DF 020 - EL
Principle of measurement
The accelerated particles are stopped in the cup and the caught electric charge is detected as a corresponding electric current flow going to ground.The current is limited by a shunt resistance (optional) between the cup and ground. This resistor must not be chosen to high. The withstand voltage of the FC is 4kV.
The Faraday Cup is moved into the beam by means of the air actuated feedthrough DL 270; for vacuum sealing of the movable parts a metall bellow is provided.
The copper cup is water-cooled; the tube guiding the water to the cup is also used as electric conductor for the beam current.
Suppression of secondary particles
The suppression of secondary particles is done by the suppressor cylinder which can (should) be connected to a high voltage source. Oberserving particles with positive charge, the right suppressing voltage is found when the measured beam remains constant. Furthermore the secondary particles are suppressed by a magnetic field excited by permanent magnets (magnet yoke), which is most important observing particles with negative charge.
In front of the cup and suppressor cylinder an aperture with an opening of 100mm is installed. Here the trigger can (should) be connected which is effecting an interlock. So the cup is protected against an incident beam. During measurement the current on the aperture should be zero to make sure that the whole beam is caught in the cup.
The Faraday Cup is designed for the measurement of beams with the following characteristics:
- Type of beam: H+ or H-
- Pulse length: 1,2*10-3 sec
- Repetition frequency: fr = 50 1/sec
- Length of pulse pause: Tp = 0,019 sec
- Duty cycle: duty = 0,06
- Pulse power: Pg = 10kW
- Mean power: Pm = 600W
- Max. beam diameter: d = 100mm