Query: Precision Laser Beam Path Tracking Control System for Position Measurement Using PSD Senso

Candidate papers:

abstract: Position sensitive detector (PSD) is an optical position sensor that can measure a position of the light spot in one or two dimensions on sensor surface. The PSD is precision semiconductor optical sensor that produces output currents related to the "Centre of mass' of light incident on the surface of the device used in the measurement there are many advantages including a good positioning accuracy for fast response time and very simple signal conditioning circuits. A precise control system has been designed in this paper using a new and modern algorithm with a closed loop system to obtain accurate tracking of the position and speed of the radiation used in the measurement of the specific physical process. The proposed control model about laser beam path controlled using a new type of controller named PSD fuzzy controller with feedback through PSD sensor, also the FOC method was applied to the hybrid stepper motor to control the position and speed with four rings feedback. The algorithm will realize better rise time and less overshoot better and detailed analysis is carried out to confirm the viability of the proposed system.
author_names: Nihad Abdalla

Shi Liu

Ahmed Abdelrahim
title: Precision Laser Beam Path Tracking Control System for Position Measurement Using PSD Sensor
year: 2020

abstract: This paper describes tracking optoelectronic system for intelligent and exact controlling of laser beam path depend on position sensor detector (PSD) as feedback backup, in this paper presents a precise control system using a new modern algorithm with a closed loop system to determine the ideal position and speed of the laser beam path for measuring process, laser beam source is stable and fixed. The feature of the control system proposed in this paper is that the design of the adaptive and repetitive control are independent because each design is based only on the model plant, the system itself defines the situation and angle rotating by a two hybrid stepper motor with specific mechanisms. Field oriented control (FOC) method is presented to demonstrate effectiveness. For real time embedded controller. A series of experiments have been conducted to realize better transient response specifications. Part of this paper proposed a nonlinear system predictive model strategy applying based on the local model and some optimization method to solve the control problem for a nonlinear part to obtain accurate results.
author_names: Nihad Abdalla

Shi Liu

Ahmed Abdelrahim
title: Precision Laser Tracking For Beam Path Control With PSD Fuzzy Controller
venue: 2020 Asia Energy and Electrical Engineering Symposium (AEEES)
year: 2020

abstract: Most embed control system is working on the coordinates measurement and trajectory to track an object in the space need to a particular type of controller include specific algorithm. In this paper we explore designing optoelectronic system for intelligent and exact controlling of laser beam path depend on position sensor detector(PSD) in This paper presents a precise control system using a new and modern algorithm with a closed loop system to determine the ideal position of the laser beam path for measuring process, laser source is stable and fixed. We need to used mirrors to reflect ray to the laser beam path. It rotating by hybrid stepper motors. Field Oriented Control (FOC) method is presented to demonstrate effectiveness. For real time embedded controller. The system itself defines the situation and angle of each mirror. Series of experiments has been conducted to realize better transient response specifications.
author_names: Nihad Abdalla

Shi Liu

Ahmed Abdelrahim
title: Laser Beam Path Control Using a PSD Fuzzy Controller
venue: 2019 4th International Conference on Power and Renewable Energy (ICPRE)
year: 2019

abstract: When related to a single and good contrast object or a laser spot, position sensing, or sensitive, detectors (PSDs) have a series of advantages over the classical camera sensors, including a good positioning accuracy for a fast response time and very simple signal conditioning circuits. To test the performance of this kind of sensor for microrobotics, we have made a comparative analysis between a precise but slow video camera and a custom made fast PSD system applied to the tracking of a diffuse reflectivity object transported by a pneumatic microconveyor called Smart Surface. Until now, the fast system dynamics prevented the full control of the smart surface by visual servoing, unless using a very expensive high frame rate camera. We have built and tested a custom and low cost PSD based embedded circuit, optically connected with a camera to a single objective by means of a beam splitter. A stroboscopic light source enhanced the resolution. The obtained results showed a good linearity and a fast (over 500 frames per second) response time which will enable future closed loop control by using PSD.
author_names: Ioan Alexandru Ivan

