Recently, a research team from the Shanghai Institute of Optics and Fine Mechanics (SIOM) of the Chinese Academy of Sciences (CAS) generated few-permille level near-GeV electron beams with laser wakefield accelerator (LWFA) via density-tailored plasma. Such high-quality electron beams will boost the development of compact intense coherent radiation sources. This work was published in Physical Review Letters on May 25.
The researchers manipulated the self-focusing of the laser pulse by tailoring the plasma density. Thus, the degree of the nonlinearity of the wakefield can be controlled which enables a transformation from a highly nonlinear one with a step structure to a less nonlinear one with a sawtooth-like structure. Such a sawtooth-like structure can be used to remove the positive energy chirp of the electron beam.
In the experiments, they found that the evolution of the laser pulse and the injection phase of the electron beam can be optimized by adjusting the focal position and the plasma density. This optimization ensures that the electron beam is injected at the end of the density down ramp. Therefore, the electron beam slips back to the rear of the bubble during the defocusing of the laser and gets dechirped.
Finally, electron beams with a peak energy of near GeV and minimal energy spread of 2.4‰ were obtained with a single-stage gas jet, which is the smallest obtained from LWFA.
Aiming at the development of LWFA, the researchers developed the 200-TW ultra-intense and ultra-short laser facility with high focused beam quality and stability. This facility provides a high-quality driving light source for related physical research.
This work was supported by the National Natural Science Foundation of China, the Strategic Priority Research Program (B), the Youth Innovation Promotion Association of CAS, and the Natural Science Foundation of Shanghai.
Featured image: Measured e-beams energy spectra. (a) The raw energy spectra of 15 shots with energy spreads ranging from 2.4‰–4.1‰; (b) The spatially integrated energy spectrum of the 13th shot in (a). (Image by SIOM)
Reference: L. T. Ke, K. Feng, W. T. Wang, Z. Y. Qin, C. H. Yu, Y. Wu, Y. Chen, R. Qi, Z. J. Zhang, Y. Xu, X. J. Yang, Y. X. Leng, J. S. Liu, R. X. Li, and Z. Z. Xu, “Near-GeV Electron Beams at a Few Per-Mille Level from a Laser Wakefield Accelerator via Density-Tailored Plasma”, Phys. Rev. Lett. 126, 214801 – Published 25 May 2021. DOI: https://doi.org/10.1103/PhysRevLett.126.214801
Research used a novel technique originally developed at the University of Warwick
A team of physicists, including the University of Warwick, have proved that a subatomic particle can switch into its antiparticle alter-ego and back again, in a new discovery revealed today.
An extraordinarily precise measurement made by UK researchers using the LHCb experiment at CERN has provided the first evidence that charm mesons can change into their antiparticle and back again.
For more than 10 years, scientists have known that charm mesons, subatomic particles that contain a quark and an antiquark, can travel as a mixture of their particle and antiparticle states, a phenomenon called mixing. However, this new result shows for the first time that they can oscillate between the two states.
Armed with this new evidence, scientists can try to tackle some of the biggest questions in physics around how particles behave outside of the Standard Model. One being, whether these transitions are caused by unknown particles not predicted by the guiding theory.
The research, submitted today to Physical Review Letters and available on arXiv, received funding from the Science and Technology Facilities Council (STFC).
Being one and the other
In the strange world of quantum physics, the charm meson can be itself and its antiparticle at once. This state, known as quantum superposition, results in two particles each with their own mass – a heavier and lighter version of the particle. This superposition allows the charm meson to oscillate into its antiparticle and back again.
Using data collected during the second run of the Large Hadron Collider, researchers from the University of Oxford measured a difference in mass between the two particles of 0.00000000000000000000000000000000000001 grams – or in scientific notation 1×10-38g. A measurement of this precision and certainty is only possible when the phenomenon is observed many times, and this is only possible due so many charm mesons being produced in LHC collisions.
As the measurement is extremely precise, the research team ensured the analysis method was even more so. To do this, the team used a novel technique originally developed by colleagues at the University of Warwick.
