A REMOTELY DEPLOYED LASER SYSTEM

Transcription

1 DRNL/CP A REMOTELY DEPLOYED LASER SYSTEM FOR VIEWING/METROLOGY* Philip T Spampinato, Robert E Barry,Joseph N Herndon, and Madhavan M Menon Robotics and Process Systems Division Oak Ridge National Laboratory PO Box 2008 Oak Ridge, TN spampinatop@ornlgov Telephone: (423) The submitted manuscript has been authored by a contractor of the US Government under contract No DE-AC05-960R22464 Accordingly, the US Government retains a nonexclusive royalty-free license to publish or reproduce the published form of t h s contribution, or allow others to do so for US Government purposes' To be presented at the ANS SthTopical Meeting on Robotics and Remote Systems, April 25-29, 1999, Pittsburgh, Pennsylvania * This research was sponsored by the Office of Fusion Energy Sciences, US Department of Energy, under contract DE-AC05-960R22464 with Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp

2 DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof

3 DISCLAIMER Portions of this document may be illegible in electronic image products Images are produced from the best available original document

4 A REMOTELY DEPLOYED LASER SYSTEM FOR VIEWINGLMETROLOGY Philip T Spampinato, Robert E Barry, Joseph N Herndon, and Madhavan M Menon (Oak Ridge National Laboratory) PO Box 2008, Oak Ridge, TN lUSA spampinatop@ornlgov Tel: ABSTRACT A metrology system is being developed for in-vessel inspection of present day experimental, and next generation fusion reactors It requires accurate measuring capability to verify sub-millimeter alignment of plasma-facing components in the reactor vessel A metrology system capable of achieving such accuracy for next generation reactors must be compatible with the vessel environment of high gamma radiation, high vacuum, elevated temperature, and magnetic field This environment requires that the system must be remotely deployed A coherent, frequency modulated laser radar system that is capable of correcting for environmental vibration meets these requirements The metrologhiewing system consists of a compact laser transceiver optics module which is linked through fiber optics to the laser source and imaging units, that are located outside of the harsh environment The deployment mechanism configured for a next generation reactor was telescopic-mast positioning system This paper identifies the requirements for the metrologyhiewing system having precision ranging and surface mapping capability, and discusses the results of various environmental tests 1 Introduction The International Thermonuclear Experimental Reactor (ITER) was the next generation fusion reactor that was the basis for establishing the design requirements for the metrology system The performance and survival of plasma-facing Components (PFC) located within the reactor s vacuum vessel depend on precise alignment and positioning with respect to the plasma edge A remotely deployed and controlled three-dimensional metrology system was being developed to periodically verify the condition of the ITER in-vessel components and measure surface erosion These requirements are highlighted below, however, the use of this inspection system in present day fusion experiments does not require radiation hardening, and most likely will not require operation in magnetic fields This system has two basic functions: (1) frequent inspection to establish the dimensional status of in-vessel components and (2) extensive checking of in-vessel components and plasma-facing surfaces during scheduled maintenance shutdowns Figure 1 shows the inspection system deployed in the reactor vessel 1 Log No 35

5 *obewith )r Head Figure 1 The laser metrologyhiewing system deployed in the reactor vessel 2 Design Requirements The interior surface area of the ITER vessel was approximately 1500 m2in order to achieve acceptable mapping times, ten metrology systems were required; however, as few as three may be sufficient to map all surfaces for smaller present day reactors Each system had to be capable of acquiring in-vessel dimensional data accurately under harsh environmental and radiological conditions for ITER, and the test results indicated that these could be met, however, the requirements are significantly relaxed for present day machines For ITER, the equipment would have to withstand gamma radiation levels of 3 x lo4 Gy/h, operating in a 200 C environment, in vacuum conditions The undeployed system will be subjected to a cyclic magnetic field that peaks at 015 Tesla (T) In addition, there was a requirement to deploy the system into a constant magnetic field of 62 T And the system also had to function during scheduled maintenance activities when the vessel was to be at atmospheric pressure 2 Log No 35

