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64 Cards in this Set
- Front
- Back
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What is the Modulator and what does it do?
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The modulator supplies a pulsed DC power of a few microseconds in duration
to the klystron or magnetron and at the same time signals the electron gun to inject electrons into the accelerator portion of the wave guide. |
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What does the power supply send power to?
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Modulator
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To the right of the modulator is what?
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Magnetron or Klystron
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What does the purpose of the either the Magnetron or Klystron?
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These devices convert the pulsed DC power into microwave radiation that
is supplied to the Accelerator tube. |
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What else does the modulator supply?
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Electron Gun
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What does the electron gun do?
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Supplies the electrons to the accelerator tube on the command of the modulator
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What is the wave guide system and what does it do?
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The wave guide systems are made of copper tubing that are used to transport microwave energy from the Magnetron or Klystron to the accelerating tube.
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Why are tubing used instead of wiring?
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Because these are high frequencies, energy is much more efficiently transported using tubing rather than wiring.
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Describe the Accelerator tube
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This is a copper tube with washers placed one
quarter wavelength apart of the incoming microwave wave frequency. In the wave guide microwave energy is transferred to the electrons in the form of kinetic energy. There are two types of wave guides. First employs what is called the travelingwave and the second, is what is called the standing wave. Both types of wave guides transfer energy from the microwave energy coming in to the electrons. Next is the accelerator tubeof the wave guide. |
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Which bending magnet will have more penumbra? 90 or 270 degree?
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90 degree.
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What will you find in the treatment head of the machine that will enable the usage of electrons & Photons?
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- For the Electron Beam will use the scattering foil
- For the Photon Beam a Tungsten target. |
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What comes after the Tungsten target?
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Are the Primary Fixed Collimators which determine the maximum extent of the radiation field
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What comes after the Primary Collimators?
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There is a carousel, which is a rotating disk
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The Rotating Disk...
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Houses the x-ray beam Flattening filters and the electron beam scattering foil.
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When using photons describe the actions that the rotating disk will do?
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The Carousel will continue to rotate until it gets to the proper flattening filter for that "Specific Energy" that you need to use.
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What does the electron gun do?
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Supplies the electrons to the accelerator tube on the command of the modulator
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What is the wave guide system and what does it do?
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The wave guide systems are made of copper tubing that are used to transport microwave energy from the Magnetron or Klystron to the accelerating tube.
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Why are tubing used instead of wiring?
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Because these are high frequencies, energy is much more efficiently transported using tubing rather than wiring.
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Describe the Accelerator tube
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This is a copper tube with washers placed one
quarter wavelength apart of the incoming microwave wave frequency. In the wave guide microwave energy is transferred to the electrons in the form of kinetic energy. There are two types of wave guides. First employs what is called the travelingwave and the second, is what is called the standing wave. Both types of wave guides transfer energy from the microwave energy coming in to the electrons. Next is the accelerator tubeof the wave guide. |
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Which bending magnet will have more penumbra? 90 or 270 degree?
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90 degree.
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What will you find in the treatment head of the machine that will enable the usage of electrons & Photons?
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- For the Electron Beam will use the scattering foil
- For the Photon Beam a Tungsten target. |
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What comes after the Tungsten target?
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Are the Primary Fixed Collimators which determine the maximum extent of the radiation field
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What comes after the Primary Collimators?
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There is a carousel, which is a rotating disk
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The Rotating Disk...
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Houses the x-ray beam Flattening filters and the electron beam scattering foil.
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When using photons describe the actions that the rotating disk will do?
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The Carousel will continue to rotate until it gets to the proper flattening filter for that "Specific Energy" that you need to use.
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After the Carousel comes the....
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Ionization Chambers
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There are two Ionization Chambers, why?
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There are two of these chambers in the machine, one is used for backup in case the other fails.
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What is purpose of the Chambers?
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It is the charge collected by the chambers that is used to shut down the machine.
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What comes next after the Ionization Chambers?
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The Secondary Collimators (or adjustable collimators)
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What are the Secondary Collimators used for?
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These are used to give the appropriate field sizes for the radiation tx field.
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Describe how the flattening filter is manufactured, what is the specific reason?