There are only four types of particle in the Standard Model, the theory that explains particle physics, that can turn into their antiparticle. The mixing phenomenon was first observed in Strange mesons in the 1960s and in beauty mesons in the 1980s. Until now, the only other one of the four particles that has been seen to oscillate this way is the strange-beauty meson, a measurement made in 2006.
A rare phenomenon
Professor Guy Wilkinson at University of Oxford, whose group contributed to the analysis, said:
“What makes this discovery of oscillation in the charm meson particle so impressive is that, unlike the beauty mesons, the oscillation is very slow and therefore extremely difficult to measure within the time that it takes the meson to decay. This result shows the oscillations are so slow that the vast majority of particles will decay before they have a chance to oscillate. However, we are able to confirm this as a discovery because LHCb has collected so much data.”
Professor Tim Gershon at University of Warwick, developer of the analytical technique used to make the measurement, said:
“Charm meson particles are produced in proton–proton collisions and they travel on average only a few millimetres before transforming, or decaying, into other particles. By comparing the charm meson particles that decay after travelling a short distance with those that travel a little further, we have been able to measure the key quantity that controls the speed of the charm meson oscillation into anti-charm meson – the difference in mass between the heavier and lighter versions of charm meson.”
A new door opens for physics exploration
This discovery of charm meson oscillation opens up a new and exciting phase of physics exploration; researchers now want to understand the oscillation process itself, potentially a major step forward in solving the mystery of matter-antimatter asymmetry. A key area to explore is whether the rate of particle-antiparticle transitions is the same as that of antiparticle-particle transitions, and specifically whether the transitions are influenced/caused by unknown particles not predicted by the Standard Model.
Dr Mark Williams at University of Edinburgh, who convened the LHCb Charm Physics Group within which the research was performed, said:
“Tiny measurements like this can tell you big things about the Universe that you didn’t expect.”
The result, 1×10-38g, crosses the ‘five sigma’ level of statistical significance that is required to claim a discovery in particle physics.
Ground-breaking image reconstruction and analysis algorithms developed for surface-based MicroBooNE detector filter out cosmic ray tracks to pinpoint elusive neutrino interactions with unprecedented clarity
How do you spot a subatomic neutrino in a “haystack” of particles streaming from space? That’s the daunting prospect facing physicists studying neutrinos with detectors near Earth’s surface. With little to no shielding in such non-subterranean locations, surface-based neutrino detectors, usually searching for neutrinos produced by particle accelerators, are bombarded by cosmic rays—relentless showers of subatomic and nuclear particles produced in Earth’s atmosphere by interactions with particles streaming from more-distant cosmic locations. These abundant travelers, mostly muons, create a web of crisscrossing particle tracks that can easily obscure a rare neutrino event.
Fortunately, physicists have developed tools to tone down the cosmic “noise.”
A team including physicists from the U.S. Department of Energy’s Brookhaven National Laboratory describes the approach in two papers recently accepted to be published in Physical Review Applied and the Journal of Instrumentation (JINST). These papers demonstrate the scientists’ ability to extract clear neutrino signals from the MicroBooNE detector at DOE’s Fermi National Accelerator Laboratory (Fermilab). The method combines CT-scanner-like image reconstruction with data-sifting techniques that make accelerator-produced neutrino signals stand out 5 to 1 against the cosmic ray background.
“We developed a set of algorithms that reduce the cosmic ray background by a factor of 100,000,” said Chao Zhang, one of the Brookhaven Lab physicists who helped to develop the data-filtering techniques. Without the filtering, MicroBooNE would see 20,000 cosmic rays for every neutrino interaction, he said. “This paper demonstrates the crucial ability to eliminate the cosmic ray backgrounds.”
Bonnie Fleming, a professor at Yale University who is a co-spokesperson for MicroBooNE, said, “This work is critical both for MicroBooNE and for the future U.S. neutrino research program. Its impact will extend notably beyond the use of this ‘Wire-Cell’ analysis technique, even on MicroBooNE, where other reconstruction paradigms have adopted these data-sorting methods to dramatically reduce cosmic ray backgrounds.”
