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Feature

Building an instrument to map the universe in 3-D

The future Dark Energy Spectroscopic Instrument will be mounted on the Mayall 4-meter telescope. It will be used to create a 3-D map of the universe for studies of dark energy. Photo courtesy of NOAO

Dark energy makes up about 70 percent of the universe and is causing its accelerating expansion. But what it is or how it works remains a mystery.

The Dark Energy Spectroscopic Instrument (DESI) will study the origins and effects of dark energy by creating the largest 3-D map of the universe to date. It will produce a map of the northern sky that will span 11 billion light-years and measure around 25 million galaxies and quasars, extending back to when the universe was a mere 3 billion years old.

Once construction is complete, DESI will sit atop the Mayall 4-Meter Telescope in Arizona and take data for five years.

DESI will work by collecting light using optical fibers that look through the instrument's lenses and can be wiggled around to point precisely at galaxies. With 5,000 fibers, it can collect light from 5,000 galaxies at a time. These fibers will pass the galaxy light to a spectrograph, and researchers will use this information to precisely determine each galaxy's three-dimensional position in the universe.

Lawrence Berkeley National Laboratory is managing the DESI experiment, and Fermilab is making four main contributions: building the instrument's barrel, packaging and testing charge-coupled devices, or CCDs, developing an online database and building the software that will tell the fibers exactly where to point.

The barrel is a structure that will hold DESI's six lenses. Once complete, it will be around 2.5 meters tall and a meter wide, about the size of a telephone booth. Fermilab is assembling both the barrel and the structures that will hold it on the telescope.

"It's a big object that needs to be built very precisely," said Gaston Gutierrez, a Fermilab scientist managing the barrel construction. "It's very important to position the lenses very accurately, otherwise the image will be blurred."

DESI's spectrograph will use CCDs, sensors that work by converting light collected from distant galaxies into electrons, then to digital values for analysis. Fermilab is responsible for packaging and testing these CCDs before they can be assembled into the spectrograph.

Fermilab is also creating a database that will store information required to operate DESI's online systems, which direct the position of the telescope, control and read the CCDs, and ensure proper functioning of the spectrograph.

Lastly, Fermilab is developing the software that will convert the known positions of interesting galaxies and quasars to coordinates for the fiber positioning system.

Fermilab completed these same tasks when it built the Dark Energy Camera (DECam), an instrument that currently sits on the Victor Blanco Telescope in Chile, imaging the universe. Many of these scientists and engineers are bringing this expertise to DESI.

"DESI is the next step. DECam is going to precisely measure the sky in 2-D, and getting to the third dimension is a natural progression," said Fermilab's Brenna Flaugher, project manager for DECam and one of the leading scientists on DESI.

These four contributions are set to be completed by 2018, and DESI is expected to see first light in 2019.

"This is a great opportunity for students to learn the technology and participate in a nice instrumentation project," said Juan Estrada, a Fermilab scientist leading the DESI CCD effort.

DESI is funded largely by the Department of Energy with significant contributions from non-U.S. and private funding sources. It is currently undergoing the DOE CD-2 review and approval process.

"We're really appreciative of the strong technical and scientific support from Fermilab," said Berkeley Lab's Michael Levi, DESI project director.

Diana Kwon

Editor's note: The DESI collaboration meeting takes place at Fermilab from May 27-29.

Photos of the Day

Growing sumac

A sumac bush grows near the Lederman Science Center. Photo: Leticia Shaddix, PPD
Look closely, and you'll see very young sumac leaflets emerging from the sumac bud. Photo: Leticia Shaddix, PPD
In the News

Eight things to know as the Large Hadron Collider breaks energy records

From Forbes, May 21, 2015

The big news story in high-energy physics at the moment is the news that the Large Hadron Collider (LHC) is finally colliding protons at something close to the energy it was designed for. This comes after a couple of years of operation at half the intended energy, after some components failed on the initial start-up, followed by a couple of years of down time as they pulled everything apart and replaced the faulty connections.

I am very much not a particle physicist, but given the wide interest in the LHC generally, I figured it would be worth a post on a few of the things people might be wondering about as the LHC begins colliding protons at 13 TeV.

Read more

From the Accelerator Physics Center

Progress towards muon accelerator capabilities

Mark Palmer

Mark Palmer, director of the Muon Accelerator Program, wrote this column.

