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 DGIST develops 20 times faster biosensor
24.04.2017 | DGIST (Daegu Gyeongbuk Institute of Science and Technology)

nachricht New quantum liquid crystals may play role in future of computers
21.04.2017 | California Institute of Technology

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: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>



Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

Latest News

DGIST develops 20 times faster biosensor

24.04.2017 | Physics and Astronomy

Nanoimprinted hyperlens array: Paving the way for practical super-resolution imaging

24.04.2017 | Materials Sciences

Atomic-level motion may drive bacteria's ability to evade immune system defenses

24.04.2017 | Life Sciences

More VideoLinks >>>