MicroBooNE is one of three detectors that form the international Short-Baseline Neutrino program at Fermilab, each located a different distance from a particle accelerator that generates a carefully controlled neutrino beam. The three detectors are designed to count up different types of neutrinos at increasing distances to look for discrepancies from what’s expected based on the mix of neutrinos in the beam and what’s known about neutrino “oscillation.” Oscillation is a process by which neutrinos swap identities among three known types, or “flavors.” Spotting discrepancies in neutrino counts could point to a new unknown oscillation mechanism—and possibly a fourth neutrino variety.
Brookhaven Lab scientists played a major role in designing the MicroBooNE detector, particularly the sensitive electronics that operate within the detector’s super-cold liquid-argon-filled time projection chamber. As neutrinos from Fermilab’s accelerator enter the chamber, every so often a neutrino will interact with an argon atom, kicking some particles out of its nucleus—a proton or a neutron—and generating other particles (muons, pions) and a flash of light. The charged particles that get kicked out ionize argon atoms in the detector, knocking some of their electrons out of orbit. The electrons that form along these ionization tracks get picked up by the detector’s sensitive electronics.
“The whole trail of electrons drifts along an electric field and passes through three consecutive planes of wires with different orientations at one end of the detector,” Zhang said. “As the electrons approach the wires, they induce a signal, so that each set of wires creates a 2D image of the track from a different angle.”
Meanwhile, the flashes of light created at the time of the neutrino interaction get picked up by photomultiplier tubes that lie beyond the wire arrays. Those light signals tell scientists when the neutrino interaction took place, and how long it took the tracks to arrive at the wire planes.
Computers translate that timing into distance and piece together the 2D track images to reconstruct a 3D image of the neutrino interaction in the detector. The shape of the track tells scientists which flavor of neutrino triggered the interaction.
“This 3D ‘Wire-Cell’ image reconstruction is similar to medical imaging with a computed tomography (CT) scanner,” Zhang explained. In a CT scanner, sensors capture snapshots of the body’s internal structures from different angles and computers piece the images together. “Imagine the particle tracks going through the three wire planes as a person going into the scanner,” he said.
Untangling the cosmic web
It sounds almost simple—if you forget about the thousands of cosmic rays that stream through the detector at the same time. Their ionization trails also drift through the scanning wires, creating images that look like a tangled web. That’s why MicroBooNE scientists have been working on sophisticated “triggers” and algorithms to sift through the data so they can extract the neutrino signals.
By 2017, they had made substantial progress reducing the cosmic ray noise. But even then, cosmic rays outnumbered neutrino tracks by about 200 to 1. The new papers describe further techniques to reduce this ratio, and flip it to the point where neutrino signals in MicroBooNE now stand out 5 to 1 against the cosmic ray background.
The first step involves matching the signals revealed by particles generated in neutrino interactions with the exact flashes of light picked up by the photomultiplier tubes from that interaction.
“This is not easy!” said Brookhaven Lab physicist Xin Qian. “Because the time projection chamber and the photomultiplier tubes are two different systems, we don’t know which flash corresponds to which event in the detector. We have to compare the light patterns for each photomultiplier tube with all the locations of these particles. If you’ve done all the matching correctly, you will find a single 3D object that corresponds to a single flash of light measured by the photomultiplier tubes.”
Brooke Russell, who worked on the analysis as a Yale graduate student and is now a postdoctoral fellow at DOE’s Lawrence Berkeley National Laboratory, echoed these comments on the challenge of light-matching. “Given that the charge information is in some cases not fully complementary to the light information, there can be ambiguities in charge-light pairings on a single-readout basis. The algorithms developed by the team help to account for these nuances,” she said.
Still, the scientists must then compare the timing of each track with the time accelerator neutrinos were emitted (a factor they know because they control the accelerator beam). “If the timing is consistent, then it is a possible neutrino interaction,” Qian said.
