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 that 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 physicist Robert Bussard, as an improvement over the fusor. His company, EMC2, Inc., developed the initial devices for the U.S. Navy.

Mechanism

Fusor

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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, which are often referred to as grids. They are placed inside a vacuum chamber. The outer cage has a positive voltage against the inner cage. Typically, deuterium gas is puffed in this chamber. It heats up past its ionization temperature, making a positive ion. 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 can raise the temperature of the grid as well as wear it down. These strikes conduct away mass and energy from the plasma.

In fusors, the potential well is made with a wire cage. Because most of the ions and electrons 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

This is a sketch of a MaGrid in a polywell

The main problem with the fusor is that the inner 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. These are put inside a vacuum chamber [5]

  • A set of positively charged electromagnet coils arranged in a polyhedron. The most common arrangement is a six sided 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. These shoot electrons into the center of the ring structure. Once inside, the electrons are confined by the magnetic fields. This has been measured in polywells using Langmuir probes.[6][7][8] Electrons that have enough energy to escape through the magnetic cusps can be re-attracted to the positive rings. They can slow down and return to the inside of the rings along the cusps. This reduces conduction losses, and improves the overall performance of the machine.[9] The electrons act a negative voltage drop attracting positive ions. This is a virtual cathode.
  • Gas puffers at corner. Gas is puffed inside the rings. It ionizes, when it reaches the electron cloud. As ions fall down the potential well, the electric field does work on the ion, heating it to fusion conditions. The ions build up speed. They can slam together in the center and fuse. Ions are electrostatically confined raising the density and increasing the fusion rate.

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][10][11]

Magnetic trapping models

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

Magnetic fields exert a pressure on the plasma. This is measured using a beta number.

\beta = \frac{p}{p_{mag}} = \frac{n k_B T}{(B^2/2\mu_0)} [12]

This is the ratio of plasma pressure to the magnetic field. Most experiments on polywells involve low-beta plasma regimes (where β < 1).[13] where the plasma pressure is weak compared to the magnetic pressure. Depending on what beta number is used. There are several models of magnetic trapping in polywells[citation needed]. Recent test have indicated that plasma confinement is enhanced in a magnetic cusp configuration when β (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. (http://journals.aps.org/prx/abstract/10.1103/PhysRevX.5.021024)

Magnetic mirror

Magnetic mirror dominates in low beta conditions. Both ions and electrons are reflected from high to low density fields. This is known as the magnetic mirror effect.[14] The polywell's rings are arranged so the densest fields are on the outside, trapping electrons in the center. This can trap particles at low beta values.

Cusp confinement

This is a picture of cusps inside the polywell. The Line cusp runs along the seam between two electromagnets. The funny cusp is the cusp between three magnets, running along the corners. The point cusp lies in the middle of one electromagnet.

In high beta conditions, the machine may operate with cusp confinement.[15] This is an improvement over the simpler magnetic mirror confinement.[16] 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.[17]

Free-boundary plasma

In 1955, Harold Grad theorized that a high-beta plasma pressure combined with a cusped magnetic field would improve plasma confinement.[18] This worked by diamagnetic plasma rejecting the external fields and plugging the cusps. This system would be a much better trap for material.

Cusped confinement was explored theoretically [19] and experimentally.[20] 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.

This figure shows the development of the proposed “wiffle ball” confinement concept. Three rows of figures are shown: the magnetic field, the electron motion and the plasma density inside the polywell. (A) The field is the superposition of six rings in a box. In the center is a null point - a zone of no magnetic field.[8] The plasma is magnetized, meaning that the plasma and magnetic field intermix. (B) As plasma is injected, the density rises. (C) As the plasma density rises, the plasma becomes more diamagnetic, causing it to reject the outside magnetic field. As the plasma presses outwards, the density of the surrounding magnetic field rises. This tightens the corkscrewing motion of the particles outsides the center. A sharp boundary is formed.[21] A current is predicted [18][19] to form on this boundary. (D) If the pressures find equilibrium at a beta of one, this determines the shape of the plasma cloud. (E) In the center, there is no magnetic field from the rings. This means that its motion inside the field free radius should be relatively straight or ballistic.[8]

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 [21] providing evidence that the effect is real, based on x-ray measurements and magnetic flux measurements during the experiment.