6 3 Laser Radar Metrology System 31 Design Description A lightwave signal from the laser source sweeps linearly in frequency with time Lightwave signals which have traveled to the target or through the local oscillator fiber optic loop will have a delay which results in a constant beat frequency when the two signals are mixed at the detector This beat frequency is proportional to the path Iength difference between the target path and the local oscillator path This laser metrology system is designed to interface with a deployment mechanism, probably in the form of a telescoping boom Fiber optic connections, cooling fluid, and power signals will be provided through the deployment system to the laser scanner interface The scanner package will be completely self contained with all umbilical connections vacuum rated The connection of the scanner package to the deployment mast wii1 be designed for hands-on maintenance and handling, for a rad-worker wearing anti-contamination clothing The laser scanner is based on a frequency modulated, coherent laser radar (CLR) system under development by Metricvision (formall Coleman Research Corporation), with modifications by Oak Ridge National Laboratory (OWL) Y MetricVision s previous work in this area yielded a precision laser radar system with a wide field of view, extremely high range resolution, and a high degree of programmability ITER requirements however, demanded that a totally different sensor head and additional components be added to the current computer system in order to meet the ITER operational scenarios An additional challenge was to develop the metrology system for operation in a magnetic field inside the reactor vessel The sensor was to be used with the reactor field coils energized, hence electromagnetic devices such as electric motors for driving the system could be used in the vicinity of the sensor head Operation in the magnetic field requires that electric drive motors must be placed remotely from the CLR, and position sensors also must not be electro-magnetically based, or they must be placed remotely from the sensor Figure 2 shows a design configuration that meets the requirements of the laser scanning system 3 Log No 35

7 C C A -1T MAST INTERFACE D \ AZIMUTH ENCODER MANIFOLD SUPPLY ROTATIONAL BEARING ELEVATION ENCODER CABLE AND HOS E SPIRAL =?7 HEAT EXCHANGER COOLANT LINE SECTION C-C! HEAT EXCHANGER SECTION C-C SECTION D-D Figure 2 The design configuration for the ITER in-vessel inspection system 32 Operation The CLR will be capable of 18 meter range measurements with a precision of approximately 10 micrometers The design has a field of view that is +/- 185" in azimuth and 100" in elevation This is accomplished by sweeping a 7" azimuth x 100" elevation scan around the vertical axis of the CLR mast The resolution will be programmable from 1 point per mm' to 1point per cm' The data that is obtained is either range data which can be used to precisely measure PFC erosion, or reflectance data which can be used to create picture quality images without the use of illumination The CLR head steers the rangefinder laser beam, focuses the beam, and provides feedback on beam direction The next element is the rotary joint to steer the beam in the azimuthal direction and provide coarse positioning Fine sweeping is provided by an acousto-optic (AO) device within the sensor Below the rotary joint is the main sensor body which houses the focusing optics, the acousto-optic cell for beam steering, and a nodding mirror A polarization maintaining (PM) optical fiber carries the beam to the CLR head The beam is focused ' and passes into the A 0 crystal where it is swept from side to side The beam then passes through a wedge window, and then to the nodding mirror The wedge window is provided to angle the beam so that the nodding mirror can scan straight down 4 Log No 35

8 33 Radiation Effects on Sensor Components Little data exists on the compatibility of certain key components of the CLR system in a high radiation environment The A 0 scanner and the polarization maintaining fiber fall into this category In the A 0 device, the effect of high gamma radiation on the TeOz crystal was not known Samples of the TeOz crystal and the PM fiber were tested under high gamma radiation at the High Flux Isotope Reactor (HFIR) facility at ORNL Although the radiation produced noticeable discoloration (radiation induced browning) after the equivalent of 1000 h of ITER exposure, there was no noticeable effect on the transmission characteristics of the crystal in the wavelength range of interest Identical results were obtained for a second crystal Therefore, it was concluded that the basic TeO2 crystal is sufficiently rad-hard for the ITER application Future tests should include radiation exposure of the complete A 0 device including the lithium niobate electro-acoustic transducer The conclusions from the fiber irradiation were: (1) there was degradation in laser transmission with radiation dose, but the deterioration can be readily compensated by gain adjustments, and (2) although sufficient data was not collected for a graphic plot, the ratio of the two polarization components measured at two discrete intervals was constant, suggesting that the polarization did not change with radiation 34 Magnetic Field Effects Preliminary estimates have been made regarding the effects of operating the device in steady magnetic fields of up to 62 T The direction of the field is poloidal, and therefore is orthogonal to the direction of probe deployment The force on the boom during insertion is in the axial direction (only about 100 N for an insertion velocity of 1 d m i n ) and can be further reduced by reducing the insertion velocity The J X B forces acting on the electrical leads of the A 0 device also appear not to be problematic The primary challenge is to design a remote actuating device for adjusting and monitoring the mirror position that can operate reliably, Testing of three crucial components was done in the High-Field (Magnetic) Test Facility at ORNL The A 0 device, an optical precision encoder, and a piezo actuator were successfully operated in a field of 12 Tesla However, a second, capacitive encoder did not operate properly in the magnetic field 4 Precision Measurements 41 Range Measurements Several candidate materials are considered suitable for plasma facing structures Since the range accuracy of most laser based ranging systems is highly dependent on the 'surface material type, the materials proposed for ITER were analyzed to assess their effect on range measurements The materials investigated were beryllium, tungsten, and a carbon fiber composite (graphite) Each material was placed in a rotary stage and moved through a range of angles between 0 and 90 degrees with approximately 100 measurements made at each angle The standard deviation of the highest quality range measurements were found to be acceptable at angles of incidence up to 85 degrees2 5 Log No 35

