Graffiti art reflects an experiment’s excitement on the walls

October 31, 2011 | 4:27 pm

The three concrete blocks CERN installed to contain waste at the CMS experiment were ugly and needed paint, according to Niels Dupont-Sagorin, who is in charge of safety at the site. But a quote from contractors for a basic white coat of paint turned out to be pricey. So, he thought, why not make the paint job an artistic investment? A few months later, the site now sports two physics-themed outdoor frescoes done by a local graffiti artist, with one design by a retired CMS researcher.

“My idea was to ask some graffiti artists because I’m from the suburbs of Paris and into street art,” Dupont-Sagorin said. But here on the Swiss-French border, “I didn’t actually know at which door to knock.”

Then one day, while driving from the Meyrin, Switzerland, campus over to the CMS site, Dupont-Sagorin saw something at a roundabout that made him stop. A man was spray painting a billboard with information about an upcoming event in a way Dupont-Sagorin quite liked. He stopped and asked if the man did this work for hire. Indeed, the painter was a freelance artist who goes by the street name Loodz [pictured above with Dupont-Sagorin]. They exchanged information, and Dupont-Sagorin went home to check out Loodz’s website.

“Immediately, I noticed he was good,” Dupont-Sagorin said. “But he’s paid, you know, not a graffiti terrorist.”

He sent Loodz a picture of the blank concrete blocks and also took the opportunity to send a shot of another long blank wall at the entrance to the CMS Control Room.

Loodz sent back some proposal sketches. Dupont-Sagorin was happy with one of them, a dark sketch of the universe dotted with tiny white stars. But the second design lacked something; he thought a more CERN-specific piece would be more fitting.

He asked for suggestions from Michael Hoch, a CMS physicist and himself a curator-creator of many an art project at the experimental site. Hoch knew just whom to ask about the wall: now-retired CMS researcher Sergio Cittolin.

In 1994, Cittolin made a design depicting the evolution of the universe after the Big Bang. This was first used for LHC outreach on a “magic box” toy, a Jacobs-ladder-like cube whose sides flap open never-endingly to reveal inner designs. Later he revamped the sketch into one long image that was adapted into a banner on the CMS website.

Hoch thought Sergio’s creation would work perfectly on the blank wall by the CMS control room. Dupont-Sagorin agreed, noting that its origins also connected to the experiment nicely. With Sergio’s permission, he sent high-definition photos of the banner to Loodz, who merged them with photos of the wall in order to plan the final piece.

Funding ultimately came from the CMS Outreach office and the Experiment Area Manager in the Engineering Department. Loodz did all the art himself, entirely in spray paint, and finished both the wall and then the concrete blocks of the waste area in just 10 days.

“I’m really happy with it,” Dupont-Sagorin said. “I’d like to have money to do it elsewhere.” He has a keen personal interest in outreach and even works as a CERN tour guide on the side. “The shape of your message, your presentations – everything you do is important,” he said.

At his worksite, the physics community clearly agrees.

Amy Dusto

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LHC finishes 2011 proton run

October 31, 2011 | 9:46 am

Operators emptied the LHC of protons in the last beam dump of 2011 on Sunday. Image: CERN

The Large Hadron Collider guided beams of protons along a collision course for the last time this year on Sunday, Oct. 30.

During the LHC’s 2011 run smashing protons into other protons, the machine produced 400 trillion collisions, CERN announced in a press release today. The LHC ran for about 180 days and delivered almost six times as much data as originally expected for the year. The CMS and ATLAS general-purpose experiments collected more than 5 inverse femtobarns of data.

This week, LHC operators will test various aspects of the accelerator and detectors to prepare for future runs. Then they will get ready for four weeks of lead-ion collisions. In the meantime, experimentalists will continue analyzing data from proton-proton collisions in the hunt for new physics.

Kathryn Grim

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Scientists still seek explanation for faster-than-light neutrino result

October 28, 2011 | 6:24 am

Physicist Dario Autiero asked the scientific community to examine the OPERA experiment's surprising results at a seminar on behalf of the OPERA collaboration. Image: CERN

Scientists on the OPERA experiment announced last month that they had measured neutrinos traveling faster than the speed of light. Either this was the start of a revolution or the result of a systematic error. Being scientists, they assumed the latter and asked for help finding the glitch.