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To compensate for the high intesity at the center of the beam you need to place a flattening filter in the path of the x-ray beam, which is thicker at the center then at the edges
** This gives a flat beam profile across the field of the pt. |
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What is the advantage for using 270º bending magnet over a 90º bending magnet?
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Using a 90º bending magnet will have larger penumbra while using a 270º will have less.
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Describe how the electrons move through the magnetic field and what occurs.
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As the electrons transverse the magnetic field they will come together and merge at one point on the target.
Because of this focusing of the electrons on the target the penumbra characteristics will improve. |
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Magnetron Description
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The Magnetron is made of from a solid copper metal disk in which resident cavities have been cut out.
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What is at the center of the disk as well as the outer rim?
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At the center of the Disk is a Cathode(--) and the outer rim is the anode (+).
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Electron Movement...
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Electron spiraling in to the anode generating microwave radiation.
-RF Signal will continue to oscillate around the Magnetron, electrons act like wind blowing past a bottle. *** Eventually the electron will collide with the cavity and flow into the cavity. |
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Klystron.....
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Is made up of several different components
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Cathode Filament (--)
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First is the Cathode Filament which supplies electrons to the system.
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What is the first cavity called>
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Buncher
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What is the Buncher connected to?
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Connected to the Incoming Wave Guide
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What else is the Buncher connected to?
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The Drift Tube
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What is the Drift tube Connected to?
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The Second Cavity know as the "Catcher"
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And the Catcher is connected to?
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Connected to the "Outgoing Wave Guide" and also the electron beam collector.
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Buncher
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Low energy microwaves radiation enters the first cavity, buncher
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What is significant of the Electron Stream?
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Is accelerated by negative pulse of voltage.
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What is Velocity Modulation?
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The microwaves interact in the cavity and set up an alternating electric field which
interacts with the electrons in a process known as velocity modulation. |
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When does Velocity Modulation Occur?
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When the electrons enter the 1st cavity with the electric field building up in a positive direction.
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As the electrons exit the first cavity what is the speed of the electrons?
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Variation in Electron Speeds
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What happens to the electrons as they arrive at the Catcher Cavity?
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They suffer deceleration as the kinetic energy of the electrons are converted into HIGH POWER MICROWAVES.
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What is the purpose of the Electron Beam Collector?
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The residual energy of the electron beam is dissipated in the electron beam collector.
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What happens to the Low Energy Microwaves?
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Usually are taken from the output of the 2nd cavity and are fed back into the 1st cavity.
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What are the two types of accelerating tubes?
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1) Traveling Wave
2) Standing Wave |
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Traveling Wave Guide description?
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Consists of a hollow copper tube with metal washers placed inside.
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What is the signifigance of the Washers?
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They are initially spaced closer together at the beginning of the wave guide and are uniformly spaced further on.
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What is the reason for the spacing?
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is that initially as the electron gains energy there speed is increasing, thereby necessitating the increased spacing of the washer as the electron travel down the wave guide. This will allow for the electrons and the microwave radiation to stay in step.
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What happens as the electrons gain energy?
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they very quickly approach the
speed of light. Then spacing of the washers becomes uniform, because at this point an increase in energy by the electrons is NOT manifested as an increase in speed BUT as an increase in mass. |
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How does the Sanding Wave Guide differ form the Traveling WG?
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The spacing of the washers are at equal distances.
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How many cavities does the Sanding Wave Guide cover?
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4 Cavities.
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What are the 2 dynamics for the standing wave Guide?
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1) Forward Waves
2) Backward or reflected waves. |
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Do Forward and Reflected wave occur at the same time? T/F
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True, they occur at the same time
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Because of the early layout of the Standing wave guide, what happens to the electrons traveling within the tube?
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The Cavities were the electron fields cancel out.
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What did they do to solve this problem?
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Moved the Cavities offline and reduced the size.
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Note about the Standing Wave Guide
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Because of the off-axis cavities the central axis beam cavities have the capability of optimizing for electron acceleration
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QA for Linacs:
Electron output constancy, how often are they checked? |
3% and all electron energy must be checked at least 2 times per week.
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