Fermi National Laboratory

Volume 27  |  April 2004  |  Number 4
In This Issue  |  FermiNews Main Page

Movin' On Up

by Matthew Hutson

"Run II is not a construction project," Dan Lehman of the Department of Energy said in July of 2003. Lehman directs the DOE's Construction Management Support Division and regularly conducts reviews of large DOE projects. After reviewing Fermilab's Run II Luminosity Upgrade plan last July, he said, "Run II is a complex campaign of operations, maintenance, upgrades, R&D, and studies."

Joe Dey
Engineer Joe Dey working on the RF system for slip stacking. Dey is viewing the transient beam loading on the Main Injector cavities in the frequency domain using a vector signal analyzer. - Photo by Reidar Hahn
A campaign. "He got it just right," Jeff Spalding said. "We've kind of taken that as our theme." Spalding is Project Manager for the Upgrade, which began last summer and will continue until the end of the run in 2009. "The Upgrade plan is a living plan," Spalding continued, "with adjustments and improvements as we continue to learn from operations and from the R&D."

Experts from this and other labs around the world define each element of the plan through a series of technical reviews. These reviews, organized by Pushpa Bhat of the Computing Division, are essential to make sure that the plan is technically sound.

The singular term Upgrade belies the plural nature of the project, which includes upgrades to seven of the eight linked accelerators. The Accelerator, Technical, Particle Physics, and Computing Divisions will perform upgrades continually during scheduled annual shutdowns and in the hours between data-collecting sessions.

The campaign to increase "integrated luminosity," or the number of proton-antiproton collisions in the Tevatron over time, is broken down into six major phases. The major Phase 1 project nearing completion is "slip stacking." In the Tevatron, protons outnumber antiprotons—also called pbars—by 10 to one, so the number of antiprotons produced forms the bottleneck for luminosity. Slip stacking will break the bottleneck.
Ioanis Kourbanis and Kiyomi Seiya
Project manager Ioanis Kourbanis and postdoc Kiyomi Seiya in the Main Injector control room. - Photo by Reidar Hahn

To create pbars, the Main Injector sends a batch of protons towards the Antiproton Source, where they hit a stainless steel target. Slip stacking doubles the number of protons hitting the target. When in operation, two Booster batches of protons will travel around in MI at different speeds. When one slides up next to the other, they are combined together in one batch.

But first the MI needs more radio frequency power to drive the protons around the ring. So Ioanis Kourbanis and MI technicians are doubling the number of RF amplifiers.

"We're pretty optimistic that we're going to finish on time and we're going to get our goal," Kourbanis said.

During Phase 2, the Recycler will near completion. In January the AD achieved its first data taking session, or store, in the Tevatron using pbars transferred from the Recycler after more than a year of setbacks.

"Sergei Nagaitsev put together a very aggressive plan for [last year's] shutdown and got a lot of support," Spalding said. "He added new capability, he added new diagnostics, and he did a thorough bake-out of the vacuum system, and basically solved the problem."

Alexander Shemyakin
Alexander Shemyakin of the Electron Cooling project. - Photo by Reidar Hahn
The biggest project for Phase 2, and perhaps the riskiest element of the entire Upgrade, is electron cooling. When protons hit the target, the pbars emerge as a poof of hot gas. By the time the pbars make it all the way to the Tevatron, they travel in orderly bunches. This transformation from random to ordered is called cooling.

An electron accelerator will create a cold electron beam and inject it into the Recycler. The electrons will mix with the pbars, and the more erratic pbars will share their thermal energy with the electrons. After 20 meters, a magnet will redirect the electrons away from the pbars.

Alexander (Sasha) Shemyakin manages the electron cooling research at the Wide Band lab in the fixed target area. Electron cooling has been used before, but "nobody has done it with a beam this powerful," he said. In June, the team will move their equipment to MI31 next to the Recycler, and in August during the shutdown they'll install the final elements into the Recycler. They hope to have the process working by late 2005.

With the Recycler and electron cooling fully operational, the transfer of pbar stacks from the Accumulator to the Recycler will be automated. Transfers will require only a minute and happen every half hour.

With electron cooling in place, the AD can focus on another type of cooling during Phase 3: stochastic cooling. Stochastic cooling has been compared to separating green paint into blue and yellow one molecule at a time. A sensor detects which particles in a hot beam are misbehaving and applies microwaves to set them in order. Stochastic cooling is used in the Debuncher, the Accumulator, and the Recycler. Elvin Harms, in charge of stochastic cooling in the Antiproton Source, calls this technique a bit of "radiofrequency gymnastics."

Another group will upgrade "stacktail cooling" in the Accumulator, which further refines the pbar stacks.

Phases 4, 5, and 6 will focus mostly on helping the Tevatron more efficiently use pbars. The beams of protons and pbars, each about half a millimeter thick, travel around the Tevatron in opposite directions while twisting around each other like cords in a rope. Separated by only five millimeters, their mutual electrical attraction "shaves" some of the particles off each beam.

