Equipment Operating Manual for X-ray Framing Camera Project

Last Revision by: Peter Susalla / 1 January, 2004

Table of Contents

Part 1: General Introduction x

Part 2: Operating Procedures

Part 3: Vacuum System x

Part 4: X-ray Source x

Part 5: X-ray Framing Camera x

Part 6: Miscellany x

Part 7: Appendix x

Part 8: Glossary x

Part 1 – General Introduction

This manual is designed to be a step-by-step guide to operation of the Drake Lab vacuum system and associated x-ray framing camera instrumentation, as well a general reference for the above. The reader will find a complete guide for all facets of the experiment, including pumping down and repressurizing the vacuum chamber, changing out instrumentation, manipulating and using the x-ray source, and taking pictures with the framing camera. This guide will also contain other information useful to the understanding of the operation of the system as pertinent. Fundamental concepts relative to these procedures will be discussed briefly to provide a basic introduction to the user, and will largely be qualitative in nature. A bibliography will be provided of cited works and for further reading on these topics. At the end of this guide the user will also find a glossary of terms and an appendix for formulae and acronyms. There is also an accompanying binder of manufacturer’s instruction manuals for all of the appropriate equipment.

A Checklist (in green font) with primary instructional steps will be found in Part 2. Before operating any of the equipment read the safety warning on the following page. Throughout the text additional safety warnings will be bold and red, while operation caveats will be bold on yellow. It is of the utmost importance, for the safety of the user and others using the lab that these warnings be fully read and understood.

WARNING: The use of this equipment risks exposure to high voltages, high temperatures and some hazardous chemicals. All users of the system are expected to take proper cautions, wear protective equipment when necessary, have completed basic OSEH laboratory training and system checkout training administered by Dr. Drake, Eric Harding or Peter Susalla. For specific safety warnings on the equipment being used, consult this manual and the manufacturer’s user guide. This lab is compliant with OSEH regulations and maintains a chemical inventory and Standard Operating Procedures for dangerous substances. Emergency contact information can be found by the lab phone, in the ‘Chemical Hygiene Plan’ binder (the ‘Big Red Book’), and on the door to the lab. Call one of the emergency contact personnel if there is ever any doubt about a procedure or a problem arises. Contact numbers are posted near the phone for the Department of Public Safety and OSEH. Call 911 immediately in the event of a medical emergency or fire.

Part 2 – Operating Procedures

2.1 – Introduction

This section provides a convenient and thorough checklist for operating all of the main pieces of equipment necessary to produce data from the framing camera. It is worth reiterating that the user must follow all operational and safety warnings listed below. Failure to do so could cause damage to the instruments or injury to the operator.
2.2 – Vacuum System Startup and Shutdown Procedures:

2.2.1 – Startup:

This section is a checklist for pumping the system down from atmospheric to operating pressure.

  1. See that all external valves are closed, and that all flanges are properly bolted or clamped together.
  1. Verify that the Electro-Pneumatic Gate Valve (EPGV) is closed (switch to ‘off’) and that the main system nitrogen valve is open (the small ball valve under the flow hood, not the two needle purge valves).
  1. Make sure both manual gate valves are open all of the way (turn counter-clockwise).
  1. Turn on the scroll pump by plugging it into the power strip on the floor of the vacuum rack. The scroll pump will produce a loud, ‘gurgling’ sounds for a 20-30 seconds while it starts up; this is usual.
  1. Once the scroll pump has been operating for 2-3 minutes, open the EPGV, which will expose the vacuum chamber to the pump. There will be an audible change in the scroll pump as air is pumped out. After a few minutes the system should reach a rough vacuum; confirm this with the convection gauge (which should read less than 100mtorr)
  1. Plug in the turbo pump fans (the cord with the large, yellow plug)
  1. Once the system is at 100mtorr or lower, turn on the turbo pump (lower right-hand button)
  1. After a few minutes, turn on the ion gauge controller and the ion gauge filament.
  1. The system should reach a pressure in the 10-5 torr range within 30 minutes.

2.2.2 – Instrument Change-out:

This section is a checklist for removing and replacing either the x-ray source or the Maxmodule while the main system is left under pressure.

  1. Close the manual gate valve seals off the appropriate volume.
  1. Open the needle valve to allow a slow flow of nitrogen into the airlock. If the Maxmodule is being removed, loosen the four retaining bolts (and hold onto it!!), as there is no pressure release valve. The airlock should reach atmospheric pressure in a few seconds.
  1. Remove the instrument and seal the exposed end with aluminum foil or a flange cap, purging with nitrogen to keep the airlock as clean as possible.
  1. Return the instrument after modifications have been made and bolt it securely back into place.
  1. Turn off the ion gauge filament.
  1. Close the EPGV. This will cause pressure to rise in the turbo pump foreline, so complete the following steps as quickly as possible.
  1. Open the ball airlock ball valve, exposing the volume to the scroll pump.
  1. Wait at least 30 seconds, and then close the airlock ball valve.
  1. Open the airlock gate valve. At this point an audible change will be heard in the turbo pump as it works to bring the newly exposed volume down to a high vacuum.
  1. Open the EPGV.
  1. Turn on the ion gauge filament.