Despite what some headlines have suggested, the question of whether the result is correct is still up in the air. Experimentalists have not been able to establish how the experiment is flawed, and yet theorists have not been able to determine how its conclusion could be true.

“There’s no model that explains it,” said CERN theorist Gian Giudice.

Scientists have posted dozens upon dozens of reactions to the OPERA result on the arXiv, an open-source archive of scientific papers, since scientists announced it on Sept. 23. But each proposed explanation contradicts other established measurements in particle physics.

“Things have moved quite fast in these past few weeks,” Giudice said. “In my opinion, we’ve almost reached the point of saturation. The situation looks pretty grim.”

Finding the glitch

Experimentalists could ease theorists’ minds if they could find a problem with the original measurement. Plenty of people have tried, said Antonio Ereditato, spokesperson for the OPERA experiment.

“After our seminar when we requested collaboration, we got some 700 emails,” he said.

Gran Sasso in Italy. Image courtesy of Andrea Parisse through a Creative Commons license.

People asked whether OPERA physicists had taken into account the rotation of the Earth, general relativity, continental drift and other factors that might affect their measurement. In response, the OPERA collaboration has explicitly calculated some of the effects they had originally argued would be negligible.

Those trying to explain the OPERA result have quite a job to do in clearing up the difference between the measured speed of the neutrinos and the speed of light.

Neutrinos that the OPERA collaboration studied appeared to beat light by 60 nanoseconds traveling the 730 kilometers between CERN in Switzerland and Gran Sasso National Laboratory in Italy. “But light only takes 2.4 milliseconds to make this trip,” he said. “Imagine a faraway galaxy emitting light and neutrinos. Depending on the distance, you could have neutrinos arriving 10 or more years earlier than light.”

The new calculations did not cast doubt on the result, Ereditato said. “One actually increased our effect by 2 nanoseconds.”

OPERA will add these details to their scientific paper this month, addressing scientists’ queries but leaving open the question: If neutrinos cannot travel faster than light, what is causing this mistaken measurement?

“If it were something obvious, it would’ve certainly come out during these weeks,” Giudice said. “I think the majority of physicists agree the job was done very carefully.”

A challenge from theory

One challenge to the validity of the OPERA result that has received media attention recently stems from a theoretical paper by physicists Andrew Cohen and Sheldon Glashow, a Nobel laureate.

Cohen and Glashow wrote that, if a neutrino were to surpass the speed of light, it would emit pairs of electrons and positrons, thus losing energy during flight. We see a similar effect when particles are able to outpace light while traveling through water.

The OPERA experiment, in addition to a neighboring experiment, ICARUS, found several examples of neutrinos that managed to arrive at Gran Sasso with high levels of energy in tact, meaning that they had not lost electron-positron pairs as predicted during their journey. Scientists also did not detect stray electron-positron pairs coming from the traveling neutrinos. It seems the radiation Cohen and Glashow predicted did not occur.

Physicists on the MINOS collaboration plan to double-check the OPERA result. Image: Fermilab

If Cohen and Glashow are right, the neutrinos traveling from CERN to Gran Sasso did not beat the cosmic speed limit. However, their prediction has not been proven experimentally, and in science, experimental results trump theoretical predictions.

The scientific community’s best option seems to be waiting for a second opinion from the MINOS neutrino experiment at Fermilab. MINOS physicists will take a similar measurement next year after making an upgrade to their detector in December. They may be able to collect enough data before a long shutdown next summer. But if not, the scientists at OPERA and the rest of the world might need to wait more than a year for an answer.

For now, the mystery remains, and the hunt for answers continues.

Read update:
Faster-than-light neutrino measurement withstands new test

Kathryn Grim

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The Tevatron: a training ground beyond particle physics

October 25, 2011 | 8:41 am

Beyond smashing together billions of protons and antiprotons over the course of its 28 years of operations, Fermilab’s Tevatron also served as a launching pad for many careers, often in fields beyond particle physics.

Ron Moore now helps operate the 17 MeV cyclotron at Mass General Hospital. The accelerator produces radioisotopes used for medical diagnosis.

Take Ron Moore, the former head of Fermilab’s Tevatron Department, for example.

