. (August 1992). "The Polywell: A Spherically Convergent Ion Focus Concept" (PDF). Fusion Science and Technology (American Nuclear Society) 22 (1): 42–49. 
  8. ^ a b Krall, Nicholas A.; Coleman, Michael; Maffei, Kenneth C.; Lovberg, John A.; Jacobsen, R. A.; Bussard, Robert W. (18 April 1994). "Forming and Maintaining a Potential Well in a Quasispherical Magnetic Trap" (PDF). Physics of Plasmas (American Institute of Physics, published January 1995) 2 (1): 146–158. Bibcode:1995PhPl....2..146K. doi:10.1063/1.871103. 
  9. ^ a b c doi:10.1063/1.3655446
    This citation will be automatically completed in the next few minutes. You can jump the queue or expand by hand
  10. ^ Spalding, Ian (29 October 1971). "Cusp Containment". In Simon, Albert; Thompson, William B. Advances in Plasma Physics 4. New York: Wiley Interscience Publishers: John Wiley & Sons. pp. 79–123. ISBN 9780471792048. 
  11. ^ Haines, M. G. (1977). "Plasma containment in cusp-shaped magnetic fields". Nuclear Fusion 17 (4): 811. doi:10.1088/0029-5515/17/4/015.  edit
  12. ^ a b c US patent 4826646, Bussard, Robert W., "Method and apparatus for controlling charged particles", issued 1989-05-02, assigned to Energy/Matter Conversion Corporation, Inc. 
  13. ^ a b Grad, Harold (February 1955). "Proceedings from Conference on Thermonuclear Reactions". University of California Radiation Laboratory, Livermore. p. 115. 
  14. ^ magnetohydrodynamic stability, j Berkowitz, h grad, p/376
  15. ^ review paper, m g Haines, nuclear fusion, 17 4(1977)
  16. ^ a b Park, Jaeyoung; Krall, Nicholas A.; Sieck, Paul E.; Offermann, Dustin T.; Skillicorn, Michael; Sanchez, Andrew; Davis, Kevin; Alderson, Eric et al. (1 June 2014). "High Energy Electron Confinement in a Magnetic Cusp Configuration". arXiv:1406.0133v1 [physics.plasm-ph].
  17. ^ Bussard, Robert W.; Krall, Nicholas A. (February 1991). Electron Leakage Through Magnetic Cusps in the Polywell Confinement Geometry (PDF) (Technical report). EMC2-DARPA. EMC2-0191-02. 
  18. ^ a b c d e f g h "The Advent of Clean Nuclear Fusion: Super-performance Space Power and Propulsion", Robert W. Bussard, Ph.D., 57th International Astronautical Congress, October 2–6, 2006
  19. ^ M. Scheffer (17 April 2013). "Lockheed Martin announces compact Fusion Reactor plans". FuseNet. 
  20. ^ a b doi:10.1063/1.4824005
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  21. ^ a b Chen, F. (1984). Introduction to Plasma Physics and Controlled Fusion 1. New York: Plenum. pp. 30–34. ISBN 978-0-306-41332-2. 
  22. ^ a b Van Norton, Roger (15 July 1961). The motion of a charged particle near a zero field point (PDF) (Technical report). New York: Magneto-Fluid Dynamics Division, Institute of Mathematical Sciences, New York University. MF23 NYO-9495. 
  23. ^ doi:10.1088/0029-5515/18/1/008
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  24. ^ a b c d e f Robert Bussard (lecturer) (2006-11-09). "Should Google Go Nuclear? Clean, cheap, nuclear power (no, really)" (Flash video). Google Tech Talks. Google. Retrieved 2006-12-03. 
  25. ^ a b Carr, Matthew (2013). Electrostatic potential measurements and point cusp theories applied to a low beta polywell fusion device (Thesis). The University of Sydney. OCLC 865167070. 
  26. ^ Polywell simulation 3D on YouTube
  27. ^ a b c d Carr, M.; Khachan, J. (2013). "A biased probe analysis of potential well formation in an electron only, low beta Polywell magnetic field". Physics of Plasmas 20 (5): 052504. Bibcode:2013PhPl...20e2504C. doi:10.1063/1.4804279.  edit
  28. ^ Bussard, Robert W.; King, Katherine E. (April 1991). Electron Recirculation in Electrostatic Multicusp Systems: 1–Confinement and Losses in Simple Power Law Wells (PDF) (Technical report). EMC2-DARPA. EMC2-0491-03. 
