Applications of the IEEE-1394 CCD Camera for Beam Diagnostics in NSRRC

Transcription

1 Applications of the IEEE-1394 CCD Camera for Beam Diagnostics in NSRRC C. J. Wang, C. H. Kuo, Teno Yang, K. H. Hu, S. Y. Hsu, Jenny Chen, and K. T. Hsu National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30077, Taiwan, R.O.C. Abstract. A new generation digital CCD camera with IEEE-1394 interface has been adopted for the diagnostics purpose recently. The applications include synchrotron radiation monitor of the booster synchrotron, synchrotron radiation monitor of the storage ring, and the intensified digital camera for transient profile measurement. Wider dynamic range and the flexibility of the digital camera provide various functional enhancements for the diagnostics purpose. The effort and achievement will be summarized in this report. INTRODUCTION Imaging applications in the accelerator community are most often utilized to measure beam profile and interference fringes. The beam profile may convert form fluorescence and various optical diagnostics (SR, OTR, DR, etc.) [1,2,3]. Usually, the synchrotron light source radiation monitor measures beam profile and beam size of the synchrotron radiation light source for performance optimization, routine operation checks, and various beam physics studies. The monitor should be able to resolve minor transverse beam instability and movement. This tool has been useful for characterizing properties of electron beam analysis since its operation ten years ago. For example, the beam emittance is calculated from the measured beam size. By using the digital IEEE-1394 camera system [3,4], we are able to eliminate the frame-grabber stage of processing and directly transfer data at maximum rates of 400 MB/sec. IEEE is a mature bus technology supported by almost all modern computer operating systems. To improve the desired functions of the synchrotron light monitoring system [5], a major upgrade of the data acquisition and analysis system has been implemented recently. The main goals are to increase signal transmission quality, dynamic range, and linearity of the profile monitor, and better supports for data analysis. The integration of the system with the control system will be described in the following sections. Some results are also described in the system functional demonstration. The new technique and instrument are also a necessary part of the booster from previous operation experience, such as measuring transverse beam profile with various 462

2 operating and ramping energies. To provide many dynamic booster parameters, this diagnostic tool must be synchronously and automatically operated. The beam profile measurement system consists of optics, image data acquisition, and data analysis. This system is based on a new generation digital camera, which supports a wider dynamic range and faster transient image data acquisition. FEATURES OF THE IEEE-1394 CAMERA AND REASONS FOR ITS CHOICE Using a fully digital camera has two major advantages over the analog CCD camera. First, the A/D conversion is performed closer to the CCD sensor, keeping the amount of electronic noise to a minimum degree. Once the digitized signal is immune to noise, we can implement long haul (10 m ~ 10 3 m) applications in the accelerator research field. Various long hops solution is supported by the IEEE-1394 A/B interface. The noise immunity and isolation provided by this solution must be welcome in the accelerator environment. Secondly, unlike analog camera systems, digital systems do not suffer from pixel jitter. Each captured pixel value corresponds to a well-defined pixel on the CCD chip. In addition, high quality CCD sensors have a wider dynamic range and produce an excellent image in a low light environment. The IEEE-1394 interface is a hot pluggable and self-configuring, high performance serial bus interface that is capable of 400-Mbit/sec data transmission and will be enhanced to 3.2 Gbit/s for next generation products. The interface supports asynchronous (guaranteed delivery) and isochronous (guaranteed bandwidth and latency) data transfers. Therefore, data streams between devices are real-time with guaranteed bandwidth and no error correction needed. The IEEE-1394 complies with the memory mapped model on the IEEE1212 Command and Status Register (CSR) architecture standards with 64-bit addresses, which means standardized addressing, well-defined control and status registers standard transactions, and compatibility with other IEEE bus interfaces. Each node is re-clocked before data re-transmission. It is also a cost effective solution from the system integration point of view. Low cost scientific IEEE-1394 general-purpose CCD cameras were chosen for this stage of upgrade. These cameras were the QICAM series of QImaging. A progressive scan interline CCD sensor gives a resolution of 1.4 million pixels in the 10/12-bit digital output. The QICAM FireWire/IEEE-1394 digital interface offers ease of use and installation with one single wire connection between the camera and computer. There is no frame grabber or additional power supply required. Frame rates of up to 100 fps can be achieved with binning and ROI selection. The QICAM is compact with a C-mount for easy mounting of various lenses. An SDK is available for integration into custom applications. The software-driven camera allows you to set camera parameters on the fly and ensure that the captured image is the same as the preview image. Featuring improved gain control, reduced read noise, 8 x 8 binning, and enhanced readout electronics, QImaging's line of Fast 1394 Digital cameras delivers sustained data rates of 40 megabytes/sec, full resolution 12-bit sampling at 20 MHz, and frame rates of up to 290 fps. The Intensified Retiga utilizes an 18-mm Gen III image intensifier with high-speed intensifier gate control for nanosecond exposures. 463

