Alignment Monitoring Research Articles

Performance of semitransparent silicon strip sensors for high precision optical alignment monitoring systems

Novel semitransparent optical position sensors ("ALMY sensors") have been developed for the alignment monitoring systems of modern large-area tracking detectors. The high transmittance of up to 90% allows to align more than 10 sensors along a collimated laser beam. A position resolution of 1 /spl mu/m and an uncertainty in the deflection of the traversing laser beam of less than 3 /spl mu/rad have been achieved for sensitive areas of several square centimeters. For the thin-film amorphous silicon sensors, the required laser intensity could be minimized such that the performance is not deteriorated by aging effects.

Semi-transparent silicon strip sensors for the precision alignment of tracking detectors

Novel semi-transparent optical position sensors (‘ALMY sensors’) have been developed for the alignment monitoring systems of modern large-area tracking detectors. More than 10 sensors can be aligned along one laser beam. The thin-film amorphous silicon strip sensors provide up to 90% transmittance for red laser light combined with minimum beam distortion and a typical position resolution of 1 μm over a sensitive area of several square centimeters.

A silicon micro vertex detector for the ZEUS experiment

At the time of the HERA luminosity upgrade in the year 2000, the ZEUS experiment will be extended with a silicon micro-vertex detector. The barrel part of this vertex detector is a 60 cm long cylinder with silicon sensors arranged around the beam pipe. The forward part consists of four circular-shaped disks. In this paper the design criteria are explained. Since the front-end electronics are incorporated inside the active volume of the detector an important issue is the cooling. In addition, the alignment monitoring and geometrical survey scheme are presented.

The control and data acquisition system of a laser in-vessel viewing system

This paper presents the dedicated control and data acquisition system (CADAS) of a new laser in-vessel viewing system that has been developed for inspection purposes in fusion experiments. CADAS is based on a MC68060 microprocessor and on-site developed VME instrumentation. Its main aims are to simultaneously control the laser alignment system as well as the laser beam deflection for in-vessel scanning, acquire a high-resolution image and support real-time data flow rates up to 2 Mbyte/s from the acquisition modules to the hard disk and network. The hardware (modules for control and alignment acquisition, scanning acquisition and monitoring) as well as the three levels of software are described.

Real-time three-dimensional motion analysis for patient positioning verification

Background and purpose: This paper describes the technology and methods involved in a system for automatically checking the position of patients at radiotherapy units. This is proposed for improving the accuracy in the irradiation geometrical set-up, which is a crucial factor in radiotherapy quality control. Materials and methods: The system is based on real-time opto-electronics and close-range photogrammetry and detects multiple passive markers placed on selected patient skin landmarks. Patient alignment and position monitoring is carried out by comparing the current three-dimensional positions of the markers with those of an initial reference position acquired during the simulation procedure and/or the first irradiation session. The system was used to measure the accuracy of conventional laser centering techniques for patient repositioning. Inaccuracies due to breathing and random movements were also taken into account. Professional technicians were asked to reposition three volunteer subjects carefully using a traditional laser centering procedure. Results: The results revealed significant repositioning errors even in highly controlled conditions, affecting particularly body areas relatively far from the skin reference points used for laser alignment. Conclusions: The outcome of the experimental application of this technology confirms its potential as a tool for patient repositioning and automatic detection of any errors caused by breathing or other unpredictable movements. The real-time feedback on the patient's position given by the system provides operators with appropriate visual indices and allows them to take suitable countermeasures in case of significant failures. In addition, the use of the system output for automatic position control is envisaged.

Investigation of electronic packaging materials by using a 6-axis mini thermo-mechanical tester

Most existing mechanical testers are at most bi-axial and in general too large for microelectronic materials and structures. Existing mini testers are primarily single axis without any active specimen alignment monitoring and adjustment capability. Fundamental investigation needs to be conducted for packaging materials in terms of deformation and fracture processes, constitutive laws, and failure quantities. In this paper, a unique 6-axis sub-micron thermo-mechanical fatigue tester is described, including some calibration work for both load cell and machine stiffness. For the first time, an active specimen alignment monitoring and adjustment was demonstrated on a single lap shear sample, assisted by a high resolution laser moiré measurement system. This paper also presents results for two types of polymer films, one lead-free solder alloy, and some other conventional materials. In particular, deformation and failure mechanisms for two polymer films have been discussed.

The optical alignment monitoring system of CHORUS (RASNIK)

For the first time, several imaging RASNIK optical alignment systems have been installed in a running experiment. Calibration, performance, and results of datataking are reported.

