Rare Isotope data collection is handled by a gas filled, delta-E detector, a set of NIM amplifiers and logic modules, a CAMAC peak holding ADC, a CAMAC multichannel counter and a CAMAC list processor.
A list processor is a CAMAC module which performs CAMAC I/O operations independently of the computer. It contains a large RAM so the data from the I/O operations it performed can be stored.
The detector contains up to six plates for measurement of Etotal, dE1, dE2, dE3, dE4, and dE5.
The analog outputs from the NIM amplifiers, a trigger signal generated by the NIM electronics and gated by a signal from the jumping electronics are fed into the peak holding ADC.
A program is loaded into the list processor by AccelNET and the list processor is enabled. Each time the ADC receives the trigger signal from the NIM electronics it performs a conversion. At the end of the conversion the ADC asserts a LAM signal.
The list processor waits for the LAM from the peak holding ADC to trigger it. Each time the list processor is triggered it runs the program which has been loaded into it.
The program performs a number of CAMAC I/O operations to copy the data from the ADC to the list processor and clear the LAM. It then goes to sleep until the next trigger.
Periodically data collection is paused, and the data collected in the list processor's internal memory are uploaded to the computer.
The rare isotope data collection system uses two channels of the CAMAC multichannel counter.
The ADC trigger signal from the NIM electronics is split and is sent to the ADC and to one channel of the CAMAC counter module. Each time the ADC is triggered the counter is incremented. This provides a count of the number of ADC triggers supplied by the NIM electronics. When the data are uploaded from the list processor this register is read and a parameter containing the total number of ADC triggers is updated.
When the uploaded data are processed the number of events contained in the data block is counted and a parameter containing the total number of events processed by the list processor is updated.
If the ADC is already busy performing a conversion when another trigger is received, a particle event will be missed. By comparing the two numbers one can get an idea of the number of missed events (detector system pileup). Normally the number of missed events is very small, usually less than 0.1% of the total number of events.
Another channel of the counter module is used to count the number of jumping cycles which have occurred. It is connected to a signal from the jumping electronics which causes the counter to increment at the end of each jumping cycle. Each time the list processor is triggered the cycle number is read from the counter and placed in the block of event data. This allows individual events to be stamped with the cycle number in which they occured.
All aspects of rare isotope data collection are controlled by configuration files. Parameters such as the number of channels of data read from the ADC can be changed. This makes it possible to use the system with other types of particle detectors and perhaps use the system for other types of event counting.
For example, a solid state detector requiring only one ADC channel could be used. The program loaded into the list processor would be changed to only retrieve data from a single channel. This has the side effect of allowing more events to be stored in the list processor's memory and decreasing the data collection dead time because a smaller number of CAMAC I/O operations need to be performed.
It is also possible to locate CAMAC hardware needed for other types of experiments in the same CAMAC crate and load different programs into the list processor for the various configurations.