Levitating Laser Heating Techniques for Synchrotron Radiation Experiments.

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1 Levitating Laser Heating Techniques for Synchrotron Radiation Experiments. A Thesis submitted to Aberystwyth University in the subject of Physics for the Degree of Master of Philosophy. By Stephen David Fearn February 2009

2 Abstract This project is about the design, development and construction of individual components and equipment associated with a 125 watt Carbon Dioxide laser heated aerodynamic furnace that was capable of levitating and melting a 2mm sphere in a dedicated containerless nozzle. The technique allows a specimen to be heated to 3000º Kelvin, and the purity of the sample to be investigated without contamination. This novel experiment was designed and tested at Aberystwyth University, and subsequently installed and operated on the Synchrotron Radiation Source 6.2 x-ray beamline. Experiments using the laser heated aerodynamic furnace on refractory oxides at high temperatures have allowed the successful investigation of structural dynamics at the nano and atomic level, by the use Rapid2 detectors, with particular interest in the recalescence and supercooled regions, with subsequent investigations resulting in the discovery and observations of the polyamorphic rotor.

3 Acknowledgements I would like to take this opportunity for thanking all those people who contributed both directly and indirectly, to the completion of this thesis. Prof. G. Neville Greaves for showing the confidence in allowing me to do this thesis and in giving me a free reign in the design and development of this exciting experiment. Dr Tudor Jenkins for his guidance and support in the writing of this thesis. Dr Dave Langstaff for his help and support in the initial development of the LabVIEW software. Dr Martin Wilding, Dr Florian Kagl and all the academic staff of the Institute of Mathematics and Physics. Dr Louis Hennett for his guidance of the experiment as it has developed over the last few years. Mr Clive Willson for his continual support. Mr John Parry and Mr David Francis for their outstanding contribution in the mechanical fabrication of the experiment, and their continual support in the development of the instrumentation. Mr Les Dean and Mr Dave Lewis for the help in electronic designs. Dr Chris Martin 6.2 beamline Daresbury Laboratories for all the outstanding contributions towards the success of this facility, from initial installation to operational experiments. Mr Alfie Nield for all his technical help and support during the initial installations onto the Daresbury Beamline. All the staff of the Daresbury laboratory.

4 Levitating Laser Heating Techniques for Synchrotron Radiation Experiments Contents Chapter 1 Overall Design Bench Optics table Breadboard Polycarbonate box Pyrometer mounts Sample holder Mirrors External Interfacing References Appendix Detail plans of beamline 6.2 Chapter 2 Carbon Dioxide Laser Inductive heating Laser Operation Synrad evolution laser RF3000 laser power supply Environmental control facilities UC2000 Laser controller Laser Diode Auxiliary Signal Connector Conclusions References 29

5 Chapter 3 Optical Pyrometry Choice of Optical Pyrometry Black body radiation Luxtron optical pyrometer Basic pyrometer operation Pyrometer Input Options Sample Alignment Daresbury Synchrotron Experimentation LabVIEW Conclusions References Luxtron calibration report 41 Chapter 4 Mass Flow Controller Volume reservoir Brooks mass flow controller Description of mass flow controller Computer use of DDE Software Conclusions and Future experiments 47 Appendix MODEL 5850S 48 Flowtech Calibration Certificate 49 Chapter 5 Laser Power Meter Introduction Probe 51

6 5.3 RS232 serial communication Experimental procedure Further investigations 53 Appendix Certificate of Calibration Power Instrument 54 Certificate of Calibration Powermeter Probe 55 Chapter 6 Optics Objectives and initial configuration Optics table Beam Splitter Mirrors Focusing lenses Fixed focal length mirrors Mirror alignment Daresbury configuration Remote control mirrors Thermal mirrors Final mirror choice 66 Appendix Circuit diagram of servo controller 67 Acknowledgements 67 Chapter 7 Nozzle Design and Sample Stage for liquid levitation Boron Nitride nozzles Sample sphere characteristics during levitation Nozzle dimensions Aluminium nozzles 73

7 7.5 Water cooled sample stage Sample stage vertical adjustment Future developments of the sample stage 77 Chapter 8 79 X-ray beam alignment 8.1 X-ray beam characteristics Beam size Establishing datum Line Beam alignment and size GDA software XAFS table Horizontal nozzle alignment Vertical nozzle position Detector systems Conclusions References 90 Chapter 9 LabVIEW Software Control LabVIEW LabVIEW interfacing D/A conversion LabVIEW software Laser and software status Manufacturing anomalies and interference Optical Pyrometry LabVIEW control software Vertical sample stage interface External triggering 103

