ISS Utilization: CAL
ISS Utilization: CAL (Cold Atom Laboratory)
The CAL instrumentation, developed at NASA/JPL (Jet Propulsion Laboratory), Pasadena, California, will probe the wonders of quantum physics when it launches to the International Space Station. The CAL facility recently hit a milestone of making an ultra-cold quantum gas with potassium, a high-tech feat that puts it on track for launch next year. The planned flight to space is in August 2017. 1) 2)
"Studying gases that have been cooled down to extreme temperatures is key to understanding how complexity arises in the universe, and allows us to test the fundamental laws of physics in a whole new way," said Robert Thompson, project scientist for the Cold Atom Laboratory at JPL.
Researchers with CAL are interested in a state of matter called a Bose-Einstein Condensate (BEC), which happens when all the atoms in a very cold gas have the same energy levels. Like dancers in a chorus line, the atoms become synchronized and behave like one continuous wave instead of discrete particles.
On Earth, gravity limits how long scientists can study Bose-Einstein condensates because this form of matter falls to the bottom of any apparatus used to study it. In microgravity, such condensates can be observed for longer periods of time. This would allow scientists to better understand the properties of particles in this state and their uses for tests of fundamental physics. Ultra-cold atoms in microgravity may also be key to a wide variety of advanced quantum sensors, and exquisitely sensitive measurements of quantities such as gravity, rotations and magnetic fields.
Using lasers, magnetic traps and an electromagnetic "knife" to remove warm particles, CAL will take atoms down to the coldest temperatures ever achieved.
In February 2015, the team created their first ultra-cold quantum gas made from two elemental species: rubidium and potassium. Previously, in 2014, CAL researchers made Bose-Einstein condensates using rubidium, and were able to reliably create them in a matter of seconds. This time, the cooled rubidium was used to bring potassium-39 down to ultra-cold temperatures.
"This marked an important step for the project, as we needed to verify that the instrument could create this two-species ultra-cold gas on Earth before doing so in space," said Anita Sengupta, the project manager for CAL, based at JPL. "We were able to cool the gases down to about a millionth of a degree Kelvin above absolute zero, the point at which atoms would be close to motionless," said JPL's David Aveline, the CAL testbed lead.
That sounds inconceivably cold to mere mortals, but such temperatures are like tropical beach afternoons compared to the ultimate goal of CAL. Researchers hope to cool atoms down to a billionth of a degree above absolute zero when the experimental facility gets to space.
One area of science to which CAL will contribute is called Efimov physics, which makes fascinating predictions about the ways that a small number of particles interact. Isaac Newton had fundamental insights into how two bodies interact — for example, Earth and the moon — but the rules that govern them are more complicated when a third body, such as the sun, is introduced. The interactions become even more complex in a system of three atoms, which behave according to the odd laws of quantum mechanics.
Under the right conditions, ultra-cold gases that CAL produces contain molecules with three atoms each, but are a thousand times bigger than a typical molecule. This results in a low-density, "fluffy" molecule that quickly falls apart unless it is kept extremely cold.
"The way atoms behave in this state gets very complex, surprising and counterintuitive, and that's why we're doing this," said Eric Cornell, a physicist at the University of Colorado and the National Institute of Standards and Technology, both in Boulder, and member of the CAL science team. Cornell shared the 2001 Nobel Prize in physics for creating Bose-Einstein condensates.
At a recent meeting at JPL, researchers associated with the mission gathered to discuss ongoing developments and their scientific goals, which range from dark matter detection to atom lasers. They included Cornell, who, along with co-investigator Peter Engels of Washington State University, is leading one of the CAL experiments. "CAL science investigators could open new doors into the quantum world and will demonstrate new technologies for future NASA missions," said CAL Deputy Project Manager Kamal Oudrhiri at JPL.
The CAL (Cold Atom Laboratory) project office is at JPL, which is developing the instrument in-house. CAL is a joint partnership of JPL, NASA's International Space Station Program Office at theJSC ( Johnson Space Center) in Houston, and the Space Life and Physical Sciences Branch at NASA HQ. The CAL Project Scientist is Rob Thompson at NASA/JPL.
