LAPD Data Acquisition System

The picture above illustrates the LAPD experimental cycle. We start with the detection of a wave, shown is a magnetic pickup loop. The loop is inside the machine and is driven in 3D by computer controlled stepping motors. We then digitize the signal and store the resulting time series on local disk. The probe is them moved to a new location and the process is repeated until a one, two, or three-dimensional dataset is acquired. The data are then moved to workstations which process the raw data and generate anything from line plots to stereo-pair, three-dimensional movies of complicated plasma processes.

The LAPD-U uses a very effective data acquisition system which was recently upgraded. It enables users to control the position of the probes throughout the volume of the machine and to digitize signals applied or received by probes.  The present system has twelve independent digital-to-analog (D/A) channels, which can operate at up to 5 GHz each.  The digitizers reside in a VXI crate and are manufactured by Tektronix.  A second set of 32, slower (100 MHz) digitizers reside in the main lab area and are connected to the data acquisition system by a fiber optic link.  As need arises, more digitizers will be acquired.  The data acquisition system also supports control and data input from GPIB devices.  With the use of VXI switches and D/A conversion, control of external devices is also possible.  The image below shows the data acquisition and control room:

The data acquisition control center has a large monitor (which displays incoming data and machine state information) and smaller monitors to interact with the data acquisition system.  A VXI crate with fast digitizers is in the red rack on the left.  Several other computers control the stepping motors, the lasers and do housekeeping and machine protection.