Mihaita Nicolae Ardeleanu

Guillaume J Laurent
title: High Dynamics and Precision Optical Measurement Using a Position Sensitive Detector (PSD) in Reflection Mode: Application to 2D Object Tracking over a Smart Surface
venue: Sensors
year: 2012

abstract: A position sensitive detector/device (PSD) is a sensor that is capable of tracking the location of a laser beam on its surface. PSDs are used in many scientific instruments and technical applications including but not limited to atomic force microscopy, human eye movement monitoring, mirrors or machine tool alignment, vibration analysis, beam position control and so on. This work intends to propose a new application using the PSD. That is a new microscopy system called scanning PSD microscopy. The working mechanism is about putting an object on the surface of the PSD and fast scanning its area with a laser beam. To achieve a high degree of accuracy and precision, a reliable framework was designed using the PSD. In this work, we first tried to improve the PSD reading and its measurement performance. This was done by minimizing the effects of noise, distortion and other disturbing parameters. After achieving a high degree of confidence, the microscopy system can be implemented based on the improved PSD measurement performance. Later to improve the scanning efficiency, we developed an adaptive local scanning system to scan the whole area of the PSD in a short matter of time. It was validated that our comprehensive and adaptive local scanning method can shorten the scanning time in order of hundreds of times in comparison with the traditional raster scanning without losing any important information about the scanned 2D objects. Methods are also introduced to scan very complicated objects with bifurcations and crossings. By incorporating all these methods, the new microscopy system is capable of scanning very complicated objects in the matter of a few seconds with a resolution that is in order of a few micrometers.
author_names: Mehdi Rahimi

Yantao Shen
title: PSD microscopy: a new technique for adaptive local scanning of microscale objects
venue: Robotics and biomimetics
year: 2017

abstract: NASA Tech Briefs, February 2010 A laser tracker (LT) is an important coordinate metrology tool that uses laser interferometry to determine precise distances to objects, points, or surfaces defined by an optical reference, such as a retroreflector. A retroreflector is a precision optic consisting of three orthogonal faces that returns an incident laser beam nearly exactly parallel to the incident beam. Commercial retroreflectors are designed for operation at room temperature and are specified by the divergence, or beam deviation, of the returning laser beam, usually a few arcseconds or less. When a retroreflector goes to extreme cold (35 K) however, it could be anticipated that the precision alignment between the three faces and the surface figure of each face would be compromised, resulting in wavefront errors and beam divergence, degrading the accuracy of the LT position determination. Controlled tests must be done beforehand to determine survivability and these LT coordinate errors. Since conventional interferometer systems and laser trackers do not operate in vacuum or at cold temperatures, measurements must be done through a vacuum window, and care must be taken to ensure window induced errors are negligible, or can be subtracted out. Retroreflector holders must be carefully designed to minimize thermally induced stresses. Changes in the path length and refractive index of the retroreflector have to be considered. Cryogenic vacuum testing was done on commercial solid glass retroreflectors for use on cryogenic metrology tasks. The capabilities to measure wavefront errors, measure beam deviations, and acquire laser tracker coordinate data were demonstrated. Measurable but relatively small increases in beam deviation were shown, and further tests are planned to make an accurate determination of coordinate errors. This work was done by Raymond G. Ohl and Bradley J. Frey of Goddard Space Flight Center, Joseph M. Stock of SGT, Inc. Joseph C. McMann of QinetiQ North America, and Tmitri J. Zukowski of Research Support Instruments. For further information, contact the Goddard Innovative Partnerships Office at (301) 286 5810. GSC 15702 1 Optical Testing of Retroreflectors for Cryogenic Applications Commercial uses include cryogenic metrology on aerospace structures and optical metrology instrumentation. Goddard Space Flight Center, Greenbelt, Maryland
author_names: Alex Abramovici

Jacob Chap

Peter G Halverson
title: Optical Testing of Retroreflectors for Cryogenic Applications
year: 2010

