8-Pack Team Makes Progress on Linear Collider Technology
By Heather Rock Woods
The Next Linear Collider’s (NLC) 8-Pack team has surpassed a crucial hurdle in the quest to develop a new linear collider to search for the
Universe’s missing particles.
One of the new 75 MW klystrons developed at SLAC that
will power a ‘2-pack’ RF system this year.
courtesy of David Schultz)
The project squeezed an incredible 475 megawatts (MW) of power into a
succinct 400-nanosecond (ns) pulse of radio frequency (RF) power. This
short-lived peak power (400 billionths of a second) is more than that
produced by some nuclear power plants.
"This was a real challenge," said David Schultz (NLC), the physicist
who heads the 8-Pack Project. He added, "No one had pushed power this
long, this hard and this high."
This landmark demonstration proves that particle physicists can
successfully supply the high power that is needed to accelerate electrons
to the tremendous energies required to keep a new linear collider within
the 20-mile-long design goal.
The International Linear Collider Technical Review Committee rated the
RF supply system as one of the two most critical goals to reach in order
to consider building an X-band (so-called "warm") linear collider. The
physics community expects to select either an X-band collider or a
superconducting collider by the end of this year.
"This is a great step towards the full TeV-energy mission of the linear
collider," said David Burke, head of the NLC collaboration.
On December 4, Sami Tantawi (ARDA) announced that the innovative RF
supply station delivered the desired 475 MW, 400 ns pulse at a frequency of 11.424
gigahertz (GHz). Days later, the new system began routinely producing 570
MW, which is more than three times the peak RF power and four times the
frequency SLAC currently generates to run the world’s longest and most
powerful linear accelerator.
"There were cheers all around, back-slapping and hand-shaking. This
accomplishment was two years in the making," Schultz said.
An X-band collider would need over 2,000 such RF supply stations to add
65 mega-electron volts (MeV) of energy to an electron bunch for every
meter the bunch travels. SLAC is close to meeting the second technical
requirement for an X-band collider: accelerating structures, the pipes the
electrons travel in, that can reliably sustain that high accelerating
gradient (65 MeV per meter). These two major collider elements will be
tested together this spring at the NLC Test Accelerator (NLCTA).
"We’re enthusiastic about this next step—using the RF supply station to
power the accelerating structures being built at Fermilab, SLAC and KEK,"
The team designed and assembled the new RF system, originally using a
pack of eight klystrons (the tubes that generate RF power). The current
8-Pack station needs only four klystrons, which will be replaced this year
with just two klystrons of a new design. These new 75 MW klystrons, a
joint project of the Klystron Department and the U.S. industry CPI,
recently performed to full specifications for a warm linear collider.
The 8-Pack klystrons are powered by short, high-voltage pulses from a
new modulator with pioneering solid-state switches.
The RF power from the klystrons is funneled to the Stanford Linac
Energy Doubler (SLED II) system, which triples the power and shortens the
pulse by a factor of four. Tantawi and his group designed revolutionary
new components for the SLED system, enabling it to operate in dual mode,
where the RF power is transmitted in two modes to pack more power into a
pulse in a shorter space.
"We were rewarded when all these parts got integrated and operated
together in perfect harmony," Tantawi said. "This machine is a beautiful
work of art that gave its designers and creators a deep sense of
Tantawi and Schultz are now running a series of performance tests to
ensure the RF systems are sustainable and reliable under the operating
conditions of a linear collider that runs around the clock.
"We want to understand stability and other factors that are important
if you need to build 2,000 of these," said Tantawi.
All together, the RF supply system achieves more power, with the
promise of a much longer lifetime than the current systems used at