The algorithm developed by the Brookhaven team brings the ratio down to one neutrino for every six cosmic ray events.
Rejecting additional cosmic rays gets a bit easier with an algorithm that eliminates tracks that completely traverse the detector.
“Most cosmic rays go through the detector from top to bottom or from one side to the other,” said Xiangpan Ji, a Brookhaven Lab postdoc working on this algorithm. “If you can identify the point of entry and exit of the track, you know it’s a cosmic ray. Particles formed by neutrino interactions have to start in the middle of the detector where that interaction takes place.”
That brings the ratio of neutrino interactions to cosmic rays to 1:1.
An additional algorithm screens out events that start outside the detector and get stopped somewhere in the middle—which look similar to neutrino events but move in the opposite direction. And one final fine-tuning step rules out events where the light flashes don’t match well with events, to bring the detection of neutrino events to the remarkable level of 5 to 1 compared with cosmic rays.
“This is one of the most challenging analyses I have worked on,” said Hanyu Wei, the Brookhaven Lab postdoctoral fellow leading the analysis effort. “The liquid-argon time projection chamber is a new detector technology with lots of surprising features. We had to invent many original methods. It was truly a team effort.”
Zhang echoed that sentiment and said, “We expect this work to significantly boost the potential for the MicroBooNE experiment to explore the intriguing physics at short baselines. Indeed, we’re looking forward to implementing these techniques in experiments at all three short-baseline neutrino detectors to see what we learn about neutrino oscillations and the possible existence of a fourth neutrino type.”
This work was funded by the DOE Office of Science. The Fermilab Accelerator Complex that creates the neutrinos for MicroBooNE and the other short-baseline neutrino experiments is a DOE Office of Science user facility.
Brookhaven National Laboratory is supported by the U.S. Department of Energy’s Office of Science. 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, visit https://www.energy.gov/science/.
Physicists discuss the possibility of using particle accelerators to detect or even generate gravitational waves
In particle accelerators like the Large Hadron Collider (LHC), charged particles bob and weave in magnetic and electric fields, following tightly corralled trajectories. Their paths are computed assuming a flat Euclidean space-time, but gravitational waves – first observed by the LIGO and Virgo detectors in 2015 – crease and stretch this underlying geometry as they ripple out across the universe. For the past 50 years, there has been intermittent interest in the possibility of detecting observable resonant effects as a result of this extra curvature of the fabric of space-time, as the particles whizz around the accelerators repeatedly at close to the speed of light.
Advances in accelerator technology could now usher in an era of gravitational-wave astronomy in which particle accelerators play a major role. To explore this tantalising possibility, over 100 accelerator experts, particle physicists and members of the gravitational physics community participated in a virtual workshop entitled “Storage Rings and Gravitational Waves” (SRGW2021), organised as part of the European Union’s Horizon 2020 ARIES project. During this meeting, they explored the role that particle accelerators could play in the detection of cosmological backgrounds of gravitational waves. This would provide us with a picture of the early universe and give us hints about high-energy phenomena, such as high-temperature phase transitions, the nature of inflation and new heavy particles that cannot be directly produced in the laboratory.
Lively discussions at the SRGW2021 workshop – the first, apart from an informal discussion at CERN in the 1990s, to link accelerators and gravitational waves and bring together the scientific communities involved – attest to the prospective role that accelerators could play in detecting or even generating gravitational waves. The great excitement and interest prompted by this meeting, and the exciting preliminary findings from this workshop, call for further, more thorough investigations into harnessing future storage rings and accelerator technologies for gravitational-wave physics.
This text was extracted from the full meeting report in CERN Courier, where you can learn more about gravitational-wave research using particle accelerators.
The Dark Matter Particle Explorer (DAMPE) collaboration reported the precise measurement of the energy spectrum of cosmic ray helium nuclei from 70 GeV to 80 TeV energies on May 18, 2021.
For the first time, DAMPE reveals a softening structure at about 34 TeV energies in the helium spectrum with a high significance (~4.3σ). Together with the softening energy of the DAMPE proton spectrum, the results are consistent with a charge-dependent softening energy of protons and helium nuclei.
