1. 18
trillion eV
Highest proton
beam energy
at LHC in 2009
3. 5
trillion eV
Proton beam
energy target
for LHC in 2010
7
trillion eV
Max LHC proton
beam energy —
a goal for 2013
Large Hadron Collider finally set to
begin regular proton beam collisions
Accelerator will be limited to half power for 18 to 24 months
By Ron Cowen
After more than a year of delays, the most
powerful atom smasher on Earth is finally
ready for regular collisions of its two
proton beams, expected to begin around
March 1. But to help safeguard CERN’s
Large Hadron Collider from further electrical problems, the accelerator will run
at only half its maximum energy for the
next 18 months to two years, said Steve
Myers, CERN’S director for
accelerators and technology,
during a talk on February 13.
That decision all but guarantees a new and major delay
in discovering new elementary particles including the
long-sought Higgs boson,
whose existence would
account for why subatomic
particles have mass.
Starting in mid-March, each of the
twin beams of protons accelerated by
the Large Hadron Collider are expected
to carry an unprecedented energy of
3. 5 trillion electron volts. But that’s just
half the 7 TeV per beam that the particle
accelerator is designed to have, Myers
noted. The collider, situated outside
Geneva, won’t run at full power until
2013, he said.
The lower-than-designed operating
energy aims to ensure that the collider
doesn’t suffer any additional electrical problems. In September 2008, an
electrical short in the system powering
some of the collider’s superconducting
magnets forced a shutdown of the accelerator for more than a year. The short
caused a thermal runaway in a section
of the superconducting magnetic system, not only damaging magnets but
also flooding part of the 27-kilometer
accelerator with helium gas.
After a yearlong set of repairs during
which about 106 magnets were either
refurbished or replaced and 6,500 new
detectors were added to the system’s
magnetic protection system along with
250 kilometers of new cable, that particular problem “can never happen again,”
said Myers.
But during tests in April 2009, scientists discovered another set of problems.
Electrical flaws were found in copper bus
bars housing superconducting cables.
The copper problem is
not a complete showstopper
but means that the LHC can
operate safely only at 3. 5 Te V
per beam. At higher energies, the faulty connection
could vaporize the copper
and cause further damage
to the collider. After 2011,
Late last year, the LHC achieved
what was then the highest energy of any
accelerator — 1. 18 Te V per beam, beating
out the Fermilab’s Tevatron in Illinois.
Because of all the delays with the LHC,
the Tevatron’s operating life has already
been extended two years, to 2011, and
Fermilab scientists are closely watching
the LHC’s progress to determine whether
they might keep the Tevatron working
until 2012, said Joseph Incandela of the
University of California, Santa Barbara.
In the meantime, even operating the
LHC at 3. 5 TeV per beam will take physicists “into new territory,” Incandela
said, where the discovery of new physics, including signs of a new theory of
elementary particles known as super-symmetry, is still possible. s
The collider is
expected to
finally achieve
its maximum
energy of
7 TeV
per beam
in 2013.
Improving dental dosimetry
A tiny chip of tooth enamel can tell
the tale of radiation exposure, Barry
Pass of Howard University in Washington, D.C., reported February 16.
Radioactivity creates long-lived
unpaired electrons when it hits tooth
enamel; the higher the dose, the
more unpaired electrons. Researchers can detect this signal with
electronic paramagnetic resonance,
which relies on electromagnetic
waves hitting the tooth and interacting with the unpaired electrons. This
technique once required so much
enamel that an entire tooth might
need to be extracted. Using a higher
frequency of electromagnetic waves,
Pass and colleagues were able to
determine radiation doses from samples as small as 2 milligrams. These
“enamel biopsies” must be removed
from the tooth, but are so small that
they don’t interfere with the tooth’s
function. — Laura Sanders
Shaving extra dimensions
Any extra dimensions of space
curled inside the three that humans
inhabit are less than 50 microme-
ters in diameter, physicists reported
February 15. Ted Cook of the Uni-
versity of Washington in Seattle and
colleagues used a torsion pendulum
to probe how gravity works at small
scales. If the force’s strength dif-
fers from expected when objects
are very close, it could indicate that
gravity leaks into extra dimensions.
Earlier work showed that gravity’s
pull is normal when objects are 56
micrometers apart, meaning any
extra dimensions must be smaller
than that. But Cook’s setup is twice
as sensitive, allowing him to winnow
the limit even further. He eventually
hopes to push the limit below 30
micrometers. — Lisa Grossman
www.sciencenews.org
March 13, 2010 | SCIENCE NEWS | 9