This month, Moore is starting a new endeavor as a medical physicist with a joint appointment at Harvard University and Massachusetts General Hospital in the Nuclear Medical & Molecular Imaging Division of the Department of Radiology. In his new role, he will help run a 17 million electronvolt (MeV) accelerator that makes radioisotopes used for medical diagnosis, such as PET scans, and conduct research about new imaging techniques.

Besides leaving the picturesque cornfields of Illinois for the collegiate charm of Boston, Moore realizes that he will have a few adjustments to make after working with the world’s largest proton-antiproton accelerator for the past 10 years.

“For starters, I can practically put my arms around the accelerator at Mass General,” Moore says with a grin.

Cutting your teeth on a machine like the Tevatron, however, prepares you for just about anything an accelerator might throw at you—no matter its shape, size or function.

“At Fermilab, you learn lots of accelerator skills because running a complex machine like the Tevatron is not trivial,” says Roger Dixon, head of Fermilab’s Accelerator Division. “Ron saw the technical problems, and he saw the solutions. That particular skill applies anywhere.”

The application
At 4 a.m. every morning, the accelerator at Mass General begins operating to produce Flourine-18, Carbon-11 and Nitrogen-13, the three main isotopes that the hospital uses. Once the accelerator makes the isotopes, they get transported through a pipeline in the hospital to the chemistry lab where chemists prepare them for the specified medical procedure. The isotope is then transported to imaging, where it will either get injected into the patient’s bloodstream or inhaled as part of a gas.

Mass General is currently one of 300 hospitals in the United States that has an in-house accelerator to produce medical isotopes for diagnostic procedures, including bone scans, gastrointestinal studies and cancer detection. Medical physicists like Moore keep the accelerators running on a daily basis in order to supply the hundreds of medical isotopes that are needed for patients every day.

“You’re running the accelerator every day for patients. Uptime is very important,” Moore says. “The focus is on running and not to set a record store, like it was at the Tevatron.”

When inside the human body, the isotope emits positrons—the opposite of electrons. When a positron hits an electron, it gives off energy and a detector tracks its movement and location to create an image that doctors use to diagnose disease and select effective treatments. Different isotopes have different purposes, and chemists can combine them with substances that aid in the diagnostic process.

When looking for a tumor, for example, chemists will combine Flourine-18 with a sugar to make the isotope go to areas of high metabolism in the patient. Because tumors have very high rates of metabolism, Flourine-18 laced with sugar will go right to that spot and illuminate it.

Prior to joining Mass General, Ron Moore was the head of the Tevatron Department at Fermilab.

The runner
Moore first became interested in medical physics when he needed to have a bone scan last December.

An avid runner, Moore started experiencing chronic pain in his shin. With the help of an isotope, a bone scan revealed the source of his pain—a small fracture in his tibia.

“I have always been interested in medical applications and how accelerators can be used for direct benefits for society,” Moore says.

A longtime member of the CDF experiment at Fermilab, Moore also brings decades of particle detector experience to Mass General and will work on medical imaging research.

For example, the medical physics community is actively working to develop real-time imaging using PET scans during proton cancer therapy treatments. Moore hopes to apply his background in high-energy physics detector development and electronics to the real-time imaging efforts.

And now that Moore’s tibia is all healed, when he isn’t running the accelerator, he’s hoping to find time to run along the banks of the Charles River, getting to know his new town.

Elizabeth Clements

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SLAC physicists using physics simulation tool to make cancer therapy safer

October 24, 2011 | 4:45 pm

This story first ran in SLAC Today on Oct. 20, 2011.

Joseph Perl described how he and his colleagues are turning the simulation toolkit Geant4 into a powerful application for medical physicists. Image by Helen Shen.

Tiny particles are making a big difference in the world of cancer therapy. And SLAC physicists—experts in particle transport—are using computer simulations to make those therapies safer.

At the Oct. 10 SLAC Colloquium, the lab’s own Joseph Perl described how he and his colleagues are turning the simulation toolkit Geant4 into a powerful application for medical physicists. Originally designed to track subatomic particles in high-energy physics experiments, Geant4 can also map proton paths through patients’ bodies during radiation treatment.

In radiation treatment, subatomic particles inflict DNA damage on dividing cells—both healthy and cancerous—causing them to commit suicide. The technique works because rapidly growing cancer cells are more likely to be dividing at any given time, and thus are more likely to be killed; but a smaller proportion of healthy cells are also susceptible to damage.