8 9.10 Future developments 104 Chapter 10 Laser Shutter Laser beam shutter Construction and operation Shutter Status Remote indicator Remote shutter key control box System upgrade Conclusions 112 Chapter 11 Safety Protocol and video diagnostics Safety factors for the use of class 4 lasers Interlock control system Experimental alignment Laser Emergencies Emergency Kill switches Laser safety glasses Polycarbonate enclosure Smoke detector Ceramic beam stops Welding glass filters Compressed air Compressed gases Chilled water Video camera surveillance 123

9 11.15 Radio cameras Microscope camera Sample plane video camera External safety camera High speed camera Recording video imaging of liquid drops 127 Appendices 1. Photo-Sonics Specification sheet 2. Interlock and shutter circuit diagram 3. Standing orders Chapter 12 Results Melting Recalescence Supercooling High and low density transition Future experiments Conclusions Twin laser system Twin laser shutter Video monitoring References Published papers 141

10 List of Figures Figure A. Schematic operation of the laser furnace in conjunction with the equipment on the 6.2 beamline at the Daresbury Synchrotron Radiation Source. 3 Figure B. Molten sample levitating at 2000º K in the x-ray beam, picture taken through Pb window of the 6.2 beamline hutch Side elevation schematic, illustrating optimal sample position with respect to x-ray beam position and wide (WAX) and small (SAX) angle detectors Schematic plan and side view, illustrating initial component layout with respective dimensions Side and front view of all experimental components in position assembled on the optics bench on the dedicated laser stand at the Aberystwyth Material Physics Laboratory Plan view looking into the polycarbonate enclosure during furnace development Internal view of the polycarbonate box during initial setup on the 6.2 beamline Beamline view of the levitating furnace during setup with the guide laser illuminating the levitating sample; also in view are the sample stage cooling pipes and the gas delivery pipes Levitation furnace installed into the 6.2 beamline at Daresbury Laboratory Inductive heating and levitating techniques Schematical laser operation Synrad evolution laser attached via adjustable legs to optics bench RF3000 controller and dedicated power supply a) Chilled water pump unit for regulating temperature through the heat exchanger. 22 b) Heat exchanger for dissipating heat from the laser head through the demineralised water system at Daresbury Laboratory UC2000 laser controller incorporating manual and remote control of the laser Computer serial communication serial port and LabVIEW digital to analogue communication port. 24

11 2.8 Externally coupled laser diode used for optical alignment of the carbon dioxide laser Remote monitoring indicator box for showing RF3000 and laser status; also included is solenoid activation indicator to confirm that the shutter is operational Position of the optical pyrometer head with respect to the high temperature levitating sample Graph illustrating relationship between relative energy and wave length Luxtron optical pyrometer Schematic block diagram of the operative of the Luxtron optical pyrometer Initial development layout of the pyrometer position prior to beamline installation Final position using H bridge support enabling the pyrometer to straddle the x-ray delivery tube Laser diode adaptor used for optical pyrometer alignment onto the levitating sample H bridge pyrometer configuration suitable for straddling the x-ray delivery tube RS232 pin identification and protocol Computer port communication and Luxtron communication facilities Schematic layout requirements of control gas delivery for levitation Schematic operation of the Brooks mass flow controller, enabling controlled delivery of gas to the sample head for levitation Computer communications port and mass flow controller setup RS232 interconnections between digital mass flow controller and computer Manufacturer schematics of the Brooks mass flow controller Molectron laser power meter Molectron power head Schematic experimental layout of power meter Powermeter instrument calibration certificate. 54

12 5.5 Powermeter probe calibration certificate Sample stage position on the 6.2 Beamline with x-ray and laser beam paths Schematical component layout of aerodynamic laser-heated furnace Schematic experimental layout of plain mirrors and carbon dioxide focusing lenses Illustration of relative positions of focused mirrors and respective focal lengths Video image taken from the microscope camera illustrating levitating molten sample with heated beam position Mirror profiles illustrating vertical and horizontal adjustment, allowing accurate positioning of the laser beam onto the sample Confined geometry of the levitator laser furnace installed on the 6.2 beamline Server motors illustrating vertical mirror position adjustment Master and slave control box used for remotely controlling the accurate position of mirrors Customized mirror heat sink for dissipating heat generated by laser power including remote vertical pitch adjustment Circuit design of servo controlled motors, adapted for mirror motor control Examples of boron nitride nozzles showing the dimensions of the sample throat and gas inlet Boron nitride nozzle viewed through electron microscope Polished surface structure of Boron nitride nozzle Nozzle schematic for cup and cone shaped designs Illustration of sample instability during levitation Nozzle design and cooled sample stage Plan view of cooled sample stage incorporating gas inlet and x-ray beam path Profile view of cooled sample stage illustrating optical pyrometer and laser beam path. 75

