RA3. Experimental Equipment - Digital Pixies at HRIBF
(R. Grzywacz [Univ. of Tennessee], spokesperson)
After a succesfull series of experiments[1-9], the nearly decade-old digial-data acquisition sytem based on CAMAC DGF4C boards found its new-generation successor in the Pixie16 modules. These boards were developed and are manufactured by XIA LLC, a Silicon Valley high-tech company who also developed the DGF4C units. The main advantages of the Pixie16-based system are: higher digitization frequency (100MHz), higher channel density (16 ch per board) and implementation of the fast readout (PCI), which enables much higher data throughput than previously used CAMAC-based system. Pixie16 is much better suited to systems with high channel count.
The main task of intergration of the Pixie16 at HRIBF was unertaken by the University of Tennessee researchers and postdocs. The libraries provided by XIA LLC were used in order to build the readout codes. Pixie-generated data-stream is formatted in such a way that it is compatible with the HRIBF's acquisition system. The new analysis codes (including event builder) were written. The software evolved from the original DEC-Fortran code (used with the DGF4C units), to the new C- and C++ based codes with built-in possibility of using either SCAN or ROOT suites for histogramming. A control software was developed using command line and GUI. All Pixie16-based systems use PC computers running Linux operating system.
This new system was already used in several experiments serving a broad range of detectors, including semiconductor, gas and scinitillator detectors. Only parameters of the on-board codes need to be modified to suit particular detector type. The new system proved to be very stable and reliable . Recently Pixie16 was used during the EBSS 2010 Summer School to demonstrate the advantages of digital electronics . Presently at HRIBF the prototype-generation boards Pixie16 Rev A, and a newest type pixie16 Rev D are avialable. The latter uses a revamped internal architecture and a new, more efficient readout scheme.
One example of the experimental application of the Pixie16-based system is in decay-spectroscopy studies at LeRIBSS facility . A purely digital system was used to acquire gamma-ray data from clover detectors and beta decays from fast-plastic scintillator detectors. The main advantage of using the Pixie16 system was the time stamping allowing for flexible-time correlations between decays. Pixie16 was also used at the Recoil Mass Spectrometer (RMS)  in experiments searching for new proton and alpha emitters. These experiments took advantage of the board's capabilities for real-time operations, in particular, the complex-pulse shape-based triggering ability and large data throughput. There are also future plans to employ the Pixie16-based system in super-heavy element research .
Recently significant development was made in exploring the capabilities of using the Pixie16 for fast-timing applications with plastic scintillators of the VANDLE detector system. The timing resolution of 200 ps have been demonstrated using new algorithms [17,18]. Presently a new 500-MHz-based system called Pixie500 is being impleneted at HRIBF for specialized electronic fast-timing applications.
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17. M. Madurga, et al., CAARI 2010, to be published.
18. R. Grzywacz, http://fribusers.org/4_GATHERINGS/2_SCHOOLS/2010/lectures.html.