February 6, 2004  


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. (Photo 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," Burke said.

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 satisfaction."

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 accelerators worldwide.


The Stanford Linear Accelerator Center is managed by Stanford University for the US Department of Energy

Last update Tuesday February 10, 2004 by Emily Ball