(BEING CONTINUED FROM 31/10/14)
is the process of creating new atomic nuclei from pre-existing nucleons (protons and neutrons). It is thought that the primordial nucleons themselves were formed from the quark–gluon plasma from theBig Bang as it cooled below two trillion degrees. A few minutes afterward, starting with only protons and neutrons, nuclei up to lithium and beryllium(both with mass number 7) were formed, but only in relatively small amounts. Some boron may have been formed at this time, but the process stopped before significant carbon could be formed, because this element requires far higher products of helium density and time than were present in the short nucleosynthesis period of the Big Bang. The Big Bang fusion process essentially shut down due to drops in temperature and density as the universe continued to expand. This first process of primordial nucleosynthesis was the first type of nucleogenesis to occur in the universe.
The subsequent nucleosynthesis of the heavier elements required heavy stars and supernova explosions. This theoretically happened as hydrogen and helium from the Big Bang (perhaps influenced by concentrations of dark matter), condensed into the first stars 500 million years after the Big Bang. The elements created in stellar nucleosynthesis range inatomic numbers from 6 (carbon) to at least 94 (plutonium)—and possibly even 98 (californium), which has been debateably claimed as detected in spectra from supernovae. Synthesis of these heavier elements occurs either by nuclear fusion (including both rapid and slow multiple neutron capture) or by nuclear fission, sometimes followed by beta decay.
By contrast, many stellar processes actually tend to destroy deuterium and isotopes of beryllium, lithium, and boron which collect in stars, after their primordial formation in the Big Bang. Quantities of these lighter elements in the present universe are therefore thought to have been formed mainly through billions of years of cosmic ray (mostly high-energy proton) mediated breakup of heavier elements residing in interstellar gas and dust.
- 1 History
- 2 Processes
- 3 The major types of nucleosynthesis
- 4 Empirical evidence
- 5 See also
- 6 References
- 7 Further reading
Z)Are old secrets behind Lockheed’s new fusion machine?
The defense firm Lockheed Martin sent tech geeks into a frenzy yesterday when it revealed a few scant details of a “compact fusion reactor” (CFR) that a small team has been working on at the company’s secretive Skunk Works in Palmdale, California. The company says that its innovative method for confining the superhot ionized gas, or plasma, necessary for fusion means that it can make a working reactor 1/10 the size of current efforts, such as the international ITER fusion project under construction in France.
Being able to build such a small and presumably cheap reactor would be world-changing—ITER will cost at least $20 billion to build and will only prove the principle, not generate any electricity. But with little real information, no one is prepared to say that Lockheed’s approach is going to spark a revolution. “You can’t conclude anything from this,” says Steven Cowley, director of the Culham Centre for Fusion Energy in Abingdon, U.K. “If it wasn’t Lockheed Martin, you’d say it was probably a bunch of crazies.”
The Lockheed team predicts that it will take 5 years to prove the concept for the new reactor. After that, they estimate it would take another 5 years to build a prototype that would produce 100 megawatts (MW) of electricity—enough for a small city—and fit on the back of a truck. AWeb page with video on the Lockheed site even talks of powering ships and aircraft with a CFR.
Lockheed statements reveal little about the nature of the reactor. Aviation Week yesterday carried the most detailed account having interviewed the team leader, Thomas McGuire.
Fusion seeks to release energy from inside atomic nuclei by getting light nuclei, usually isotopes of hydrogen, to fuse together to form helium. The problem is that nuclei are all positively charged and so repel each other. To get them close enough to fuse it is necessary to heat a plasma—a gas of nuclei and electrons—to more than 100 million degrees Celsius so that the nuclei travel at high enough speeds to fuse when they collide with each other. The challenge in building a fusion reactor is to confine the plasma such that it does not touch the sides of its container, because its temperature would melt any metal. Most reactors, such as tokamaks like ITER, use powerful magnetic fields for confinement.
From Lockheed photographs of the CFR, it shows similarities to a magnetic configuration known as a cusp geometry, perhaps one known as a “picket fence.” The images show a series of ring-shaped electromagnets arranged in a row, like curtain rings on a rail. If it is a picket fence, then plasma would be confined along the axis running down the middle of the rings and the electromagnets produce a series of magnetic fields that bulge out toward the central plasma—a series of cusps. The effect of this is that if a charged particle near the axis moves outwards it starts to experience a magnetic field pushing it back. This is gentle at first but the farther the particle strays from the axis, the more strongly it is pushed back toward the center. This makes the confined plasma less prone to instabilities that plague other types of fusion containment.
