The First Experiment at the LCLS
Join the adventure as Linda Young (Argonne Chemical Sciences and Engineering Division) publishes updates on the progress of her group as they carry out the first experiment to use the U.S. Department of Energy's Linac Coherent Light Source—the next-generation laser x-ray source at the SLAC National Accelerator Laboratory—which produces pulses of x-rays more than a billion times brighter than the most powerful existing sources.
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Tuesday, October 6, 2009, Last Day at the LCLS
Left: The AMO Control Room is a dynamic environment; workers install new monitors. Right: Argonne researchers during a quiet moment when the beam is being tuned for ultrashort-pulse (sub-10 fs) operation on Monday, October 5; left to right: Bertold Krassig, Linda Young, Yuelin Li, Steve Southworth, and Steve Pratt.
Run is officially over at 8 am. It is a ROD (Repair Opportunity Day). Many activities are scheduled and Christoph has made a long list to be carried out in preparation for experiments down the line. In the AMO hutch there is a flurry of activity: installing gas cabinets, exhaust ducts, work benches, laser safety certification. An activity that affects us is the installation of three large monitors in the AMO control room. For the experimenters of the first run, the sprint is over, but for John and Christoph this is only the first of 11 experiments before Christmas shutdown.
We clean up our papers strewn about in the AMO control room, make copies of the data book, with Steve Pratt mastering the non-intuitive controls of the copy machine. For us, there is the fun ahead: data analysis and paper writing. For this, we will be relying on Robin Santra, whose calculations, carried out with Nina Rohringer, have formed the basis for our experimental proposal.
We have our end-of-run celebration on the rooftop patio of the Near Experimental Hall at 1 pm, with sparkling cider in accordance with DOE rules, and are happy to meet and mingle with the machine physicists, operators, software engineers, and all those who made it happen. The impromptu celebration was logistically enabled by Irene Hu. Good feelings all around as we celebrate a first run that exceeded all expectations!
Later in the day, we socialize with a few collaborators at the SLAC Guest House. We are joined, unexpectedly, by Eric Rohlfing, who within DOE might be termed Mr. LCLS, as he was the original proponent of the scientific case for the machine. Somehow this seems a fitting end to the first experiment.
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Monday, October 5, 2009, Day 5 at the LCLS
A strip chart reflecting photon energy, pulse duration and pulse energy of the LCLS over 2 days.
Last full day of the run. We start out at the Main Control Center at 8 am. The room is packed and we are late by a few minutes. Clearly this meeting runs with military precision, as does the machine where the switchover to 20-pC, few-femtosecond operation began simultaneously. Mike Stanek reports on the weekend operations, shown in the chart, that to machine operators must seem like a timeline from beyond. Can’t those users decide what they want? However, to us, it was simply exploring the parameter space needed to make definitive statements and we were delighted that the machine response could be so immediate, and from our perspective, effortless.
Bringing up the 20-pC, sub-10-fs operation was a tour-de-force – orchestrated by Paul Emma, Zhirong Huang, and James Turner. Then we were given yet another option from the menu. Do you want to put in 13 additional undulators to slightly increase pulse energy and stability, at the cost of bunch length? It only takes 2 minutes. Decisions, decisions. We decide to go for the shortest pulse.
While the machine physicists were bringing up the super-short-pulse mode, much progress on improving the experimental end was made. The Ohio State team of Gilles Doumy and Chris Roedig took the opportunity to work on the magnetic bottle diagnostic chamber. Meanwhile, Matt Weaver, data acquisition software guru, had been quietly working away in his corner. When he demonstrates his new software that saves and reloads experimental data acquisition parameters with a single GUI button, there is a hearty, heartfelt round of applause. This saves the us from having to load ~50 parameter fields and a minimum of 5 minutes of clicking. And, big news, Elliot Kanter is now able to replay the data, which is streaming in at ~200 Mb/min onto 4 processors.