abstract: A laser tracker (LT) is an important coordinate metrology tool that uses laser interferometry to determine precise distances to objects, points, or surfaces defined by an optical reference, such as a retroreflector. A retroreflector is a precision optic consisting of three orthogonal faces that returns an incident laser beam nearly exactly parallel to the incident beam. Commercial retroreflectors are designed for operation at room temperature and are specified by the divergence, or beam deviation, of the returning laser beam, usually a few arcseconds or less. When a retroreflector goes to extreme cold .35 K) however, it could be anticipated that the precision alignment between the three faces and the surface figure of each face would be compromised, resulting in wavefront errors and beam divergence, degrading the accuracy of the LT position determination. Controlled tests must be done beforehand to determine survivability and these LT coordinate errors. Since conventional interferometer systems and laser trackers do not operate in vacuum or at cold temperatures, measurements must be done through a vacuum window, and care must be taken to ensure window induced errors are negligible, or can be subtracted out. Retroreflector holders must be carefully designed to minimize thermally induced stresses. Changes in the path length and refractive index of the retroreflector have to be considered. Cryogenic vacuum testing was done on commercial solid glass retroreflectors for use on cryogenic metrology tasks. The capabilities to measure wavefront errors, measure beam deviations, and acquire laser tracker coordinate data were demonstrated. Measurable but relatively small increases in beam deviation were shown, and further tests are planned to make an accurate determination of coordinate errors.
author_names: Raymond G Ohl

Bradley J Frey

Joseph M Stock

Joseph C McMann

Tmitri J Zukowiski
title: Optical Testing of Retroreflectors for Cryogenic Applications
year: 2010

abstract: This thesis presents optical metrology systems using laser and position sensitive detectors (PSDs) In this area, a new diffraction strain measurement technique is developed, implemented, analyzed and characterized. Related research work on the optical metrology components is also included, dealing with position sensitive detectors analysis and laser beam applications. The research in optical metrology systems using lasers and PSDs comprises development of a novel whole field strain measurement technique and its implementation as Multipoint Diffraction Strain and Tilt Sensor using Moire Interferometer and Multichannel PSD. All the different variations of diffraction strain sensors as developed by different researchers up to date, measure single point strain on the sample only. Concurrently, the whole field strain measurement techniques like Moire Inteiferometry and ESPI have their own shortcomings like lengthy fringe processing and image subtraction algorithms. Additionally, they face obvious degradation in their spatial resolution at lower strain values owing to the sparse fringes. On the contrary, the developed system has the unique feature of direct and near real time diffraction based strain and tilt measurement at a large array of points on the sample surface. The system uses simultaneous position tracking of smaller beamlets diffracted differently from different regions of the component surface under test. Using this setup, whole field strain and tilt distribution patterns over the component body can be obtained immediately without the need for fringe processing. Furthermore, the system also has capability of measuring rotation and shear strain, making it a truly versatile whole field strain sensing system. Simultaneous strain and tilt measurement at more than one thousand points is being reported in this research. Complete microcomputer based implementation of this system is described. Detailed characterization and analysis of the developed system is presented along with some important development decisions. The system offers a promising combination of features like direct and fast calculation of whole field strain with a fine spatial resolution and good sensitivity. These make this technique suitable for precision applications in structures, mechanics and micro mechanics, while offering a considerable saving in time and equipment cost. Work on Optical Metrology components starts with a unique analysis of position sensitive detectors used in noisy industrial environment, where several other light sources also coexist and thus produce unpredicted effects on PSD output. Many researchers of other photo sensors have analyzed their performance in presence of these stray noises, while this problem has many times been outlined in context of PSDs too. Nonetheless, detailed performance analysis of PSDs with stray optical noises is very much needed. For this purpose, these stray noises are described and modeled with respect to the operation of PSDs. Then the response of the detectors is analyzed in the presence of these spurious signals. The experimental results are compared with the results from the proposed mathematical model and it is observed that the measured performance is within a fraction of a percent of the calculated one. The analysis of systematic errors encountered during data collection is also presented. The study is expected to be very useful for the accurate and precise use of PSDs based sensors in the industrial units like production lines, workshops and others. Following this, the work on laser beams analyzes their use in a novel material processing technique. Laser welding of galvanized steel sheets in lap configuration is the challenging problem being investigated for more than two decades, originating due to the difference in the melting points of steel and zinc. Earlier solutions are either insufficient for desired results or too cumbersome to be realized in practice. For this purpose, dual laser beams method is being discussed modld and analyzed, involving a precursor beam and a higher power welding beam. The first beam cuts a slot, thus making an exit path for the zinc vapours, while the second beam performs the needed welding. The work also presents some experiments performed on the shop floor using this method, along with the metallurgical analysis from laboratory showing successful absence of zinc in the weld area. Owing to its simpler approach and lesser time consumption, this technique is expected to be very attractive in terms of workshop implementation and welding throughput.
author_names: Iqbal Salman
title: OPTICAL METROLOGY WITH LASERS AND POSITIONS SENSITIVE DETECTORS
year: 2007