Cusp geometries were first proposed in the 1950s by Harold Grad of New York University but were abandoned because experiments showed such machines would be leaky: Particles could escape through the gaps between one electromagnet and the next. Some cusp ideas have been revived in more recent devices such as the Polywell, which creates a 3D rather than linear cusp geometry. According to Aviation Week, the CFR would use superconductors in its electromagnets—not available to researchers in the 1950s—which would provide stronger magnetic fields and so improve confinement. Lockheed statements refer to combining the best parts of several confinement approaches. Cowley thinks they may also be using a technique called a field-reversed configuration (FRC), in which helical magnetic fields are induced in the plasma so that it confines itself. FRCs again date back to the late 1950s and 1960s but tend to be very short-lived, lasting on the order of a millisecond. “They’re probably trying to create an FRC inside a picket fence,” Cowley speculates.
*Update, 17 October, 10:53 a.m.: Three U.S. patent applications filed on 9 October by McGuire reveal more details about the reactor. It does appear to be some sort of cusp geometry device but more complicated than a picket fence. It also appears to have a structure known as a magnetic mirror at either end. This acts as a magnetic plug to stop particles from escaping along the axis of the device.
One potential problem with the device that has been pointed out by scientists who have spoken with ScienceInsider is that it appears to have electromagnet coils made from superconductor inside the reaction vessel. If they were in that position in a working fusion reactor, the superconductor would be destroyed by the high-energy neutrons that are a product of fusion reactions. Other designs that use high-temperature superconductors have more than a meter of shielding to protect magnets from neutrons, although researchers at the Massachusetts Institute of Technology believe this could be reduced to as low as 77 centimeters. Even if it was possible to reduce this to 70 cm and such shielding was added to Lockheed’s current design, researchers say it would make the device 18 meters across, not the 7 meters that the company is claiming.
Posted in Physics
By Daniel Clery /10/14
EE)NASA’s robot astronaut inspiring tech advances here on Earth
A humanoid robot aboard the International Space Station is inspiring technology that could be useful to both astronauts and people on Earth.
NASA’s Robonaut 2, which arrived at the orbiting lab in 2011, has human-like arms and hands capable of performing simple tasks such as flipping switches and grasping objects. The robot was originally designed to do work outside the station, potentially reducing the number of time-consuming and strenuous spacewalks required of astronauts.
However, the technology developed during the Robonaut program has inspired other ideas and is being adapted into several spinoffs that have application both in space and on Earth, NASA officials said. [Photos: Robonaut 2, NASA’s Robot Butler for Astronauts]
First, scientists converted Robonaut into a full exoskeleton called X1 that can help astronauts exercise and stay healthy while spending long periods in space. But X1 also has potential application closer to home; scientists think paraplegia or stroke patients could use the skeleton to regain some lost motion here on Earth.
NASA robotics engineers worked with researchers at the Florida Institute for Human and Machine Cognition to create the exoskeleton, which straps on over the shoulders and back and covers the legs. Motorized joints installed at the hips and knees allow the wearer to take halting steps.
The exoskeleton can also be programmed to resist movement, making it a useful device for astronauts who need to exercise two hours a day to mitigate the long-term effects of microgravity exposure. (Without exercising, long periods of time in microgravity can cause muscles to shrink and bones to weaken.)
Robonaut also inspired Roboglove, a glove designed with flexible tendons that can assist grip force. On spacewalks, astronauts must repair and maintain the outside of the orbiting lab. But zero gravity combined with a bulky spacesuit can make even simple tasks difficult.
“Due to pressurization of the suit, it’s like squeezing a balloon every time you move your hand,” Lyndon Bridgwater, senior robotics engineer at NASA’s Johnson Space Center in Houston, said in a statement. “That causes extreme fatigue and even injury. We’re looking at putting the hardware and actuator in the glove itself to provide muscle augmentation for the hand.”
Finally, scientists think Robonaut could be useful for telemedicine. Tests at the Methodist Hospital in Houston have shown it’s possible for Robonaut to guide a user’s hand to stick a needle in a vein. In the future, scientists think Robonaut could assist astronauts performing medical procedures in space with doctors supervising from Earth.
“The robot could stabilize an injured individual or do nursing-level work, even on Earth,” Ron Diftler, Robonaut project manager, said in a statement. “That essentially transports a doctor’s skill and presence to somewhere the doctor can’t go or, in an emergency situation, where it would be dangerous for a person to go.”
Robonaut 2 has thus far been humanoid only from the waist up; it launched to the space station without any legs. But a pair of legs for the robot arrived at the orbiting complex aboard SpaceX’s unmanned Dragon cargo craft in April, so Robonaut 2 will soon get quite a bit taller.
By Kelly Dickerson
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