Around 1:30 pm, the machine physicists deliver the short-pulse x-ray beam. On the monitor, the pulse length reads ~3.2 fs, approximately 100? shorter than the long-pulse operation! We adjust our target density for the reduced pulse length and happily measure for the rest of the day/night, requesting beam energy changes, as usual. We are careful to get a data run going before the 4:30 pm scheduled visit of the DOE personnel, reviewers, and PULSE scientists. When they arrive, the 20-person occupancy of the AMO data control room is exceeded and some people are forced to leave. We chat with the various people who are interested to see the first x-ray laser experiment in action. Someone suggests that this is like being in a zoo – a petting zoo. But we’re happy with our results, and we don’t mind sharing that.
Posted by Linda Young
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Sunday, October 4, 2009, Day 4 at the LCLS
Sunday in the Main Control Room. Left to right: Matt Cyterski, Shawn Alverson, Mike Stanek, Johnny Warren, and Rick Iverson.
Again quiet in the Main Control Room meeting at 8 am. We experimenters come and since we were confident in the success of the beamtime, we actually take some time to meet the machine physicists and operators who have been performing so heroically. Nice to have a face to go with the name on the other end of the phoneline. We take a tour of the control room and see an eclectic mix of high-tech display channels and equipment from another era. Particularly noticeable to me, coming from another national lab, were the blue cloth chairs coming from the demise of the Superconducting Super Collider, and the charming LCLS main control panel. We discuss diagnostics and then I remember that at Friday’s meeting I had promised Mark that he could have 20 minutes for laser maintenance. Oops. But the LCLS was performing so well, that we forgot about it.
Getting back to the experiment, we scrutinize the hypersatellite data, and decide we need to make a few more checks before proceeding. What if Bertold’s calibration was wrong? Yuelin’s plot of the hypersatellite/Auger yield was a bit perplexing. Better check. So we proceed to take spectra at several x-ray energies to confirm the identification of the hypersatellite and watch its disappearance as we set the energy below the threshold. After several hours of checks, we are satisfied!! We move on to the next problem of understanding the high-intensity x-ray absorption when the photon energies are insufficient to touch the inner shell.
Our last big challenge will be to understand the interaction of ultrashort x-ray pulses with neon. This is a challenge for the accelerator physicists as well, and we’ve tentatively scheduled this change for 8 am on Monday morning.
Meanwhile, feeling so pleased with the results of the run, we go for lunch and start to plan a small end-of-run celebration for Tuesday – after the run is over. Of course, permission must be obtained from higher ups and an email to Jo Stohr, Director of LCLS, elicits a favorable, helpful response.
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Saturday, October 3, 2009, Day 3 at the LCLS
A bit quieter in the Main Control Room meeting at 8 am on Saturday morning. After verifying the dynamics of x-ray multiphoton absorption at energies below the hollow atom threshold, we began the search for hollow neon. We initially thought that the simplest signature of hollow atom production would be to monitor the photoelectron peaks – but it soon became apparent that the “hypersatellite” Auger electron peaks were more easily distinguishable. Since the Auger electrons are ejected isotropically, unlike photoelectron peaks which concentrate along the polarization axis, we were able to obtain these signals in all five photoelectron spectrometers simultaneously. The very first spectrum, taken with a relatively long pulse length, showed a definitive hypersatellite signature!! Basically, that means a new peak appeared in the electron energy spectrum – one at the correct energy, as deduced by Bertold’s painstaking calibration of the electron spectrometers.
Next comes the part that many scientists relish: Let’s make that peak bigger. So we called up the Main Control Room and ordered “More peak power, please.” They obliged in a mere 10 minutes by increasing the bunch compression to yield a pulse approximately three times shorter, ~80 fs and an intensity ~1.5 greater. With this new shorter pulse duration, we proceeded to explore the intensity dependence of the hypersatellite peak.