Figure 1: JPL's David Aveline and Anita Sengupta are seen with the physics package for the Cold Atom Laboratory, which includes a vacuum chamber where ultra-cold quantum gases are made (image credit: NASA/JPL-Caltech)
Background: The quest for ever colder temperatures has been a major theme of physics for over a century, leading to such breakthroughs such as the discovery of superfluidity and superconductivity, and more recently to the development of laser cooling techniques and the observation of dilute atomic-gas BECs (Bose-Einstein Condensates) and super-fluid Fermi gases.
Beyond the great interest in the scientific aspects of these phenomena, these advances have also been at the heart of several important devices from SQUIDS (Superconducting Quantum Interference Devices) to lasercooled atomic clocks and atom interferometer-based sensors such as a gravity gradiometer for global gravity mapping.
The 2011 NRC (National Research Council) Decadal Survey report, "Recapturing a Future for Space Exploration, Life and Physical Sciences Research for a New Era," recommended a set of high priority areas in Fundamental Physics which includes research related to the physics and applications of quantum gasses. The Cold Atom Laboratory (CAL) will be a multi-user facility designed to study ultra-cold quantum gases in the microgravity environment of the International Space Station (ISS). One of the primary goals of this facility will be to explore a previously inaccessible regime of extremely low temperatures where interesting and novel quantum phenomena can be expected.
CAL will be a facility for the study of ultra-cold quantum gases in the microgravity environment of the International Space Station (ISS). It will enable research in a temperature regime and force free environment that is inaccessible to terrestrial laboratories. In the microgravity environment, up to 20 second long interaction times and as low as 1 pK (1 picokelvin) temperatures are achievable, unlocking the potential to observe new quantum phenomena. The CAL facility is designed for use by multiple scientific investigators and to be upgradable/maintainable on orbit. CAL will also be a pathfinder experiment for future quantum sensors based on laser cooled atoms.
Science mission objectives:
The CAL science mission objectives are derived from the microgravity decadal survey. CAL utilizes the microgravity environment of the International Space Station (ISS) to form, create, and study ultra-cold quantum gases. CAL will be a technology and science pathfinder mission with the first ever demonstration of the following areas:
• Laser cooling of Rubidium (Rb) in a space environment
• Laser cooling of Potassium (K) in any microgravity environment
• Dual species laser cooling in a space environment
• Magnetic trapping in a space environment
• Evaporative cooling in a space environment
• BEC (Bose Einstein Condensate) in a space environment
• Degenerate Fermi gas in any microgravity environment
• Dual species degenerate gases, both Bose-Bose and Bose-Fermi in any microgravity environment
• Delta-kick Cooling to temperatures below 100 pK (pico Kelvin)
• Interaction times greater than 5 seconds
• Atom interferometry in a space environment.
As CAL is a multi-used facility, it will allow the scientific community to propose experiments using the instrument with the following over-arching capabilities:
• Study dual species degenerate gases, both Bose-Bose and Bose-Fermi in microgravity
• Study 87Rb, 3941K and 40 K, and interactions between mixtures with residual kinetic energy below 100 pK with free expansion times greater than 5 seconds.
• Study the properties of quantum gases in the presence of external magnetic fields tuned near interspecies or single-species Feshbach resonances.
• Demonstrate atom interferometry with a Bragg beam
• Demonstration of Delta-Kick Cooling and Evaporative Cooling in a space environment.
