From DOE’s Fermi National Accelerator Laboratory(US): “Testing wraps up for first Fermilab-designed cryomodule for PIP-II accelerator”

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From DOE’s Fermi National Accelerator Laboratory(US) , an enduring source of strength for the US contribution to scientific research world wide.

March 1, 2021
Brianna Barbu

There is a first time for everything. Sometimes that thing is a highly complex machine designed to accelerate an 800-million-electronvolt proton beam to enable decades’ worth of cutting-edge experiments at the United States’ foremost particle physics laboratory.

In January, scientists and engineers at the Department of Energy’s Fermilab successfully completed phase-one testing on a prototype of the first superconducting cryomodule to be fully designed, assembled and tested at Fermilab for the PIP-II accelerator.

“It isn’t often that we have the privilege and opportunity of going through the entire life cycle of such complex structures, from design to testing,” said Donato Passarelli, the Fermilab engineer leading the technical coordination effort for the cryomodule.

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Building something as complex as a superconducting cryomodule takes the efforts of an entire team of scientists, engineers and technicians. This picture was taken in January 2020 in Fermilab’s Industrial Center Building at the end of the SSR1 cryomodule assembly. Credit: Lynn Johnson, Fermilab.

Accelerating Fermilab science

The Proton Improvement Plan-II, or PIP-II for short, is a highly anticipated upgrade to Fermilab’s accelerator complex. The PIP-II accelerator will replace Fermilab’s existing linear accelerator to enable the necessary power and versatility for the Fermilab-hosted international Deep Underground Neutrino Experiment and other next-generation experiments.

Cryomodules are the major building blocks of a superconducting linear particle accelerator. Each cryomodule houses a “string” of superconducting cavities, which impart energy to the particle beam through an electromagnetic field, as well as magnets that keep the beam focused. Every component is carefully designed to boost the beam as efficiently as possible.

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Each SSR1 cryomodule contains eight superconducting cavities and four focusing magnets. Credit: Fermilab.

The 215-meter-long PIP-II accelerator will use 23 cryomodules of five different accelerating structure types connected end-to-end. When the beam has passed through all of them, the particles will be traveling at 84% the speed of light — over 560 million miles per hour.

The recently completed cryomodule from Fermilab houses a cavity type called SSR1- short for single-spoke resonator- type 1. Positioned as the second cryomodule in the accelerator beamline, the SSR1 cryomodule is designed to efficiently accelerate particles traveling at about 20% of the speed of light. Each SSR1 cryomodule will contain eight superconducting cavities and four focusing magnets.

PIP-II which is supported by the DOE Office of Science is the first U.S. accelerator project that will have significant contributions-including some of PIP-II’s cryomodules-from international partners. Research institutions in the U.S. France India Italy Poland and the United Kingdom are all developing different parts of the accelerator. Collaborators at India’s Bhabha Atomic Research Center contributed one of the superconducting cavities for the SSR1 prototype.

The challenge is the opportunity

“Of course, it’s not the first cryomodule built at Fermilab,” said Fermilab engineer Vincent Roger, who leads the engineering design of PIP-II cryomodules, “but it was the first time at Fermilab to fully design and build a cryomodule from scratch.”

SSR1 was the first single-spoke resonator cryomodule built in the United States and only the second in the world, so the Fermilab team often found itself in somewhat uncharted territory. It was challenging, but also a big opportunity to innovate.

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Cryomodules of five different types, one of which is the SSR1 pictured here, boost the energy of the beam. Credit: Tom Nicol, Fermilab.

“When I first started on this project, the facility to perform the assembly was brand-new, and we were faced with having to design the techniques almost from scratch,” said Mattia Parise, the Fermilab engineer heading up string assembly for the SSR1 cryomodule. His team had to creatively adapt existing knowledge to a new scheme to put the cavities and magnets together.

When they tested their prototype in late 2020, scientists and engineers rigorously checked that the cryomodule components maintained their structural integrity and electromagnetic performance. In the test, they cooled the module to minus 456 degrees Fahrenheit, powered up the cavities and magnets, and finally accelerated a beam through the cryomodule.

The prototype SSR1 cryomodule successfully met all of the PIP-II project specifications, and the team is now analyzing the test data and refining their analytical models to better predict the cryomodules’ performance in the future.