13 7.9 Vertical sample stage movement incorporating analogue and digital feedback Customised levitator head with sample stage cooling designed to minimalise air scatter Prototype aerodynamic levitator module designed to handle oxidising liquids and sufficiently small to be installed within the 60 cm radius space within the WAXS detector Illustrating the position of the sample holder with respect to the X-ray beam position and the WAXS / SAXS detectors Profile illustration position of the sample and levitation stage with respect to the X-ray beam path and the WAXS / SAXS detector Theodolite image illustrating central data line taken using a mobile phone camera Screen shot view of the GDA software illustrating the position and control of all 5 sets of slits X-ray sensitive paper positioned behind the sample, indicating beam position and size X-ray beam attenuation graph for horizontal sample position Polaroid image illustrating the shadow of drill position and sample holder in x-ray beam Drill position on top of the sample stage enabling horizontal position of the x-ray beam X-ray attenuation as the drill bit passes through the beam in the vertical position Block diagram and specification of Rapid2 detector WAXS detector template allowing accurate repositioning of the detector in the x-ray beam Instrumentation for laser heating and temperature measurement controlled by LabVIEW Flow diagram of LabVIEW software initialisation for computer laser control Adlink Technology digital to analogue interface board which gives proportional output to the UC2000 laser controller Schematic of digital to analogue convertor used to control UC2000 laser controller. 95

14 9.5 Analogue output connections of the Adlink Technologies interface board used to control the UC2000 laser controller LabVIEW construction block diagram window designed to communicate with the UC2000 laser controller and Luxtron optical pyrometer Front panel interface for LabVIEW control of laser heating and temperature monitoring Synrad software specification anomaly Co plot of pyrometer output and laser power for a levitating super cooled drop, showing intermediate interference spikes LabVIEW software flow diagram for initialising and communicating with the Luxtron optical pyrometer Detailed vertical adjustment of liquid drop height at different temperatures LabVIEW stepper motor control of vertical sample stage, with analogue and digital feedback potentiometers for sample position Schematical layout of laser shutter position Laser beam shutter schematics Internal layout of the laser shutter illustrating the default position of the laser beam stop, the default return springs, interlock beam micro switches, the two way operating pneumatic ram and solenoid actuator External layout of laser shutter incorporating solenoid status indicator, pneumatic ram and two way actuator Laser shutter circuit diagram, incorporating air pressure switch, beam block position monitoring and status indicators Remote laser status indicator panel and solenoid activation indicator Remote shutter key control panel, with shutter status indicators, remote shutter closing and emergency laser disable panic button. 111

15 10.8 Remote shutter control circuit diagram Final operational laser shutter with compressed air indicator for monitoring air flow into two-way pneumatic ram Schematic diagram of laser levitator furnace interlock system and how it integrates with experimental beam line interlock system Experimental hutch interlock hazard display panel on MPW beam line Laser interlock control panel Laser emergency stop and shutter control box Polycarbonate box on test bench and polycarbonate box installed onto beamline Plan layouts of video cameras Radio camera on optical mount Video footage of liquid sample Microscope camera Video monitor illustrating the calibrated position of the liquid sample in the x-ray beam Photo-Sonic high speed camera remotely controlled to study molten samples Experimental control desk incorporating LabVIEW laser and pyrometer control computer, mass flow control computer, and video camera monitoring station and recording facilities Real time video capture of levitating molten sample, illustrating laser beam hot spot Co plot illustrating heating and cooling cycle of alumina, highlighting the melting stage and recalescence regions as special regions of interest SAXS data for supercooled AY15, AY20 and AY25 liquids revealing the intensity of random fluctuation measured at the Synchrotron Radiation Source beamline Changes to the principle peak for AY20 between 2392K and 1515K, measured at the Synchrotron Radiation Source beam line Oscillating rotor. 136

16 12.6 Sequential rotating images of the liquid sample in the supercooled region Video images A to F illustrating horizontal rotation. Fluctuating image brightness for one pixel area compared with pyrometer output for one 4-s cycle. 180º rotations take 600ms, after which the bead is virtually stationary Pyrometer readings of oscillating polyamorphic rotor. 138

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