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).[22][23]

In February 2013, Lockheed Martin Skunk Works announced a new compact fusion machine, the high beta fusion reactor,[24] which may be related to the biconic cusp and the polywell[according to whom?], and working at β = 1.

Other behavior

Single-electron motion

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.

As an electron enters a magnetic field, it feels a Lorentz force and corkscrews. The radius of this motion is the gyroradius. As it moves it loses some energy as x-rays, every time it changes speed. The electron spins faster and tighter in denser fields, as it enters the MaGrid. 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 edges of the MaGrid field and corkscrew tighter along the denser magnetic field lines.[13][25] This is typical electron cyclotron resonance motion. Their gyroradius shrinks and when they hit a dense magnetic field they can be reflected using the magnetic mirror effect.[26][27][28] Electron trapping has been measured in polywells with Langmuir probes.[6][7][8]

A visualization of the electron flow in a polywell has been made in 3D simulations by Indrek Mare.[29]

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.[30] 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.

Plasma recirculation

Plasma recirculation would significantly improve the function of these machines. It has even been argued that efficient recirculation is the only way they could be viable.[31][32] If electrons or ions can move through the space without striking a surface, it reduces conduction losses. Bussard stressed this; specifically emphasizing that electrons need to move through all cusps of the machine.[33][34]

This is one model of the ion energy distribution inside a polywell.[31] This model assumes a maxwellian ion population, broken into different groups. (1) The ions which do not have enough energy to fuse, (2) the ions at the injection energy (3) the ions that have so much kinetic energy that they escape.

Models of energy distribution

This is one model for the electrons energy distribution inside a polywell.[35] It is argued that the region of unmagnetized space leads to electron scattering, this leads to a monoenergetic distribution with a cold electron tail. This is supported by 2 dimensional particle-in-cell simulations.

As of 2015 it has not been determined conclusively what the ion or electron energy distribution is. The energy distribution of the plasma can be measured using a Langmuir probe. This probe absorbs charge from the plasma as its voltage is changed, making a I-V Curve.[36] From this signal, the energy distribution can be calculated. The energy distribution both drives, and is driven by several physical rates.[31] For instance: the electron and ion loss rate, the rate of energy loss by radiation, the fusion rate and the rate of non-fusion collisions. The collision rate may vary greatly across the system[citation needed]:

  • At the edge: where ions are slow and the electrons are fast.
  • At the center: where ions are fast and electrons are slow.

Critics have argued that both the electrons and ion populations have bell curve distribution;[31] that the plasma is thermalized. The justification given is that the longer the electrons and ions move inside the polywell, the more interactions they undergo leading to thermalization. This model for [31] the ion distribution is shown here.

Supporters have also modeled the plasma as nonthermal.[33] The reason for this is the high amount of scattering in devices' center.[37] Because there is no magnetic field, electrons scatter a great deal in this region. They argue that this scattering leads to a monoenergetic distribution, like the one shown here. This argument is supported by 2 dimensional particle-in-cell simulations.[37] Bussard argued that constant electron injection would have the same effect.[5] Such a distribution would help maintain a negative voltage in the center, improving machine performance.[5]

Considerations for net power

Fuel type

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,[38] 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 using direct energy conversion. Direct conversion has realized a 48% power efficiency [39] and has an 80-90% theoretical efficiency.[14]

Lawson criterion

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.[40]

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.[40] 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.

Net Power = Efficiency *(Fusion - Radiation Loss - Conduction Loss)

  1. Net Power is the net power for any fusion power plant.
  2. Efficiency how much energy is needed to drive the device and how well it collects power.
  3. Fusion is rate of energy generated by the fusion reactions.
  4. Radiation is the energy lost as light, leaving the plasma.
  5. Conduction is the energy lost, as mass leaves the plasma.

