Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 50 (2017)

Zero suppression performance evaluation of GET electronics
using SπRIT TPC experimental data
G. Jhang,∗1,∗2 J. Barney,∗2,∗3 G. Cerizza,∗2,∗3 J. Estee,∗2,∗3 B. Hong,∗1,∗2 T. Isobe,∗2 M. Kaneko,∗2,∗4M. Kurata-Nishimura,∗2 J. W. Lee,∗1,∗2 W. G. Lynch,∗2,∗3 T. Murakami,∗2,∗4 C. Santamaria,∗2,∗3M. B. Tsang,∗2,∗3 and Y. Zhang∗2,∗5 for the SπRIT collaboration
Zero suppression is of great importance in acquiring
data with a TPC equipped with GET electronics1) because of its huge data size. For example, the SπRITTPC2) has 12,096 channels, which result in an event
size of ∼6.7 MB without zero suppression. With theaverage disk writing rate observed during the ﬁrst series of the SπRIT experiment, ∼60 Hz, data throughput corresponds to ∼402 MB/s.3)
The performance of three diﬀerent types of zero suppression (two hardware and one software types) is evaluated through the software simulation of hardware
zero suppression based on the observation from theexperiment. Below is a brief explanation of the datastructure from the GET electronics. Single channel
data are composed of pairs of ADC and elapsed timefrom the trigger (time bucket, TB). Figure 1 shows
the display of ADC-TB pairs from GET electronics.
In full readout mode, ADC values are sorted sequentially so that TB information is omitted to reduce thedata size. In the zero-suppression mode, however, TB
information is indispensable because only some of theADC-TB pairs are stored. As a result, the data size ofa channel in the zero-suppression mode is greater thanthat in the full readout mode when the threshold is set
to 0.
Hardware zero-suppression mode 1 writes all theADC values in a channel above the threshold. The
data size is greater than the size in the full readout
mode unless the number of ﬁred channels is less thanhalf of the number of total channels. The mean number of ﬁred channels of 132 Sn+124 Sn collision eventsis ∼6900 out of 12,096 with a threshold of 0.05% of
the maximum ADC value. The data size of zerosuppression mode 1 is 114% of the full readout datasize.
Mode 2 writes ADC values above the threshold only.
With the same conditions as those used in mode 1,mode 2 results in merely 14% of the full readout datasize. One disadvantage of this mode is that it is difﬁcult to determine the baseline because the mode removes all the signals below the threshold.
The software zero-suppression mode we designedkeeps 5 more ADC-TB pairs at every crossing pointof the signal to the threshold value. For example, in
∗1
∗2
∗3
∗4
∗5

Department of Physics, Korea University
RIKEN Nishina Center
NSCL and Dept. of Physics and Astronomy, Michigan StateUniversity
Department of Physics, Kyoto University
Department of Physics, Tsinghua University- 171 -Fig. 1 the largest pulse at the center cross the thresholdat 90 TB and 115 TB. The software zero-suppression
mode keeps not only 90∼115 TBs, but also 84∼89 and116∼120 TBs. We also added a feature to reduce thedata size using the fact that ADC-TB pairs above thethreshold are not random but sequential from the pointcrossing the threshold. By writing the ﬁrst TB of thecrossing point and the number of TBs, we could makethe data size 10% smaller than what it would be if we
simply follow the rule of hardware zero suppression.
The data size of software zero suppression is 21% of
the full readout data size. Moreover, the suppression
process is performed after the baseline is determined
and matched to 0. However, the software zero suppression also has disadvantages in that it involves anadditional process after acquiring data and consumes
additional disk space for processing.
In summary, hardware zero-suppression mode 1 will
be extremely useful when only a few tracks are generated. The use of zero-suppression mode 2 is eﬃcientwhen the baseline determination is not a problem. The
software zero suppression is more ﬂexible but requires
computational and storage resources and must be performed oﬄine.

Signal fromGET elecronics

ThresholdFig. 1. Baseline-matched signal from GET electronics (redsolid curve). Zero suppression mode 1 stores complete
curves on the ﬁgure if there exists a part above thethreshold (solid green line). On the other hand, mode
2 stores the parts above the threshold only. Softwarezero suppression stores 5 more ADC-TB pairs at eachcrossing point to the threshold.

References1) E. Pollacco et al.: Physics Procedia 37, 1799 (2012).
2) R. Shane et al.: Nucl. Inst. Meth. A 784, 513 (2015).
3) T. Isob e et al.: In this report.