Minimizing collateral damage is a tough problem for medical physicists who design radiation treatments.

“To perfect this stuff, what we have to understand really is where are the particles going?” Perl said. “We have to understand particle transport when we’re designing the medical linacs,” the accelerators that deliver the particles to patients. “We have to understand particle transport when we’re talking about how the beams actually penetrate the body.”

Computer simulation tools such as EGS4, developed at SLAC in the 1970s, have helped medical physicists predict the behavior of X-rays and gamma rays. Now, Geant4 offers the ability to model proton beams, too.While Perl is SLAC’s only Geant4 team member working on medical physics applications, he works with four other partners on more general Geant4 capabilities. Together they constitute the second-largest team in the international Geant4 collaboration.

In contrast to the X-ray beams used in traditional therapies, which go all the way through the body, proton beams dump their energy at a specific depth. Medical physicists can target a tumor at one depth and avoid deeper and shallower tissues by tweaking the energy levels of one or more beams. Proton beam therapy may be particularly useful in children, for whom stray radiation can stunt growth and cause secondary cancers in adulthood.

Geant 4 relies on a technique called Monte-Carlo simulation, which models each proton moving through the body in a series of random steps. At each step, the program essentially casts a die to guess where the particle will move next. Over many steps, the program shows where protons are most likely to end up.

Unlike many other tools, Geant4 can also simulate the effect of tissues, such as the rib bones, that may move in and out of the proton beam as a patient breathes. Such obstructions can block some radiation from the intended target, while simultaneously allowing some tissue to soak up unnecessary radiation. Geant4 can potentially help medical physicists program beams to track a moving target and deliver a constant dosage to the tumor.

Geant4 is freely available to anyone who wants to use it, but in its current form may be challenging to some novices. “It’s a really fancy techno-Lego kit,” said Perl, but the box does not come with any ready-made toys.

To address this problem, SLAC’s Geant4 team has joined Massachusetts General Hospital and the University of California-San Francisco, in a four-year collaboration funded by the National Institutes of Health. The project, headed by Perl, will help medical physicists customize their simulations without disrupting the program’s innermost workings.

“If we can make it easier for people to use,” Perl said, “the more likely they are to use things right.”

- Helen Shen

Symmetry Intern

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Advancements in proton therapy cause for celebration

October 21, 2011 | 9:43 am

This article first appeared in Fermilab Today on Oct. 21, 2011.

A fully commissioned and operational gantry room. Image courtesy of ProCure Proton Therapy Centers

In 1946, founding Fermilab director Robert Wilson was one of the first to tout the benefits of proton therapy. The cancer treatment has since been lauded as a way to minimize damage to healthy tissue while focusing a finely calibrated beam directly on the tumor – an impossibility for radiation treatments based on X-rays or gamma rays. Yet protons were not used within a hospital facility until 1990 with Fermilab’s construction of a particle accelerator at Loma Linda University Medical Center. Since then, the industry has grown and the technology has evolved. Worldwide, 37 centers use proton therapy and more than 73,000 patients have been treated.

The ProCure facility in nearby Warrenville, Ill., one of only nine centers in the U.S., is completing its first year of proton therapy. The facility uses an accelerator called the Cyclotron to administer the proton therapy. One distinction that sets the Cyclotron apart from other accelerators is that the particles are sped up to just 230 MeV, an energy high enough to treat tumors as deep as 32 cm within a patient.

The proton therapy process begins with the transformation of hydrogen gas into plasma. The Cyclotron speeds up the particles and isolates the protons along a curve of magnets that lead to one of four rooms within the treatment center. With the aesthetics of a set piece from “2001: A Space Odyssey,” a large gantry device rotates the beam line on a track and the patient, lying on a platform, is precisely positioned by a large robotic arm similar to ones used in automotive manufacturing. Here the proton beam is slowed to an energy that will reach the tumor and be absorbed by the cancer cells but go no further, while a brass aperture on the nozzle narrows the beam into the shape of the tumor. For the beam to be a precise match to the tumor, the aperture is designed for each individual patient.

Mingcheng Gao worked with DZero as the detector went operational and is thrilled to use the skills he gained at Fermilab as a senior medical physicist at the ProCure facility.

“The technology is advancing quickly,” he said.