The common softening is likely an imprint of a nearby cosmic ray source, e.g., a supernova remnant. The softening energy, which is likely Z-dependent for protons and helium nuclei, corresponds to the acceleration upper-limit of such a nearby source.
DAMPE, also known as “Wukong”, is a space satellite dedicated to high-energy cosmic ray and gamma-ray observations. Besides probing the nature of dark matter particles, one of the main scientific goals of DAMPE is to precisely measure the energy spectra of cosmic ray particles.
DAMPE has an excellent energy resolution (for electrons and gamma-rays), a very good particle identification capability, and a reasonably large acceptance, making it well suitable for the studies of precise spectral structures of cosmic rays. Cosmic rays (CRs) are energetic particles coming from outer space. They are mostly made up of nuclei of various elements, together with small amounts of electrons/positions, gamma-ray photons, and neutrinos.
Cosmic rays are generally believed to originate from extreme astrophysical objects, e.g. supernova remnant (SNR), accretion by black hole, etc. Therefore, CRs are a unique probe to explore the astrophysical laws under extreme environments. The origin, acceleration, and propagation of CRs are very interesting and fundamental questions in modern physics and astrophysics, which remain unanswered after a century-long observation and research.
The energy spectrum of CRs, which represents the relation of particle flux to energy, is expected to be a power-law form according to the canonical shock acceleration of particles. Precise measurement of the energy spectrum of CRs is the key to understanding those fundamental questions of cosmic ray physics.
Protons and helium nuclei, are the most two abundant components of cosmic rays, which account for more than 99% in total cosmic rays. The excellent charge resolution enables DAMPE to have a powerful capability to identify proton and helium, and precisely measure their spectra respectively. Fig. 1 shows the excellent charge measurement of DAMPE at two typical energies.
Since the launch at the end of 2015, the DAMPE detector has been working very stably in-orbit for four years. Significant progresses in the observations of cosmic ray electrons/positions, protons, and helium nuclei have been achieved. With the continuous operation and data collection of DAMPE, it is expected that more and more high-quality data will shed new light on the fundamental questions about cosmic ray physics.
With the first 30 months on-orbit data, the DAMPE collaboration obtained the precise measurement of the energy spectrum of cosmic ray protons from 40 GeV to 100 TeV energies. The DAMPE result shows that the proton spectrum is not compatible with the paradigm of a unique power-law in a wide energy range.
Especially, DAMPE newly discovered a spectral “softening” (drop behavior) at about 14 TeV energies. The break energy is expected to be the acceleration limit of a possible nearby cosmic ray source.
The DAMPE result has significantly improved the measurement accuracy of helium spectrum in the energy range above TeV. The spectrum of CR helium shows a very similar TeV structure with the one of CR proton, which suggests a common origin of them.
Reference: F. Alemanno et al. (DAMPE Collaboration), “Measurement of the Cosmic Ray Helium Energy Spectrum from 70 GeV to 80 TeV with the DAMPE Space Mission”, Phys. Rev. Lett. 126, 201102 – Published 18 May 2021. Link to paper
Research team presents a new type of particle accelerator
Since they are far more compact than today’s accelerators, which can be kilometers long, plasma accelerators are considered as a promising technology for the future. An international research group has now made significant progress in the further development of this approach: With two complementary experiments at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and at the Ludwig-Maximilians-Universität Munich (LMU), the team was able to combine two different plasma technologies for the first time and build a novel hybrid accelerator. The concept could advance accelerator development and, in the long term, become the basis of highly brilliant X-ray sources for research and medicine, as the experts describe in the journal Nature Communications (DOI: 10.1038/s41467-021-23000-7).
In conventional particle accelerators, strong radio waves are guided into specially shaped metal tubes called resonators. The particles to be accelerated – which are often electrons – can ride these radio waves like surfers ride an ocean wave. But the potential of the technology is limited: Feeding too much radio wave power into the resonators creates a risk of electrical charges that can damage the component. This means that in order to bring particles to high energy levels, many resonators have to be connected in series, which makes today’s accelerators in many cases kilometers long.
