Stephen Sekula

Dallas, TX, USA

Husband; Associate Professor of Physics; I teach at SMU in Dallas, TX; I study the Higgs Particle with the ATLAS Experiment at the Large Hadron Collider at CERN; writer and blogger; drummer; programmer; teacher; scientist; traveler; runner; gardener; open-source aficionado.

  • LS2 report: The Proton Synchrotron’s magnets prepare for higher energies

    ParticleNews at 2019-02-13T11:27:36Z

    "LS2 report: The Proton Synchrotron’s magnets prepare for higher energies"

    LS2 report: The Proton Synchrotron’s magnets prepare for higher energies

    achintya Wed, 02/13/2019 - 09:35
    PS Magnets consolidation during LS2
    PS Magnets consolidation during LS2 (Image: CERN)

    The Proton Synchrotron (PS), which was CERN’s first synchrotron and which turns 60 this year, once held the record for the particle accelerator with the highest energy. Today, it forms a key link in CERN’s accelerator complex, mainly accelerating protons to 26 GeV before sending them to the Super Proton Synchrotron (SPS), but also delivering particles to several experimental areas such as the Antiproton Decelerator (AD). Over the course of Long Shutdown 2 (LS2), the PS will undergo a major overhaul to prepare it for the higher injection and beam intensities of the LHC’s Run 3 as well as for the High-Luminosity LHC.

    One major component of the PS that will be consolidated is the magnet system. The synchrotron has a total of 100 main magnets within it (plus one reference magnet unit outside the ring), which bend and focus the particle beams as they whizz around it gaining energy. “During the last long shutdown (LS1) and at the beginning of LS2, the TE-MSC team performed various tests to identify weak points in the magnets,” explains Fernando Pedrosa, who is coordinating the LS2 work on the PS. The team identified 50 magnets needing refurbishment, of which seven were repaired during LS1 itself. “The remaining 43 magnets that need attention will be refurbished this year.”

    Specifically, one of the elements, known as the pole-face windings, which is located between the beam pipe and the magnet yoke, needs replacing. In order to reach into the magnet innards to replace these elements, the magnet units have to be transferred to a workshop in building 151. Once disconnected, each magnet is placed onto a small locomotive system that drives them to the workshops. The locomotives themselves are over 50 years old, and their movement must be delicately managed. It takes ten hours to extract one magnet. So far, six magnets have been taken to the workshop and this work will last until 18 October 2019.

    The workshop where the magnets are being treated is divided into two sections. In the first room, the vacuum chamber of the magnets is cut so as to access the pole-face windings. The magnet units are then taken to the second room, where prefabricated replacements are installed.

    As mentioned in the previous LS2 Report, the PS Booster will see an increase in the energy it imparts to accelerating protons, from 1.4 GeV to 2 GeV. A new set of quadrupole magnets will be installed along the Booster-to-PS injection line, to increase the focusing strength required for the higher-energy beams. Higher-energy beams require higher-energy injection elements; therefore some elements will be replaced in the PS injection region as part of the LHC Injectors Upgrade (LIU) project, namely septum 42, kicker 45 and five bumper magnets.

    Other improvements as part of the LIU project include the new cooling systems being installed to increase the cooling capacity of the PS. A new cooling station is being built at building 355, while one cooling tower in building 255 is being upgraded. The TT2 line, which is involved in the transfer from the PS to the SPS, will have its cooling system decoupled from the Booster’s, to allow the PS to operate independent of the Booster schedule. “The internal dumps of the PS, which are used in case the beam needs to be stopped, are also being changed, as are some other intercepting devices,” explains Pedrosa.

    The LS2 operations are on a tight schedule,” notes Pedrosa, pointing out that works being performed on several interconnected systems create constraints for what can be done concurrently. As LS2 proceeds, we will bring you more news about the PS, including the installation of new instrumentation in wire scanners that help with beam-size measurement, an upgraded transverse-feedback system to stabilise the beam and more.

    More pictures of the PS magnets are available on CDS:

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  • Build The Peach!

    Jason Self at 2019-02-01T14:37:58Z

    Build the peach! Build the peach!