As the night rolled around, and the night crew ambled in with cookies and snacks, the day crew of seven (from Argonne, Ohio State, and Western Michigan) went for Chinese food. Not a bad day’s work to have first evidence for x-ray driven hollow atom production!!
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Friday, October 2, 2009, Day 2 at LCLS
In the data room, the band of software gurus and Christoph Bostedt, AMO Instrument Scientist.
From left to right: Matt, Christoph, Jason, Amadeo and Marc.
Started the day at the Main Control Center meeting at 8 am. A sleepy Steve Southworth reported our non-intuitive results of the owl shift that longer pulses create higher ionization states for a given photon pulse energy. Meanwhile, Matthias Hoener, starting a shift at 4 am, was skillfully aligning the electron spectrometers. Five high-resolution electron time-of-flight spectrometers must point at the interaction region – a 1-micron diameter by 1-mm cylinder of ionized gas. Amazingly, this was done by noon, with only a single glitch: a cable not being plugged in correctly. We requested a “benign” x-ray energy below the hollow atom threshold to calibrate the efficiency of the spectrometers and obtain a baseline for other phenomena, such as hollow atom production. We were rewarded by fine angular distribution data that show that LCLS x-rays eject many electrons from a single atom along the horizontal polarization axis of the LCLS. Both the electrons from the inner-shell and those from the outer-shell are ejected in this direction…giving an indication of mechanism of charge state production.
As we users were busily gazing at data, the software crew was working nonstop to provide data acquisition capabilities, in the same busy room. It must be difficult to concentrate on coding with the constant chatter of users in the background. Jason heroically fixed motor controllers, Matt worked on incorporating user-friendly online data analysis tools, Amadeo worked on incorporating machine parameters into our data stream.
Because it was an interesting day, we were visited toward the end of the day by our collaborators, PULSE Institute Director Phil Bucksbaum, David Reis, and their students and postdocs. They had been distracted by a DOE review of their program, but needed a break from that to enjoy fresh data from LCLS!
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Readying the Experiment
John Bozek, Jean-Charles Castagna, and Dan Cox search for leaks on the high-field physics chamber.
Day 1: Full of anticipation, Steve Southworth and I headed over to the Near Experimental Hall after breakfast. Just like all physics experiments, this one started off chasing leaks. As Murphy’s Law would have it, baking out did not improve the vacuum, just the opposite. Thus at 7:30 am, we found John Bozek, Jean Claude, Don, and others crawling over the apparatus hunting for the leak. Eventually, after 4 hours of intensive searching they identified a faulty forepump.
Meanwhile, Joe Frisch and the accelerator operators used the time to measure the x-ray pulse duration and peak power as a function of bunch compressor current. This confirmed their earlier measurements giving confidence in the reproducible performance of the x-ray laser. As the AMO hutch was “brought back on-line” and checked for safety, the machine operators had time to do a beam-based alignment that will enable more rapid changes of energy without realignment. The improved performance brought the following e-mail from Paul Emma (SLAC Accelerator Research Division):
“In celebration of the first user run, the LCLS is running like a top today with 2-keV photons, 2.4-mJ of x-ray pulse energy, and an unprecedented <5% rms shot-to-shot FEL power stability. This thing seems to like users!”
Even after the vacuum problem was resolved, bringing back the High Field Physics chamber into operation after the bakeout required considerable finesse and teamwork from many people with different expertise. Motor controller malfunctions, a short in the ion spectrometer repeller plate, data acquisition hiccups were somewhat expected and par for the course. Eventually, the ion spectrometer was ready to go around 4 pm and we became ready to optimize the x-ray focusing. This involves minute tweaks on Kirkpatrick-Baez mirrors to focus the x-ray beam to ~1 micron. By 11 pm we were ready to measure ion charge state spectra as a function of x-ray pulse duration—here we used the measurements the machine physicists had made earlier in the day as a guide. With Steve, Elliot, and others working through the night, we were rewarded with some interesting preliminary results that may reflect the unusual spiky nature of the SASE x-ray pulse, i.e., a dramatic change in the production of fully-stripped neon as a function of pulse length.
