Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Beam-beam compensation scheme doubles proton-proton collision rates at RHIC


Smashing more protons produces more data for exploring physics questions

Accelerator physicists at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory have successfully implemented an innovative scheme for increasing proton collision rates at the Relativistic Heavy Ion Collider (RHIC). More proton collisions at this DOE Office of Science User Facility produce more data for scientists to sift through to answer important nuclear physics questions, including the search for the source of proton spin (see:

Brookhaven Lab accelerator physicist Wolfram Fischer stands next to the electron lensing apparatus at the Relativistic Heavy Ion Collider (RHIC), a particle accelerator/collider at the US Department of Energy's Brookhaven National Laboratory.

Credit: Brookhaven National Laboratory

"So far we have doubled the peak and average 'luminosity'-measures that are directly related to the collision rates," said Wolfram Fischer, Associate Chair for Accelerators of Brookhaven's Collider-Accelerator Department and lead author on a paper describing the success just published in Physical Review Letters. And, he says, there's potential for further gains by increasing the number protons from the injectors even more.

Colliding polarized protons

RHIC is the world's only polarized proton collider, capable of sending beams of protons around its 2.4-mile-circumference racetrack with their internal magnetic axes (also known as spins) aligned in a chosen direction. Colliding beams of such "spin polarized" protons and manipulating the spin directions gives scientists a way to explore how their internal building blocks, quarks and gluons, contribute to this intrinsic particle property.

Data at RHIC have revealed that both quarks and gluons make substantial contributions to spin, but still not enough to explain the total spin value. More data will help resolve this spin mystery by reducing uncertainties and allowing nuclear physicists to tease out other unaccounted for contributions.

But getting more protons to collide is an ongoing challenge because, as one beam of these positively charged particles passes through the other, the particles' like charges make them want to move away from one another.

"The strongest disturbance a proton experiences when it travels around the RHIC ring is when it flies through the other proton beam," Fischer said. "The result of the positive charges repelling is that the protons get deflecting kicks every time they fly through the oncoming beam."

Opposite charge produces opposite push

The size of the repulsive kick depends on where the proton flies through the beam, with protons about halfway from dead center to the outside edge of the beam's cross-section experiencing the largest outward push. Particles closer to the center or the outer edge of the cross-section experience less repulsion.

Because of the variable shape of this effect-increasing to a peak and then decreasing with distance from the beam's center-it's impossible to correct using magnets. "The magnetic field strength in magnets increases steadily from the center out," Fischer said.

So instead, the scientists turned to using oppositely charged particles to produce a compensating push in the opposite direction.

"We've implemented electron lensing technology to compensate for these head-on beam-beam effects," Fischer said.

Essentially, they use an electron gun to introduce a low-energy electron beam into a short stretch of the RHIC accelerator. Within that stretch, the electrons are guided by a magnetic field that keeps them from being deflected by the more energetic protons. As the protons pass through the negatively charged electron beam, they experience a kick in the opposite direction from the repulsive positive charge, which nudges the protons back toward the center of the beam.

"It's not a glass lens like you'd find in a camera," Fischer said, "but we call the technique 'electron lensing' because, like a lens that focuses light, the electron beam changes the trajectory of the protons flying through it."

Riding the optical wave

The scientists also take advantage of certain "optical" properties of RHIC's particle beams to ensure the method's efficacy.

"Ideally you would like to produce these compensating pushes right where the collisions happen, within the STAR and PHENIX detectors," Fischer said. "But then the experiments wouldn't work anymore. So we placed the electron lenses, one on each beam, at a certain distance from the detectors-called the optical distance-where they have an effect at the same point in the 'phase' of the particle beam that's inside the detectors."

Like a wave of light or sound that oscillates up and down in amplitude at a given frequency, the particles that travel around RHIC also oscillate a tiny bit. As long as the nuclear physicists know the frequency of the oscillations and give their electron-lensing kicks at the same point in that oscillation that the particles reach within the detector, the effect will compensate for the proton repulsion the particles experience at that distant location.

So far, the scientists have doubled the proton-proton collision rates at RHIC. They could potentially get even higher gains by increasing the number of protons injected into the machine.

"The key challenge will be to maintain the high degree of polarization the experiments need to explore the question of proton spin," Fischer said. But he insists there is clear potential for even higher proton-proton luminosity.


This work was performed by many people in the Collider-Accelerator Department and the Superconducting Magnet Division at Brookhaven National Laboratory, and was funded by the DOE Office of Science (NP). The scientists also acknowledge the U.S. LHC Accelerator Research Program (LARP) for support of beam-beam simulations, and researchers around the world especially the electron lens experts at Fermi National Accelerator Laboratory.

Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE's Office of Science by Brookhaven Science Associates, a limited-liability company founded by the Research Foundation for the State University of New York on behalf of Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit applied science and technology organization.

Related Links

Scientific paper: "Operational Head-on Beam-Beam Compensation with Electron Lenses in the Relativistic Heavy Ion Collider"

Media Contact

Karen McNulty Walsh


Karen McNulty Walsh | EurekAlert!

More articles from Physics and Astronomy:

nachricht Streamlining accelerated computing for industry
24.08.2016 | DOE/Oak Ridge National Laboratory

nachricht Lehigh engineer discovers a high-speed nano-avalanche
24.08.2016 | Lehigh University

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Streamlining accelerated computing for industry

PyFR code combines high accuracy with flexibility to resolve unsteady turbulence problems

Scientists and engineers striving to create the next machine-age marvel--whether it be a more aerodynamic rocket, a faster race car, or a higher-efficiency jet...

Im Focus: X-ray optics on a chip

Waveguides are widely used for filtering, confining, guiding, coupling or splitting beams of visible light. However, creating waveguides that could do the same for X-rays has posed tremendous challenges in fabrication, so they are still only in an early stage of development.

In the latest issue of Acta Crystallographica Section A: Foundations and Advances , Sarah Hoffmann-Urlaub and Tim Salditt report the fabrication and testing of...

Im Focus: Piggyback battery for microchips: TU Graz researchers develop new battery concept

Electrochemists at TU Graz have managed to use monocrystalline semiconductor silicon as an active storage electrode in lithium batteries. This enables an integrated power supply to be made for microchips with a rechargeable battery.

Small electrical gadgets, such as mobile phones, tablets or notebooks, are indispensable accompaniments of everyday life. Integrated circuits in the interiors...

Im Focus: UCI physicists confirm possible discovery of fifth force of nature

Light particle could be key to understanding dark matter in universe

Recent findings indicating the possible discovery of a previously unknown subatomic particle may be evidence of a fifth fundamental force of nature, according...

Im Focus: Wi-fi from lasers

White light from lasers demonstrates data speeds of up to 2 GB/s

A nanocrystalline material that rapidly makes white light out of blue light has been developed by KAUST researchers.

All Focus news of the innovation-report >>>



Event News

The energy transition is not possible without Geotechnics

25.08.2016 | Event News

New Ideas for the Shipping Industry

24.08.2016 | Event News

A week of excellence: 22 of the world’s best computer scientists and mathematicians in Heidelberg

12.08.2016 | Event News

Latest News

3-D-printed structures 'remember' their shapes

29.08.2016 | Materials Sciences

From rigid to flexible

29.08.2016 | Life Sciences

Sensor systems identify senior citizens at risk of falling within 3 weeks

29.08.2016 | Medical Engineering

More VideoLinks >>>