- Email: [email protected]
The layout and performance of the Lund nuclear microprobe trigger and data acquisition system
Nuclear Instruments and Methods in Physics Research B 158 (1999) 141±145
www.elsevier.nl/locate/nimb
The layout and performance of the Lund nuclear microprobe trigger and data acquisition system Mikael Elfman *, Per Kristiansson, Klas Malmqvist, Jan Pallon Department of Nuclear Physics, Lund Institute of Technology, Box 118, SE-221 00 Lund, Sweden
Abstract Recently a new data acquisition system has been installed at the Lund nuclear microprobe facility. The trigger layout for this beam scanning and data acquisition system that support a great variety of simultaneously techniques (PIXE, STIM, RBS, and NRA) is presented in detail. The technical status, total trigger throughput and data ¯ow is described. Examples of typical system performance for PIXE, STIM and RBS obtained during routine runs are discussed. Details on hardware and software speci®cations are given. Ó 1999 Elsevier Science B.V. All rights reserved. PACS: 07.75.H; 07.05.K; 07.05.R; 41.75.A; 07.78; 61.18B Keywords: Acquisition system; Multi-parameter; Multi-detector; Trigger layout; High count-rates
1. Introduction Recently a new data acquisition system has been installed at the Lund nuclear microprobe facility [1]. In the development of a new nuclear microprobe set-up, the data acquisition system is one of the most important parts. Many papers have been written about the subject, where each group have selected their own approach [2±7]. The basic hardware of our new system has earlier been described in [8], and as we discussed there, a high maximum data throughput is needed for certain applications (STIM, RBS, and Secondary Electron Images) with very high count-rates. In this paper
*
Corresponding author. Fax: +46-46-2224709; e-mail: [email protected]
we measure acquisition performance during these high count-rate conditions. The trigger layout for the beam scanning and data acquisition system are discussed. The total trigger throughput, dead time and data ¯ow is measured. Details on hardware and software are described.
2. Data management and performance The acquisition process consists of two dierent modes: ``acquisition computer sort and display mode'' (Note: this mode is normally not used, the data are sorted and displayed with a few seconds delay on the second computer) and ``second computer sort and display mode'' (Normal Event Mode). The measurements on the system were carried out during an actual microbeam run. The
0168-583X/99/$ - see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 9 ) 0 0 4 9 7 - 8
142
M. Elfman et al. / Nucl. Instr. and Meth. in Phys. Res. B 158 (1999) 141±145
PIXE signal was detected with a Kevex Si(Li) detector of 50 mm2 active area and a measured energy resolution of approximately 155 eV at the 5.9 keV Mn Ka peak in 135° angle relative to the beam. By varying the proton beam current the count rate could be changed. The signal was split into four parts and fed into four ADCs with a count rate up to 120 000 c/s each. Each event is tagged with correct digital X, Y value, directly shifted out from the in crate DAC module that controls the beam position. This means that the X and Y coordinates occupy space in the memory for each event. Common for both acquisition modes are that when the in crate buer memory (16 k) is full (or nearly full), a LAM request is generated and the memory buer is emptied through a CAMAC command. Both modes are strongly dependent on the actual processor speed. In this test we used a computer with a 90 MHz PPC processor, the ``acquisition computer sort and display mode'' obviously demands more CPU time and is aected more severely by the lack of available CPU time at high count-rates. By comparing Fig. 1(a) and (b) this eect is seen very clear. A distinct level can be seen in Fig. 1(a), this represents the maximum throughput at an input trigger rate of 7 kHz in all four ADCs at the same time (33 KB/s), but in event mode it still didnÕt reach the maximum transfer rate of 65 kHz (90 KB/s). ItÕs obvious that the buer memory ¯ag has been set (10% of the memory left) and this gives a LAM request to the computer, but there is no available processor time to take care of the request. In the mean time the buer memory sets the ``full'' ¯ag and the CAMAC crate interrupts the acquisition and needs to wait for the computer to empty the memory. This creates the major part of the dead time shown in Fig. 2(a) and (b). The data transfer rates can be increased many times by just changing to an available 350±450 MHz PPC processor. In event mode (Fig. 2(b)) the data throughput is more than double compared to the sort and display mode. When the data are written to the disc it can immediately be sorted on an o line powerful computer, and presented in any way on the second computer. It is possible to change sort conditions and start the sort all over again without aecting
Fig. 1. (a) Data throughput in KB/s in acquisition computer sort and display mode (Note: this mode is normally not used, the data are sorted and displayed with about one second delay on the second computer), (b) Data throughput in KB/s in second computer sort and display mode (Normal Event Mode).
