Advanced pulse processing for Time-of-Flight ERD

Department of Physics, University of Jyväskylä, P.O.B. 35, FI-40014 Jyväskylä, Finland
Time-of-flight ERD instrumentation is often based on traditional peak-sensing ADCs and time to amplitude (TAC) converters. An advanced timestamping data acquisition setup for these ADCs allows the monitoring of beam-induced damage and setting the coincidence criteria post-acquisition [1]. The use of gas ionization chambers (GIC) as an energy detector in ToF-ERD has become popular recently. To make the most of the detector, it makes sense to capture not just the pulse height from the anode of the GIC, but full traces of anode, Frisch grid and cathode pulses. The timing and shapes of these pulses can be used to achieve position sensitivity [2] and even particle species discrimination.  A complete data acquisition and pulse processing setup for ToF-ERD in Jyväskylä [3] consists of a fast amplifier, an analog discriminator and a CAEN N6751 digitizer for the time-of-flight and three Amptek CoolFET preamplifiers and a CAEN N6724 digitizer for the GIC. A desktop computer running Linux is connected to the digitizers over a CONET optical link. The computer runs in-house developed acquisition software with a user-friendly graphical user interface built using Qt 5. The software can process the raw events to list data during the acquisition with customizable software algorithms.  In this presentation the used algorithms and software design are described. The time-of-flight digitization is shown to have a <200 ps resolution, which is comparable to a well-tuned CFD+TDC setup and improved hydrogen detection efficiency. By capturing full traces of all signals various effects affecting the detection efficiency, resolution and background can be studied in detail. The digitization of GIC signals is shown to reduce unwanted background by making possible tighter coincidence criteria and rejection of certain events by pulse shape.   

[1] M. Rossi, P. Rahkila, H. Kettunen, M. Laitinen, Nucl. Instrum. Meth. B 347 (2015) 39
[2] J. Julin, M. Laitinen, T. Sajavaara, Nucl. Instrum. Meth. B 332 (2014) 271
[3] M. Laitinen, M. Rossi, J. Julin, T. Sajavaara, Nucl. Instrum. Meth. B 337 (2014) 55