Figure 2: CAL Mission architecture (image credit: NASA/JPL)
• March 6, 2017: In the summer 2017, an ice chest-sized box will fly to the International Space Station, where it will create the coolest spot in the universe. Inside that box, lasers, a vacuum chamber and an electromagnetic "knife" will be used to cancel out the energy of gas particles, slowing them until they're almost motionless. This suite of instruments is called the Cold Atom Laboratory (CAL), and was developed by NASA's Jet Propulsion Laboratory in Pasadena, California. CAL is in the final stages of assembly at JPL, ahead of a ride to space this August on SpaceX CRS-12. 6)
Figure 3: Left: The image (science module) shows the vacuum chamber installed inside a magnetic shield. Right: The image (science instrument) is the quad locker that contains the electronics, lasers, and science module (image credit: NASA/JPL)
• May 19, 2016: The Atom Interferometer enabled flight vacuum assembly has arrived at JPL for system integration and test. This unit will use laser pulses to split and recombine atomic wave packets and to measure the quantum interference of the matter waves. The purpose is to demonstrate the technology and techniques needed for these space-based sensors to probe for dark matter and to test quantum mechanics and Einstein's equivalence principle. 7)
• January 29, 2014: NASA's Physical Science Research Program will fund seven proposals, including one from NASA's Jet Propulsion Laboratory, Pasadena, Calif., to conduct physics research using the agency's new microgravity laboratory, which is scheduled to launch to the International Space Station in 2017. 8)
The chosen proposals came from research teams, which include three Nobel laureates, in response to NASA's research announcement NNH13ZTT002N: "Research Opportunities in Fundamental Physics." The following proposals will receive a total of about $12.7 million over a four- to five-year period:
- Dan Stamper-Kurn, University of California, Berkeley, "Coherent magnon optics"
- Jason Williams, Jet Propulsion Laboratory, "Fundamental Interactions for Atom Interferometry with Ultracold Quantum Gases in a Microgravity Environment"
- Eric Cornell, University of Colorado, Boulder, "Zero-G Studies of Few-Body and Many-Body Physics"
- Nathan Lundblad, Bates College, "Microgravity dynamics of bubble-geometry Bose-Einstein condensates"
- Georg Raithel, University of Michigan, Ann Arbor, "High-precision microwave spectroscopy of long-lived circular-state Rydberg atoms in microgravity"
- Nicholas Bigelow, University of Rochester, "Consortium for Ultracold Atoms in Space"
- Cass Sackett, University of Virginia, Charlottesville, "Development of Atom Interferometry Experiments for the International Space Station's Cold Atom Laboratory".
NASA/JPL is developing the Cold Atom Laboratory. The facility is managed by the International Space Station Program at NASA's Johnson Space Center in Houston, Texas.
• Oct. 18, 2013 (update): NASA has set a due date for proposals submitted to the NASA Research Announcement (NRA) NNH13ZTT002N, entitled "Research Opportunities in Fundamental Physics." The deadline for the receipt of proposals has changed from October 16, 2013, to November 5, 2013. — Initial (July 13, 2013): NASA has released a Research Announcement entitled "Research Opportunities in Fundamental Physics." This NRA solicits research proposals from Principal Investigators from U.S. institutions to participate in NASA's Cold Atom Laboratory (CAL) facility on the International Space Station (ISS). CAL is a multi-user facility designed to study ultra-cold atoms and degenerate quantum gases in microgravity. 9)
• The 2011 NRC (National Research Council) Decadal Survey report, "Recapturing a Future for Space Exploration, Life and Physical Sciences Research for a New Era," recommended a set of high priority areas in Fundamental Physics which includes research related to the physics and applications of quantum gasses.
Launch: CAL is manifested on a Dragon logistics flight of SpaceX-12 to the ISS on a FT Falcon-9 vehicle in a PCV (Pressurized Cargo Vehicle) in soft-stowage. The launch site is KSC (Kennedy Space Center) LC-39A, Cape Canaveral, FL (Ref. 3).
Orbit: Near circular orbit, altitude of ~ 400 km, inclination = 51.6º.
After docking with the ISS, the CAL payload will be installed by astronauts into an EXPRESS (EXpedite the PRocessing of Experiments to Space Station) Rack inside the the U.S. Destiny module, a pressurized "shirt-sleeves" laboratory aboard the ISS. CAL will take up the entire top half of one EXPRESS rack. Once installed, there will be no further astronaut involvement; the instrument is operated remotely from the ground via sequence control. Test sequences will be developed by the CAL operations team in conjunction with Principal Investigators (PIs). The phase one mission duration will last up to 36 months dedicated to flight PI led research. An extended mission of up to five years is expected, with upgrades to the facility possible. Data will be downloaded and distributed to PIs within several weeks of collection. Short periods of near real-time operation will also be available if desired.
