ADwin-Pro-II Real-Time Data Acquisition & Control
CAS DataLoggers provided the data acquisition and control solution for a professor of physics, specifically focusing on cold atom physics at a major university. They began running an experiment producing ultracold quantum gases containing either bosons and fermions. The experiment took place under high vacuum inside a pyrex glass cell. Researchers collected the atoms in a magneto-optical trap (MOT) which consisted of 6 laser beams for each atomic species and a magnetic trap produced by two external coils with counter propagating current. While the MOT was on, bright purple LEDs caused light-assisted desorption of atoms from the walls of the cell so that they could be captured in the MOT.
After a brief moment of optical molasses (with the lasers on but no magnetic field), the atoms were gently transported vertically about 5 cm to within 200 μm of a magnetic chip trap by changing the shape of the magnetic field with additional energized coils. Current passing through a wire on the chip, along with external coils, was used to tightly trap the atoms. Radio frequency signals passed through another wire on the chip, which changed the shape of the trap and allowed the hottest atoms to escape, thus lowering the average energy of the ultracold atoms. This evaporative cooling could produce quantum degenerate gases, Bose-Einstein condensates or degenerate fermions. To undertake this incredibly demanding application, the physics department needed a modular data acquisition and control system capable of highly-accurate measurements in real-time with precise control of ramping analog outputs.
The research team installed an ADwin-Pro-ll Real-Time Data Acquisition and Control System to provide them with precise timing and deterministic control of the experiment’s processes. The ADwin system’s analog outputs were used to control current in the coils and wires on the chip and the frequencies and amplitudes of the lasers. Additional analog outputs were programmed to step, ramp, or follow an S-shaped curve as desired. Easy programming of the ADwin Pro-ll’s analog channels provided a simple way to control many devices in the lab. The digital channels were used to open shutters, trigger frequency sources, flip polarity of current sources, and trigger cameras. Several digital channels were also used to serially program frequency sources and for pattern generation outputs. Signals from the digital channels went to a digital buffer consisting of optical isolators to prevent ground loops in the system.
The ADwin-Pro-ll data acquisition system came housed in a 19’ rack-mountable enclosure. The system featured up to 480 analog inputs, digital I/Os or a combination of these, and was also available in half and quarter rack sizes with DC powered versions also available. Different I/O modules allowed the ADwin-Pro-ll to be configured as needed for specific uses. Communication with the host PC is via 100 Mbps Ethernet. Plug-in boards supported analog and digital I/Os, counter/timers, PWM signals, thermocouples, and RTD’s, 5B or 8B signal conditioning modules, serial, CAN, and Fieldbus communication. The ADwin-Pro-ll’s high-performance ZYNQ ARM processor with its own local memory handled system management, data acquisition, on-line processing and control of outputs. Processing of each measurement could occur immediately after each acquisition.
For some cold atom physics experiments, the researchers chose to transfer these cold atoms from the magnetic chip trap to an optical dipole trap – crossed laser beams which caught the atoms as the chip trap was turned off. This purely optical trap gave experimenters the freedom to adjust the external magnetic field as they pleased, giving them the ability to address Feshbach resonances and to tune the interactions between the atoms. To image the atoms at the end of an experiment, the trap was turned off, the cloud expanded, and a pulse of laser light cast a shadow of the atoms onto a CCD camera. From the size, shape, and density of the shadow, the team could determine the cloud’s physical properties.
The ADwin-Pro-ll’s user-friendly software offered the research team powerful capabilities. With ADbasic, users defined the processing sequences being executed on the ADwin hardware. After being loaded on the ADwin system by ADbasic or a graphical PC user interface, the real-time processes executed independently of the PC. ADbasic contained the functions to access all inputs and outputs as well as functions for floating-point operations, process control and communication with the PC. A library was provided which contained standard functions, e.g. for filtering, various examples for counter use, closed-loop controllers, function generators, etc. which led to a faster program implementation.
Every aspect of this cold atom physics experiment required the precise control provided by the ADwin-Pro-ll system. Voltage controlled acousto-optical modulators altered the frequency and amplitude of the laser light, while seven external coils, as well as wires on the chip, created the magnetic field. The way these magnetic fields switched on and off was important to maintain the temperature of the cloud. The team used voltage-controlled power supplies to control the current through these coils and wires. Other equipment including radio and microwave frequency sources, shutters and cameras required well-timed triggers.
Integration with MATlab and Simulink provided another means to configure the ADwin. Due to the innate, fast compile time, experiment parameters could be rapidly modified to suit the researchers’ goals as frequently as they desired. Compile times for new settings were measured in seconds, not hours.
The university’s physics department benefitted in several important ways following installation of the ADwin-Pro-ll Real-Time Data Acquisition and Control System. Using up to 480 analog/digital I/O inputs and a high-performance ARM processor, the ADwin-Pro-ll system performed real-time measurements with extremely high accuracy and also performed all the necessary control functions for the experiment with the precision required. The system’s modular design offered researchers the flexibility to configure and expand the system as the research experiments grew. Additionally, ADwin’s intuitive ADbasic and ADTools software added visualization, graphing and display features and ensured that the experiment continued uninterrupted independent of the PC operating system.
For further information on the ADwin Real-Time Data Acquisition and Control System, other data acquisition devices, or to find the ideal solution for your application-specific needs, contact a CAS Data Logger Application Specialist at (800) 956-4437 or request more information.