John Lawson used this equation to estimate some conditions for net power [40] based on a Maxwellian cloud.[40] 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):[40] "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

In his thesis[32] and his 1995 publication,[31] 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.[31]
  • The fuel was evenly mixed throughout the volume.[31]
  • The plasma was isotropic, meaning that its behavior was the same in any given direction.[31]
  • The plasma had a uniform energy and temperature throughout the cloud.[31]
  • 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.[31] 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.[41] The loss of density inside the core would reduce fusion rates.
  • The potential well was broad and flat.[31]

Based on these assumptions, Rider used general equations[42] 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.[31] His conclusions were that the device suffered from "fundamental flaws".[31]

By contrast, Bussard has argued[23] 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.[43][44] 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.[45][46] Bussard calculated that a polywell reactor with a radius of 1.5 meters would produce net power fusing deuterium.[47]

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.[48]

Energy capture

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 is expected.[49] In experiments, direct conversion has demonstrated a conversion efficiency of 48%.[50]

History

In the late 1960s there were several investigations of polyhedral magnetic fields as a possibility to confine a fusion plasma.[51][52] 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,[17] though in 2006 he appears to claim to have re-discovered the idea independently.[53]

HEPS

Research was funded first by the Defense Threat Reduction Agency beginning in 1987 and later by DARPA.[7]: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.[54] This machine was a large (190 cm across) machine, where the rings were placed outside of the vacuum chamber.[7]: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.[54] The United States Navy began providing low-level funding to the project in 1992.[55] Results from the HEPS program were published by Nicholas Krall in 1994.[54]

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.

Robert Bussard founded Energy/Matter Conversion Corporation, Inc. (aka EMC2) in 1985[7][17] 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.[53] In 1993, it received a grant from the Electric Power Research Institute to examine the use of this machine in power production.[53] In 1994, The company received small grants from NASA and LANL.[53] Starting in 1999, the company was primarily funded by the US Navy.[53]

One early design was WB-1, which had six conventional magnets in a cube. This device was 10 cm across.[53] 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.[7] 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.[53] 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.[53]

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,[23][56] 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.[57][58] 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.[59]

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,[60] if true, it would enable a model only ten times larger to be useful as a fusion power plant.[23]

WB-6

Funding became tighter and tighter. According to Bussard, "The funds were clearly needed for the more important War in Iraq."[58] 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.[23][56] Drive voltage on the WB-6 tests was about 12.5 kV, with a resulting potential well depth of about 10 kV.[23] 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.[61] 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

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 [62] The company's military-owned equipment was transferred to SpaceDev, which also hired three of the team's researchers.[58] 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?"[7] He also presented and published an overview of the work at the 57th International Astronautical Congress in October 2006.[23] He presented at an internal Yahoo! Tech Talk on April 10, 2007.[63] 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"[57] 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." [23] Robert W. Bussard died in October 6, 2007 from multiple myeloma at the age of 79.[64]

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."[65]

Bridge funding 2007–09

Reassembling team

In August 2007, EMC2 received a $1.8M U.S. Navy contract to continue the reactor development.[66] Before Bussard's death in October, 2007,[67] 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

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.[68][69] 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.[70]

FY 2008 work

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.[71] In October 2008 the US Navy publicly pre-solicited two more contracts[72][73] also targeted toward EMC2 as preferred supplier. These two tasks were to develop better instrumentation and to develop an ion injection gun.[74][75] 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."[76]

Navy contract 2009 to 2014

2009

In January 2009 the Naval Air Warfare Center pre-solicited another contract for "modification and testing of plasma wiffleball 7"[77] 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.[78] The citation occurs 166 pages into the document, and suggests development of the device for 'Domestic Energy Supply / Distribution'. In September 2009, the Recovery Act funded the Navy in the amount of $7.86M to construct and test a WB-8.[79] The Navy contract has an option for an additional $4.46M [79] The new device increases the magnetic field strength eightfold over WB-6.[80]

2010

In 2010, the team made steady progress in each quarter[81] In the first quarter: the focus 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.[81] In the second quarter the team did construction, procurement and relocation of personnel and chamber. The fourth quarter stated that WB8 was fully under construction, progress made on theoretical modeling of the Polywell. Two full-time physicists hired.[81] The location of work was also updated to San Diego.[82]

2011

In 2011, Jaeyoung Park became President of Energy Matter Conversion Corporation.[83] 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"[84] In the first quarter: WB-8 device construction was completed and the first plasma was generated successfully on Nov. 1, 2010.".[81] In the second quarter the WB-8 device was operating as designed [81] In addition, 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.".[81] By the third quarter over 500 high power plasma shots had happened.[85] In the fourth quarter: 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.[86]

2012

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 wiffleball. 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,[87] 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."[88]

Going public

2014

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.[18][21] Whether the plasma is thermalized or not remains to be demonstrated experimentally. These findings have been presented by the CEO Dr. Jaeyoung Park at UC Irvine.[89] UCLA,[90][91] University of Wisconsin Madison,[92] University of Maryland,[93] the Annual 2014 Fusion Power Associates meeting [94] Princeton University and the 2014 IEC conference.