That is why experts are eagerly working on an alternative: plasma acceleration. In principle, short and extremely powerful laser flashes fire into a plasma – an ionized state of matter consisting of negatively charged electrons and positively charged atomic cores. In this plasma, the laser pulse generates a strong alternating electric field, similar to the wake of a ship, which can accelerate electrons enormously over a very short distance. In theory, this means facilities can be built far more compact, shrinking an accelerator that is a hundred meters long today down to just a few meters. “This miniaturization is what makes the concept so attractive,” explains Arie Irman, a researcher at the HZDR Institute of Radiation Physics. “And we hope it will allow even small university laboratories to afford a powerful accelerator in the future.”
But there is yet another variant of plasma acceleration where the plasma is driven by near-light-speed electron bunches instead of powerful laser flashes. This method offers two advantages over laser-driven plasma acceleration: “In principle, it should be possible to achieve higher particle energies, and the accelerated electron beams should be easier to control,” explains HZDR physicist and primary author Thomas Kurz. “The drawback is that at the moment, we rely on large conventional accelerators to produce the electron bunches that are needed to drive the plasma.” FLASH at DESY in Hamburg, for instance, where such experiments take place, measures a good one hundred meters.
This is precisely where the new project comes in. “We asked ourselves whether we could build a far more compact accelerator to drive the plasma wave,” says Thomas Heinemann of the University of Strathclyde in Scotland, who is also a primary author of the study. “Our idea was to replace this conventional facility with a laser-driven plasma accelerator.” To test the concept, the team designed a sophisticated experimental setup in which strong light flashes from HZDR’s laser facility DRACO hit a gas jet of helium and nitrogen, generating a bundled, fast electron beam via a plasma wave. This electron beam passes through a metal foil into the next segment, with the foil reflecting back the laser flashes.
In this next segment, the incoming electron beam encounters another gas, this time a mixture of hydrogen and helium, in which it can generate a new, second plasma wave, setting other electrons into turbo mode over a span of just a few millimeters – out shoots a high-energy particle beam. “In the process, we pre-ionize the plasma with an additional, weaker laser pulse,” Heinemann explains. “This makes the plasma acceleration with the driver beam far more effective.”
Turbo ignition: Almost to the speed of light within just one millimeter
The result: “Our hybrid accelerator measures less than a centimeter,” Kurz explains. “The beam-driven accelerator section uses just one millimeter of it to bring the electrons to nearly the speed of light.” Realistic simulations of the process show a remarkable gradient of the accelerating voltage in the process, corresponding to an increase of more than a thousand times when compared to a conventional accelerator. To underscore the significance of their findings, the researchers implemented this concept in a similar form at the ATLAS laser at LMU in Munich. However, the experts still have many challenges to overcome before this new technology can be used for applications.
In any case, the experts already have possible fields of application in mind: “Research groups that currently don’t have a suitable particle accelerator might be able to use and further develop this technology,” Arie Irman hopes. “And secondly, our hybrid accelerator could be the basis for what is called a free-electron laser.” Such FELs are considered extremely high-quality radiation sources, especially X-rays, for ultra-precise analyses of nanomaterials, biomolecules, or geological samples. Until now, these X-ray lasers required long and expensive conventional accelerators. The new plasma technology could make them much more compact and cost-effective – and perhaps also affordable for a regular university laboratory.
Featured image: Numerical rendering of the laser-driven acceleration (left side) and a subsequent electron-driven acceleration (right side), forming together the hybrid plasma accelerator. Image: Alberto Martinez de la Ossa, Thomas Heinemann
Publication: T. Kurz, T. Heinemann, M. F. Gilljohann, Y. Y. Chang, J. P. Couperus Cabadağ, A. Debus, O. Kononenko, R. Pausch, S. Schöbel, R. W. Assmann, M. Bussmann, H. Ding, J. Götzfried, A. Köhler, G. Raj, S. Schindler, K. Steiniger, O. Zarini, S. Corde, A. Döpp, B. Hidding, S. Karsch, U. Schramm, A. Martinez de la Ossa, A. Irman: Demonstration of a compact plasma accelerator powered by laser-accelerated electron beams, in Nature Communications, 2021 (DOI: 10.1038/s41467-021-23000-7)
The National Superconducting Cyclotron Laboratory (NSCL) reached an important milestone on 16 April with first acceleration of beam in the ReAccelerator facility ReA6.