“If we want to be successful in developing superconducting accelerator technology for PIP-II, we need to continually check and refine the details,” Passarelli said.

Beaming into the future

The prototype cryomodule incorporates several other innovative features besides the cavity design: for example, strongback technology, in which the cavities are connected to a common support frame rather than each other. The strongback frame is at room temperature, so that the cavities and other internal components contract together and stay aligned while they are cooled to near absolute zero.

Computer vision techniques monitor the alignment with hair’s-breadth accuracy, using cameras focused on reflective glass balls attached to each cavity and magnet. The computer monitors the cameras to measure if and how components move and ensure that the internal parts stay in alignment. This type of computer monitoring can also enable more automation in the assembly process.

These features will be carried forward into the next sections of the accelerator, so the team is effectively validating aspects of multiple designs at once with this prototype. The biggest difference between the different superconducting cryomodules is the type of cavities they house. The cavity shapes in each successive cryomodule change as the beam is propelled to higher and higher energies, but the layout of the elements surrounding them will be standardized as much as possible.

“Our main ideas will carry over to the other types of cryomodules designed at Fermilab because our test results show that the concepts work,” Parise said. “We know that we did a good job, and we have more knowledge now about why the systems behave like they do.”

The success of this prototype is thus not only a milestone for PIP-II but a glimpse of things to come for Fermilab. It also reinforces Fermilab’s position as a leader in the global superconducting accelerator community and a valuable partner for future projects.

“It’s important to us as a team because we successfully overcame many technical and scientific challenges,” Passarelli said. “And it’s important for the lab because it brings together knowledge from generations of Fermilab scientists, engineers and technicians to validate a concept that will be adapted for other PIP-II cryomodules.”

See the full article here.


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Fermi National Accelerator Laboratory(US), located just outside Batavia, Illinois, near Chicago, is a United States Department of Energy national laboratory specializing in high-energy particle physics. Since 2007, Fermilab has been operated by the Fermi Research Alliance, a joint venture of the University of Chicago, and the Universities Research Association (URA). Fermilab is a part of the Illinois Technology and Research Corridor.

Fermilab’s Tevatron was a landmark particle accelerator; until the startup in 2008 of the Large Hadron Collider (LHC) near Geneva, Switzerland, it was the most powerful particle accelerator in the world, accelerating antiprotons to energies of 500 GeV, and producing proton-proton collisions with energies of up to 1.6 TeV, the first accelerator to reach one “tera-electron-volt” energy. At 3.9 miles (6.3 km), it was the world’s fourth-largest particle accelerator in circumference. One of its most important achievements was the 1995 discovery of the top quark, announced by research teams using the Tevatron’s CDF and DØ detectors. It was shut down in 2011.

In addition to high-energy collider physics, Fermilab hosts fixed-target and neutrino experiments, such as MicroBooNE (Micro Booster Neutrino Experiment), NOνA (NuMI Off-Axis νe Appearance) and SeaQuest. Completed neutrino experiments include MINOS (Main Injector Neutrino Oscillation Search), MINOS+, MiniBooNE and SciBooNE (SciBar Booster Neutrino Experiment). The MiniBooNE detector was a 40-foot (12 m) diameter sphere containing 800 tons of mineral oil lined with 1,520 phototube detectors. An estimated 1 million neutrino events were recorded each year. SciBooNE sat in the same neutrino beam as MiniBooNE but had fine-grained tracking capabilities. The NOνA experiment uses, and the MINOS experiment used, Fermilab’s NuMI (Neutrinos at the Main Injector) beam, which is an intense beam of neutrinos that travels 455 miles (732 km) through the Earth to the Soudan Mine in Minnesota and the Ash River, Minnesota, site of the NOνA far detector.

In 2017, the ICARUS neutrino experiment was moved from CERN to Fermilab.

In the public realm, Fermilab is home to a native prairie ecosystem restoration project and hosts many cultural events: public science lectures and symposia, classical and contemporary music concerts, folk dancing and arts galleries. The site is open from dawn to dusk to visitors who present valid photo identification.

Asteroid 11998 Fermilab is named in honor of the laboratory.

Weston, Illinois, was a community next to Batavia voted out of existence by its village board in 1966 to provide a site for Fermilab.