  29. ^ Bussard, Robert W.; King, Katherine E. (July 1991). Electron Recirculation in Electrostatic Multicusp Systems: 2–System Performance Scaling Of One-Dimensional "Rollover" Wells (PDF) (Technical report). EMC2-DARPA. 
  30. ^ a b c d e f g h i j Rider, T. H. (1995). "A general critique of inertial-electrostatic confinement fusion systems" (PDF). Physics of Plasmas 2 (6): 1853. doi:10.1063/1.871273.  edit
  31. ^ "Development of the indirect drive approach to inertial confinement fusion and the target physics basis for ignition and gain" John Lindl, Physics of Plasma, 1995
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  33. ^ Rider, Todd Harrison (June 1995). Fundamental limitations on fusion systems not in equilibrium (Thesis). Massachusetts Institute of Technology. OCLC 37885069. 
  34. ^ Nevins, W. M. (1995). "Can inertial electrostatic confinement work beyond the ion–ion collisional time scale?" (PDF). Physics of Plasmas 2 (10): 3804. doi:10.1063/1.871080.  edit
  35. ^ Lyman J Spitzer, "The Physics of Fully Ionized Gases" 1963
  36. ^ Bussard, Robert W.; King, Katherine E. (August 1991). Bremmstrahlung Radiation Losses in Polywell™ Systems (PDF) (Technical report). EMC2-DARPA. EMC2-0891-04. "Table 2, p. 6." 
  37. ^ Bussard, Robert W.; King, Katherine E. (5 December 1991). Bremsstrahlung and Synchrotron Radiation Losses in Polywell™ Systems (PDF) (Technical report). EMC2-DARPA. EMC2-1291-02. 
  38. ^ Bussard, Robert W. (19 February 1991). Collisional Equilibration (PDF) (Technical report). EMC2-DARPA. EMC2-0890-03. 
  39. ^ Bussard, Robert W. (19 February 1991). Core Collisional Ion Upscattering and Loss Time (PDF) (Technical report). EMC2-DARPA. EMC2-1090-03. 
  40. ^ Safe, Green, Clean – the p-B Polywell: A Different Kind of Nuclear, p. 66
  41. ^ Chacón, L.; Miley, G. H.; Barnes, D. C.; Knoll, D. A. (2000). "Energy gain calculations in Penning fusion systems using a bounce-averaged Fokker–Planck model" (PDF). Physics of Plasmas 7 (11): 4547. doi:10.1063/1.1310199.  edit
  42. ^ Rosenbluth, M. N.; Hinton, F. L. (1994). "Generic issues for direct conversion of fusion energy from alternative fuels". Plasma Physics and Controlled Fusion 36 (8): 1255. doi:10.1088/0741-3335/36/8/003.  edit
  43. ^ Keller, R.; Jones, I. R. (June 1966). "Confinement d'un Plasma par un Système Polyédrique à Courant Alternatif" [Plasma confinement by a polyhedral system with alternating current]. Zeitschrift für Naturforschung A (in French) 21: 1085–1089. Bibcode:1966ZNatA..21.1085K. "as cited by R.W. Bussard in U.S. Patent 4,826,646, "Method and apparatus for controlling charged particles", issued May 2, 1989, p.12." 
  44. ^ Sadowski, M. (1969). "Spherical Multipole Magnets for Plasma Research". Review of Scientific Instruments 40 (12): 1545. doi:10.1063/1.1683858.  edit
  45. ^ a b c d e f g h Robert W. Bussard (December 2006). "A quick history of the EMC2 Polywell IEF concept" (PDF). Energy/Matter Conversion Corporation. Retrieved 16 June 2014. 
  46. ^ a b c "Forming and maintaining a potential well in a quasispherical magnetic trap" Nicholas Krall, M Coleman, K Maffei, J Lovberg Physics of Plasma 2 (1), 1995
  47. ^ Posted to the web by Robert W. Bussard. "Inertial electrostatic fusion (IEF): A clean energy future" (Microsoft Word document). Energy/Matter Conversion Corporation. Retrieved 2006-12-03. 