9 42 Vibration Measurements The Metricvision CLR system incorporates a proprietary feature that allows range data to be instantly corrected for Doppler frequency shifts These could be caused by motion of the target, or motion of the deployment mast Hence, the effects of vibration can be corrected for in real time This feature could eliminate the effects on the system from building vibrations without resorting to complicated, mechanical schemes Laboratory testing was done in July 1998 to assess the data-correction feature for the moving target case and the moving mast case? The effects of vibration of the target and vibration of the mast on which the CLR is mounted were studied The vibration characteristics of the mast, using a 12 meter long mock-up of the mast designed for ITER, were measured using the CLR Doppler corrected range and velocity measurements were taken in the above experiments (Due to problems with the Doppler correction software, higher frequency range data could not be correctly acquired) Nevertheless, it was demonstrated that Metricvision s CLR-100, with a maximum data collection rate of 250 pointsk can be utilized in a vibrating environment when the vibration frequency is low (- few Hz) The high frequency limit can be extended by redesigning the device to facilitate a faster rate of data acquisition The CLR design for the ITER application would be at least four times faster than the current prototype The results of the tests show that the CLR can be utilized to measure plasma facing components in the presence of low frequency motions A brief account of the results of these measurements is provided in the following paragraphs Vibrating Target - Measurements on a vibrating target were made to determine if the motion of the target can be tracked by acquiring Doppler corrected range data at fast rates This has important applications such as studying real time motion of PFCs during plasma disruptions A loudspeaker driven by a signal generator was used as the variable frequency vibrating target Figure 3 is a schematic of the setup for the vibrating target test The CLR was focussed on the speaker diaphragm and measurements were made without using the Doppler correction feature, and using the Doppler correction 6 Log No 35

10 t I I Work tench asor Sand Figure 3 Schematic of the vibration test setup In its most basic form, the CLR produces an RF signal whose frequency is related to both the target s range and its velocity For a stationary target, an upsweep and a downsweep measurement produces the same frequency For a moving target, the upsweep measurement consists of a frequency associated with the target s range plus a component caused by the Doppler shifting of the light due to the velocity of the object In the downsweep case, this component reduces the range component Therefore, by taking the frequency difference between an upsweep and a downsweep measurement and dividing by 2, the frequency component caused by the velocity generated Doppler shift is obtained Range and velocity measurements are made at a rate of 250 measurement&, the limit of the CLR-100 Model The Doppler shift in frequency, Df, due to the target moving at a velocity V, is given by: f = 2V/L where L is the wavelength of the laser beam (1550 nm) The range data obtained with Metricvision s built-in Doppler correction function was found to be the same as that manually calculated from uncorrected data, obtained without Doppler correction, at low frequencies (Figures4 and 5 were taken at about 1 Hz) If the Doppler correction is not performed, however, the range information is not accurate, as can be seen in the data of Figure 5 compared to that of Figure 4 Actual speaker deflection was a few millimeters, not the centimeters that the uncorrected data indicate Figures 6, 7, and 8 show Doppler corrected data for 2, 4, and 8 Hz, respectively At higher frequencies a software problem within the Doppler correction function corrupted the range data, but velocity measurements could be made at frequencies up to 20 Hz Figures 9 and 10 show velocity measurements of the loudspeaker target with input signals of 10 and 20 Hz, respectively In principle the correction limits in the amplitude/frequency domain are determined by the design of the CLR For the ITER conceptual design, these limits are shown in Figure 11 The signal broadening limit determines the upper limit in frequency 7 Log No 35