2.2.3 – Shutdown:

This section is a checklist for returning the system to atmospheric pressure from the operating high vacuum.

  1. Make sure that all instrumentation and power supplies are turned off before beginning the shutdown. Failure to do so could result in damage to the instrumentor a possible electrical hazard.
  1. Make sure that the x-ray-side airlock is at high vacuum, and that the manual gate valve is open all of the way.
  1. Turn off the turbo pump. The pump’s blades will spin down on their own due to friction, so allow at least 15 minutes before completing the next step.
  1. Close the EPGV.
  1. Unplug the scroll pump from the power strip.
  1. Slowly open the x-ray-side needle valve and start a slow flow of nitrogen into the system. Watch the convection gauge and see that the pressure rises by no more than a few torr per seconde. When the system reaches atmospheric pressure nitrogen will flow out of the pressure release valve; turn off the nitrogen flow.

2.3 – X-ray Source Startup and Shutdown Procedures:

2.3.1 – Startup:

  1. Follow the Vacuum System Startup Procedure as described above. NOTE: Never run the x-ray source unless the system pressure is 10-5 torr or lower. Continually monitor the pressure throughout the use of the source, and if pressure rises to 10-5 torr, turn it off immediately.

2.Connect the anode feedthrough to the power supply labeled “Anode Voltage” with an SHV cable, and connect the two cathode feedthroughs to the back of the X-ray Source Control.

3.Connect the photodiode to the Keithley multimeter with a coaxial cable, turn it on, and set the multimeter to ‘DCI’. Allowing the multimeter at least 30 minutes to warm up will allow it zero itself properly.

4.Turn the anode power supply on and make sure it is set to 0V. Check that the Cathode Heating Current and emission control switches are all set to 0, then power the X-ray source control on.

5.Set the Cathode Heating Current dial to around ‘50’ then wait 5 minutes. The heating current should rise to around 5A.

6.Slowly increase the Cathode Heating Current to 6A. The heating current dial should read ~80-90

7.Set the emission control ‘Coarse’ switch to 8, set the anode power supply to 100V, and turn the high voltage switch on the power supply ON.

8.Slowly increase the anode voltage in increments of 500V, noting the current readout on the power supply and the analog ‘electron beam current’ meter on the X-ray Source Control: they should roughly be equal. Also note the photodiode current. It should also start to increase when anode voltage gets to around 3000V.

9.Increase the anode voltage to 4750V. The x-ray source is now at full operating power.

10.With the anode voltage at 4750kV, turn the x-ray emission ‘Coarse’ switch to 10; then increase the ‘Fine’ switch slowly. A notable increase in x-rays should be detected by the photodiode. Set the electron current to 0.5mA.

2.3.2 – Shutdown:

  1. Turn both emission control switches to zero.
  1. Set the anode power supply to 0V and turn it off.
  1. If you plan to remove the x-ray source from the system, set the cathode heating power dial to zero and turn off the Source Control. If not removing the source, set the heating power such that ~3A of current flows through the cathode. This will allow ultraviolet light and heat produced by the cathode to free water vapor trapped in the metal surrounding the source head.
  1. Disconnect all cables.
  1. Turn off the multimeter.

2.4 – RGA Startup and Shutdown Procedure

  1. Pump the system down to high vacuum. The system pressure must be below 10-4 for the RGA to function properly. Failure to pump the system below this pressure will cause damage to the RGA filament and other components.
  1. Power on the RGA head (the switch on the back of the unit). A green LED on the RGA head should indicate that it is receiving adequate power.
  1. Start the RGA software control (icon is on the desktop of the control PC)
  1. Open a connection with the RGA head: click on the small ‘plug’ icon on the toolbar and select ‘connect.’
  1. Turn on the RGA filament: click the filament icon on the toolbar. A greed LED on the RGA head should indicate that the filament is operating correctly.
  1. If desired, turn on the Electron Multiplier by click the button on the toolbar (another LED should light on the RGA head).
  1. From the menus select the type and range of RGA scan desired. Generally, the RGA can either run in ‘analog’ or ‘histogram’ mode, scanning from 1 to 200 amu. See the RGA200 Manual for more information about these modes.
  1. Select (total pressure mode) from the (menu) to have the RGA display the total pressure. This will require a new scan.
  1. RGA scans can be printed to any printer from the ‘File’ menu.
  1. To turn off the RGA: Turn off the electron multiplier and the filament. The LEDs should turn off.
  1. Disconnect the software link between the RGA and the computer.
  1. Close the RGA program.
  1. Power off the RGA head.