3 Intensifier controls provide independent trigger and gate control to allow multiple high-speed exposures within a single frame. The intensifier is fiber-optically coupled to a high resolution 1360 x 1035 progressive interline CCD. The Intensified Retiga camera is Fast 1394 interfaced for simple connectivity. External synchronization and trigger features allow for highly synchronized imaging. The camera and intensifier control are done via IEEE-1394 bus. SYNCHROTRON RADIATION MONITOR FOR THE BOOSTER SYNCHROTRON HARDWARE CONFIGURATION The synchrotron radiation monitor of the booster consists of an image forming, image capture, CCD digital camera and analysis tools. This system is functioning with simple optics. A lens with focal length 500 mm is used to perform 2:1 optics. The band-pass filter is centered at 550 nm with 10-nm band-passes. The camera is working at external trigger mode. A motorized stage can move the CCD camera to accommodate various operating condition ranges. The system block is shown in Fig. 1. The optics has been optimized to minimize measured error resulting from diffraction as well as depth of field effects. Narrowed band-pass filters are used to reduce chromatic aberration and to extend the dynamic range of the CCD camera. The essentialities of the optics are to optimize the diffraction effect, depth of field and curvature. The FireWire IEEE-1394 CCD camera with 12 bits resolution was chosen to improve the functionality of the image capture and to increase dynamic range (a USB2- and Ethernet-based scientific CCD camera also emerges on the market at this moment). The camera embedded ADC on board provides exposure time control and multi-exposures. Long hauling extension of the IEEE-1394 interface is done with the aid of a fiber optical IEEE-1394 bus extender in the present system. Bending Magnet Molybdenum Mirror ρ = m Orbit Height : 1250 mm Lens f = 500 mm Camera Server Control Network Trigger IEEE-1394 Firewire Polarizer BPF, 550 nm, 10nm FWHM Qimaging QICAM Digital Camera FIGURE 1. Synchrotron radiation monitor optic layout of the booster synchrotron. 464

4 SYNCHROTRON RADIATION MONITOR FOR THE STORAGE RING HARDWARE CONFIGURATION The synchrotron radiation monitor hardware structure of the storage ring is almost the same as that of the booster. An achromatic lens is used to perform 1:1 optics. The band-pass filter is centered at 400 nm with a bandwidth of 10 nm. The camera is working at internal trigger mode. A motorized stage can move the neutral intensity filter before the CCD camera to extend the dynamic range. The system block diagram is shown in Fig. 2. Intensified CCD camera with beam splitter is also applied to observe turn-by-turn beam profiles to support various beam dynamic studies. Qimaging FireWire Digital Camera SiC Mirror Lens, f = 500 mm Double Slits Filter & Polarizer Q1 Q2 Q3 Bending Magnet ρ = m R1BM3 SD Q4 SF 3 o Port Lens f = 2895 mm Polarizer BPF, 400 nm, 10nm FWHM Motorized Step Neutral Density Filter Control Network Trigger (Optional) Serial bus IEEE-1394 Firewire Storage Ring SR Monitor Server FIGURE 2. The optic layout of the storage ring synchrotron radiation monitor. SOFTWARE ENVIRONMENT INTEGRATION The control software is separated into two layers. One is the remote node; the other is local node. The remote node is a normal control console based on LINUX PC that includes image data access and booster parameter control (database access). These client applications run via a LabVIEW server to configure CCD parameters, acquire the image and extract feature parameters from the image. This software of the node is located on workstation/unix and PC/Linux control consoles with commercial software MATLAB and LabVIEW installed. VI pages for routine operation are supported to operate the monitor that is useful for adjusting beam performance. The local node is based on a windows-based PC running the LabVIEW environment; that includes 1394 camera control, network service, image processing, and data analysis. This layer is to capture image and to perform pre-processing works. 465

5 This part of the front-end PC also handles some camera parameter control including trigger sources, exposure time, times of multiple exposures, etc. A local display page must be supported at the same time for local operating and verifying. Control Applications AP Consoles Computers (Compaq WS/Unix) (PC/Linux) Optics Hardware Diagnostics Program Database Logging Program Static Database Service Program Or Data Logging & Archiving Parameter Page Program Static Database Alarm Checking System Status Program Display Data Access Routines Dynamic Database (Slow Orbit, 10 update/sec) Data Access Routines Data Update Service Program IEEE-1394 CCD Camera SR Monitor SR Monitor Server Real-Time Trend Display Machine Parameters Service Routines Device Control Service Program CCD Control & Image Acquisition Machine Modeling (MPAP,APAP) LabVIEW Interface Matlab MEX Interface LabVIEW LabVIEW VI MATLAB SR Monitor Access Matlab Scripts AP Software Components On Control Consoles Control Ethernet PC/Windows LabVIEW Server Image Analysis e - External Trigger (Optional) FIGURE 3. Software environment of the IEEE-1394 imaging system The local PC is an image server to receive control commands from clients via TCP/IP protocol. This server is configured into a multithread software environment. These threads, based on the LabVIEW environment, include a digital camera driver, Ethernet communication, a database control code interface node (CIN), data processing and analysis by the Levenberg-Marquardt method CIN, and local/remote computer current status displays. These status displays include beam size, beam profile, beam image, the trigger delay relative to injection timing of the booster, and system debugging information. Image processing and analysis include extracting the orthogonal profile and beam tilt information of the profile. The pattern reorganization of syntax approach is to identify beam object and reduce beam instability inference. A least square fit is supported to extract beam size and center position. A statistical image analysis tool to analyze spatial moment will be implemented soon to achieve better real-time performance. The display page is broadcasted to the whole institute via a CATV system, and it is web accessible. For the demand user, MATLAB scripts are also supported; the users can configure their measurement by themselves and gain the benefit of the powerful image analysis toolbox in the package. A functional block diagram of the software environment is shown in Fig