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  • Astronomy Picture of the Day for 2019-01-26 12:30:01.764936

    Astronomy Picture of the Day (Unofficial) at 2019-01-26T18:30:03Z

    Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

    2019 January 26
    See Explanation.  Clicking on the picture will download
the highest resolution version available.

    The Umbra of Earth
    Image Credit & Copyright: Antonio Finazzi

    Explanation: The dark, inner shadow of planet Earth is called the umbra. Shaped like a cone extending into space, it has a circular cross section most easily seen during a lunar eclipse. For example, on January 21 the Full Moon slid across the northern half of Earth's umbral shadow, entertaining moonwatchers around much of the planet. In the total phase of the eclipse, the Moon was completely within the umbra for 63 minutes. Recorded under clear, dark skies from the hills near Chiuduno, Italy this composite eclipse image uses successive pictures from totality (center) and partial phases to trace out a large part of the umbra's curved edge. Reflecting sunlight scattered by the atmosphere into Earth's shadow, the lunar surface appears reddened during totality. But close to the umbra's edge, the limb of the eclipsed Moon shows a distinct blue hue. The blue eclipsed moonlight originates as rays of sunlight pass through layers high in the upper stratosphere, colored by ozone that scatters red light and transmits blue.

    Tomorrow's picture: crossing the sky

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  • Astronomy Picture of the Day for 2019-01-23 12:30:02.300728

    Astronomy Picture of the Day (Unofficial) at 2019-01-23T18:30:03Z

    Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

    2019 January 23
    See Explanation.  Clicking on the picture will download
the highest resolution version available.

    Orion over the Austrian Alps
    Image Credit & Copyright: Luk Vesel

    Explanation: Do you recognize this constellation? Through the icicles and past the mountains is Orion, one of the most identifiable star groupings on the sky and an icon familiar to humanity for over 30,000 years. Orion has looked pretty much the same during the past 50,000 years and should continue to look the same for many thousands of years into the future. Orion is quite prominent in the sky this time of year, a recurring sign of (modern) winter in Earth's northern hemisphere and summer in the south. Pictured, Orion was captured recently above the Austrian Alps in a composite of seven images taken by the same camera in the same location during the same night. Below and slightly to the right of Orion's three-star belt is the Orion Nebula, while the four bright stars surrounding the belt are, clockwise from the upper left, Betelgeuse, Bellatrix, Rigel, and Saiph.

    New: Instagram page features cool images recently submitted to APOD
    Tomorrow's picture: the cold eclipse

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  • dw at 2019-01-22T20:55:35Z

    Who should I be following? No one has posted anything in 3 hours. Last comment appears to have been 2 hours ago...

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    I got nothing. :-)

    My feed has been fairly quiet of late as well. That said, and have been chatty of late.

    Stephen Sekula at 2019-01-23T00:32:14Z

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  • The @Debian 10 'buster' release freeze has begun --

    Debian Project at 2019-01-21T00:15:07Z

    The @Debian 10 'buster' release freeze has begun --

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  • JanKusanagi at 2019-01-17T19:03:10Z

    I feel relaxed already! 😌

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  • Astronomy Picture of the Day for 2019-01-14 12:30:02.260530

    Astronomy Picture of the Day (Unofficial) at 2019-01-14T18:30:03Z

    Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

    2019 January 14
    See Explanation.  Clicking on the picture will download
the highest resolution version available.

    Meteor and Milky Way over the Alps
    Image Credit & Copyright: Nicholas Roemmelt (Venture Photography)

    Explanation: Now this was a view with a thrill. From Mount Tschirgant in the Alps, you can see not only nearby towns and distant Tyrolean peaks, but also, weather permitting, stars, nebulas, and the band of the Milky Way Galaxy. What made the arduous climb worthwhile this night, though, was another peak -- the peak of the 2018 Perseids Meteor Shower. As hoped, dispersing clouds allowed a picturesque sky-gazing session that included many faint meteors, all while a carefully positioned camera took a series of exposures. Suddenly, a thrilling meteor -- bright and colorful -- slashed down right next the nearly vertical band of the Milky Way. As luck would have it, the camera caught it too. Therefore, a new image in the series was quickly taken with one of the sky-gazers posing on the nearby peak. Later, all of the images were digitally combined.

    Tomorrow's picture: heart & soul

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  • Jason Self at 2019-01-14T02:05:49Z

    I removed 15 of the 16 RAM modules and the computer boots into the Trisquel installer just fine. It would appear the problems can be explained away with bad memory. Time to break out Memtest86+...

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    at 2019-01-15T00:05:23Z

    What? You don't know what a TARDIS is?

