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GSI-ACCELERATORS-14 GSI SCIENTIFIC REPORT 2009 142 Charge-Frequency-Converter (QFW) Test Board and Results H. Flemming**, S. Löchner**, H. Reeg*, M. Witthaus*, GSI, Darmstadt, Germany Overview GSI Beam Diagnostics department recently started investigations on an economic solution for profile grid electronics. The front-end amplifiers and control devices presently used are outdated, very expensive and important parts, like low noise amplifiers, have long delivery times and/or have been discontinued by the manufacturer. For the FAIR beamlines, around one hundred profile grid systems will be needed. The QFW CMOS-ASIC (Charge- Frequency-Converter [1][3]), developed by the Experiment Electronics department (EE) is a very promising candidate for a new design of the profile grids, due to it’s high dynamic range without the need for any range switching. After first tests with the 4-channel QFW module [2], it was decided to develop a new board, more related to practice and with additional electronic features (Fig. 1). Fig. 1: New QFW-board with PIC micro-controller, display LEDs, current divider, LVDS-/LV-TTL-drivers. Hard- and Software The experimental board shown in Fig. 1 consists of: • 4-channel QFW II • current divider (for extended measuring range) • LVDS- or LV-TTL outputs drivers • power-supply for external devices (+3.3V/+5V) • ICD-interface • two precision voltage sources • micro-controller Microchip® PIC 18FL4520 • several LEDs, hex-switch and two push-buttons This board was designed in order to check the QFW in different operational modes, thus enabling measurements in the experimental areas of GSI. It was negotiated between Bio-Physics dept. and EE to add a selectable current divider onto the board, making it possible to measure currents up to 20 mA, of course dependent on the values of the circuit elements. Free-programmable LEDs, push buttons, a hex-switch and several I/O channels allow for adoption of the board to different measurement tasks. *Beam Diagnostics ** Experiment Electronics Output pulses and overload-bits are fed to their connector plugs through LVDS- or LV-TTL-drivers. The micro-controller software was programmed in assembler via Microchip MPLAB®. The hex-switch allows changing range and polarity. After Power-On or Reset with the related buttons, the micro-controller transfers the necessary instructions to the QFW interface, whereupon operation starts. Measurement Results The QFW was tested under different conditions. At first the agreement with the results from the QFW datasheet and jitter behaviour was checked, and then tests under different ambient temperatures and different levels of Xradiation were carried out (see [4] for more information). A jitter around 0.1 ppt or better at each particular current value was detected by using an HP time interval analyser 5372A. The linearity of the frequency outputs fulfils the requirements for future profile grid electronics. Also the frequency deviation between each channel and a reference signal was investigated. This deviation is better than 1 % Full Scale. The temperature behaviour studies were performed in a climatic exposure cabinet. Many measurement series were done between 0°C and 50°C. The results show a deviation of 0.7 % only, with respect to the 20°C reference. Presently, all these results show that the QFW ASIC can be used in a new design for profile grid electronics. Additional comprehensive tests are in progress. Outlook A new QFW board equipped with 8 ASICs will be developed in 2010, in collaboration with the EE department. This prototype will be controlled by an existing FPGA-I/O VME board (VUPROM) . A LabVIEW program will control the measurements. First beam tests of the prototype will be performed with a 2x16-wire profile grid in an experimental beamline at GSI. The board will also be used for further characterisation of the QFW ASIC. References [1] H. Flemming, QFW II Preliminary Datasheet, GSI, 2008 [2] H. Flemming, QFW Module Preliminary Datasheet, GSI, 2007 [3] H. Flemming, E. Badura, A High Dynamic Charge to Frequency Converter ASIC, GSI Scientific Report, 2004 [4] S. Löchner, Total Ionising Dose Studies of the QFW ASIC, GSI Scientific Report, 2009.
GSI SCIENTIFIC REPORT 2009 GSI-ACCELERATORS-15 Temperature and Spectroscopic Studies on Inorganic Scintillating Materials E. Gütlich 1,2 , W. Ensinger 2 , P. Forck 1 , K. Gütlich 1 , R. Haseitl 1 , and B. Walasek-Höhne 1 1 GSI, Darmstadt, Germany; 2 Technical University Darmstadt, Darmstadt, Germany At the GSI UNILAC scintillating screens are used for transverse beam profile monitoring. For high current beam operations inorganic scintillators were investigated and numerical analysis of the recorded images was performed. The light yield, imaged beam width and higher statistical moments show strong dependence on the scintillating materials deployed [1, 2] and their temperature. Detailed temperature studies were carried out using a Ni layer (as a heating loop) sputtered on the backside of the ZrO2 screen. Additionally, the spectral response of the materials was mapped for different temperature levels (RT-300 o C), using a spectrometer. During the measurements, heating power was kept constant but the temperature of the sample was increasing due to the energy deposition of the impinging ion beam. As shown in Fig. 1 the light yield and imaged beam width for ZrO2 irradiated by the proton beam increase with temperature, except the initial phase which is difficult to interpret. In the temperature range from 125 - 250 o C, the light yield increases by the factor of 4 and the imaged beam width by 1.5. These results clearly point out that the temperature of the scintillators is critical for high current operations. Spectra of the scintillation light show a temperature dependance [3] as depiced in Fig. 2. For the broad band at 480 nm a slight shift to higher wavelengths is observed during the heating process. The bands around 400 and 725 nm are affected by the temperature, as well. For the spectra obtained with the proton beam, a sharp line around 515 nm occurred which is not observed for T a 24+ beam. Additionally, this line is not influenced by the change of screen temperature (Fig. 2). Several scintillating materials like Al2O3, Quartz etc. were investigated under various beam conditions (H + as well as heavy elements up to U 28+ ). Different readings of the imaged beam width for various materials were found. Further more, spectroscopic studies on different materials show a significant dependence of the spectra on the used ion species. A detailed discussion of these topics can be found in [3] and will be further investigated. References [1] E. Gütlich et al., “Scintillation Screen Investigations at UNI- LAC”, 2007/2008 GSI Scientific Report, pp. 105/pp. 126. [2] E. Gütlich et al., “Scintillation Screen Investigations for High Current ion Beams at GSI-LINAC”, BIW’08, Lake Tahoe, May 2008, p. 100, http://www.jacow.org/. [3] E. Gütlich et al., “Scintillation screen investigations for high current ion beams”, SCINT’09, Jeju, June 2009, IEEE Transactions on Nuclear Science, accepted for publication in June 2010 issue. Figure 1: Temperature dependence of light yield and beam width for ZrO2. Parameters of H + beam: 300-500 macro-pulses of 4 ms lenght, 2 Hz repetition rate with 3.5 · 10 11 ppp at 4.8 MeV/u. �� Figure 2: Scintillation light specra of ZrO2 for irradiation with H + (for the beam parameters see Fig. 1.) and T a 24+ (beam parameters: 1 Hz repetition rate with 8.8 · 10 9 ppp in 100 µs pulse length at 11.4 MeV/u. The spectra are averaged over 1000 images and are not corrected for photocathode (top) and spectrometer efficiency. 143
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