ReA6 is the upgraded ReAccelerator facility at NSCL and the Facility for Rare Isotope Beams. It will provide broader opportunities for nuclear physics experiments with higher beam energies than the previous ReA3.
A nitrogen-14 beam with the charge state of +6 was accelerated to 10.2 MeV/u using the new ReA6 beta=0.085 quarter-wave-resonator cryomodule. The new cryomodule and associated cryogenics and radio frequency systems worked well and operated as expected. The nitrogen beam was delivered to both end stations in the ReA6 experimental area achieving 100 percent transmission through the superconducting linear accelerator and beam-transport lines.
The accelerator optics is capable of providing the beam size as needed by users. A neon-20 beam with a different charge-to-mass ratio was also accelerated and delivered to the end stations achieving 100 percent transmission and similar beam sizes.
This milestone signals that ReA6 will be ready for the NSCL Stand-Alone ReA6 program, which will begin on 12 May.
A project team of High Intensity Heavy-ion Accelerator Facility (HIAF) from the Institute of Modern Physics of the Chinese Academy of Sciences has recently achieved great results in research on power supply control with high power, high precision and fast cycle. The results were published in IEEE Transactions on Industrial Electronics.
HIAF will provide highest pulse current heavy ion beams in the world. In order to avoid the loss of beam caused by the avalanche effect generated by the space charge and the strong flow dynamic vacuum, the next generation of high intensity accelerators should accelerate ions quickly to high energy, which requires the extremely fast current change rate and high dynamic tracking precision of the magnet power supply. Thus, it is essential to improve the control accuracy of the magnet power supply for HIAF.
In order to improve the tracking precision of the magnet power supply with a wide dynamic range, the researchers proposed a new analytical model with optimal control method and kinetic inductance fine-tuning method.
They carried out the experiment on a 200 Hz triangular wave scanning magnet power supply. They then successfully identified the kinetic inductances corresponding to different triangular waves and used these kinetic inductances to calibrate the model. The current error at the end of each switching cycle is controlled from 0.5 A to 0.015 A, which is close to the measurement accuracy limit. Therefore, the method was verified.
The new method greatly improves the control accuracy and is of great significance for the fast cycle acceleration mode of the next generation of high-current heavy ion accelerators.
This work was supported by the national key research program “Key Beam Physics and Core Technology Pre-research for a New Generation of High Current Heavy Ion Accelerator”.
Featured image: The experiment results of 200A waveform by scanning power supply. (Image from IEEE Transactions on Industrial Electronics)
Breakthrough greatly enhances the ultrafast resolution achievable with X-ray free-electron lasers.
A large international team of scientists from various research organizations, including the U.S. Department of Energy’s (DOE) Argonne National Laboratory, has developed a method that dramatically improves the already ultrafast time resolution achievable with X-ray free-electron lasers (XFELs). It could lead to breakthroughs on how to design new materials and more efficient chemical processes.
An XFEL device is a powerful combination of particle accelerator and laser technology producing extremely brilliant and ultrashort pulses of X-rays for scientific research. “With this technology, scientists can now track processes that occur within millions of a billionth of a second (femtoseconds) at sizes down to the atomic scale,” said Gilles Doumy, a physicist in Argonne’s Chemical Sciences and Engineering division. “Our method makes it possible to do this for even faster times.”
“It’s like trying to photograph the end of a race when the camera shutter might activate at any moment in the final ten seconds.”