Last week, as part of the Muon Accelerator Program (MAP) Spring Collaboration Meeting at Fermilab, many of us were privileged to hear a seminar by Nobel laureate Carlo Rubbia. He described his vision for developing muon accelerator capabilities in support of a muon-based Higgs factory. A major thrust of his seminar was to emphasize the need to complete a demonstration of muon ionization cooling.

Muon ionization cooling is a method to reduce the transverse and longitudinal sizes of a muon beam to the dimensions required for future muon accelerators. For the past three years, the MAP collaboration has targeted the key demonstrations required to realize muon ionization cooling. This has included extensive design and simulation of cooling channel concepts capable of providing the performance required for neutrino factories and muon colliders; development of radio-frequency (RF) cavities that can reliably operate in the strong magnetic fields of a cooling channel; tests of those cavity designs in the MuCool Test Area (MTA) at Fermilab; and prototyping and construction of RF cavities and magnets for an initial demonstration of ionization cooling at the Muon Ionization Cooling Experiment (MICE).

Over the last several months, crucial progress has been made in our preparations for the MICE demonstration, which is based at the Rutherford Appleton Laboratory in the UK. This international effort will provide the first operational demonstration of the integrated beam optics and RF hardware required for an actual cooling channel suitable for a muon accelerator complex.

MICE will be ready to begin commissioning for the first of two major rounds of experimental studies early next month. Through mid-2016, the experiment will study the performance of absorber materials proposed for muon cooling channels. These studies will provide important data with which we can refine our detailed models of the cooling process. After approximately one year of experimental time in this configuration, the cooling channel will be extended to include a pair of RF modules (which comprise cavities and associated instrumentation) to reaccelerate the muons, as well as an additional focusing magnet to complete the cooling channel optics. Data in the final configuration will be obtained starting in mid-2017.

Here at Fermilab, a critical MICE milestone was passed earlier this month: a prototype RF module achieved stable operation in the magnetic field of the MTA test magnet with a nominal gradient of 11 megavolts per meter, exceeding the MICE specification of 10.3 MV/m. (The gradient is one measure of how effectively a cavity can transfer energy to a particle beam.) In the MICE cooling channel, each RF module sits adjacent to a focus coil magnet. For our test in the MTA, the cavity was placed adjacent to our test magnet, the original prototype for the focus coil, which is capable of producing a 5-Tesla field in its bore. On May 5, we informed DOE that the module acquired more than 3 million pulses in the tested configuration, with no breakdown events.

The excellent results are testament to the careful work that went into preparing the MICE module. The cavity was prepared with an electropolished surface, as is commonly used for superconducting RF cavities, at Lawrence Berkeley National Laboratory. The LBNL group also simulated key aspects of the cavity's performance in magnetic field. In the MTA, a team from Berkeley Lab, Fermilab, the Illinois Institute of Technology, Rutherford Appleton Lab and the University of Strathclyde carried out the prototype test program.

The path is now clear to complete construction of the remaining MICE RF hardware and obtain the first cooling demonstration data by 2017.

In order to mark the start of the detailed study of ionization cooling with MICE, RAL will host a special public science event on June 25.

The prototype MICE 201-megahertz RF module, with the copper cavity mounted, is shown during assembly at Fermilab. A titanium nitride-coated beryllium window covers the cavity iris. The six tuner arms, attached to the cavity body, provide roughly 400 kilohertz of tuning range. Photo courtesy of Y. Torun, IIT
In Brief

Science Next Door June newsletter now online

The June edition of Science Next Door, Fermilab's monthly community newsletter, is now available online. View it or subscribe to get the latest about the laboratory's public events, including tours, lectures, arts events and volunteer opportunities.

Safety Update

ESH&Q weekly report, May 25

This week's safety report, compiled by the Fermilab ESH&Q Section, contains no incidents.

See the full report.

In the News

Retired Chicago physicist's Nobel Prize up for auction, $325,000 to start

From Chicago Tribune, May 26, 2015

A retired experimental physicist has put up his 1988 Nobel Prize for auction, and the minimum bid is $325,000.

"The prize has been sitting on a shelf somewhere for the last 20 years," 92-year-old Leon Lederman said in a phone conversation from his home in eastern Idaho. "I made a decision to sell it. It seems like a logical thing to do."

The online auction being conducted by Nate D. Sanders Auctions closes Thursday evening, but only when the final bid has stood unchallenged for half an hour.

Read more