    Don't you have a plain old dictionary? 😆

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  • This weekend we have a Debian Bugsquashing Party in Venlo #Debian #BSP #Party

    Debian Project at 2019-01-11T22:15:05Z

    This weekend we have a Debian Bugsquashing Party in Venlo #Debian #BSP #Party

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  • JanKusanagi at 2019-01-11T19:18:58Z

    Some giant took a bite out of the Sun!!!!! 😱

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  • JanKusanagi at 2019-01-08T04:48:14Z

    Gifted. But the thing about the Navier-Stokes problem was just a background thing. It was just funny to see it mentioned 😆

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  • JanKusanagi at 2019-01-08T02:10:51Z

    Weird, I was under the impression that it was day 7... 🤔

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  • New blog post: "Debian is back in the Mastodon/GNU Social fediverse, follow"

    Laura Arjona Reina at 2018-12-21T12:36:07Z

    New blog post: "Debian is back in the Mastodon/GNU Social fediverse, follow"

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    Cool, but I already follow @Debian Project right here 😎

    JanKusanagi at 2018-12-21T13:28:48Z

  • Stephen Michael Kellat at 2019-01-06T18:07:41Z

    I had to move off to

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  • JanKusanagi at 2019-01-06T17:54:40Z

    I think at least the first one is. IIRC @Laura Arjona Reina was on it and had to move.

    She might have commented on it on her feed 😄

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  • Astronomy Picture of the Day for 2019-01-04 12:30:02.139948

    Astronomy Picture of the Day (Unofficial) at 2019-01-04T18:30:02Z

    Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

    2019 January 4
    See Explanation.  Clicking on the picture will download
the highest resolution version available.

    Ultima Thule Rotation Gif
    Image Credit: NASA, Johns Hopkins University APL, Southwest Research Institute

    Explanation: Ultima Thule is the most distant world explored by a spacecraft from Earth. In the dim light 6.5 billion kilometers from the Sun, the New Horizons spacecraft captured these two frames 38 minutes apart as it sped toward the Kuiper belt world on January 1 at 51,000 kilometers per hour. A contact binary, the two lobes of Ultima Thule rotate together once every 15 hours or so. Shown as a blinking gif, the rotation between the frames produces a tantalizing 3D perspective of the most primitive world ever seen. Dubbed separately by the science team Ultima and Thule, the larger lobe Ultima, is about 19 kilometers in diameter. Smaller Thule is 14 kilometers across.

    Tomorrow's picture: on the Far Side

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  • I have three words for you...

    JanKusanagi at 2019-01-04T19:46:36Z



    Suck 😠

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  • Startup Time for Ion Collisions Exploring the Phases of Nuclear Matter

    ParticleNews at 2019-01-04T16:27:37Z

    "Startup Time for Ion Collisions Exploring the Phases of Nuclear Matter"

    Startup Time for Ion Collisions Exploring the Phases of Nuclear MatterPress Releasexeno Fri, 01/04/2019 - 09:01119

    19th year of operations at the Relativistic Heavy Ion Collider will continue search for critical point in transition from protons and neutrons to quark-gluon plasma.


    The Relativistic Heavy Ion Collider (RHIC) is actually two accelerators in one. Beams of ions travel around its 2.4-mile-circumference rings in opposite directions at nearly the speed of light, coming into collision at points where the rings cross.

    UPTON, NY—January 2 marked the startup of the 19th year of physics operations at the Relativistic Heavy Ion Collider (RHIC), a U.S. Department of Energy Office of Science user facility for nuclear physics research at Brookhaven National Laboratory. Physicists will conduct a series of experiments to explore innovative beam-cooling technologies and further map out the conditions created by collisions at various energies. The ultimate goal of nuclear physics is to fully understand the behavior of nuclear matter—the protons and neutrons that make up atomic nuclei and those particles’ constituent building blocks, known as quarks and gluons.

    Many earlier experiments colliding gold ions at different energies at RHIC have provided evidence that energetic collisions create extreme temperatures (trillions of degrees Celsius). These collisions liberate quarks and gluons from their confinement with individual protons and neutrons, creating a hot soup of quarks and gluons that mimics what the early universe looked like before protons, neutrons, or atoms ever formed.

    “The main goal of this run is to turn the collision energy down to explore the low-energy part of the nuclear phase diagram to help pin down the conditions needed to create this quark-gluon plasma,” said Daniel Cebra, a collaborator on the STAR experiment at RHIC. Cebra is taking a sabbatical leave from his position as a professor at the University of California, Davis, to be at Brookhaven to help coordinate the experiments this year.

    STAR is essentially a house-sized digital camera with many different detector systems for tracking the particles created in collisions. Nuclear physicists analyze the mix of particles and characteristics such as their energies and trajectories to learn about the conditions created when ions collide.