The price of building and running each proton therapy center has been the field’s greatest hindrance for decades. After 22 months of construction, the ProCure center ultimately cost $150 million to build. Yet with the increasing demand for proton therapy, Gao sees proton treatments playing a larger role in fighting cancer.

“The cost will definitely go down in the future,” he said.

Brad Hooker

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Accelerator soup: Scientists to mix elements in LHC to study recipe for heavy-ion collisions

October 20, 2011 | 9:29 am

CERN physicist Detlef Kuchler holds a purified sample of lead used to create heavy ions for the LHC. Photo by M. Brice / CERN

Superman may have superpowers, but Batman has the ingenuity to be just as heroic with the help of gadgets. Scientists at CERN are channeling the Dark Knight to try to make their biggest gadget, the Large Hadron Collider, perform a feat that counters its very design principles but may give them a better understanding of the early universe. They’ll have about 40 hours total to make it work.

Instead of colliding two beams of protons or two beams of much heavier lead ions, as the LHC usually does, operators will try to collide one of each in the coming weeks. On October 31, they will test the process for 16 hours, and two weeks later they’ll get another 24. That’s all the time they decided they could take from the precious month of data-collecting they will give the experiments during the upcoming lead-lead run. If it works, a proton-lead ion research program could be in place for November 2012.

The scientists undertaking the task of colliding protons and lead want to collect benchmark information about single beams of lead ions to get a better picture of what’s going on in lead-lead collisions. For that, the tiny proton acts as a probe of the more massive lead ion.

Theorist Urs Wiedemann explained that it’s a bit like making soup. A meticulous chef wants to know exactly what happens at each step of a recipe. This includes both the initial state of the individual ingredients – onions sautéed or raw? – as well as the final outcome inside the pot. Otherwise the chef can’t make informed changes. Similarly a physicist needs to know the individual properties of both of the elements he or she wants to collide, as well as what their smashing produces, in order to get the full picture for analysis.

After years of experiments, the quarks and gluons in the proton are well characterized; those in the lead ion are not. So, in a proton-lead ion collision, all unexpected effects can be attributed to the lead ion. With this knowledge, scientists will be able to make predictions about lead-lead collisions. “I can only test my theory of ion collisions if I know what is collided,” Wiedemann said. Colliding a proton with a heavy ion serves to “switch off the confounding factors,” he said.

Snapshot of two lead nuclei just after impact. Image by Henning Weber / CERN

Colliding protons and lead ions also gives scientists the potential to discover new physics phenomena, Wiedemann said. For this reason, all the experiments around the ring are interested in taking data during the collisions.

Scientists still need to test whether the technique will work in the LHC, said accelerator physicist John Jowett. The machine was built with a 2-in-1 magnet design: Both beams are controlled with the same magnetic field. This helps keep everything inside the ring symmetric when the beams inside match. Collisions and kicks, when one beam’s electromagnetic field pushes the other beam slightly off course, happen in the same place on each turn, a fundamental principle of stability for circular accelerators.

Protons and lead ions have different masses and charges, so they are not equally affected by the same magnetic field. The biggest challenges in this type of run are to inject and then control the beams as they ramp up from low to high energy. At lower energies, a beam of protons makes one extra lap around the LHC every 15 seconds. Since a proton beam makes about 11,000 laps per second, this discrepancy is small. But it is still enough to shift where the proton and lead-ion beams kick each other with every turn. As energy in the accelerator increases to its peak of 3.5 TeV and the beams get closer to light speed, however, relativity makes the 15 seconds stretch out little by little. At some point the difference between the beams becomes small enough that it can be overcome with a minor adjustment in their orbits – essentially the proton ends up going just a bit farther than the lead does, so they both take the same time to make one revolution.

The CERN accelerator complex. Image: CERN

To further complicate things, the more intense the beams get, the worse the effects each beam has on the other. The need to reach a certain level of intensity, roughly a measure of the amount of particles in a beam, puts a limit on how much data the experiments can extract. So, even if researchers can manage to inject two different beams in the accelerator, they will also need to make them with enough intensity for the method to be considered feasible.

The accelerator does have built-in flexibility despite having only one magnetic field: It has independent RF systems for each beam. These adjust electromagnetic frequencies inside a special cavity at one point around the ring, which controls each beams’ speed and orbit length. The LHC also has a powerful automatic feedback system that reacts to effects in the pipe by serving counter-kicks. This helps to keep the beams stable.

