Information for Researchers
The Cold Atom Lab (CAL) is a multi-user facility for the study of degenerate quantum gases in the microgravity environment of the International Space Station (ISS). CAL will be designed to be a simple but versatile experimental facility, capable of producing ultra-cold samples of several atomic species and loading them into optical lattices, very weak magnetic traps, or into a freefalling state, and studying them under a variety of conditions. CAL will also be designed to be upgradable to meet the needs of specific future investigations.
An initial NASA Research Announcement (NRA) was released on July 13 (http://coldatomlab.jpl.nasa.gov/news/FunPhysicsResearch/) to solicit investigations related to the CAL. The selections were made in 2014 for the first set of flight investigators.
Overview of the Instrument
The Cold Atom Laboratory will be a compact, atom-chip based apparatus, capable of trapping both Rubidium (87Rb) and Potassium (either 39K or 41K), and of producing degenerate gases of each species, or of mixtures of Rb and either of the K isotopes, after a few seconds of collection and cooling. The atom chip approach is chosen because of power and volume constraints, though for many applications investigators may transfer the atoms into either a weak trap away from the chip, or into an optical lattice. CAL will launch in June 2017, in a foam-lined soft stowage cargo bag in an as yet to be named launch vehicle. After it is delivered to the station, astronauts will install it in an EXPRESS rack inside 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 (P.I.'s). The phase one mission duration will last up to 36 months dedicated to flight P.I. 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 PI's within several weeks of collection. Short periods of near real-time operation will also be available if desired.
A summary of the Cold Atom Laboratory mission objectives:
- CAL will be a multi-user facility for the study ultra-cold quantum gases in the microgravity environment of the International Space Station;
- CAL will study Rb87, K39 and K41, and interactions between mixtures of Rb and either of the K isotopes;
- CAL will study delta-kick cooling techniques to produce samples with residual kinetic energy below 100 pK and free expansion times greater than five seconds; and
- CAL will study the properties of 87Rb, 39K, and 41K quantum gases loaded into optical lattices, in the presence of external magnetic fields tuned near interspecies and single species Feshbach resonances.
Additional features of the CAL system include the ability to image samples at high resolution through a window in the optical chip; with separate, wide field-of-view imaging also available. In each case standard absorption imaging will be utilized. Preparations of samples of atoms in arbitrary mixtures of internal states are facilitated by adiabatic rapid passage and microwave hyperfine state control. Table 1 gives the preliminary specifications of the facility.
|87Rb Condensate number||>200000|
|41K Condensate number||>100000|
|39K Condensate Number||>100000 at a phase space density one half of that needed for Bose-Einstein Condensation|
|Condensate Lifetime||>10 Seconds|
|Bragg Beam / Atom Interferometer||0.75 mm diameter at 785 nm|
|Magnetic Field Bias||Variable up to 90 G|
|Feshbach Fields||Switching >2 G in less than 1 ms|
|Imaging resolution through atom chip window||<3 micron|
|Imaging resolution for imaging expanded samples||<20 micron|
Table 1. Preliminary performance specifications of the CAL facility
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.
The Atom Chip
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, 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 microns 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 P.I.'s will have input into this design.
Figure 1 "Dimple" trap wire configuration