  48. ^ a b Final Successful Tests of WB-6, EMC2 Report, currently (July 2008) not publicly available
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  50. ^ a b c SirPhilip (posting an e-mail from "RW Bussard") (2006-06-23). "Fusion, eh?". James Randi Educational Foundation forums. Retrieved 2006-12-03. 
  51. ^ "Inertial Electrostatic Confinement Project – University of Wisconsin – Madison". Iec.neep.wisc.edu. Retrieved 2013-06-17. 
  52. ^ Possibly he assumed that the ion energy distribution is fixed, that the magnetic field scales with the linear size, and that the ion pressure (proportional to density) scales with the magnetic pressure (proportional to B²). The R7 scaling results from multiplying the fusion power density (proportional to density squared, or B4) with the volume (proportional toR³). On the other hand, if it is important to maintain the ratio of the Debye length or the gyroradius to the machine size, then the magnetic field strength would have to scale inversely with the radius, so that the total power output would actually be lower in a larger machine.
  53. ^ Robert L. Hirsch, "Inertial-Electrostatic Confinement of Ionized Fusion Gases", Journal of Applied Physics, v. 38, no. 7, October 1967
  54. ^ There is this clause in the "Solicitation, Offer and Award" for the "plasma wiffleball development project", awarded on March 3, 2009, to Matter Conversion Corporation:

    5252.204-9504 DISCLOSURE OF CONTRACT INFORMATION (NAVAIR) (JAN 2007) (a) The Contractor shall not release to anyone outside the Contractor's organization any unclassified information (e.g., announcement of contract award), regardless of medium (e.g., film, tape, document), pertaining to any part of this contract or any program related to this contract, unless the Contracting Officer has given prior written approval. (b) Requests for approval shall identify the specific information to be released, the medium to be used, and the purpose for the release. The Contractor shall submit its request to the Contracting Officer at least ten (10) days before the proposed date for release. (c) The Contractor agrees to include a similar requirement in each subcontract under this contract. Subcontractors shall submit requests for authorization to release through the prime contractor to the Contracting Officer.

  55. ^ Askmar summary of IEC fusion
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  81. ^ Park, Jaeyoung (12 June 2014). SPECIAL PLASMA SEMINAR: Measurement of Enhanced Cusp Confinement at High Beta (Speech). Plasma Physics Seminar. Department of Physics & Astronomy, University of California, Irvine: Energy Matter Conversion Corp (EMC2). 
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  83. ^ WIRED video on YouTube
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  86. ^ Khachan, Joe; Carr, Matthew; Gummersall, David; Cornish, Scott; Israel, Adam; Bandara, Rehan; Ren, Johnson (14–17 October 2012). "Overview of IEC at the University of Sydney" (PDF). 14th US-Japan Workshop on Inertial Electrostatic Confinement Fusion. University of Maryland, College Park, MD. 
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  90. ^ "Iran to build nuclear fusion producing plant". Trend News Agency. 13 November 2012. Retrieved 2013-02-08. 
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  96. ^ Talk. "Commercial Applications of IEC Devices" Web presentation, performed by Devlin Baker, 22 October 2013.
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  99. ^ US application 2010284501, Rogers, Joel Guild, "Modular Apparatus for Confining a Plasma", published 2010-11-11, assigned to Rogers, Joel Guild 
  100. ^ US patent 8279030, Baker, Devlin & Bateman, Daniel, "Method and apparatus for electrical, mechanical and thermal isolation of superconductive magnets", issued 2012-10-02, assigned to Magnetic-Electrostatic Confinement (MEC) Corporation 
  101. ^ US application 2013012393, Bateman, Daniel & Pourrahimi, Shahin, "Apparatus to confine a plurality of charged particles", published 2013-01-10, assigned to Bateman, Daniel and Pourrahimi, Shahin 
  102. ^ Talk. "Numerical Simulations of IEC Plasmas." Web presentation, Performed by Devlin Baker, November 5, 2013
  103. ^ Talk. "Commercial Applications of IEC Devices" Web presentation, performed by Devlin Baker, December 3, 2013.
  104. ^ http://www.radiantmatter.com/content/farnsworth-fusor, Accessed: 12/25/2013
  105. ^ "A Green Sun (The Fusion Age)" by Charles Gray, August 7, 2011, Amazon Digital Services

External links[edit]