the actual data acquisition; also the data is automatically stored in time sequence. 3. Electronic set up and trigger layout Since the data acquisition system is a multiparameter and multi-detector system, the fast electronic set up includes a user selectable master coincidence trigger facility. By pressing buttons on the LeCroy coincidence units (Fig. 3), one can easily select which of the connected detectors you want triggers from. The energy outputs are pro-
M. Elfman et al. / Nucl. Instr. and Meth. in Phys. Res. B 158 (1999) 141±145
143
coincidence with each other. At the same time the time information is picked o with a zero crossing discriminator and the relative detection time is measured with a time to pulse height converter. The ADCs, gated by the master gate acquire both the energy spectrum and the time spectrum. The number of counts in the coincidence ``time'' peak is directly proportional to the hydrogen concentration. 3.2. The IL and Q system branch The anode signal from the PM tube is fed into a leading-edge discriminator for lower level energy selection, then the signal enters the coincidence unit ± CU which produces the gate for the energy signal. The output with low energy cut o is connected into the ADC. 3.3. The particle elastic scattering analysis (PESA) system branch
Fig. 2. (a) Data throughput (%) in: Acquisition computer sort and display mode (Note: this mode is normally not used, the data are sorted and displayed with about one second delay on the second computer), (b) Data throughput (%) in: second computer sort and display mode (Normal Event by Event mode Mode).
cessed through spectroscopy ampli®ers (Tennelec TC244). The dierent branches are described below. 3.1. The hydrogen system branch When a proton hits a hydrogen atom, particles are emitted at a 90° angle relative to each other. The two SBDs detect both the scattered p and H particles and spectroscopic energy information is extracted from both detectors [9]. The signal generates a trigger if the signal from both SBDs are in
This system is mainly used to measure C, N and O and for that an SBD is used in the backscattering direction. It is also used for NRA (e.g. Boron measurements [10]), and then an annular detector is used. The fast signal from the spectroscopy ampli®er is used to produce the gate for the energy signal and to measure dead time in the system. 3.4. The STIM system branch A collimated windowless photodiode (Hammamatsu S1223-01N 2028 (4 mm2 )) acts as a detector, the signal is ampli®ed by a preampli®er and a spectroscopy ampli®er. The fast count rate signal from the spectroscopy ampli®er is used to create the gate for the energy signal. 3.5. The PIXE system branch This is a typical PIXE standard branch. A Si(Li) (Kevex 50 mm2 active area) acts as a detector at 135° angle to the beam and the Tennelec spectroscopy ampli®er TC454 is used as main ampli®er. The fast count rate signal from the
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M. Elfman et al. / Nucl. Instr. and Meth. in Phys. Res. B 158 (1999) 141±145
Fig. 3. The Lund NMP Trigger layout. PIXE branch: Si(Li) ± Kevex detector of 50 mm2 active area, AMP ± Tennelec spectroscopy ampli®er TC454, TTL/NIM ± TTL to NIM converter, CU ± Lecroy 465 coincidence unit, Gate Gen ± Gate Generator, LOG FI/FO ± Logic Fan in Fan out. STIM branch: DIODE ± windowless semiconductor diode, PA ± pre ampli®er, the rest of the branch similar to PIXE branch. PESA branch: similar to STIM branch. IL branch and Q branch: LE ± leading edge discriminator LeCroy LRS4608C, CI ± charge integrator. H ± system branch: SBD ± surface barrier detector, ZCD ± zero crossing discriminator, TPHC ± ORTEC 467 time to puls height converter. Time branch: pulser ± NIM pocket pulser.
