1. Techniques of Vacuum and Basics of High Voltage (3/3) Pauli Heikkinen Jyväskylä University

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

3. Electric rigidity Bend the particle beam with an electric field

4. Bending voltage E.g. V acc =130 MV d = 5 mm  = 1 m V bend = 1.3 MV !!!!!!!!!!! Bending very difficult!!! Very high voltages

5. High voltage devices Einzel lens Electrostatic deflector

6. Power supplies P (+) N (-) R (+ or -)

7. High voltage conditioning At first the electrodes don’t 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…

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

9. Connectors/cables High-voltage connectors –SHV High-voltage cables –Check the specifications before use

10. Sparking High pressure –Free electrons in residual gas –Atmosphere, dry air: 10 6 V/m –Vacuum: 10 7 V/m –Depends on geometry (slightly)

11. Sparking in the presence of B Magnetic field guides electrons –B along E: no help –B perpendicular to E: helps

12. 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 (  ) is >1).

13. V o = (2  d/ ) 2 (m e c 2 )/(  e) where: V o is the voltage between the sides of the cavity m e = mass of electron = wavelength d = spacing between walls c = speed of light (3x10 8 m/s) e = charge on an electron Multipactoring threshold

14. 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