abstract: This paper describes the development of a miniature assembly cell for micro electromechanical systems (MEMS) Potential applications of the developed assembly cell are assembly of miniature optical systems, integration of optoelectronics, such as laser diodes with CMOS, and epitaxial lift off (ELO) of thin films used in optoelectronic devices. The cell utilizes a transparent electrostatic gripper and uses several disparate sensing modalities for position control: computer vision for part alignment with respect to the gripper, a fiber coupled laser, and a position sensitive detector (PSD) for part to assembly alignment. Assembly experiments indicate that the gripping force and stage positioning accuracy are sufficient for insertion of 500mm wide parts in 550 mm wide slots etched in silicon wafers. Details on the cell operation, the control algorithm used and their limitations are also provided. INTRODUCTION Although MEMS devices are usually fabricated via massively parallel photolithographic techniques, in some instances, sequential assembly is required. For example, heterogeneous integration for vertical cavity surface emitting lasers (VCSEL s) with silicon based CMOS circuitry requires placement of the laser die onto a silicon substrate containing the electronic circuitry. Further applications include the assembly of dense arrays of high aspect ratio structures such as electrode arrays in IC probe cards. These assembly and packaging operations are costly and usually constitute the largest portion of the device's total cost. In order to increase the manufacturing throughput and reduce the re tooling costs, it is desirable to develop flexible assembly schemes, allowing for quick adaptation to various part geometries and configurations. Responding to this need, a considerable effort from the private sector and government investments led the development of visually servoed robotic systems, which utilized computer vision to generate knowledge about the position of objects in the robot's work space [1 3] Research focused on microassembly with visual servoing [4,5] has developed excellent image processing techniques for robot control in real time [6] Two dimensional limitations of the imaging systems has also been addressed with research on the extraction of three dimensional position information using techniques known as "depth from focus" or multiple CCD arrays [2,7] In parallel with the software improvement several research groups have also developed micro grippers actuated with electrostatic comb drives, thermal actuators or piezo actuators for use under computer vision controlled robotic systems. In most cases these grippers are application specific, and thus require retooling when parts with variable geometry are used. Further, the gripping force is applied point or edge wise, increasing the possibility of local surface damage due to stress concentrations. The present work describes our effort to implement a micro assembly cell based on a previously developed optically transparent electrostatic micro gripper for visual servoing. When compared to other approaches such as vacuum gripping [8] this technique has the advantages of applying a uniform and controllable clamping force, uses a transparent gripper, which allows complete observation of the part and can accommodate parts with different planar geometry. Thus pick and place of Vertical Cavity Surface Emitting Lasers (VCSELS) [9] lift off of thin fragile films are a few of the potentially relevant applications of this assembly technique. II. SYSTEM LAYOUT AND OPERATION The layout of the system is graphically represented in Figure 1below. The system is controlled by personal computer equipped with frame grabber board (Sensoray Inc. USA) and motion control board (PCI 7344 Controller, National Instruments Inc. USA) CCD camera provides the signal for the frame grabber (L 902K Watec Inc. USA) A servo amplifier (MC 4SA, National Aperture Inc. USA) transfers the signal from the PCI 7344 to two motorized linear stages (MM4 MX, National Aperture Inc. USA) One of the stages is attached to platform, designed to support the electrostatic gripper. A PSD (S5990 01, Hamamatsu Inc, Japan) and a 653 nm laser (FIB 635 1SM LaserMax, Inc) are attached to the gripper platform. The laser is coupled to a GRIN collimated lens. The gripper platform is attached to one of the linear stages. A xyz translational stage (Newport, Inc, USA) supports a gimbal mirror mount (Edmund Industrial Optics, USA) The mount is situated in front of the platform and supports a slotted Si wafer. The laser beam reaches the surface of the wafer at an angle. The reflected beam is directed to the 1 Author to whom the correspondence should be addressed (enikov@engr.arizona.edu) PSD by using optical prism. Motions of the platform in the direction of the stage carry out linear scans over the surface of the wafer. Figure 1. Block diagram of