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New Accelerator Technique Doubles Particle Energy
ZonkerWilliam writes "Plasma wake particle accelerators are making surprisingly quick advances. It was a just a little while ago we had GeV acceleration in 3cm. Now they are capable of doubling the energy of electrons. 'Imagine a car that accelerates from zero to sixty in 250 feet, and then rockets to 120 miles per hour in just one more inch. That's essentially what a collaboration of accelerator physicists has accomplished, using electrons for their race cars and plasma for the afterburners. Because electrons already travel at near light's speed in an accelerator, the physicists actually doubled the energy of the electrons, not their speed.'"
One of these days those crazy scientists are going to do something and we will all just disappear into a mass of energy.
in 5, 4, 3, 2, 1...
The kinetic energy is proportional to speed^2 (E=1/2 m v^2), so a car at 120mph has 4 times the energy of a car at 60mph. Thus, doubling in energy is not like doubling in speed.
That's essentially what a collaboration of accelerator physicists has accomplished, using electrons for their race cars and plasma for the afterburners.
Those sound like really small physicists.
Wizard Needs Food, Badly
E=mv^2/2 only for small values of v.
The other formula for E, you might have heard of, is E=mc^2. m = \gamma m_0, where m_0 is the rest mass, \gamma = 1 / sqrt(1 - \beta^2), and beta = v/c. I.e.,
E=m_0 c^2/sqrt(1 - v^2/c^2)
For very small values of v (relative to c), 1/sqrt(1-v^2/c^2) \approx = (1/2)v^2/c^2, which leads back to your formula - but the approximation is only valid for v
Ben Hocking
Need a professional organizer?
I assume you are referencing Dimopoulos and Landsberg's paper http://prola.aps.org/abstract/PRL/v87/i16/e161602 . There is nothing to worry about. These physicists proposed that if certain theories were true (M theory, quantum loop gravity, super symmetry) then the energy densities seen in the RHIC or LHC experiments could produce something "mathematically analogous" to a black hole. There is no possibility under any current theory that an event horizon could form and attract matter.
I jammed a butter knife into a 220v circuit when I was a toddler and became a diembodied electromagnetic life-force with super powers.
Other than a morbid fear of lightning rods and antistatic wrist-straps, it pretty much rocks.
They increased the mass of the electrons by 1.65064935 × 10-27 hundredweight in 0.00032808399 football fields. Sorry, I don't know how much that is in SUVs.
Seriously, though, this is a neat trick. (Yes, IAAP)
Unless you're irrational, that is.
im in ur
I actually do some work on this with the PWFA group at USC (i'm an undergrad research assistant). It really is amazing! We can reach acceleration gradients of around 60 GeV/m, compared to something like 40 MeV/m for a normal accelerator. It works like this: .or at least something close to that!
1. The electrons travel down the main linac in carefully spaced "bunches", and get accelerated to around 43 GeV over a course of ~3KM (this is at the main beam at SLAC).
2. A (in the last experiment) 1.2m long Lithium plasma "oven" is at the end of the beam, which the electrons are directed into.
3. The first, or "driving," bunch goes through the plasma, and repels all of the electrons it gets near, leaving an "empty" wake behind it, where only the positively charged ions are.
4. The positive charge behind the driving beam pulls it backwards, causing it to lose energy. At the same time, a "witness" bunch placed strategically within the wakefield gets pulled forward by the positively charged ions. The witness gains energy while the driver loses energy.
5. Voila! One bunch now has twice the energy, and one bunch now has none . .
The main caveat is that you're upward-limited by your entering energy, so you still need a huge Linac to accelerate the bunches to begin with. This will likely get tacked on in the form of a "plasma afterburner" to a normal linac, such as in the setup at SLAC.
I'm perfect in every way, except for my humility.
As I understand it, luminosity is one major reason why this technology is not yet ready for prime time (i.e. not in time for the proposed ILC). You can't just accelerate a few particles to high energies and say you are done. You're looking for rare processes, so you need to create many consistent particle collisions per second in a tiny area. This means you need to have a tight, "bright" beam. The Tevatron has a luminosity of ~2e+32 interactions/cm^2/s now, the LHC may eventually reach 1e+34, and the goal for the ILC is more like 2e+34. Plasma wakefield systems are now demonstrating large increases in energy over short distances, but it's very difficult to daisy-chain them together to reach high total energies with any significant luminosity.
Cue people who pretend they understand the science...
As mentioned, there are some of us around here who are actual scientists. However, there are no details in the article, thus no science to understand. All I found were crappy analogies with afterburners and some hand-wavey crap about plasma. I'm pretty sure that if it were as easy as running some crap through a plasma to accelerate it, it would have been done some time ago. And there are a number of pertinent questions:
Why do they have to use a 2-mile accelerator if the plasma can do in a foot what it takes the 2 miles to do?
Why can't it be longer?
How is the plasma chamber set up? I'm guessing it's probably an coupled with an RF field, which can accelerate a plasma, but details, come on!