The laboratory was founded in 1969 as the National Accelerator Laboratory; it was renamed in honor of Enrico Fermi in 1974. The laboratory’s first director was Robert Rathbun Wilson, under whom the laboratory opened ahead of time and under budget. Many of the sculptures on the site are of his creation. He is the namesake of the site’s high-rise laboratory building, whose unique shape has become the symbol for Fermilab and which is the center of activity on the campus.

After Wilson stepped down in 1978 to protest the lack of funding for the lab, Leon M. Lederman took on the job. It was under his guidance that the original accelerator was replaced with the Tevatron, an accelerator capable of colliding protons and antiprotons at a combined energy of 1.96 TeV. Lederman stepped down in 1989. The science education center at the site was named in his honor.

The later directors include:

John Peoples, 1989 to 1996
Michael S. Witherell, July 1999 to June 2005
Piermaria Oddone, July 2005 to July 2013
Nigel Lockyer, September 2013 to the present

Fermilab continues to participate in the work at the Large Hadron Collider (LHC); it serves as a Tier 1 site in the Worldwide LHC Computing Grid.

Current state

Since 2013, the first stage in the acceleration process (pre-accelerator injector) in the Fermilab chain of accelerators takes place in two ion sources which turn hydrogen gas into H− ions. The gas is introduced into a container lined with molybdenum electrodes, each a matchbox-sized, oval-shaped cathode and a surrounding anode, separated by 1 mm and held in place by glass ceramic insulators. A magnetron generates a plasma to form the ions near the metal surface. The ions are accelerated by the source to 35 keV and matched by low energy beam transport (LEBT) into the radio-frequency quadrupole (RFQ) which applies a 750 keV electrostatic field giving the ions their second acceleration. At the exit of RFQ, the beam is matched by medium energy beam transport (MEBT) into the entrance of the linear accelerator (linac).

The next stage of acceleration is linear particle accelerator (linac). This stage consists of two segments. The first segment has 5 vacuum vessel for drift tubes, operating at 201 MHz. The second stage has 7 side-coupled cavities, operating at 805 MHz. At the end of linac, the particles are accelerated to 400 MeV, or about 70% of the speed of light. Immediately before entering the next accelerator, the H− ions pass through a carbon foil, becoming H+ ions (protons).

The resulting protons then enter the booster ring, a 468 m (1,535 ft) circumference circular accelerator whose magnets bend beams of protons around a circular path. The protons travel around the Booster about 20,000 times in 33 milliseconds, adding energy with each revolution until they leave the Booster accelerated to 8 GeV.

The final acceleration is applied by the Main Injector [circumference 3,319.4 m (10,890 ft)]. Completed in 1999, it has become Fermilab’s “particle switchyard” in that it can route protons to any of the experiments installed along the beam lines after accelerating them to 120 GeV. Until 2011, the Main Injector provided protons to the antiproton ring [circumference 6,283.2 m (20,614 ft)] and the Tevatron for further acceleration but now provides the last push before the particles reach the beam line experiments.

Proton improvement plan

Recognizing higher demands of proton beams to support new experiments, Fermilab began to improve their accelerators in 2011. Expected to continue for many years, the project has two phases: Proton Improvement Plan (PIP) and Proton Improvement Plan-II (PIP-II).

PIP (2011–2018)

The overall goals of PIP are to increase the repetition rate of the Booster beam from 7 Hz to 15 Hz and replace old hardware to increase reliability of the operation. Before the start of the PIP project, a replacement of the pre-accelerator injector was underway. The replacement of almost 40 year-old Cockcroft–Walton generators to RFQ started in 2009 and completed in 2012. At the Linac stage, the analog beam position monitor (BPM) modules were replaced with digital boards in 2013. A replacement of Linac vacuum pumps and related hardware was expected to be completed in 2015. A study on the replacement of 201 MHz drift tubes is still ongoing. At the boosting stage, a major component of the PIP is to upgrade the Booster ring to 15 Hz operation. The Booster has 19 radio frequency stations. Originally, the Booster stations were operating without solid-state drive system which was acceptable for 7 Hz but not 15 Hz operation. A demonstration project in 2004 converted one of the stations to solid state drive before the PIP project. As part of the project, the remaining stations were converted to solid state in 2013. Another major part of the PIP project is to refurbish and replace 40 year-old Booster cavities. Many cavities have been refurbished and tested to operate at 15 Hz. The completion of cavity refurbishment was expected in 2015, after which the repetition rate can be gradually increased to 15 Hz operation. A longer term upgrade is to replace the Booster cavities with a new design. The research and development of the new cavities is underway, replacement was expected in 2018.