the assembly cell. The gripper consists of a glass substrate with transparent thin film electrodes on top. The electrodes are coated with an insulator [10] The optical transparency of the gripper makes possible the use of real time visual servoing to align the part with respect to the gripper using the CCD camera. To achieve this the pattern of the gripper itself is used. Figures 2 (a) and (b) show the gripper and gripper/part assembly respectively. Figure 2. (a) Figure 2. (b) (a) Gripper Electrodes. (b) A part clamped to the gripper. Both the ITO electrodes and the part are clearly seen. Figure 3. Stage with gripper platform mounted. Figure 3 shows the laser, the collimator, the PSD and the gripper integrated into a "gripper platform" Fine adjustment of the collimator's optical axis was achieved by two compressed o rings threaded over the collimator housing. First alignment of a part with respect to the gripper is performed, through the use of an image based visual servoing. After pick up of a part, the surface of the receptacle wafer is scanned for a slot. Upon alignment part insertion is fulfilled via the manual x y z stage. Image based visual servoing is implemented by employing the Sum of Square Differences (SSD) search algorithm [11] Two SSD algorithms are used: spiral SSD algorithm and sequential SSD algorithm. The spiral search starts from the last known feature position and probes for a match in a spiral manner. The sequential search performs consecutive line scanning. Spiral mode is used for detection of parts with known initial location. Sequential mode is used when no estimate for the initial location of the tracked feature is available. Figure 4 shows a screen capture of the software interface developed for visual servoing. In this particular example three features marked with rectangles are selected for tracking. Two features (chess pattern) belong to the gripper and one feature (edge of the part) is selected for centering between the other two. Feature 1 x x Part to be picked up Feature 2 Figure 4. Screen capture of part/gripper alignment. Optical servoing aligns the part with respect to a slot on the wafer. Successful alignment is indicated by a minimum in the total reflected light intensity measured by the PSD detector. Real time alignment is achieved through an intensity minimizing procedure, which utilizes measurements from the PSD sensors and from the magnetic encoder of the linear stage servomotor. Encoder information is also used for feed forward position control of the linear stage. Two control algorithms for intensity minimization were tested spatial derivative method and hill climbing algorithm. The first one is based on a real time spatial derivative estimation of the PSD signal. The second one is based on intensity minimum search with a predefined step size. II. SYSTEM IDENTIFICATION A simplified block diagram of the main components is shown in Figure 5 using first order holder equivalents of the continuous signals with sampling time ms Ts 5 2 2.1 LINEAR STAGE AND ENCODER The linear stage/motor is modeled as a second order system containing a single time constant due to the inertial load of the system s s a s V s X t 1 0 (1) (s V and (s X are the Laplace transform of the motor input voltage and the linear position of the stage respectively. 138 0 0 Vms m a m and ms 6 13 t were determined experimentally by applying a step voltage to the motor and recording the velocity output (t x& The servo amplifier gain is 25 1 G Lag in the feedback path of the system is caused by the processing time required for analog to digital and digital to analog signal conversion, performing floating point calculations and feature tracking. Among these, the latter is most significant and ranges between 36 ms and 111ms for a 64 x 64 pixels feature in a 128 x 128 pixels search window. The time delay during optical feedback (PSD) with 5 point sliding differentiation rule (see section 3.2) was significantly shorter ms T 5 2 Figure 5 depicts the system using first order holder equivalents of the continuous signals with sampling time ms T 5 2 Figure 5. Block diagram of the SIMULINK model. 2.2 Reflected Intensity Distribution Mathematical model has been developed to describe the intensity of the reflected laser beam as a function of the position of the slot in the receptacle wafer. The intensity of the laser is modeled using the Gaussian distribution. It is assumed to be symmetric: 2 0 2 0 2 0 2 max w y y x x e I y x I (2) 0 w is the beam waist, 0 x and 0 y are the coordinates of the center of the beam. To model the power acquired by the reflected intensity y x I ref the y x I distribution was convoluted with a characteristic function of the slot otherwise 1 2 2 and 2 2 x 0 h y h y y w x w x y x H H H H H (3) H x and H y are the coordinates of the centroid and w h are the width and the height of the slot. The power of the si
author_names: Eniko T Enikov