11 Even Timesiamn meas Figure 4 Doppler Corrected Range Measurements from a loudspeaker with a 1Hz input signal II Range vs time for 1 HZ speaker vibration 4276 ',2,*s Figure 5 Range Measurements from a loudspeaker with a 1Hz input signal (no Doppler correction) - Even Timestamp range meas 2HZ Doppler Corrected Figure 6 Range measurements from a loudspeaker with a 2Hz input signal and Doppler correction 8 Log No 35

12 r Even timestamp range meas, 4HZ doppler corrected sample no (WS d s a m p l e ) I - Figure 7 Range measurements from a loudspeaker with a 4Hz input signal and Doppler correction -_ I Figure 8 Range measurements from a loudspeaker with an 8Hz input signal and Doppler correction 1Ohz vibration, velocity meas doppler corrected n nnu "a, "_ ~~ ~ sample no (008 dsample) Figure 9 Velocity Measurements from a loudspeaker with a 10 Hz input signal 9 Log No 35

13 ~ velocity meas for 20 HZ speaker 0, Figure 10 Velocity Measurements from a loudspeaker with a 20 Hz input signal These results show that the CLR could be utilized to study the motion of PFCs in real time, during plasma disruptions And from such measurements, the forces acting on the PFCs during disruptions can be estimated Vibrational Frequency (Hz) 100 Figure 11 Doppler-shift correction range for vibration 10 Log No 35

14 Mast Vibration A mock-up of the mast designed for ITER application was constructed The mock-up consisted of a 4335 in long "schedule 10" stainless steel pipe The natural frequency of this mast is given by: fn = (1732/2~)[(EIg)/0236 w 14)05 Hz, where, E = 30 x lo7 psi, I = 843 in4, w = 063 lb/in, and g = 3864 ids2 For the dimensions mentioned above, the natural frequency is calculated to be 118 Hz The natural frequency of the mast was measured using the CLR The mast was deflected by nudging its tip by 1 cm, and the deflections were measured as a function of time using the CLR Doppler corrections were applied to the data to take into account the movement of the mast The data, shown in Figure 12 yields a natural frequency of 104 Hz [1/(120 samples x 008 sedsample)], which is in good agreement with the calculated value 3Jg,,,, Figure 12 Range measurements vs time for the mast mockup, vibrating at its natural frequency Conclusions A remotely operated FM coherent laser radar system is being developed to remotely measure and view plasma facing surfaces in fusion reactors The work to date shows that the system is capable of providing both qualitative and quantitative information regarding PFC conditions Encouraging results were obtained from the testing of critical components for radiation tolerance and magnetic field tolerance, and Doppler correction tests demonstrated the ability of the system to correct data taken in vibration conditions Although the device is being developed for metrology and inspection of fusion reactor components, it can also be applied wherever precision measurements are required in areas that are inaccessible 11 Log No 35

15 Acknowledgments This research was sponsored by the Office of Fusion Energy Sciences, US Department of Energy, under contract DE-AC05-960R22464 with Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp This report is an account of work assigned to the US Home Team under Task Agreement No, N23TD15FU within the Agreement among the European Atomic Energy Community, the Government of Japan, the Government of the Russian Federation, and the Government of the United States of America on Cooperation in the Engineering Design Activities of the International Thermonuclear Experimental Reactor ( ITER EDA Agreement ) under the auspices of the International Atomic Agency (IAEA) The report has not been reviewed by the ITER Publications Office References 1 R E Barry, M M Menon, and A Slotwinski, A Three Dimensional Remote Metrology System for the International Thermonuclear Experimental Reactor, Proc American Nuclear Society Meeting, San Francisco, Calif (1995) 2 P Spampinato, R E Barry,M M Menon, M A Dagher, A Slotwinski, A Laser Scanning System for Metrology and Viewing in ITER, Proc Sivth International Symposium on Robotics and Manufacturing,Montpellier, France (1996) 3 Final Report: Development of In-Vessel Viewing/Metrology Equipment, ITER US Home Team for Remote Handling, Robotics and Process Systems Division, Oak Ridge National Laboratory, Oak Ridge, TN (1998) 12 Log No 35