2.4 – Framing Camera Procedure:

  1. Connect the Maxmodule to the back of the system with four 10-32 machine screws and washers.
  1. Follow vacuum startup procedure.
  1. Connect the phosphor and MCP to the appropriate current meters with SHV cables; the current meters should already be connected to power supplies.
  1. Connect the CCD camera to the computer with a 15-pin VGA cable and a 1/8” audio plug that powers the cooling fan.
  1. Shroud the camera assembly with the large vinyl sleeve and use other strips of cloth to block out any potential light leaks.
  1. Take a long (10 minute) exposure to check the background light level. Adjust the light shroud accordingly. Save the background image.
  1. Turn on the CCD by starting the “SpectraSource CCD” program. The camera is thermoelectrically cooled, so allow at least 30 minutes before exposing.
  1. Follow x-ray source startup procedure
  1. Make sure the RGA filament is turned off; cross-talk between RGA ions and the framing camera will occur.
  1. Take a few test exposures between 1-5 minutes long (depends on type of MCP) to make sure all parts are functioning properly.

Part 3 – The Vacuum System

3.1 – Introduction:

(pic of vac sys)

The Drake Lab primary vacuum system uses a two stage pumping system to achieve pressures in the ‘high vacuum’ regime inside of a stainless steel chamber. This chamber has an approximate volume of _____ These low pressures (~10-5 torr) are necessary for proper operation of the x-ray source and the x-ray framing camera. The first stage utilizes a roughing/backing pump which removes the bulk of the air from the vacuum chamber and provides foreline pressure for the high vacuum pump. System pressure is monitored through two separate vacuum gauges that supplement each pump. The vacuum system also uses two ‘airlocks’ for the primary instrumentation, which allows the instruments to be removed and replaced while the vacuum pumps continue to operate, keeping the system cleaner and reducing the time necessary to change out the instrumentation.

This part will contain information on basic vacuum concepts, proper handling habits and detailed information on the vacuum pumps and components. A section on vacuum system bakeout and the residual gas analyzer is included at the end of this section.

3.2 – Basic Vacuum Concepts

3.2.1 – Units

The unit for pressure, in the SI unit system, the standard for all scientific applications, is the Pascal (Pa), defined as 1 kg/m/s2 , or 1 N/m2. Derived from the Pascal are the bar (105 Pa) and the millibar (100 Pa). The standard atmosphere (atm) is also defined in terms of Pa (101,325 Pa)

Units not derived from SI units are the mmHg and the torr, which are equivalent and are equal to 1/760 atm. A conversion gives 1 Torr = 133.3 Pa, or 102 if doing back-of-the-envelope type magnitude calculations.

Due to convention and tradition, the unit of pressure most widely used by the vacuum science industry in the United States is the torr. Professional journal articles, especially those published outside of the U.S., will give pressures in terms of Pascals. Our lab and the vacuum hardware we utilize, as well as all of the pressures defined in this manual use torr, to comply with this convention.

3.2.2 – Gas Flow

The subject of gas flow in a vacuum system is a very lengthy and detailed subject, far too broad to even scratch the surface in this section. Here we will discuss a couple of the primary concepts that will serve as important stepping stones to the world of Vacuum Science. For an exhaustive look at gas theory please consult J.M. Lafferty, Foundations of Vacuum Science and Technology, pp. 1-149; a copy of which is in the lab.

The flow of gas in a vacuum system can be divided into two regimes: the first called the continuum or viscous flow, and the second called molecular flow. There is a third regime, called transitional flow, that, like the name implies, governs the transition from continuum to molecular flow.

The theory of continuum flow governs the behavior of gas when the interactions between the gas molecules is the main factor (i.e. the mean free path of each molecule is relatively short). During continuum flow gas behaves like a fluid, and can thus be treated hydrodynamically. Continuum flow can be thought of as the pressure region between atmospheric pressure and a rough vacuum.

Molecular flow is the name given to the regime where the behavior of the gas is determined through interactions with the walls of the vacuum system, and not between molecules (the mean free path is thus relatively long). In this flow regime the gas must be thought of as individual particles, and not as a fluid in the case of continuum flow. Molecular flow is the dominant regime when the system is at a ‘high’ vacuum, which is the operating pressure for the experiments.

Conductance is the term given to the resistance of the flow of a gas to the size and orientation of vacuum components. Like electrical conductance (or resistance, the reciprocal), a low gas conductance means it is harder for gas to flow, and the opposite for high conductance. Conductance will have a significant effect on the pumping speed of a vacuum chamber, and though the longer a system pumps down the less effect conductance has, it is necessary to factor in when designing or operating a vacuum system. For some basic conductance equations, see Appendix ??

3.2.3 – Outgassing