Natural Science Forum / Physics / Particle Physics / February 2007

plasma particle accelerator smashes record
18:09 14 February 2007
NewScientist.com news service
Mason Inman
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 A metre-long plasma-powered particle accelerator can boost electrons'
energy to the same degree as a conventional machine 3-kilometres-long,
experiments show. For all it does, the diminutive accelerator is also
relatively simple, consisting of a metal tube filled with gas.

Physicists use accelerators to crash particles together at enormous speeds.
The debris from these collisions can reveal exotic particles and new
phenomena. But particle accelerators, which normally accelerate particles
using empty cavities filled with electromagnetic fields, need to be
kilometres-long to attain such speeds. They also cost billions of dollars to
build.

Mark Hogan at the Stanford Linear Accelerator Center in California, US, is
developing an alternative. Together with colleagues at SLAC and at the
University of California in Los Angeles, US, Hogan has created a much more
compact plasma-powered accelerator.

"Taking the beam from a standard accelerator, we've been able to double the
energy [from 42 gigaelectronvolts to 84 GeV]," Hogan says.

Trillions of electrons
In experiments, SLAC's linear accelerator was used to fling a "packet" of
trillions of electrons into a steel tube filled with lithium gas. When the
electron beam hit the gas, it created plasma and knocked some electrons free
from the gas atoms.

The electrons zoom around the electron beam - in its "wake" - and while this
plasma wake put a drag on most of the beam's electrons, it also gives some
of them a huge kick, boosting them forward.

In 2005 researchers used a similar method to boost electrons' energy by
about 10%. This boost of several GeV was a record at the time for the
biggest acceleration over such a short distance. The new experiment has
smashed that record by scaling up the plasma tube to nearly 1 metre in
length.

One-shot deal
"This is an incredible breakthrough," says Harry Weertz of the Argonne
National Laboratory in Illinois, US. "Now they have to work on the details,"
he adds, so that plasma accelerators could be used for real experiments.

Weerts also points out that it has not been possible to pass electrons
through a string of plasma accelerators, to repeatedly boost their speed. As
it stands, a huge boost from plasma is a one-shot deal.

Another downside, as in all these plasma accelerators, is that the incoming
electron beam loses a lot of intensity. In this case, only about 1% of the
electrons in the beam made it up to the highest energy.

Only last week, physicists announced plans to build the next big particle
accelerator, the International Linear Collider. This will stretch 35
kilometres and will cost about $15 billion.

http://www.newscientisttech.com/article/dn11186?DCMP=NLC-nletter&nsref=dn11186