Faraday Cups

NEC Faraday cups are designed for accurate measurement of ion beam intensity.

Applications

NEC manufactures various types of Faraday cups for a variety of applications involving the monitoring of ion beam currents. Our 3 standard models are:

FC18: For applications involving high energy or high current
FC50: For applications requiring maximum beam clearance when the cup is retracted
FC28: For applications involving nanosecond pulsed beams

Design

The configuration of NEC Faraday cups varies from model to model dependent upon power rating and application requirements. However, all NEC Faraday cups are equipped with electron suppression assemblies and can be biased for accurate beam current readings. The suppressor is necessary to return secondary electrons, which affect the beam current readings. The cup is made of tantalum to limit neutron production.

All standard models utilize a molybdenum beam aperture that protects the insertion mechanism and assures proper operation of the suppression assembly.

The position of the Faraday cup is controlled by a pneumatic cylinder, which is actuated by air pressure. The motion is transmitted through a bellows seal to move the Faraday cup to one side of the beam path.

Below is a description of the three standard models. Custom cups based on any of these designs may be available upon request. Please contact NEC for more information.

Model	Beam Power Rating	Aperture dia.	Features
FC18	1000W	1.0″ (2.54cm)	For applications requiring high energy or high beam currents Unique tantalum cone design that decreases the effective power density on the tantalum surface to eliminate local hot spots Cone indirectly water cooled with a design that allows the use of ordinary tap water
FC50	50W	1.0″ (2.54cm)	For applications requiring maximum beam clearance when the cup is retracted Mounted on a single flange with feedthroughs to allow it to be mounted in an existing vacuum chamber Cooling by radiation only, no water cooling needed 2″ (50mm) stroke custom insertion lengths available as well as custom housings
FC28	100W	0.375″ (0.95cm)	Designed as a timing device by measuring the coincidence and/or duration of pulsed ion beams Includes a tungsten grid at the exit of the suppressor assembly to limit the spread of the delivered pulse that is affect by the transit time of the beam across the gap between the grid and the target It is a fixed Faraday cup – it cannot be removed from the beam path and therefore limited to usage at the end of the beamline

The above beam power ratings are for a continuous beam with a diameter of 3mm or greater and with appropriate cooling.

Accessories

A complete Faraday cup system includes a Faraday cup, a controller for actuation, and either a picoammeter or logarithmic amplifier for current reading. NEC offers a local controller and a remote controller, as well as log amps and picoammeters as needed. See the Related Documents below for further information on these accessories.