The Tevatron uses 22 separators, pairs of metal plates generating electrical fields, to keep the two beams apart. One option is to add more separators, but this is expensive. The other option is to increase the voltage of the separators. Vladimir Shiltsev, Head of the Tevatron Department, and a team led by Ron Moore and Peter Limon, are researching new materials for the plates and doing beam studies. They should know by the end of 2004 whether they will install new separators or upgrade the existing ones.

A beam in the Tevatron contains 36 separate bunches. After crossing paths inside CDF and DZero, the bunches get wider, some more than others. One solution is to install a magnet called an electron lens that can turn on and off rapidly enough to narrow individual bunches. Currently one lens is in testing at the Tevatron, with another on the way. "These are top-notch experiments," Shiltsev said. "It's the first electron lens ever." Scientists at the LHC are watching closely to see if it works.

Fermilab also collaborates with SLAC, LBL, and Budker Institute of Nuclear Physics in Russia to study these "beam-beam" effects.

Several improvements have already increased luminosity. During the last shutdown an alignment task force installed TevNet, a GPS-based system for measuring magnet movement and correcting misplacement. These changes allow the corrector magnets to run at lower currents. The stores have increased from 15 hours to 30 hours.

The beamline between the target and the Debuncher ring has also been widened slightly to increase Debuncher acceptance of pbars. A team is currently studying the beamline using optical surveys, beam-based alignment techniques, and documentation to increase acceptance by rebuilding or relocating components or steering the beam differently. Ten quadrupole magnets in the Debuncher have been placed on motorized stands, and 20 more will receive the same treatment. Significant improvements in the Debuncher should continue to build up into 2007.

The Computing Division's major contribution will be an upgrade to the Tevatron Beam Position Monitor, or BPM, system, in collaboration with the AD. At 240 points around the Tevatron, the particle beams pass through BPM's, which tell the operators how close the beams are to the center of the ring. The monitors send their data to 27 service buildings stationed above the ring, which process the data and send it to the main control room. The BPM group will replace all of the electronics in the service buildings. They will also rewrite much of the software for reading the data out, storing it, and analyzing it.

Jim Walton (left) and Jeff Wittenkeller
Jim Walton (left) and Jeff Wittenkeller with one of twelve new separator polarity switches for the Tevatron. - Photo by Reidar Hahn
Steve Wolbers of the CD heads the project, and Bob Webber of AD is Deputy Head. Wolbers says that the upgrades will improve resolution by nearly a factor of 20, from 150 microns to eight microns.

A fast solution is better than a perfect solution. "The idea is to get this system in place quickly so that the Tevatron department and others can use this information," Wolbers said. The upgrade should be complete by the end of the year.

The CD will also work on hardware and software for the Tevatron Ionization Profile Monitors, or IPM's, which measure the size of the beam, and on several beam analysis projects around the lab.

Since December, the accelerators have been remarkably reliable, but according to Dave McGinnis, Technology Coordinator for the Upgrade, "the memory of December is fresh in our minds. We could at any time be down for 20 days."

Paul Czarapata, Associate Division Head of Engineering in the AD, says people have the wrong idea about maintenance; they think it's completely separate from upgrades. When something breaks you don't just fix it; you improve it. "Maintenance is a continual upgrade," he said. "You've gotta stay one step ahead." Czarapata's keeps an eye on the lifetimes of equipment, on how it's used, on the status of replacement parts, on run schedules, and a number of other factors. With so many variables, "people make careers out of just studying when to do maintenance."

Czarapata's biggest headache is securing spare parts for the Linac. The one vendor that makes the right power tubes is for sale, and its older engineers are retiring.

Accompanying the engineering changes have been some management changes. Roger Dixon took over as head of the AD last year, and he made several organizational changes. He also introduced the idea of an integration department to increase the efficiency and coherence operations. The next step was to charge Dave McGinnis with the responsibility for accelerator systems with all the systems departments reporting to him. Integration evolved naturally from that point.

"Integration is important, but more important is having the right people doing the right jobs," Dixon told me. "From the beginning I knew that the potential existed within the Division for extraordinary accomplishments. Most of these are yet to come."

Currently the integrated luminosity per week is around 11 inverse picobarnes (pb-1). At the beginning of Run II in 2001 it was around one pb-1, and by the end, it will probably reach between 28 and 47 pb-1. Total Run II integrated luminosity will probably reach between 4.4 and 8.5 thousand pb-1, or inverse femtobarnes.

"We're doing a lot better but we've got a long way to go," Spalding said. "8.5 fb-1 we think is a realistic goal if every element of the plan works the way it's designed to work. We think it's realistic to be achieved and in fact on paper you can certainly exceed it."

Even following the lower projection of 4.4, Run II would provide 30 times the integrated luminosity of Run I, and the subatomic realm holds no shortage of mysteries.

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last modified 4/8/2004   email Fermilab