Figure 4: Installation into the EXPRESS Rack with docking with ISS Sequence Control Operation from JPL (image credit: NASA)
CAL (Cold Atom Laboratory) instrumentation
The CAL instrument utilizes COTS (Commercial Off The Shelf ) hardware and software to enable a rapid development. This ensures launch to the ISS in 2017. In Figure 5, CAL is shown in its quad lock configuration. On the left are the electronics components, which are cooled with liquid heat exchangers to maintain a safe operational temperature. On the right is the science module and laser assembly. Fiber-optic coupled lasers to simplify optic-mechanical design. Forced convection with fans is used to cool the lasers and science module. On the right is the science module, which is the heart of the CAL instrument. It is encased in a magnetic shield to attenuate the the magnetic field of the earth, which varies over the course of the orbit A more detailed image of the science module is shown in the lower figure. Note the 2D and 3D laser cooling stages, optical mounts, and structure. 10) 11)
The CAL facility is designed with a modular approach, which allows for greater reliability, as it can be maintained by the astronauts, but which also offers the possibility of upgrading its capabilities. Potential upgrades could include (but are not limited to) new laser modules, new electronic components, or a new physics package (which consists of vacuum system, atom chip and associated magnetic field control, along with the optical beam delivery apparatus. PI's would be expected to assist in the specification of potential upgrades, but the engineering effort would be funded separately.
Figure 5: Illustration of the CAL instrument (image credit: NASA/JPL)
Figure 6: Left: The CAL science module with magnetic shield and right: the CAL science module without magnetic shield (image credit: NASA/JPL)
Ballistic expansion of a cold atom cloud: In CAL's Ground Testbed, a vapor of rubidium (Rb) atoms is laser cooled, magnetically trapped, transported into an atom chip trap, and then evaporatively cooled down to nanoKelvin (nK) temperatures. These ultra cold atoms are then released and observed to fall due to gravity (in terrestrial experiments such as this one). During its fall, this thermal atom cloud expands due to its finite temperature. We image the atoms with a pair of laser beam flashes; the first flash captures a "shadow" of the atom cloud, while the second flash records a reference image. We can then process the images to get the density distribution of the cloud (in these images RED is the most dense while BLACK is zero density). The expansion rate provides a measurement of the temperature of the ultra cold Rb. The snapshots in this clip indicate the time of flight in milliseconds of the dropped cloud in the upper left. The RF (Radio Frequency) is noted in the upper right corner indicating the final value of the RF knife that we applied during forced evaporative cooling. 12)
Figure 7: CAL in Express Rack (front panels removed for clarity), image credit: NASA/JPL
Over the past three decades, much advancement has been made in Earth-based laboratories in reducing the temperature of Bose Einstein Condensate (BEC) to below the condensate temperature. Inherent to these experiments is the application of an intense magneto-optical trap to hold the atoms in place to obtain the required cooling, due to the pull of gravity. Drop tower experiments have also been performed, which is a high quality microgravity environment, but interaction times are limited to less than 1 second. Formation of BECs in space-based experiments can therefore significantly increase interaction time and reduce perturbations that come from applied fields. Specifically, longer observation time for unconfined atoms. Such a space-based laboratory could lead to exploration of unknown quantum mechanical phenomena and the understanding that comes with it. 13)
Figure 8: Condensate atom cloud imaged in the IR with decreasing temperature (image credit: NASA/JPL)
Figure 9: Transition from a particle to wave nature with decreasing temperature (image credit: NASA/JPL)
What is a Bose Einstein Condensate (BEC) ?