6 PRELIMINARY TEST RESULTS Since the booster synchrotron is a 10-Hz machine, the injected beam is accelerated from 50 MeV to 1.5 GeV within 50 ms. Exposure time should be as short as possible for energy revolving measurements. The external trigger of the camera is synchronized to the 10-Hz trigger source. By adjusting the 10-Hz delay times, the different beam energy profile is captured from the camera. Available tools can adjust the 10-Hz delay time, camera exposure time, beam size analysis, and networking service. All information is also sent to a remote console. The relationship of measurement timing is shown in Fig. 4. An example of the measurement is also shown in Fig. 5. The vertical beam size is reduced when the energy is increased, and it is due to synchrotron radiation damping. Multiple exposures will be used at the low energy side due to low power radiation for measurement without a scarified linearity and dynamics range. Dipole Field (Gauss) Dipole Current (Ampere) Energy (GeV) 1.5 GeV Energy = 725 (1-cos(2πft)) MeV t = 5 ~ 50 msec f =10 Hz 50 MeV Measured Averaged Beam Size Beam Size (µm) CCD Trigger 0 to 100 msec adjustable delay CCD Exposure 0 msec 5 msec Injection CCD Exposure Time = 40 µs to 50 msec adjustable 50 msec Extraction 100 msec t FIGURE 4. Concept of the measurement sequence during energy ramping of the booster synchrotron. FIGURE 5. An example of observed beam profiles during ramping with various energies. One unit of the scale corresponds to 9.4 µm. The exposure time is 0.5 ms. 467

7 The graphic user interface at the remote console is shown in Fig. 6, which supports image access, profile access, exposure time of camera control, 10-Hz delay time control and booster beam current display. A similar user interface was implemented for the synchrotron radiation monitor for the storage ring as shown in Fig. 7. FIGURE 6. Booster synchrotron SRM user interface on control console. (a) Local control panel (b) Remote control panel FIGURE 7. Synchrotron radiation monitor control panel of the storage ring at (a) local PC/Windows and at (b) remote Workstation/Unix, PC/Linux control console. Intensified Retiga was used for low light applications. Here is an example to observe the turn-by-turn beam profile of the storage ring after setting the RF gap voltage modulation magnitude to double that of the synchrotron frequency (2 fs 50 khz); that helps to relieve the effect of the high order mode (HOM) of the cavity and to stabilize the stored beam. Modulation depth is about 5% of the total 800-kV RF gap voltage. For turn-by-turn observation, the exposure time of the camera was set to 400 ns, which is the revolution time of stored beam. Trigger input to the CCD camera is synchronized with the RF gap voltage modulation source. Different delay times after trigger were observed and shown as in Fig. 8. The horizontal beam size is at minimum when the RF gap voltage is minimal, and maximal beam size occurs at maximal gap voltage setting; also, the profile period value is relative to modulation 468

8 frequency. Stable horizontal beam size is obtained by the low speed imaging system that enables the integration procedure to be performed effectively. FIGURE 8. Observed RF gap voltage modulation effect corresponding to the beam profile. Period of the modulation signal is about 20 µsec. SUMMARY The preliminary results have shown that the purpose of wider dynamic range and better functionality of the imaging system, are all accomplished by the new generation IEEE-1394 CCD camera. Efforts put on for system integration are much lower than before. Development of various application programs to support a new imaging system is under way, and it will also provide a user-friendly interface for all kinds of users. ACKNOWLEDGMENTS The authors wish to thank Drs. J. Y. Hwang, K. K. Lin and C. C. Kuo for their comments and help for the work presented in this report. REFERENCES 1. M. Ferianis, Optical Techniques in Beam Diagnostics, Proceedings of EPAC 1998 and reference therein, pp W. P. Leemans, Survey Talk New Laser and Optical Radiation Diagnostics, Proceedings of LINAC 1998, pp K. A. Brown et al., IEEE-1394 Camera Imaging System for Brookhaven s Booster Application Facility Beam Diagnostics, Proceedings of EPAC 2002, pp A. Bank and P. Forck, Residual Gas Fluorescence for Profile Measurement at the GSI UNILAC, Proceedings of DIPAC 2003, Poster Session PM C. H. Kuo et al., Transverse Profile Measurement System at SRRC, Proceedings of EPAC 1994, pp