Bremsstrahlung Luminosity Monitoring for SCRIT Project (Report part II)

Transcription

1 Bremsstrahlung Luminosity Monitoring for SCRIT Project (Report part II) (Report part II) 1 Introduction 1.1 The SCRIT project 1.2 This Sub-project 1.3 ELPH in Sendai 1.4 RIKEN in Tokyo 1.5 Divided report 2 Method 2.1 Main goal and partial goals Main goal Partial goals 2.2 Project plan Project time and dates Project plan COLABS-program fall semester Oct Feb Project plan ICI-ECP spring semester May Aug Software 3.1 FPGA DAQ (coinboolean.vi) FPGA signal acceptance 3.2 The FPGA User interface (booleansoft.vi) 3.3 AnalyzeProgram (AP) 4 Software tests 4.1 Position monitor beta source test 5 Summary References Position monitor manual appendix 1 Introduction In this section the SCRIT research group and the basic ideas of the SCRIT project will be presented. Also this project which is subproject of the SCRIT project will be introduced. ELPH and RIKEN, the two laboratories where I have been doing my studies will also be introduced. 1.1 The SCRIT project To complete the theory for the properties of the atomic nucleus has been keeping scientists working for over a century now. The discovery of the atomic nucleus made by Ernest Rutherford in the beginning of the 20:th century was ground breaking for a new type of physics, nuclear physics. The properties for the stable nucleus is well known today, but the properties of the short-lived unstable nucleus is still puzzling scientists. The purpose for the SCRIT project is to gather information about size and structure for short-lived unstable nuclei to contribute to a supermodel for all nucleus. To test these properties The SCRIT research group will use electron scattering together with a

2 Self-Containing Radioactive Isotope Target (SCRIT), which is a completely new technique[1,2,3]. The idea is to trap the unstable nuclei in a potential well within an accelerator. While trapped, the electrons in the accelerator will scatter from the nuclei and their momentum will be analyzed with help of a drift chamber. After momentum has been analyzed, the electrons can be identified with help of a plastic scintillator. Energy can be measured with a calorimeter. Some of the energy from the scattering will be released as bremsstrahlung, this will also be detected by a calorimeter and also with a position monitor to determine the luminosity, which leads us to purpose of my sub-project for this larger project. 1.2 This Sub-project The Bremsstrahlung Luminosity Monitor is a tool that the SCRIT project will use in order to find out the the total luminosity. The knowledge of this is essential in order to determine valuable information such as charge density and size of the nuclei of interest. My task is to prepare a position monitor, this monitor will measure the number of electrons and positrons created by the bremsstrahlung and determine at which position they hit the detector. From this information one can determine the fraction of the total luminosity from bremsstrahlung. 1.3 ELPH in Sendai ELPH is shortage for Research center for ELectron PHoton science and has been the place were most of my studies have taken place. It is at ELPH I have constructed the position monitor for the project. 1.4 RIKEN in Tokyo Is the second laboratory where I have been working on the projects. At RIKEN I have been working with installing the detectors in the accelerator hall and testing the detectors with a radioactive source. Read more about RIKEN at Divided report Since this report is made to fit the two courses Projekt i fysik 30hp and Projekt i fysik 15hp at my home university,, the complete report from the course Individual Research Training in Lab which was taken at Tohoku University will be divided into two reports. The first part focus on the theoretical explanation, detector testing and circuit setup, while part II (the one you are reading right know) focus on software programming and software testing. 2 Method This section consist of the project plan, the main goal and partial goals of this project. 2.1 Main goal and partial goals This part consist of the main goals and partial goals of this project. The main goals are the goals that are supposed to be full-filled at the end of the project. The partial goals are goals to be full-filled during the project in order to complete the main goal.

3 2.1.1 Main goal The main goal of this sub-project is to build a bremsstrahlung luminosity monitor with associated software for the SCRIT research group s experiments on electron scattering of short-lived radioactive nucleus Partial goals To complete the main goals the following partial goals have to be completed: Construct bremsstrahlung luminosity monitor (Report part I) To complete this goal I have to gather knowledge in construction of scintillator detectors, Information about the different parts of the detector and the physics behind bremsstrahlung. Software programming (Report part II) To complete the detector system, a software to run the data gathering has to be developed. This will be done in LabVIEW together with FPGA module, since the detector system is suitable for that software development program. Detector testing (Report part I & II) To make sure that the detector system is working properly, a series of tests will be made on cosmic rays, tests with radioactive source will also be made. Software manual writing (Report part II) Write a manual for this detector system so that the system can be used by anyone. The manual will be attached to the second part of the report. 2.2 Project plan This part consist of the project plan and the time limitations of the project Project time and dates This project will last from October 2010 until August Notice that the COLABS program ends at the end of the fall semester and the ICI-ECP begins in the spring semester Project plan COLABS-program fall semester Oct Feb 2011 The project plan of the fall semester is presented in the table below Date Task Explanation to to Start-up, Work space setup, Theoretical Introduction to nuclear physics Introduction to detectors, software The first thing to in the beginning of the project do is to try to understand the fundamental basics and the theoretical knowledge that is required, especially theory on electron scattering and bremsstrahlung. At this time the work will consist of understanding the main concepts about detector systems and the