spectroscopy ampli®er is used to create the gate for the energy signal. 4. Conclusions A very fast multi-detector, multi-parameter CAMAC and PPC-processor based data acquisi-
tion system has been developed and tested and is now in routine use at the Lund nuclear microprobe. The system is easy to modify and upgrade and more detectors in the system is fully supported. It currently allows data to be collected, processed and presented with higher complexity and at much higher count rates than was previously possible. The system incorporates all the features
M. Elfman et al. / Nucl. Instr. and Meth. in Phys. Res. B 158 (1999) 141±145
required from a platform for future development. At the moment we are far from using the full potential and full speed of the system.
References [1] K.G. Malmquist et al., Nucl. Instr. and Meth. B 77 (1993) 3. [2] J. Pallon, Nucl. Instr. and Meth. B 44 (1990) 377. [3] N.E.G. L ovestam, Nucl. Instr. and Meth. B 36 (1989) 455. [4] U.A.S. Tapper, N.E.G. L ovestam, E. Karlsson, K.G. Malmqvist, Nucl. Instr. and Meth. B 28 (1987) 317.
145
[5] K.G. Malmqvist, N.E.G. L ovestam, J. Pallon, U.A.S. Tapper, Scan. Microsc. 3 (3) (1989) 785. [6] G.W. Grime, M. Dawson, Nucl. Instr. and Meth. B 89 (1994) 223. [7] G.W. Grime, M. Dawson, Nucl. Instr. and Meth. B 104 (1995) 107. [8] M. Elfman, P. Kristiansson, K. Malmqvist, J. Pallon, A. Sj oland, R. Utui, C. Yang, Nucl. Instr. and Meth. B 130 (1997) 123. [9] K.A Sj oland, M. Elfman, P. Kristiansson, K. Malmqvist, J. Pallon, R. Utui, C. Yang, Nucl. Instr. and Meth. B 124 (1997) 639. [10] P. Kristiansson, U. H alenius, H. Skogby, M. Elfman, K. Malmqvist, J. Pallon, these proceedings (ICNMTA-6), Nucl. Instr. and Meth. B 158 (1999) 562.
www.elsevier.nl/locate/nimb
The layout and performance of the Lund nuclear microprobe trigger and data acquisition system Mikael Elfman *, Per Kristiansson, Klas Malmqvist, Jan Pallon Department of Nuclear Physics, Lund Institute of Technology, Box 118, SE-221 00 Lund, Sweden
Abstract Recently a new data acquisition system has been installed at the Lund nuclear microprobe facility. The trigger layout for this beam scanning and data acquisition system that support a great variety of simultaneously techniques (PIXE, STIM, RBS, and NRA) is presented in detail. The technical status, total trigger throughput and data ¯ow is described. Examples of typical system performance for PIXE, STIM and RBS obtained during routine runs are discussed. Details on hardware and software speci®cations are given. Ó 1999 Elsevier Science B.V. All rights reserved. PACS: 07.75.H; 07.05.K; 07.05.R; 41.75.A; 07.78; 61.18B Keywords: Acquisition system; Multi-parameter; Multi-detector; Trigger layout; High count-rates
1. Introduction Recently a new data acquisition system has been installed at the Lund nuclear microprobe facility [1]. In the development of a new nuclear microprobe set-up, the data acquisition system is one of the most important parts. Many papers have been written about the subject, where each group have selected their own approach [2±7]. The basic hardware of our new system has earlier been described in [8], and as we discussed there, a high maximum data throughput is needed for certain applications (STIM, RBS, and Secondary Electron Images) with very high count-rates. In this paper
*
Corresponding author. Fax: +46-46-2224709; e-mail: [email protected]
we measure acquisition performance during these high count-rate conditions. The trigger layout for the beam scanning and data acquisition system are discussed. The total trigger throughput, dead time and data ¯ow is measured. Details on hardware and software are described.