PIP-II

The goals of PIP-II include a plan to delivery 1.2 MW of proton beam power from the Main Injector to the Deep Underground Neutrino Experiment target at 120 GeV and the power near 1 MW at 60 GeV with a possibility to extend the power to 2 MW in the future. The plan should also support the current 8 GeV experiments including Mu2e, Muon g−2, and other short-baseline neutrino experiments. These require an upgrade to the Linac to inject to the Booster with 800 MeV. The first option considered was to add 400 MeV “afterburner” superconducting Linac at the tail end of the existing 400 MeV. This would have required moving the existing Linac up 50 metres (160 ft). However, there were many technical issues with this approach. Instead, Fermilab is building a new 800 MeV superconducting Linac to inject to the Booster ring. Construction of the first building for the PIP-II accelerator began in 2020. The new Linac site will be located on top of a small portion of Tevatron near the Booster ring in order to take advantage of existing electrical and water, and cryogenic infrastructure. The PIP-II Linac will have low energy beam transport line (LEBT), radio frequency quadrupole (RFQ), and medium energy beam transport line (MEBT) operated at the room temperature at with a 162.5 MHz and energy increasing from 0.03 MeV. The first segment of Linac will be operated at 162.5 MHz and energy increased up to 11 MeV. The second segment of Linac will be operated at 325 MHz and energy increased up to 177 MeV. The last segment of linac will be operated at 650 MHz and will have the final energy level of 800 MeV.

Experiments:

Cryogenic Dark Matter Search (CDMS)
COUPP: Chicagoland Observatory for Underground Particle Physics
Dark Energy Survey (DES)
Deep Underground Neutrino Experiment (DUNE), formerly known as Long Baseline Neutrino Experiment (LBNE)
Holometer interferometer
ICARUS experiment Originally located at the Laboratori Nazionali del Gran Sasso (LNGS), it will hold 760 tonnes of liquid Argon.
MiniBooNE: Mini Booster Neutrino Experiment
MicroBooNE: Micro Booster Neutrino Experiment
MINOS: Main Injector Neutrino Oscillation Search
MINERνA: Main INjector ExpeRiment with νs on As
MIPP: Main Injector Particle Production
Mu2e: Muon-to-Electron Conversion Experiment
Muon g−2: Measurement of the anomalous magnetic dipole moment of the muon
NOνA: NuMI Off-axis νe Appearance
SELEX: SEgmented Large-X baryon spectrometer EXperiment, run to study charmed baryons
Sciboone: SciBar Booster Neutrino Experiment
SeaQuest
ArgoNeuT: The Argon Neutrino Teststand detector

Architecture

Fermilab’s first director, Robert Wilson, insisted that the site’s aesthetic complexion not be marred by a collection of concrete block buildings. The design of the administrative building (Wilson Hall) was inspired by St. Pierre’s Cathedral in Beauvais, France, though it was realized in a Brutalist style. Several of the buildings and sculptures within the Fermilab reservation represent various mathematical constructs as part of their structure.

The Archimedean Spiral is the defining shape of several pumping stations as well as the building housing the MINOS experiment. The reflecting pond at Wilson Hall also showcases a 32-foot-tall (9.8 m) hyperbolic obelisk, designed by Wilson. Some of the high-voltage transmission lines carrying power through the laboratory’s land are built to echo the Greek letter π. One can also find structural examples of the DNA double-helix spiral and a nod to the geodesic sphere.

Wilson’s sculptures on the site include Tractricious, a free-standing arrangement of steel tubes near the Industrial Complex constructed from parts and materials recycled from the Tevatron collider, and the soaring Broken Symmetry, which greets those entering the campus via the Pine Street entrance. Crowning the Ramsey Auditorium is a representation of the Möbius strip with a diameter of more than 8 feet (2.4 m). Also scattered about the access roads and village are a massive hydraulic press and old magnetic containment channels, all painted blue.