    STAR Phase diagram

    The STAR collaboration's exploration of the "nuclear phase diagram" so far shows signs of a sharp border—a first-order phase transition—between the hadrons that make up ordinary atomic nuclei and the quark-gluon plasma (QGP) of the early universe when the QGP is produced at relatively low energies/temperatures. The data may also suggest a possible critical point, where the type of transition changes from the abrupt, first-order kind to a continuous crossover at higher energies. New data collected during this year's run will add details to this map of nuclear matter's phases.

    By colliding gold ions at various low energies, including collisions where one beam of gold ions smashes into a fixed target instead of a counter-circulating beam, RHIC physicists will be looking for signs of a so-called “critical point.” This point marks a spot on the nuclear phase diagram—a map of the phases of quarks and gluons under different conditions—where the transition from ordinary matter to free quarks and gluons switches from a smooth one to a sudden phase shift, where both states of matter can coexist.

    STAR gets a wider view

    STAR will have new components in place that will increase its ability to capture the action in these collisions. These include new inner sectors of the Time Projection Chamber (TPC)—the gas-filled chamber particles traverse from their point of origin in the quark-gluon plasma to the sensitive electronics that line the inner and outer walls of a large cylindrical magnet. There will also be a “time of flight” (ToF) wall placed on one of the STAR endcaps, behind the new sectors.

    “The main purpose of these is to enhance STAR's sensitivity to signatures of the critical point by increasing the acceptance of STAR—essentially the field of view captured in the pictures of the collisions—by about 50 percent,” said James Dunlop, Associate Chair for Nuclear Physics in Brookhaven Lab’s Physics Department.

    STAR Detector

    RHIC's STAR detector tracks the thousands of particles produced by each ion collision. It weighs 1,200 tons and is as large as a house.

    “Both of these components have large international contributions,” Dunlop noted. “A large part of the construction of the iTPC sectors was done by STAR’s collaborating institutions in China. The endcap ToF is a prototype of a detector being built for an experiment called Compressed Baryonic Matter (CBM) at the Facility for Antiproton and Ion Research (FAIR) in Germany. The early tests at RHIC will allow CBM to see how well the detector components behave in realistic conditions before it is installed at FAIR while providing both collaborations with necessary equipment for a mutual-benefit physics program,” he said.

    Tests of electron cooling

    Before the collision experiments begin in mid-February, RHIC physicists will be testing a new component of the accelerator designed to maximize collision rates at low energies.

    “RHIC operation at low energies faces multiple challenges, as we know from past experience,” said Chuyu Liu, the RHIC Run Coordinator for Run 19. “The most difficult one is that the tightly bunched ions tend to heat up and spread out as they circulate in the accelerator rings.”

    That makes it less likely that an ion in one beam will strike an ion in the other.

    e cooling layout

    A schematic of low-energy electron cooling at RHIC, from right: 1) a section of the existing accelerator that houses the beam pipe carrying heavy ion beams in opposite directions; 2) the direct current (DC) electron gun and other components that will produce and accelerate the bright beams of electrons; 3) the line that will transport and inject cool electrons into the ion beams; and 4) the cooling sections where ions will mix and scatter with electrons, giving up some of their heat, thus leaving the ion beam cooler and more tightly packed.

    To counteract this heating/spreading, accelerator physicists at RHIC have added a beamline that brings accelerated “cool” electrons into a section of each RHIC ring to extract heat from the circulating ions. This is very similar to the way the liquid running through your home refrigerator extracts heat to keep your food cool. But instead of chilled ice cream or cold cuts, the result is more tightly packed ion bunches that should result in more collisions when the counter-circulating beams cross.

    Last year, a team led by Alexei Fedotov demonstrated that the electron beam has the basic properties needed for cooling. After a number of upgrades to increase the beam quality and stability further, this year’s goal is to demonstrate that the electron beam can actually cool the gold-ion beam. The aim is to finish fine-tuning the technique so it can be used for the physics program next year.

    Berndt Mueller, Brookhaven’s Associate Laboratory Director for Nuclear and Particle Physics, noted, “This 19th year of operations demonstrates once again how the RHIC team — both accelerator physicists and experimentalists — is continuing to explore innovative technologies and ways to stretch the physics capabilities of the most versatile particle accelerator in the world.”

    Research at RHIC is funded primarily by the DOE Office of Science (NP) and by these agencies and organizations.

    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

    Follow @BrookhavenLab on Twitter or find us on Facebook.

    Brookhaven National Laboratory

    Brookhaven National Laboratory

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