The LHC physicists plan to take baby steps – but fast ones, given the strict time constraints. First, they will simply try and inject two different elements into the LHC. If that works, they’ll try accelerating the beams. Only after that would they consider attempting actual proton-lead ion collisions.

“I hope it all works and we’re not prevented by mundane effects” such as a power outage, Jowett said. “In a month from now we should know the answer.”

Amy Dusto

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October 2011 issue of symmetry available

October 19, 2011 | 9:38 am

This month marks the 50^th issue of symmetry magazine, which published its first issue in Oct/Nov 2004. It quickly established its own quirky style with a cover of a little girl in jammies dragging an Einstein bear. 

This time around our cover shows Fermilab’s iconic Wilson Hall and an equally iconic wedge of flying geese – make that two wedges, arranged with help from Photoshop – forming an X against the sky.  That’s X as in Project X, a proposed $1.8 billion accelerator complex that would put Fermilab at the forefront of the Intensity Frontier—a realm in which scientists bring incredible numbers of particles into collision to search for extremely rare processes with a big physics impact.  Our lead feature, “Solving for X,” explains this project and its potentially far-reaching impacts.

Also in this issue:

–  A SLAC particle physics grad student changes course and puts her skills to work in developing cancer treatments.

–  Do we live in a hologram?  An experiment at Fermilab aims to find out.

– Scientists build an experiment called NOvA in the Minnesota wilderness to study neutrinos.

–  What about those neutrinos, anyhow? A deconstruction of neutrino science distills what scientists know, what they hope to learn and how that knowledge could change our view of the universe.

– Yet another use for particle accelerators: printing cereal boxes.

–  Particle physics pioneer E.O. Lawrence patents the cyclotron.

–  A 60-second explanation of symmetry–the concept, not the magazine.

Plus, as usual, an assortment of colorful briefs–Atom Smasher beer, anyone?–and highlights from our blog.

Glennda Chui

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LAGUNA large neutrino observatory design moves forward

October 18, 2011 | 2:00 pm

Editor’s note: ASPERA, the AStroParticle European Research Area, issued the following press release today, Oct. 18, about the LAGUNA large neutrino observatory. 

The kick-off meeting for the second phase of the LAGUNA’s design study starts today at CERN. The principal goal of LAGUNA (Large Apparatus for Grand Unification and Neutrino Astrophysics) is to assess the feasibility of a new pan-European research infrastructure able to host the next generation, very large volume, deep underground neutrino observatory. The scientific goals of such an observatory combine exciting neutrino astrophysics with research addressing several fundamental questions such as proton decay and the existence of a new source of matter-antimatter asymmetry in Nature, in order to explain why our Universe contains only matter and not equal amounts of matter and antimatter.

Underground neutrino detectors based on large, surface-instrumented, liquid volumes have achieved fundamental results in particle and astroparticle physics, and were able to simultaneously collect events from several different cosmic sources. Neutrinos interact only very weakly with matter so they can travel very large distances in space and traverse dense zones of the Universe, thus providing unique information on their sources and an extremely rich physics programme.

In order to move forward, a next-generation very large multipurpose underground neutrino observatory of a total mass of around 100 000 to 500 000 tons is needed. This new facility will provide new and unique scientific opportunities, very likely leading to fundamental discoveries and attracting interest from scientists worldwide.

This further step newly includes the study of long baseline neutrino beams from CERN accelerators. When coupled to such a neutrino beam, the neutrino observatory will measure with unprecedented sensitivity neutrino flavor oscillation phenomena and possibly unveil the existence of CP violation in the leptonic sector.

In addition, the observatory will detect neutrinos as messengers from further distant astrophysical objects as well as from the early universe. In particular, it will sense a large number of neutrinos emitted by exploding galactic and extragalactic type-II supernovae. The neutrino observatory will also allow precision studies of other astrophysical or terrestrial sources of neutrinos, such as solar and atmospheric ones, and will search for new sources of astrophysical neutrinos like, for example, the diffuse neutrino background from relic supernovae, or those produced in hypothetic dark matter particle annihilation in the centre of the Sun or the Earth. Furthermore, it will allow unprecedented search for the proton lifetime with sensitivities up to 10³⁵ years, pursuing the only possible path to directly test physics at the grand unified theory scale.