2. Data management and performance The acquisition process consists of two dierent modes: ``acquisition computer sort and display mode'' (Note: this mode is normally not used, the data are sorted and displayed with a few seconds delay on the second computer) and ``second computer sort and display mode'' (Normal Event Mode). The measurements on the system were carried out during an actual microbeam run. The
0168-583X/99/$ - see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 9 ) 0 0 4 9 7 - 8
142
M. Elfman et al. / Nucl. Instr. and Meth. in Phys. Res. B 158 (1999) 141±145
PIXE signal was detected with a Kevex Si(Li) detector of 50 mm2 active area and a measured energy resolution of approximately 155 eV at the 5.9 keV Mn Ka peak in 135° angle relative to the beam. By varying the proton beam current the count rate could be changed. The signal was split into four parts and fed into four ADCs with a count rate up to 120 000 c/s each. Each event is tagged with correct digital X, Y value, directly shifted out from the in crate DAC module that controls the beam position. This means that the X and Y coordinates occupy space in the memory for each event. Common for both acquisition modes are that when the in crate buer memory (16 k) is full (or nearly full), a LAM request is generated and the memory buer is emptied through a CAMAC command. Both modes are strongly dependent on the actual processor speed. In this test we used a computer with a 90 MHz PPC processor, the ``acquisition computer sort and display mode'' obviously demands more CPU time and is aected more severely by the lack of available CPU time at high count-rates. By comparing Fig. 1(a) and (b) this eect is seen very clear. A distinct level can be seen in Fig. 1(a), this represents the maximum throughput at an input trigger rate of 7 kHz in all four ADCs at the same time (33 KB/s), but in event mode it still didnÕt reach the maximum transfer rate of 65 kHz (90 KB/s). ItÕs obvious that the buer memory ¯ag has been set (10% of the memory left) and this gives a LAM request to the computer, but there is no available processor time to take care of the request. In the mean time the buer memory sets the ``full'' ¯ag and the CAMAC crate interrupts the acquisition and needs to wait for the computer to empty the memory. This creates the major part of the dead time shown in Fig. 2(a) and (b). The data transfer rates can be increased many times by just changing to an available 350±450 MHz PPC processor. In event mode (Fig. 2(b)) the data throughput is more than double compared to the sort and display mode. When the data are written to the disc it can immediately be sorted on an o line powerful computer, and presented in any way on the second computer. It is possible to change sort conditions and start the sort all over again without aecting
Fig. 1. (a) Data throughput in KB/s in acquisition computer sort and display mode (Note: this mode is normally not used, the data are sorted and displayed with about one second delay on the second computer), (b) Data throughput in KB/s in second computer sort and display mode (Normal Event Mode).
the actual data acquisition; also the data is automatically stored in time sequence. 3. Electronic set up and trigger layout Since the data acquisition system is a multiparameter and multi-detector system, the fast electronic set up includes a user selectable master coincidence trigger facility. By pressing buttons on the LeCroy coincidence units (Fig. 3), one can easily select which of the connected detectors you want triggers from. The energy outputs are pro-
M. Elfman et al. / Nucl. Instr. and Meth. in Phys. Res. B 158 (1999) 141±145
143
coincidence with each other. At the same time the time information is picked o with a zero crossing discriminator and the relative detection time is measured with a time to pulse height converter. The ADCs, gated by the master gate acquire both the energy spectrum and the time spectrum. The number of counts in the coincidence ``time'' peak is directly proportional to the hydrogen concentration. 3.2. The IL and Q system branch The anode signal from the PM tube is fed into a leading-edge discriminator for lower level energy selection, then the signal enters the coincidence unit ± CU which produces the gate for the energy signal. The output with low energy cut o is connected into the ADC. 3.3. The particle elastic scattering analysis (PESA) system branch
Fig. 2. (a) Data throughput (%) in: Acquisition computer sort and display mode (Note: this mode is normally not used, the data are sorted and displayed with about one second delay on the second computer), (b) Data throughput (%) in: second computer sort and display mode (Normal Event by Event mode Mode).