Tomorrow it is on to electron spectrometer setup and the search for hollow neon!
Filed under: data acquisition - free electron laser - LCLS - vacuum - x-ray pulse
First Day at the Linac Coherent Light Source
The AMO instrument scientists with the first LCLS users in the instrument hutch. From left to right: Christoph Bostedt, Steve Southworth, Linda Young, John Bozek, Steve Pratt and Yuelin Li. (Photo by Brad Plummer, courtesy of SLAC National Accelerator Laboratory. Read the SLAC Today article on the first LCLS experiment.)
What is it like being one of the first users at the Linac Coherent Light Source (LCLS)? Well, LCLS is a magnet for scientists, particularly at inception. So, when I went to be badged in Building 120, I was treated to the sight of Claudio Pellegrini, originator of the idea of an x-ray free-electron laser at SLAC, doing his computer-based safety training. It did the soul good to see that everyone, even the high and mighty, were subject to the same rules.
Eager to see the experiment, I drove over to the Near Experimental Hall, where the AMO (Atomic Molecular and Optical) endstation is located. The AMO endstation is a cavernous hutch with a 10-meter x 10-meter footprint. The x-ray laser beam, generated approximately 100 meters upstream, is focused to a spot of ~1 micron diameter in the center of the experimental high-field physics chamber. Five electron and one ion spectrometers view this focal volume in which the x-ray beam interacts with a gas jet. With these spectrometers, we will be able to view the mechanism by which atoms are stripped of their electrons when subjected to the intense LCLS x-ray pulses. Already during the commissioning period, it has been observed that the LCLS can strip all electrons from a neon atom in a single pulse – a process that would not happen at any other x-ray source.
Across from the AMO endstation lies a similarly spacious AMO data-acquisition room, typically a beehive of activity with walls lined with computer monitors and two giant screens displaying the LCLS parameters. When I arrived, it was unusually deserted, with only two people present, due the bakeout of the experimental chamber in progress. Jason, an Experimental Physics and Industrial Control System (EPICS) programmer, dropped his tasks to give me a quick tour and then went back to important work such as ensuring that the autosave of the motor parameters was working. It will take some time to become acquainted with the people involved at LCLS.
Today, the eve of the official start of the first experiment, was one of many meetings – four – but who’s counting. We started with a breakfast meeting of the Argonne crew at the SLAC National Accelerator Laboratory guesthouse to study the preliminary calibration of electron spectrometers. This was followed by a meeting at the Near Experimental Hall with the beamline scientists and programmers to decide upon which variables to log into the data stream. As we entered this meeting, we were unexpectedly greeted by two SLAC public relations personnel – Brad Plummer and Kelen Tuttle. After a quick round of informal photos, we got down to the task of defining variables. During this process we were visited by none other than John Galayda, head of the LCLS accelerator project, and Dale Knutson, project manager of LCLS – donning hard hats and reflective vests. Upon completion of this task, we lunched in beautiful weather, accompanied by friendly yellowjackets, with a number of colleagues from PULSE. The third meeting of the day was the “official” collaboration meeting. We had 21 people in a 22-person-occupancy room. Very useful meeting as the accelerator physicists and the scientists were all present simultaneously. Last meeting of the day was the 4:15 pm LCLS commissioning meeting at the MCC (main control center), where Bertold gave the accelerator personnel an introduction to our experiment.
This was followed by endstation-specific safety training. My last task of the day was setting up the computer account and privileges for our experiment with Amadeo and Igor. But other tasks remain and Ed, the night shift floor coordinator, will shut off the chamber bakeout at midnight to be ready for John Bozek to reconnect the cables to the apparatus in the morning. So, after this whirlwind of activity, we are settling in for a good night’s sleep and the official start of the first experiment!