Kalin V Lazarov

Lyubomir L Minkov

N C Mountain
title: Transparent Electrostatic Clamp For Visual Assembly and Packaging
year: 2004

abstract: At the Forschungszentrum Dresden Rossendorf a new neutron time of flight [Klug07] facility has been set up. Fast neutrons in the energy range from 0.1 MeV to 10 MeV are produced using pulsed electron beams from a superconducting electron linear accelerator[Gabriel00] Short beam pulses of less than 10 ps allow high resolution time of flight experiments with the aim to determine interaction cross sections of neutrons with reactor structural materials and actinides at energies matching the neutron energies in fast reactors [Salvatores08] Following experiments using a thermionic electron injector a new superconducting radiofrequency injector [Arnold07] has been built which will allow average beam currents of 0.5 mA at a repetition rate of 500 kHz. Meanwhile, first experiments on inelastic neutron scattering cross sections on Fe and total neutron cross sections on aluminium and tantalum have been performed as benchmark experiments. While photons from the de exciting transitions are being detected using a 16element BaF2 scintillator array, neutrons are measured with five low threshold plastic scintillation detectors [Beyer07] Beam normalisation is done using a calibrated U fission chamber. The preparation of actinide targets for neutron induced fission cross section measurements is under way. Experimental Setup The radiation source ELBE (Electron Linear Accelerator with High Brilliance and Low Emittance) at Forschungszentrum Dresden Rossendorf (FZD) makes use of a superconducting continuous wave electron linear accelerator delivering beams with energies up to 50 MeV. The high intensity beam with average beam currents of up to 1 mA at pulse repetition rates up to 26 MHz serves as a driver for the production of various secondary beams. Figure1 shows the layout of the accelerator facility and the beam lines for secondary radiations. Table 1 lists the available secondary beams and their primary applications. As one of the secondary beams, an intense neutron beam is being produced by bremsstrahlung photons via the (g,n) process inside a liquid lead circuit. The lead acts threefold as the electron to bremsstrahlung convertor, as the source of evaporation neutrons, as well as the heat removal medium in order to cope with the designed average electron beam power of Corresponding author: a.wagner@fzd.de Fig. 1: Layout of the accelerator facility ELBE. Two superconducting accelerator structures are located inside the accelerator hall and the liquid lead loop is situated on the upper right side inside the neutron hall. A new superconducting radio frequency injector is already installed (SRF gun) which will allow for increase in electron bunch charge by a factor of 15 as compared to the standard thermoionic injector. Recently, a 100 TW laser systems has been set up which serves for laser Thomson electron scattering experiments and laser plasma particle acceleration experiments. about 50 kW. Monte Carlo simulations using MCNP and GEANT4 were performed to characterise the neutron and photon intensities as well as time and energy distributions, and to optimise the neutron transport and shielding of the experimental setup. The design of the liquid lead loop is shown in Fig. 2. The design focuses on combining a small active volume of neutron production with a correspondingly high local heat load of about 5 kW g. As one of the possible solutions, a liquid lead loop operated at a temperature of about 630 K has been selected which is also favourable by means of induced radioactivity caused by various ,xn)and ,p) reactions as compared to e.g. liquid mercury. Nevertheless, the liquid lead loop has to be stored during shutdown phases inside a lead shielding of 200 mm thickness in order to grant access to the vault for maintenance and other experiments [Seidel07] While using lead as material for efficient neutron production (neutron separation energies Sn from 6.7 to 8.1 MeV) the beam dump is made from pure aluminium >99.9% resulting in low induced activities and low neutron generation (neutron separation energy of Al: Sn=13.1 MeV) The short beam pulses (about 5 ps FWHM) delivered by the superconducting electron accelerator provide the basis for an excellent time resolution for neutron time of flight experiments while the pulse repetition rates can be varied between 100 kHz and 26 MHz according to the demands of the experiments. With the existing electronically pulsed thermionic electron source electron pulse charges of up to 80 pC are realized allowing for a moderate average electron beam current of 16 mA at a repetition rate of 200 kHz. Fig. 2: Three dimensional rendering of the liquid lead loop installed at the ELBE facility. For reasons of radiation protection the platform containing the lead loop can be lowered into a lead housing by means of a remotely controlled spindle lifter. The intense electron beam impinges from the front left while the beam transport system is not shown here. The lead flow is driven by means of a magneto hydrodynamic pump thus avoiding mechanical contact with the fluid and avoiding mechanical feedthroughs. Thermal