Satyendra Nath Bose and Albert Einstein first proposed Bose Einstein Statistics in 1924. They theorized that there are two classes of fundamental particles in the universe, Bosons, and Fermions. Fermions cannot occupy the same quantum state, and therefore follow the Pauli Exclusion Principle. However, Bosons can occupy the same quantum state and therefore can exhibit macroscopic behavior. If a population of Bosons is reduced to a temperature below their condensate temperature, a new state of matter, called a Bose Einstein Condensate (BEC), is formed. Where the population of atoms takes on a wave like nature, eventually the same wave function, and a macroscopic matter wave is observable, as shown in Figure 1. In this state, a BEC exhibits macroscopic quantum behavior. This was proposed by Bose and later created in ground based laboratory experiments by C. Tannoudji, S. Chu, W. D. Phillips, E. A. Cornell, W. G. Ketterle and C. E. Wieman. All these scientists won Nobel prizes for their discoveries and the novel techniques to obtain the BECs.
Formation of the Condensate:
The process of laser cooling is summarized in the image below. The species of interest is exposed to a photon flux tuned to a particular resonance frequency. At resonance the photons impart momentum to the atoms. If the photon frequency is Doppler red-shifted from resonance then only atoms coming towards the laser beams will be affected. Those moving away from the laser will be unaffected by the photon flux. If laser beams are such that they are coming from all directions the atoms will be cooled from all directions. This laser cooling, lowers the atom population temperature to ~100 µKelvin, still above the condensate temperature.
The next stage of cooling is evaporative cooling with an applied Radio Frequency (RF) field. Another unique property of atoms is that for atoms above a certain energy level, when exposed to an RF field, they can be excited and essentially removed from the population, leaving behind only those at a lower energy and therefore population temperature. This is called evaporative cooling and brings the temperature of the population to much below 1 µKelvin (<< 1 µK).
The final stage of cooling is adiabatic expansion. The atoms are held and compressed on an integrated circuit with a precisely tuned magnetic field. When the field is turned off the cloud expands, and cools further. The final stage brings the population to below the nK range, and in the space environment, to the pK (10-12 K) range. The condensate is formed and can live on the order of 20 seconds in microgravity where it can be exposed to other magnetic fields, electric fields, species of condensate, and imaged.
Figure 10: Laser cooling:Formation of the condensate uses a combination of laser and evaporative cooling and adiabatic expansion (image credit: NASA/JPL)
The Atom Chip:
• Compound silicon and glass substrate technology enables both magnetic and optical control of ultra-cold atoms.
• On-window wires enable simultaneous magnetic trapping and optical manipulation.
The CAL atom chip consists of lithographically patterned wires on a silicon substrate, which forms one wall of the CAL science chamber. Currents passing through these wires, in conjunction with external bias fields, allow for the formation of magnetic traps in a variety of configurations. Condensation is typically achieved in a trap in a "dimple" configuration, consisting of a wire pattern in a "z" configuration (Figure 11), with an additional waveguide superimposed on top, as shown in the figure below. Trap frequencies can be adjusted from 50-10,000 Hz, with approximately a 6:1 ratio to radial to axial frequencies. Condensates are typically formed in a tight trap about 100 µm from the atom chip. By ramping down the bias field they can be transported away from the chip's surface into a weaker trap. In Earth's gravity it is possible to move atoms up to 400 microns from the chip's surface; in microgravity this can be extended to greater than 1.0 mm. The exact configuration of the CAL atom chip has not been finalized, and PIs will have input into this design. 14)
Figure 11: "Dimple" trap wire configuration (image credit: NASA/JPL)
Table 1: Behavior of atoms at super-low temperatures (Ref. 6)
The CAL instrumentation is designed to freeze gas atoms to a mere billionth of a degree above absolute zero. That's more than 100 million times colder than the depths of space.
"Studying these hyper-cold atoms could reshape our understanding of matter and the fundamental nature of gravity," said CAL Project Scientist Robert Thompson of JPL. "The experiments we'll do with the Cold Atom Lab will give us insight into gravity and dark energy — some of the most pervasive forces in the universe."
Figure 12: Artist's concept of a magneto-optical trap and atom chip to be used by NASA's Cold Atom Laboratory (CAL) aboard the ISS (image credit: NASA/JPL, Ref. 6)
CAL will provide an opportunity to study ultra-cold quantum gases in the microgravity environment of the space station — a frontier in scientific research that is expected to reveal interesting and novel quantum phenomena.