2015

On January 22, EMC2 presented this work at Microsoft Research.[95] EMC2 is now planning a three-year, $30 million commercial research program to prove the Polywell can work as a nuclear fusion power generator.[96]

Related projects

Prometheus Fusion Perfection

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.[97] The project officially ended in July 2013, while the blog would remain online indefinitely.[98]

University of Sydney

The University of Sydney in Australia has been conducting studies and experiments with polywell devices. To date, they have published five papers in Physics of Plasmas on this topic, one in 2010,[99] one in late 2011,[13] two in 2013 [25][30] and one in 2014.[100] They also published one PhD thesis[8] on the subject and presented their work at IEC Fusion conferences.[101][102]

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.[26] This research was presented at the 12th US-Japan Workshop on Inertial Electrostatic Confinement Fusion,[103] and summarized by John Santarius of the University of Wisconsin [104] 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.[27]

The first 2013 paper, measured a negative voltage inside a 4-inch aluminum polywell.[30] 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.[30]

Iranian Nuclear Science and Technology Research Institute

In November 2012, Trend News Agency reported that the Atomic Energy Organization of Iran had allocated "$8 million"[105] 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.[106]

University of Wisconsin

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.[107]

Convergent Scientific, Inc.

Convergent Scientific, Inc. (CSI) is an American company founded in December 2010 and based in Huntington Beach, California.[108] 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.[109][110][111] They are now making an effort to build a small-scale polywell fusing deuterium.[112][113] The company filed several patents[114][115][116] and in the Fall of 2013, did a series of web-based investor pitches.[117] 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.[118]

Radiant Matter Research

Radiant Matter[119] is an organization in the Netherlands which has built a number of fusors and has plans to build a polywell.

References in literature

The polywell has been referenced in two novels: "A Green Sun" by Charles Gray[120] and a "To Fly From Folly" by William Flint.

See also

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2

References

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  14. ↑ 14.0 14.1 "Mirror Systems: Fuel Cycles, loss reduction and energy recovery" by Richard F. Post, BNES Nuclear fusion reactor conferences at Culham laboratory, September 1969.
  15. ↑ 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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  60. ↑ 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.
  61. ↑ Robert L. Hirsch, "Inertial-Electrostatic Confinement of Ionized Fusion Gases", Journal of Applied Physics, v. 38, no. 7, October 1967
  62. ↑ 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.

  63. ↑ Askmar summary of IEC fusion
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  90. ↑ "Polywell Fusion – Electric Fusion in a Magnetic Cusp" Jaeyoung Park, Friday, December 5, 2014 - 1:00pm to 2:00pm, Physics and Astronomy Building (PAB) Room 4-330, UCLA
  91. ↑ http://www.pa.ucla.edu/events/polywell-fusion-%E2%80%93-electric-fusion-magnetic-cusp%E2%80%9D-jaeyoung-park-emc2-fusion-development-corp
  92. ↑ Talk at University of Wisconsin Madison, Monday, June 16, 2:30 PM room 106 ERB, Jaeyoung Park
  93. ↑ University of Maryland, Colloquium & Seminars, "Measurement of Enhanced Confinement at High Pressure Magnetic Cusp System", Jaeyoung Park, September 9th 2014
  94. ↑ "Polywell Fusion Electrostatic Fusion in a Magnetic Cusp", Jaeyoung Park, http://fire.pppl.gov/FPA14_IECM_EMC2_Park.pdf, Tuesday December 16, 2014 Hyatt Regency Capitol Hill 400 New Jersey Avenue NW, Washington, DC 20001
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  116. ↑ 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 
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  119. ↑ http://www.radiantmatter.com/content/farnsworth-fusor, Accessed: 12/25/2013
  120. ↑ "A Green Sun (The Fusion Age)" by Charles Gray, August 7, 2011, Amazon Digital Services

External links

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