Filed under: data acquisition - endstation - hutch
First Experiment at the Linac Coherent Light Source
Wow – the first experiment on the world’s first x-ray laser – the U.S. Department of Energy's Linac Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory! Quite an honor, quite a responsibility. It’s been less than a decade since the “First Experiments” document was compiled to make the scientific case for the construction of an x-ray free-electron laser and already we are here, with the LCLS performing substantially beyond expectations. Not only does LCLS lase, but it does so with a shorter saturation length than anticipated and also with a shorter pulse length than anticipated. All this translates to an x-ray source that is billions of times more intense than any other and that will enable snapshots of ultrafast processes, and possibly biomolecule structure determination without the need for crystallization. The rapid successful launch of this facility is a testament to the LCLS staff and the collaborations throughout the country, with, e.g., Argonne; Lawrence Livermore National Laboratory; Lawrence Berkeley National Laboratory; and the University of California, Los Angeles.
As the first users, we will investigate the nature of high-intensity x-ray absorption processes. Understanding the mechanism of photoabsorption at high x-ray intensity provides a foundation for a host of later experiments that wish to exploit LCLS’s ultrahigh x-ray intensity. Unusual phenomena may occur. Focused LCLS pulses produce an intensity of ~1018 W/cm2, corresponding to an electric field strength of ~300 V/Ångstrom, a field strength which greatly exceeds that binding electrons in atoms. For many years, field strengths of this magnitude have been produced at longer wavelengths, e.g., ~10,000 Ångstroms, and the response of an atom subject to strong electromagnetic fields at long wavelengths has been studied vigorously.
The LCLS is an x-ray source that is billions of times more intense than any other
At long wavelengths the interaction is quite different; an outer-shell electron is ripped from an atom in a tunneling process and, upon field reversal, is driven back into the atomic core. Now, for the first time we will be able to explore this strong-field regime with x-ray radiation, ~1.5-15 Ångstroms. Here, the x-ray photons interact predominantly with inner-shell electrons, and at LCLS intensities we will be able to eject inner-shell electrons faster than the femtosecond Auger refilling process, thus creating hollow atoms. Besides being an exotic state of matter, hollow atom states are precursors to enhanced x-ray damage in complex systems. To start, we will follow the evolution of the electrons in a neon atom as it is exposed to high-intensity x-ray radiation using a combination of electron and ion spectrometers. The photoabsorption process acts like a Gattling gun, with the LCLS ejecting electron bullets with the energy of each bullet identifying the electronic state from which it originated.
This experiment is really like no other that we’ve conducted at a light source. Typically, one designs, constructs, and troubleshoots an instrument and then brings it to a beamline. Here, the LCLS instrument scientists, John Bozek and Christoph Bostedt, have taken primary responsibility for the apparatus—after gathering input from the user community on specific requirements. So in the accompanying photo we, the Argonne group, sit on a fine midwestern fall afternoon as the the apparatus is being commissioned at SLAC.
Standing left to right: Elliot Kanter, Robin Santra, Phay Ho, Stephen Pratt, Stefan Pabst, Anne-Marie March.
Sitting: Linda Young, Stephen Southworth, Bertold Kraessig.
Not pictured: Yuelin Li.
Since commissioning started on August 17, we’ve gone out to help commission the high-field physics apparatus, with Bertold, Elliot, Yuelin, and finally Steve Southworth taking stints of ~1.5-week duration. The commissioning and coordination process has been planned by John and Christoph, and has included researchers from Ohio State University, Western Michigan University, and Lawrence Berkeley National Laboratory, as well as SLAC. These same researchers will be our collaborators on the first experiment. It’s really “big science” comes to light sources. Tomorrow we’re on a plane to SLAC!
Posted by Linda YoungFiled under: Argonne - free electron laser - high-intensity x-ray absorption process - LCLS - Linac Coherent Light Source - photoabsorption - SLAC