Current developments

Fermilab dismantled the CDF (Collider Detector at Fermilab) experiment to make the space available for IARC (Illinois Accelerator Research Center). Construction work has started for LBNF/DUNE and PIP-II while the NOνA and Muon g−2 experiments continue to collect data. The laboratory also conducts research in quantum information science, including the development of teleportation technology for the quantum internet and increasing the lifetime of superconducting resonators for use in quantum computers.

LBNF/DUNE

Fermilab as of 2016 stands to become the world leader in Neutrino physics through the Deep Underground Neutrino Experiment at the Long Baseline Neutrino Facility. Other leaders are CERN, which leads in Accelerator physics with the Large Hadron Collider (LHC), and Japan, which has been approved to build and lead the International Linear Collider (ILC). Fermilab will be the site of LBNF’s future beamline, and the Sanford Underground Research Facility (SURF), in Lead, SD, is the site selected to house the massive far detector. The term “baseline” refers to the distance between the neutrino source and the detector. The far detector current design is for four modules of instrumented liquid argon with a fiducial volume of 10 kilotons each. The first two modules are expected to be complete in 2024, with the beam operational in 2026. The final module is planned to be operational in 2027. A large prototype detector constructed at CERN took data with a test beam from 2018-2020. The results show that ProtoDUNE performed with greater than 99% efficiency.

LBNF/DUNE program in neutrino physics plans to measure fundamental physical parameters with high precision and to explore physics beyond the Standard Model. The measurements DUNE will make are expected to greatly increase the physics community’s understanding of neutrinos and their role in the universe, thereby better elucidating the nature of matter and anti-matter. It will send the world’s highest-intensity neutrino beam to a near detector on the Fermilab site and the far detector 800 miles (1300 km) away at SURF.
Muon g−2

Muon g−2: (pronounced “gee minus two”) is a particle physics experiment to measure the anomaly of the magnetic moment of a muon to a precision of 0.14 ppm, which will be a sensitive test of the Standard Model.

Fermilab is continuing an experiment conducted at Brookhaven National Laboratory to measure the anomalous magnetic dipole moment of the muon.

The magnetic dipole moment (g) of a charged lepton (electron, muon, or tau) is very nearly 2. The difference from 2 (the “anomalous” part) depends on the lepton, and can be computed quite exactly based on the current Standard Model of particle physics. Measurements of the electron are in excellent agreement with this computation. The Brookhaven experiment did this measurement for muons, a much more technically difficult measurement due to their short lifetime, and detected a tantalizing, but not definitive, 3 σ discrepancy between the measured value and the computed one.

The Brookhaven experiment ended in 2001, but 10 years later Fermilab acquired the equipment, and is working to make a more accurate measurement (smaller σ) which will either eliminate the discrepancy or, hopefully, confirm it as an experimentally observable example of physics beyond the Standard Model.

Central to the experiment is a 50 foot-diameter superconducting magnet with an exceptionally uniform magnetic field. This was transported, in one piece, from Brookhaven in Long Island, New York, to Fermilab in the summer of 2013. The move traversed 3,200 miles over 35 days, mostly on a barge down the East Coast and up the Mississippi.

The magnet was refurbished and powered on in September 2015, and has been confirmed to have the same 1300 ppm p-p basic magnetic field uniformity that it had before the move.

The project worked on shimming the magnet to improve its magnetic field uniformity. This had been done at Brookhaven, but was disturbed by the move and had to be re-done at Fermilab.

In 2018, the experiment started taking data at Fermilab.

LHC Physics Centre (LPC)

The LHC Physics Center (LPC) at Fermilab is a regional center of the Compact Muon Solenoid Collaboration (the experiment is housed at CERN). The LPC offers a vibrant community of CMS scientists from the US and plays a major role in the CMS detector commissioning, and in the design and development of the detector upgrade.

Particle discovery

In the summer of 1977, a team of physicists, led by Leon M. Lederman, working on Experiment 288, in the proton center beam-line of the Fermilab fixed target areas, discovered the Upsilon (Bottom quark).

On 3 September 2008, the discovery of a new particle, the bottom Omega baryon (Ω−b) was announced at the DØ experiment of Fermilab. It is made up of two strange quarks and a bottom quark. This discovery helps to complete the “periodic table of the baryons” and offers insight into how quarks form matter.