Called LAGUNA-LBNO, this design study is funded by the European Commission under the Seventh Framework Programme and will last three years. LAGUNA is one of the Magnificent Seven, the large infrastructures included in the European Roadmap for astroparticle physics developed by the ASPERA* European network of funding agencies. There is currently an intense competition worldwide to host the next generation large neutrino observatory. Europe is currently leading deep underground science with a strong expertise in this area, thanks its four long running deep underground laboratories. LAGUNA will provide an important asset for Europeans to keep this leadership in deep underground physics.

LAGUNA-LBNO brings together 300 scientists, CERN and 38 other institutions from Finland, France, Germany, Greece, Japan, Italy, Poland, Romania, Russia, Spain, United-Kingdom and Switzerland. It is coordinated by André Rubbia from ETH Zurich.

Read the full press release

Press Release

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Mirrors harness X-rays for science

October 17, 2011 | 9:09 am

SLAC first published this article on Oct. 11, 2011.

Up close, they look simple as can be: a pair of metal bars, each with one side polished to a brilliant shine. One bar faces up, the other to one side.

A K-B mirror system consists of two curved mirrors placed at right angles to each other. A parabolic mirror shape will focus a collimated beam to a point, while an elliptical mirror shape will focus a point to another point.

They’re known as K-B mirrors, sophisticated X-ray focusing tools that have a pedigree going back to the very birth of X-ray microscopy. The shiny sides can be within a nanometer of being perfectly smooth, are exquisitely shaped into a barely perceptible curve of an ellipse, and may have one or more atomically precise coatings of exotic elements like platinum or rhodium.

The “B” in K-B mirrors stands for Albert Baez, father of folk singer Joan Baez, who helped invent this ingenious focusing system in the late 1940s while a graduate student at Stanford University. The “K” is for his Ph. D. advisor and co-inventor Paul Kirkpatrick, then head of the physics department.

Their invention signaled the beginning of X-ray optics – the ability to manipulate X-rays, an energetic, penetrating form of light. Today, thousands of scientists worldwide use X-ray beams to examine the material world in atom-by-atom detail, fueling advances in energy production, electronics, environmental cleanup, new materials, nanotechnology, medicine and many other fields.

“All these years later, K-B mirrors have become an essential tool for focusing X-rays to the tiny spots that scientists need for their experiments,” said Piero Pianetta, Stanford Synchrotron Radiation Lightsource deputy director. “Between SSRL and the Linac Coherent Light Source, we have about a dozen of these mirror systems here at SLAC.”  The world’s most accurate K-B mirror system currently in use, which was recently installed at LCLS, cost $1.2 million, when all of its alignment and stability aids are figured in.

For more than 50 years after Wilhelm Röntgen discovered X-rays in 1895, no one had figured out a way to focus this mysterious, penetrating form of light. Röntgen himself had proclaimed that it would be impossible to focus X-rays with lenses. In 1922, Arthur Compton reflected X-rays from polished surfaces at “grazing” or “glancing” angles of one degree or less. There matters sat for more than two decades, when Kirkpatrick began to explore the possibility of using Compton’s technique to focus X-rays.

Reflecting light with a single curved mirror produces a severe astigmatism, focusing rays from a point source to a line. “It was Kirkpatrick’s idea that a second curved mirror placed at a right angle to the first would ‘squeeze’ that line down to a point,” Baez said later in several retrospective articles and talks. He had been teaching calculus at Stanford and also working as a lab assistant in the Physics Department when Kirkpatrick asked if he’d like to work under him as a graduate student to develop this idea.

“I jumped at the chance,” Baez recalled.

In a historic 1948 paper, Kirkpatrick and Baez introduced their mirror pair as part of the world’s first X-ray microscope. But it would be another quarter century before three other developments enabled scientists to use the mirrors productively: In the mid-1970s, machining, polishing and metal-coating techniques improved enough to make ultra-smooth surfaces that could reflect X-rays without significant scattering. Second, James Underwood, an X-ray optics pioneer who later worked at Stanford, showed how to flex the mirrors precisely into the elliptical shapes that eliminated unwanted optical aberrations. Thirdly, new X-ray sources called synchrotrons produced intense beams of X-rays for probing and unlocking the secrets of molecules and materials.