— Dan Haynes, doctoral student, Max Planck Institute for the Structure and Dynamics of Matter
One of the most promising applications of XFELs has been in the biological sciences. In such research, scientists can capture how biological processes fundamental to life change over time, even before the radiation from the laser’s X-rays destroys the samples. In physics and chemistry, these X-rays can also shed light on the fastest processes occurring in nature with a shutter speed lasting only a femtosecond. Such processes include the making and breaking of chemical bonds and the vibrations of atoms on thin film surfaces.
For over a decade XFELs have delivered intense, femtosecond X-ray pulses, with recent forays into the sub-femtosecond regime (attosecond). However, on these miniscule time scales, it is difficult to synchronize the X-ray pulse that sparks a reaction in the sample and the laser pulse that “observes” it. This problem is called timing jitter.
Lead author Dan Haynes, a doctoral student at the Max Planck Institute for the Structure and Dynamics of Matter, said, “It’s like trying to photograph the end of a race when the camera shutter might activate at any moment in the final ten seconds.”
To circumvent the jitter problem, the research team came up with a pioneering, highly precise approach dubbed “self-referenced attosecond streaking.” The team demonstrated their method by measuring a fundamental decay process in neon gas at the Linac Coherent Light Source, a DOE Office of Science User Facility at SLAC National Accelerator Laboratory.
Doumy and his advisor at the time, Ohio State University Professor Louis DiMauro, had first proposed the measurement in 2012.
In the decay process, called Auger decay, an X-ray pulse catapults atomic core electrons in the sample out of their place. This leads to their replacement by electrons in outer atomic shells. As these outer electrons relax, they release energy. That process can induce the emission of another electron, known as an Auger electron. Radiation damage occurs due to both the intense X-rays and the continued emission of Auger electrons, which can rapidly degrade the sample. Upon X-ray exposure, the neon atoms also emit electrons, called photoelectrons.
After exposing both types of electrons to an external “streaking” laser pulse, the researchers determined their final energy in each of tens of thousands of individual measurements.
“From those measurements, we can follow Auger decay in time with sub-femtosecond precision, even though the timing jitter was a hundred-times larger,” said Doumy. “The technique relies on the fact that Auger electrons are emitted slightly later than the photoelectrons and thus interact with a different part of the streaking laser pulse.”
This factor forms the foundation of the technique. By combining so many individual observations, the team was able to construct a detailed map of the physical decay process. From that information, they could determine the characteristic time delay between the photoelectron and Auger electron emission.
The researchers are hopeful that self-referenced streaking will have a broad impact in the field of ultrafast science. Essentially, the technique enables traditional attosecond streaking spectroscopy to be extended to XFELs worldwide as they approach the attosecond frontier. In this way, self-referenced streaking may facilitate a new class of experiments benefitting from the flexibility and extreme intensity of XFELs without compromising on time resolution.
The published research, “Clocking Auger Electrons,” appeared in Nature Physics.
Besides Argonne, participating organizations include Max Planck Institute for the Structure and Dynamics of Matter (Germany), Center for Free-Electron Laser Science (Germany), Universität Hamburg (Germany), Technische Universität München (Germany), Paul Scherrer Institute (Switzerland), Ohio State University, Kansas State University, Ecole Polytechnique Fédérale de Lausanne (Switzerland), Synchrotron SOLEIL (France), SLAC National Accelerator Laboratory, Dublin City University (Ireland), Technische Universität Dortmund (Germany), European XFEL GmbH (Germany), Universität Kassel (Germany), Lomonosov Moscow State University (Russia), University of the Basque Country UPV/EHU (Spain), Deutsches Elektronen-Synchrotron (Germany) and University of Bern (Germany).
The research was funded, in part, by the DOE Office of Basic Energy Sciences.
Featured image: Artistic depiction of XFEL measurement with neon gas. The inherent delay between the emission of photoelectrons and Auger electrons leads to a characteristic ellipse in the analyzed data. In principle, the position of individual data points around the ellipse can be read like the hands of a clock to reveal the precise timing of decay processes. (Image by Daniel Haynes and Jörg Harms/Max Planck Institute for the Structure and Dynamics of Matter.)