Shaft Alignment Monitoring Using 3D-Coordinate Measurement on the Heavy Icebreaker CCGS Louis S. St. Laurent

A detailed description of 3D-coordinate measurement for shaft alignment monitoring is presented. The method was used at Halifax-Dartmouth Industries Ltd. (HDIL) during mid-life modernization and refit of a heavy icebreaker, CCGS Louis S. St. Laurent. The vessel was undergoing substantial repairs of its steel structure, a significant part of which was concentrated in way of the propeller stern tubes and shaft line foundations. The application of an electronic theodolite allows measurement of the exact position of nine points along each of the three shafts within half an hour.

Design and operation of the multipulse Thomson scattering diagnostic on DIII-D (invited)

This paper describes the design and operation of a 40 spatial channel Thomson scattering system that uses multiple 20-Hz Nd:YAG lasers to measure the electron temperature and density profiles periodically throughout an entire plasma discharge. As many as eight lasers may be fired alternately for an average measurement frequency of 160 Hz, or they may be fired in rapid succession (<10 kHz), producing a burst of pulses for measuring transient events. The high spatial resolution (1.3 cm) and wide dynamic range (10 eV–20 keV) enable this system to resolve large electron density and temperature gradients formed at the plasma edge and in the scrape-off layer during H-mode operation. These features provide a formidable tool for studying L–H transitions, edge localized modes (ELMs), beta limits, transport, and disruptions in an efficient manner suitable for large tokamak operation where shot-to-shot scans are impractical. The scattered light is dispersed by interference filter polychromators and detected by silicon avalanche photodiodes. Laser control and data acquisition are performed in real time by a VME-based microcomputer. Data analysis is performed by a MicroVAX 3400. Additional features of this system include real-time analysis capability, full statistical treatment of error bars based on the measured background light, and laser beam quality and alignment monitoring during plasma operation. Results of component testing, calibration, plasma operation, and error analysis are presented.

A compact, digital, optically isolated control and support system for a field-emission source on the 200 kV STEM

In the third order corrected STEM, optimization of the probe subject to the limits of fifth order spherical aberration and chromatic aberration leads to a choice of 200 KY for the accelerating potential. In order to obtain sufficient stability at this voltage it Is necessary to house the accelerator, high voltage pover supply and electron beam source in a dry N2 pressure vessel and to cover the source housing vith a polished corona discharge shield. All support electronics for the the beam source must be mounted vlthin this shield. The field emission tip beam source requires a stable extraction voltage, a tip chamber high vacuum system, and a flashing circuit. A compact, optically isolated, digitally controlled system has been built which provides these primary functions along with support functions such as tip alignment, current and voltage monitoring and pover storage.The major concerns in design of the control system were pover conservation, transient protection, acoustic isolation and compactness.

New approaches in analysis of soft X-rays using gratings

The properties of the state-of-the art transmission gratings are discussed and put in context with reflection gratings, zone plates and multi-layer mirrors. Efficiency as well as resolution of the systems are comparable but the different approaches have widely different emphasis and fields of application. The importance of alignment and continuous monitoring of the performance of a grazing incidence monochromator is emphasized and results from an analysis of alignment effects are presented. New developments in multiple combinations of different optical elements are discussed and proposed as important applications of synchrotron radiation.

Theory of alignment monitoring by diffraction from superimposed dual gratings

Theoretical considerations are presented on characteristics of the optical-alignment technique using dual gratings. The general formulation of the diffraction pattern is derived for superimposition of dual amplitude–phase gratings, as functions of aperture ratios for gratings and separation gaps between dual gratings. Numerical analyses reveal characteristics for precise positioning control or alignment technique, which utilize the detection of the minimum value of the first-order diffraction beam or the detection of the zero cross point of the difference in intensities between +1- and −1-order diffraction light for dual gratings. Alignment errors due to variations in an incident light angle, displacement in detector position, and fabrication errors for the gratings are also discussed.

High Precision 10-cm Aperture Penta and Roof-Penta Mirror Assemblies

10-cm aperture penta and penta-roof-type mirror assemblies of unusually high precision and stability for this aperture have been designed and fabricated by Perkin-Elmer Corporation. These assemblies, which are part of the internal optical alignment monitoring subsystem of a large (122-cm) aperture telescope, provide 90 degrees deviations within +/- 1 sec of arc. In order to minimize degradation of the reflected wavefront due to variations of the thermal environment, each assembly is constructed of optical quality Cer-Vit mirror plates contacted to Cer-Vit blocks which establish and preserve the proper angular relationships between the reflecting surfaces. Thermal, vibration, and shock tests of prototype units have confirmed their inherent resistance to adverse environmental influences. In this paper, the method of construction of these prototype units is described and the results of various tests are given. Since the reflecting surfaces of the mirrors are dielectric coatings which maximize reflectivity in the 0.9-0.95-mu wavelength region but have very low reflectivity at visible wavelengths, a real-time, electrooptical interferometric technique was developed for evaluating with near-infrared radiation the wavefront deformation caused by one of these assemblies. This experimental technique is also described.