Manufacturing Bits: Oct. 29

Searching for dark energy
The first tests have been conducted on a new cosmic cartography system that will soon search for dark energy and galaxies in the universe.

The system, called the Dark Energy Spectroscopic Instrument (DESI), is a complex unit with 5,000 fiber-optic eyes. The DESI system is mounted on top of the 4-meter Mayall Telescope at the Kitt Peak National Observatory in Arizona.

DESI will measure the effect of dark energy in the universe as well as gather data for millions of galaxies and quasars in the sky. Then, the system will construct 3D maps of the universe spanning 11 billion light years.

This illustration of DESI in the Mayall Telescope dome shows the focal plane and corrector barrel (dark gray) at the top of the telescope and the spectrographs (shown in yellow) below the telescope. (Credit: DESI Collaboration)

The goal is to unravel the mysteries and origins of the universe. In theory, 4.9% of the universe consists of observable matter, such as protons, neutrons and electrons. Then, some 68.3% of the universe is dark energy, while the remaining 26.8% is dark matter.

Dark matter exists in the universe, but it is invisible to the entire electromagnetic spectrum. Thus, researchers have failed to directly observe or detect dark matter.

Dark energy is also an unknown form of energy. It is believed that dark energy is driving the expansion of the universe. Dark energy “is mysterious and acts like a constant energy density associated with empty space (‘the vacuum’) and has negative pressure,” according to the Dark Energy Spectroscopic Instrument (DESI) Web site.

In the works for years, the DESI instrument in 2018 was installed on the Mayall Telescope at the Kitt Peak National Observatory.

The Kitt Peak National Observatory is one of several astronomy facilities supported by the National Science Foundation (NSF) and the Association of Universities for Research in Astronomy (AURA). Recently, NSF and AURA consolidated several astronomy facilities into one organization called NSF’s National Optical-Infrared Astronomy Research Laboratory (OIR Lab).

DESI, one of the critical efforts within the OIR Lab organization, is a large system. DESI’s components, such as the focal plane, corrector barrel and others, weigh 11 tons, according to the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), the lead institution for DESI’s construction and operations.

DESI is installed on the Mayall telescope’s movable arm. This weighs 250 tons. It rises 90 feet above the floor in Mayall’s 14-story dome.

“DESI’s new corrector optics provides a 3-degree-diameter field of view that feeds a focal plate containing 5,000 robotic positioners,” according to DESI’s Web site.

A view of DESI’s fully installed focal plane, which features 5,000 automated robotic positioners, each carrying a fiber-optic cable to gather galaxies’ light. (Credit: DESI Collaboration)

Each positioner holds a fiber-optic cable. “Each of these fiber-toting robots is automatically positioned to fix on a preset sequence of individual galaxies and quasars so that the fibers can collect their light,” according to the site. “The positioners can be reconfigured within 3 minutes to measure the spectra of a new set of galaxies. Optical fibers mounted to the positioners extend 50 meters down the telescope to feed 10 broad-band spectrographs, each containing three detectors. The spectrographs cover a spectral range of 360 nanometers (nm) to 980 nm with a resolution of 2,000 to 5,000, enabling DESI to probe redshifts up to 1.7 for emission line galaxies and 3.5 for the lyman-α spectra from quasars.”

DESI can cycle through a new set of 5,000 galaxies every 20 minutes. The first tests were conducted in October with formal observations slated for early 2020.

“After a decade in planning and R&D, installation and assembly, we are delighted that DESI can soon begin its quest to unravel the mystery of dark energy,” said DESI Director Michael Levi of the Lawrence Berkeley National Laboratory. “Most of the universe’s matter and energy are dark and unknown, and next-generation experiments like DESI are our best bet for unraveling these mysteries.”

Finding dark matter
A European group has disclosed its latest efforts to search and weigh dark matter.

The group is part of the CRESST experiment, which stands for “Cryogenic Rare Event Search with Superconducting Thermometers.” The experiment is being conducted by a European research collaboration headed by the Max Planck Institute for Physics (MPP).

The CRESST experiment is located in an underground laboratory in Italy. It comprises of detectors that react when a dark matter particle impinges on an atomic nucleus in the detector material.

The system makes use of crystals of calcium tungstate. They are cooled to approximately minus 273 Celsius. “Should a particle of dark matter collide with an atomic nucleus in the crystal, it would increase the temperature at that point by about one millionth of a degree,” according to MPP. “This minute change can be measured by a highly sensitive thermometer in the detector. The collision also generates light flashes, which are recorded by another sensor. This second signal reveals the type of particle involved, allowing the scientists to distinguish potential dark matter events from unrelated events.”

Using 10 detectors, CRESST covers the lowest mass range of dark matter. “This is set to change. Starting in 2020, we plan to install 90 more detectors,” said Federica Petricca, group leader at the Max Planck Institute for Physics. “We have been continually improving our experimental setup over the past few years. We are currently the only group able to search in this range. If dark matter manifests itself as a very light particle, CRESST has the best chance of detecting it.”

More dark matter
Another group from Europe is also developing a system to find dark matter.

The group, called ALPS II, is being set up in a tunnel section within a former particle physics accelerator at the Deutsches Elektronen-Synchrotron (DESY) facility in Germany.

The tunnel section will house two 120-meter-long optical cavities. The section will consist of 12 superconducting accelerator magnets on each side of the wall for a total of 24 magnets.

A powerful laser system will produce light. The light is amplified by the cavity inside the magnetic field. The system, which will move into operation by 2021, will look for dark matter particles by making light shine through the wall.