In CAL's Ground Testbed, a vapor of rubidium (Rb) atoms is laser cooled, magnetically trapped, transported into an atom chip trap, and then evaporatively cooled down to nanoKelvin temperatures. These ultra cold atoms are then released and observed to fall due to gravity (in terrestrial experiments such as this one). During its fall this thermal atom cloud expands due to its finite temperature. We image the atoms with a pair of laser beam flashes; the first flash captures a "shadow" of the atom cloud, while the second flash records a reference image. We can then process the images to get the density distribution of the cloud (in these images RED is the most dense while BLACK is zero density). The expansion rate provides a measurement of the temperature of the ultra cold Rb. The snapshots in this clip indicate the time of flight in milliseconds of the dropped cloud in the upper left. The radio frequency (RF) is noted in the upper right corner indicating the final value of the RF knife that we applied during forced evaporative cooling. 15)
Figure 13: Ballistic expansion of a cold atom cloud, RF cooled atoms dropped (image credit: David C. Aveline, CAL Ground Testbed, JPL)
In CAL's Ground Testbed, a vapor of rubidium (Rb) atoms is evaporatively cooled in an atom chip trap utilizing a radio frequency (RF) "knife" that continuously slices away the hottest atoms. With the hottest atoms removed, the cloud can re-thermalize at a cooler temperature much like a hot cup of tea gets cooler over time as the hottest molecules evaporate. This RF knife's frequency is smoothly ramped down from ~30 MHz down to ~1 MHz. The lower the cut with the RF frequency, the colder and more dense the atom cloud becomes, and if done efficiently it may cross the critical temperature to achieve a Bose-Einstein Condensate (BEC). The snapshots in this clip show the decreasing size (increasing density) and decreasing temperature of the Rb cloud when lower final RF values are applied.
Figure 14: Evaporative cooling with an RF Knife using RF stages (image credit: David C. Aveline, CAL Ground Testbed, JPL)
1) "Cold Atom Laboratory Doing Cool Research," NASA/JPL, March 17, 2016, URL: http://www.jpl.nasa.gov/news/news.php?feature=6162
4) "CAL AScience Poster," URL: https://coldatomlab.jpl.nasa.gov/documents/CAL_sci_poster_0709e.pdf
5) David Aveline and the CAL Team, "The Cold Atom Laboratory: a facility for ultracold atom experiments aboard the International Space Station," APS (American Physical Society) Division of Atomic and Molecular Physics Meeting 2016, abstract #P6.003, May 2016, URL of abstract: http://adsabs.harvard.edu/abs/2016APS..DMP.P6003A
6) "NASA Wants to Create the Coolest Spot in the Universe," NASA/JPL, March 6, 2017, URL: https://www.jpl.nasa.gov/news/news.php?feature=6765
8) "Physical Science Research Proposals Selected for Cold Atom Laboratory," NASA/JPL Press Release, Jan. 30, 2014, URL: https://www.nasa.gov/content/physical-science-research-proposals-selected-for-cold-atom-laboratory
9) "NASA Research Announcement: Research Opportunities in Fundamental Physics," NASA, Oct. 18, 2013, URL: https://coldatomlab.jpl.nasa.gov/news/FunPhysicsResearch/
11) Robert Thompson, Anita Sengupta, David Aveline, James Kohel, "Cold Atom Lab oratory Science Poster," URL: http://coldatomlab.jpl.nasa.gov/documents/CAL_sci_poster_0709e.pdf
12) "Science Measurements," NASA/JPL, URL: http://coldatomlab.jpl.nasa.gov/sciencemeasurements/
13) "Science Background," NASA/JPL, URL: http://coldatomlab.jpl.nasa.gov/sciencebackground/
14) "Information for Researchers,", NASA/JPL, URL: https://coldatomlab.jpl.nasa.gov/scienceresearcher/
15) "Science Measurements," NASA/JPL, URL: https://coldatomlab.jpl.nasa.gov/sciencemeasurements/
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).