High voltage

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High voltage

• DC
• Beam steering
• Beam focusing
• Reaction product guiding (e-)
• High voltage barriers
• AC
• Acceleration
• Bunching

2
Electric rigidity
Bend the particle beam with an electric field
3
Bending voltage

• E.g.
• Vacc130 MV
• d 5 mm
• r 1 m
• Vbend 1.3 MV !!!!!!!!!!!
• Bending very difficult!!!
• Very high voltages

4
High voltage devices
Einzel lens
Electrostatic deflector
5
Power supplies

• P ()
• N (-)
• R ( or -)

6
High voltage conditioning

• At first the electrodes dont keep the desired
  high voltage
• Not necessarily a problem
• Teach the electrodes conditioning
• Increase the voltage until the current jumps
• Decrease the voltage so that the current (arc)
  drops
• Increase
• Decrease

7
Sparking

• Sparking starts from the negative electrode
  (electrons)
• Pay special attention on negative electrode
  surface
• Polish (mirror surface)

8
Connectors/cables

• High-voltage connectors
• SHV
• High-voltage cables
• Check the specifications before use

9
Sparking

• High pressure
• Free electrons in residual gas
• Atmosphere, dry air 106 V/m
• Vacuum 107 V/m
• Depends on geometry (slightly)

10
Sparking in the presence of B

• Magnetic field guides electrons
• B along E no help
• B perpendicular to E helps

11
Multipaction Multipaction is an effect that
occurs with RF fields, usually in a vacuum or low
pressure condition. Results from an ion moving
back and forth (in response to an RF field) and
knocking other electrons off the sides when it
hits. If the transit time of the electron is
nicely synchronized with the RF field, then just
as it hits, the field is right to pull the new
electrons towards the other side, and a cascading
avalanche can result (if the electron emission
coefficient (d) is gt1).
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Multipactoring threshold
Vo (2pd/l) 2 (mec2)/(pe) whereVo is
the voltage between the sides of the cavityme
mass of electronl wavelengthd spacing
between wallsc speed of light (3x108 m/s)e
charge on an electron
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Remember also

• Induced high voltages at inductances (coils)
• Abrupt current shut-off in a coil
• High voltage capacitors in electronics
• Can have HV even after power shut down