insulation, heating units, and support systems are not shown. The beam dump is made from aluminium surrounded by lead in backward and radial directions. A new superconducting radio frequency injector is already installed which in the near future will allow for an increase in electron bunch charge by a factor of 15 and repetition rates of 500 kHz. The short beam pulses together with the small neutron production volume in the lead circuit allow for an energy resolution of about 1% with a flight path of 6 m when using a fast detector stop signal (e.g. 1 ns for 1.5 MeV neutrons) Neutrons emerging from the liquid lead radiator are shaped into a beam using a 240 cm long cylindrically symmetric collimator made from borated polyethylene and lead, greatly reducing scattered neutron background and photons at the target position. Around the target, an array of 16 BaF2 scintillation detectors for the detection of secondary photons has been installed. Each detector consists of two 190 mm long prisms with hexagonal bases of 53 mm inner radius glued together and read out on both ends using fast photomultiplier tubes (PMT) The double sided readout helps to reduce background signals stemming from anode dark currents, it improves the energy resolution, and it permits the determination of the longitudinal hit position. The signals from the PMTs are processed in Hamamatsu Photonics K.K. http:/www.hamamatsu.com, PMT: R2059 01 selected with quartz windows. dedicated VME based readout units allowing for pulse shape discrimination of charged particles and photons. Fig. 3: Sketch of the setup used in neutron inelastic scattering experiments. Part a) shows the top view, and part b) shows the side view of the detector and target arrangements. Solid (dashed) lines refer to neutron (photon) tracks. Electron optical elements are not shown. Drawing is not to scale. Scattered neutrons are detected using proton recoil plastic scintillation detectors at a distance of about 1 m from the target. The plastic scintillation detectors are strips of 1000 mm length and 42 mm x 11 mm cross section read out double sided using the same PMTs as described above. The trigger threshold is selected to detect single photo electrons permitting detection limits for neutrons as low as 30 keV for detection efficiencies above 10% The design, operation, and calibration of these detectors are described in a previous publication [Beyer07] The system is optimized for high time resolution of the time of flight detectors reaching about 600 ps FWHM for the BaF2 detectors and about 860 ps FWHM for the plastic scintillation detectors in order to allow a compact setup ensuring high beam repetition rates with low pulse to pulse overlap. Scattered neutrons and photons originating from the BaF2 array are being suppressed by borated polyethylene absorbers in the direction of the neutron detectors. The distribution of random background has been determined in measurements without target. Neutron flux determination is done using a calibrated U 235 fission chamber [Gayther90] The time resolution obtained using photo induced fission amounts to about 4 ns. The data acquisition system is controlled by a VME based computer running the real time operating system LynxOS and the versatile data acquisition system MBS. The readout of the double sided BaF2 detectors is done using CAEN V874b calorimeter units providing t energy information, while the plastic scintillation neutron detector information is processed by in house made constant fraction discriminators. CAEN V1190a time to digital converters provide the timing information for both detectors. he Eljen Technology, http:/www.eljentechnology.com, EJ 200 scintillator. SS Creative Electronics Systems, http:/www.ces.ch, RIO3 8064 single board computer. GSI Multi Branch System, http:/daq.gsi.de. CAEN s.p.A. http:/www.caen.it Experiments Several experiments on interactions of fast neutrons with materials of interest for fast reactors have been performed. As a preliminary example, the inelastic scattering on iron with natural isotopic composition has been studied. Although iron is not a material of interest for transmutation studies, its importance as structural material demands high precision data for the interaction of fast neutrons occurring in fast reactors, transmutation facilities, or accelerator driven systems [Salvatores08] The detector setup is shown in Figure 3. List mode data are taken for coincident signals in the BaF2 array and the neutron detector array selecting primarily reactions with at least one photon and one neutron in the exit channel. Time of flight calibration is done using the photon flash stemming from scattered bremsstrahlung inside the radiator. The target consisted of a cylindrical slab of natural iron (isotopic composition: 5.85% Fe, 91.75% Fe, 2.12% Fe, 0.28% Fe) w
author_names: Andreas Wagner

Daniel Bemmerer

Roland Beyer

Evert Birgersson

Anna Ferrari

Eckart Grosse

Roland Hannaske

A R Junghans

Mathias Kempe

Toni Kogler

Michele Marta

Andrija Matic

Ralf Nolte

Klaus Schilling

Georg Schramm

Ronald Schwengner

F P Weiss

Dmitry Yakorev
title: FAST NEUTRON CROSS SECTION MEASUREMENTS WITH THE NELBE NEUTRON TIME OF FLIGHT FACILITY
year: 2010