A novel VME based mSR data acquisition system at PSI T. Prokscha a,Ã , R. Scheuermann a , U. Hartmann b , A. Raselli a , A. Suter a , A. Amato a , G.J. Nieuwenhuys a,c , A. Dijksmann b , F. Ga ¨ rtner b , U. Greuter b , S. Mutter b , N. Schlumpf b , E. Morenzoni a a Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland b Laboratory for Particle Physics, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland c Kamerlingh Onnes Laboratory, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands article info Keywords: Data acquisition VME abstract A new data acquisition system (DAQ) for bulk mSR and low-energy mSR (LE-mSR) has been developed at PSI. It is based on commercial and in-house VME modules, and on the MIDAS DAQ software library. The system is able to cope with the different needs of the various PSI mSR spectrometers, which was not possible with the existing CAMAC and ORTEC’s pTA-clock based DAQ systems. The VME clock is a 64-channel CAEN V1190 TDC, using the CERN HPTDC chip, with programmable time resolution of 25, 100, 200 or 800 ps. The TDC onboard memory is continuously read through the VME bus by standard PC’s or dedicated servers, using a 1-Gbit/s SIS3100/1100 VME–PCI interface. Detector rates are independently monitored using a 32-channel SIS3820 scaler module. In-house developed modules comprise an 8-channel constant fraction discriminator CFD950, a CD950 clock divider, an 8-channel linear fan-out SP950, a 16-channel NIM-ECL level converter LC950, and a programmable coincidence module FC950. All modules feature a superior performance compared to commercially available devices which allows their use also in the planned high-field mSR spectrometer where a time resolution of about 100ps is envisaged. A special external hardware logic is no longer required, since the system can deal with a rate total of 5 MHz which is sufficient for mSR spectrometers with high event rate in their active veto systems. & 2008 Elsevier B.V. All rights reserved. 1. Introduction The development of new experimental techniques generally requires the application of new data acquisition hardware and software. At PSI the upgrade program of the low-energy mSR (LEM) facility in the new mE4 area with an about one order of magnitude larger muon flux [1] demanded a change from the slow CAMAC based data acquisition system (DAQ) to faster electronics which allows the event-by-event recording at a rate of more than 1000/s without dead time losses. At the same time it was highly desirable to merge the DAQ systems of the bulk-mSR and LEM facility, with the new system being flexible and extendable in order to cope with the needs of future mSR instrument develop- ments at PSI including the capability of event-by-event data taking for test and debugging purposes. In particular, the novel DAQ should be suited for the new high-field mSR spectrometer with a field up to 10T which requires a time resolution of the detecting system of about 100ps. Furthermore, the DAQ system should have the event logic completely in software, thus avoiding the complications of a hardware solution when modifying or extending the event logic. The DAQ readout should be fast enough to handle the high total rates (up to MHz) of the active veto systems of the bulk-mSR instruments solely in software. A VME based DAQ system can fulfill all the requirements. A detailed evaluation of commercially available hardware showed that only a combined solution of commercial modules and application specific in-house modules appeared to guarantee the specified performance. Concerning input and output signals we decided to use both ECL and NIM levels. 2. Commercial VME modules The identification of a new mSR clock has been a crucial item. The new mSR clock is specified as follows: a timing resolution of 100 ps or less, with a long data window of up to 20 ms and a large number (416) of individual channels in one module to allow usage for larger segmented spectrometers and additional time-of- flight applications. The hitherto used CAMAC time-to-digital converter (TDC) LRS4208 of LeCroy and the ORTEC pico-second time analyzer pTA 9308 are either too slow for readout, no more available and with a too poor timing resolution of 1 ns (LRS4208), or limited in rate handling and expandability (pTA 9308: total rate must be less than 100kHz, limited to 16 detector tags). An ideal ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/physb Physica B 0921-4526/$ - see front matter & 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2008.11.206 Ã Corresponding author. Tel.: +4156 310 4275; fax: +4156 310 3294. E-mail address: thomas.prokscha@psi.ch (T. Prokscha). Physica B 404 (2009) 1007–1009