With more than 70 synchrotron light sources now operating or under construction around the world, K-B mirrors are made by six manufacturers: two in France and one each in Germany, Japan, the United Kingdom and United States. There are several other ways to focus X-rays, but these mirrors are popular because unlike technologies based on diffraction or refraction, they reflect most  X-ray energies approximately uniformly.

LCLS mechanical engineer Jean-Charles Castagna (foreground, right) and Dan Harrington, SSRL engineering physicist, stand by the K-B mirror system at the Stanford Synchrotron Radiation Lightsource. Their hands are resting on the chambers that hold the actual mirrors. Photo by Mike Ross.

Despite their simple design, crafting K-B mirrors has become much more complicated over the years. The first K-B mirrors were made of glass or quartz coated with a reflective metal film. Today’s mirrors are typically made from silicon crystals polished to near-atomic smoothness and then coated with ultra-thin layers of hard silicon carbide or dense metals. The shorter the X-ray wavelength being focused, the more precise the mirror surface must be.

“The mantra for X-ray mirror designers is ‘figure and finish,’” said Underwood. “Figure is the shape of the mirror and finish is its surface roughness. Many innovations over the years have improved our ability to make more accurate focusing figures and smoother mirror finishes.”

The mirror surface must be formed – or flexed – into the correct curved shape to focus the beam. This can be done in several ways. Most often, the mirror surface is polished while flat and then positioned in the beamline, supported on both ends. Then, an actuator motor applies a bending force near each end of the mirror, flexing the mirror into an ever-so-slight concave shape. Controlling the placement and amount of the force, as well as the mirror block’s shape and its supports, determines the resulting curve.

“For point-to-point focus you need an elliptical mirror shape,” said SSRL engineering physicist Tom Rabedeau. “Focusing a collimated beam to a point or vice versa requires a parabolic mirror shape.”

The mirror has to keep that shape despite being pummeled with intense high-energy X-rays. Although the X-rays are supposed to reflect off the mirror at a glancing angle, some of their energy is inevitably absorbed by the mirror, and the resulting heat buildup can warp or otherwise distort it.

The high energies of the X-ray laser pulses at the LCLS can also cause ablation, ejecting atoms from the mirror surface and reducing focus quality. Coatings can help minimize such damage. And while the mirrors are usually held in a vacuum, stray molecules owing to imperfect vacuum may stick to the mirror surface,  degrading its focus.

Temperature fluctuations can deflect the mirrors’ focal point. And when using long mirrors, designers even have to account for sagging between the mirror’s end supports due to gravity, said Nicholas Kelez, LCLS mechanical engineer. Jitter in the actual location of the X-ray beam also affects its ultimate focus.

“K-B optics are nice, since you can adjust one axis at a time,” Rabedeau said. But even a tiny error in the adjustment can throw the beam’s focus way off. For a one-meter-long mirror, “a one-micron mirror deflection means a huge 60-micron move in the focus spot 30 meters distant,” he added. Increasingly, researchers are using automatic sensor-feedback “servo” controls to fine-tune the positions of the mirrors to keep the X-rays focused accurately onto their target.

“All in all, K-B mirrors give you much better control of the focused spot shape than other X-ray focusing methods,” said Dan Harrington, SSRL engineering physicist.

The world’s best K-B mirror system currently in use is in LCLS’ Coherent X-ray Imaging (CXI). Its $300,000 mirrors were made in Japan using a precision liquid-jet method to shape the desired elliptical figure directly into the silicon, avoiding the need for mirror-bending apparatus. Each of the 350 mm-long reflecting surfaces are smooth to better than 1 nanometer surface roughness over their entire length.

A German company then built the mirrors’ enclosure, alignment system and 6-ton granite base, bringing the total price tag of $1.2 million. It can focus to a one-micron spot, and its focal plane can be moved by about half a meter to accommodate the needs of various experiments, said Sebastien Boutet, CXI instrument scientist.

CXI’s current K-B system won’t be the star of the show very much longer, however. A near-twin of that system, designed to focus the LCLS pulses down to much smaller 0.1-micron-diameter spots, has been built in Japan and is being commissioned now in Germany. Installation should begin at CXI next month.

- Mike Ross

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