cessed through spectroscopy ampli®ers (Tennelec TC244). The dierent branches are described below. 3.1. The hydrogen system branch When a proton hits a hydrogen atom, particles are emitted at a 90° angle relative to each other. The two SBDs detect both the scattered p and H particles and spectroscopic energy information is extracted from both detectors [9]. The signal generates a trigger if the signal from both SBDs are in
This system is mainly used to measure C, N and O and for that an SBD is used in the backscattering direction. It is also used for NRA (e.g. Boron measurements [10]), and then an annular detector is used. The fast signal from the spectroscopy ampli®er is used to produce the gate for the energy signal and to measure dead time in the system. 3.4. The STIM system branch A collimated windowless photodiode (Hammamatsu S1223-01N 2028 (4 mm2 )) acts as a detector, the signal is ampli®ed by a preampli®er and a spectroscopy ampli®er. The fast count rate signal from the spectroscopy ampli®er is used to create the gate for the energy signal. 3.5. The PIXE system branch This is a typical PIXE standard branch. A Si(Li) (Kevex 50 mm2 active area) acts as a detector at 135° angle to the beam and the Tennelec spectroscopy ampli®er TC454 is used as main ampli®er. The fast count rate signal from the
144
M. Elfman et al. / Nucl. Instr. and Meth. in Phys. Res. B 158 (1999) 141±145
Fig. 3. The Lund NMP Trigger layout. PIXE branch: Si(Li) ± Kevex detector of 50 mm2 active area, AMP ± Tennelec spectroscopy ampli®er TC454, TTL/NIM ± TTL to NIM converter, CU ± Lecroy 465 coincidence unit, Gate Gen ± Gate Generator, LOG FI/FO ± Logic Fan in Fan out. STIM branch: DIODE ± windowless semiconductor diode, PA ± pre ampli®er, the rest of the branch similar to PIXE branch. PESA branch: similar to STIM branch. IL branch and Q branch: LE ± leading edge discriminator LeCroy LRS4608C, CI ± charge integrator. H ± system branch: SBD ± surface barrier detector, ZCD ± zero crossing discriminator, TPHC ± ORTEC 467 time to puls height converter. Time branch: pulser ± NIM pocket pulser.
spectroscopy ampli®er is used to create the gate for the energy signal. 4. Conclusions A very fast multi-detector, multi-parameter CAMAC and PPC-processor based data acquisi-
tion system has been developed and tested and is now in routine use at the Lund nuclear microprobe. The system is easy to modify and upgrade and more detectors in the system is fully supported. It currently allows data to be collected, processed and presented with higher complexity and at much higher count rates than was previously possible. The system incorporates all the features
M. Elfman et al. / Nucl. Instr. and Meth. in Phys. Res. B 158 (1999) 141±145
required from a platform for future development. At the moment we are far from using the full potential and full speed of the system.
References [1] K.G. Malmquist et al., Nucl. Instr. and Meth. B 77 (1993) 3. [2] J. Pallon, Nucl. Instr. and Meth. B 44 (1990) 377. [3] N.E.G. L ovestam, Nucl. Instr. and Meth. B 36 (1989) 455. [4] U.A.S. Tapper, N.E.G. L ovestam, E. Karlsson, K.G. Malmqvist, Nucl. Instr. and Meth. B 28 (1987) 317.
145
[5] K.G. Malmqvist, N.E.G. L ovestam, J. Pallon, U.A.S. Tapper, Scan. Microsc. 3 (3) (1989) 785. [6] G.W. Grime, M. Dawson, Nucl. Instr. and Meth. B 89 (1994) 223. [7] G.W. Grime, M. Dawson, Nucl. Instr. and Meth. B 104 (1995) 107. [8] M. Elfman, P. Kristiansson, K. Malmqvist, J. Pallon, A. Sj oland, R. Utui, C. Yang, Nucl. Instr. and Meth. B 130 (1997) 123. [9] K.A Sj oland, M. Elfman, P. Kristiansson, K. Malmqvist, J. Pallon, R. Utui, C. Yang, Nucl. Instr. and Meth. B 124 (1997) 639. [10] P. Kristiansson, U. H alenius, H. Skogby, M. Elfman, K. Malmqvist, J. Pallon, these proceedings (ICNMTA-6), Nucl. Instr. and Meth. B 158 (1999) 562.