4 hardware interface detector/software interface for this project. If possible, programming of the software will be started here to to Christmas/New years break Construction of detector, software programming At this time the more practical task start such as constructing the detector system. Programming the software will continue during this period Project plan ICI-ECP spring semester May Aug 2011 The project plan for the spring semester is presented in the table below Date Task Explanation to to Detector system testing Buffer, finishing project report and software manual During this period the detector system will be tested and corrections in the software will be made. This period is a buffer if there would be problems during the project that will take more time than proposed from the beginning. Software manual will be written during this period. 3 Software This report will focus on how to make a software for a detector system for a grid of detectors. NI LabVIEW has been used to develop software for the detector system with an FPGA DAQ. It is not possible for a single program can run both the FPGA DAQ and the FPGA User interface. Therefore two programs were needed to be made. An additional analyzer program were also made to analyse old data and be able to start new measurements from a control room in RIKEN while operating the accelerator. In this chapter only a brief introduction to the programs will be presented, to read more about the programs please read the position monitor manual in the appendix 3.1 FPGA DAQ (coinboolean.vi) This program gets information of where the electrons and positrons hit the detector. The data is saved different counters which the user interface can load during measurements. Below is a flowchart of the program algorithm. Figure FPGA DAQ (coinboolean.vi) flowchart of software algorithm

5 The main purpose of the FPGA DAQ program is to gather information if and which of the detectors that detect electrons or positrons and send this to the FPGA User interface. Further explanation of the program will be given in appendix B (Position monitor software manual) FPGA signal acceptance It is the speed of the FPGA DAQ that limits the pulse width that can be used for the experiment, since it is the FPGA DAQ that can separate one signal from the other. The FPGA can detect a pulse if it has rising edge when a new program loop starts. That means that the program will detect a pulse if the connector i.e the TTL input, gives a true signal on the present loop and if it gave a false signal the previous loop. But the program can only detect signals at a specific time for each loop. So if one wants to be sure to detect a pulse and the loop time for the program (the time it takes for the program to collect data and make all computations for one data gathering) is 500ns the minimum pulse width that should be used is 500ns. See figure below for more details. Figure Four different scenarios for signal detection This picture above shows four different scenarios. scenario A) and B) have the same pulse width and scenario C) has an equal longer pulse width. Say that the pulses are detected at the beginning of each loop for simplicity. In A) none of the pulses will be detected because the FPGA will only read false signals at the beginning of each of the three loops. In B) the first signal will be detected since

6 the value at the connector was false in the first iteration and the value at the connector at the second iteration was true. The second pulse will not be detected since the the value at the connector was true at the second iteration and false at the third. In scenario C) the pulse will be detected since the value at the connector at iteration one was false and true at iteration two. Since the pulse size is larger than the iteration time pulses of this pulse width will always be detected unless the case is like in scenario D) since the connector will give the value of true during all three iterations, the software cannot distinguish if it is two individual pulses or one long one and therefor will only one signal be detected. For the FPGA DAQ (coinboolen.vi) the iteration time is < 350 ns. This means if the pulse width of the channels are bigger than this number all pulses can be detected, unless two signals from the same fiber reach the FPGA in less than 350 ns, then only one of the pulses will be detected just like in case D) above. 3.2 The FPGA User interface (booleansoft.vi) The logic of the FPGA User interface is explained in the flowchart below. Figure FPGA User interface (booleansoft.vi) flowchart of software algorithm The main purpose of this program is to manipulate the data that the FPGA DAQ gives and to display the data while running. The program shall also save the data so that experimental data can be analyzed after the experiment has been made. Further explanation of the program will be given in appendix B (Position monitor software manual) 3.3 AnalyzeProgram (AP) The logic of the analyze software is explained in the flowchart below.

7 Figure AnalyzerProgram (Analyzerprogram.vi) flowchart of software algorithm The main purpose of the AP is to analyze data that has been created by the FPGA User interface. Another important function of the AP is to be able to trigger the FPGA User interface to start new data gathering. Further explanation of the program will be given in the Position monitor software manual in the appendix. 4 Software tests The software tests have been carried out during the spring semester in RIKEN, Tokyo. During all experiments the voltage to the photo multipliers have been set to 950V. The discriminator threshold was set to the following values with help of the test that is described in chap 7.1: 4.1 Position monitor beta source test A test with beta source 90 Sr has been made in order to confirm that the detectors and the software is completely ready for bremsstrahlung distribution measurements. Collimator was used to make a narrow source of beta rays so that different parts of the detector could be tested. The tests were successful and show that data is consistent from different part of the detector. Below are the results from three different test were the beta source was placed at three different position.

8 Fig Beta source was placed with center approximately at position Y3 X9. The 3D plot shows the coincidence between XY detectors and the two 2D graphs show individual detector data for X and Y detectors. Fig Beta source was placed with center approximately at position Y8 X12. The 3D plot shows the coincidence between XY detectors and the two 2D graphs show individual detector data for X and Y detectors.

9 Fig Beta source was placed with center approximately at position Y12 X2. The 3D plot shows the coincidence between XY detectors and the two 2D graphs show individual detector data for X and Y detectors. 5 Summary The software testings shows that the software is ready to use for luminosity measurements at SCRIT experiment. This system I constructed surely provides a new and useful information for the SCRIT experiments. References [number] Source name Type of source Acces (e.g, homepage, ISBN) Date [1] T. Suda et al., Phys. Rev. Lett Report sa=t&source=web&cd =1&ved=0CBcQFjAA &url=http%3a%2f%2 Fiopscience.iop.org%2 F %2F267%2F1%2 F012008%2Fpdf%2F _267_1_ p df&rct=j&q=t.%20su da%20et%20al.%2c% 2009

10 20Phys.%20Rev.%20L ett%20102% &ei=87letouymthrrq evxvteaw&usg=afq jcng9iav4thzocy1v WP9qGxVFO4M- 6A&cad=rja [2] M. Wakasugi et al., Phys. Rev. Lett. 100, Report ispun11/download/ Suda_abstract.pdf 1998 [3] M. Wakasugi, T. Suda and Y. Yano, Nucl Intrum. Methods Phys. Res. A 532, 216 Report RIBF-TAC05/ 14_SCRIT.pdf 2004 Position monitor manual appendix