MODEL FC-70C FARADAY CUPSPECIFICATIONS
Faraday cup
inside groundshieldFC-70C

UHV Kapton
coaxial cableunterminatedAperture(custom size)
Figure 1 FC-70C Faraday Cup with optional 1 m cable

Aperture size
(Custom available)

1.596 mm dia.
2= 2mm area

Input power continuous

100 mW max.

Shield size

53 mm x 22 mm x 10 mm(2.1” x 0.9” x 0.4”)

Cable length19",

Operating temperature

150ºC max.

Bakeout temperature

250ºC max.

Vacuum level

10-10

Optional: 16"

torr min.

INTRODUCTION
The Kimball Physics model FC-70C Faraday cup,connected to an ammeter, is used to collect and measurecharged particle current, such as the beam emitted from anelectron or ion gun. The FC-70C is UHV compatible andbakeable to 250ºC.
The Faraday cup consists of a hollow stainless steel
cylinder closed at the base, with an appropriately-sized
aperture for collecting the electrons or ions. The standard
2aperture diameter is 1.596 mm which yields a 2.0 mm area;
however, custom aperture sizes are available. An outer,grounded box completely encloses the Faraday cup toprovide shielding. An electrical connection is made from theside of the Faraday cup to a shielded, Kapton-insulated
coaxial cable with an unterminated end. The current is thenconducted through a user-supplied vacuum electrical
feedthrough to an ammeter.
A feedthrough on a 1⅓ CF or larger flange, or a customdesigned feedthrough, is available from Kimball Physics as aseparate option.
To reduce scattering of electrons or ions collected in the
Faraday cup and to reduce secondary electron emission, theFaraday cup can be electrically biased. For electrons ornegative ions, +50 V is typically adequate, and for positive
ions, -50 V. This can be accomplished by placing a battery
between the vacuum feedthrough and the ammeter.
POWER INPUT CAUTIONS
For continuous measurement, the maximum beam
power recommended into the standard FC-70C Faraday
cup is 100 milliwatts. The Faraday cup temperature
should not be raised above 150ºC due to outgassing.
The wattage can be calculated by multiplying the beam
current times the electron acceleration voltage; for example,
1 mA at 1000 eV gives 1 W, which is much too high forcontinuous measurement. The temperature of the Faraday
cup increases approximately linearly with the power input.
A 50 mW input results in approximately 150ºC.
To use the Faraday cup at high power, measure currents
briefly and then let the Faraday cup cool down before
repeating the measurement. Due to heat capacity of the cup,a 500 mW input into the FC-70C will raise the cup
temperature from room temperature to approximately 150ºC
in 80 sec. The cup will cool from 200ºC to room temperature
in about 15 min.
Care must always be exercised with a highly focused
beam, as a high power density can bring the Faraday cup
to melting temperature. Spot size should be greaterthan 1 µm.

INSTALLATION AND OPERATING PROCEDURE

High beam power can melt Faraday cup
components. Maximum recommended
beam power into the Faraday cup is
100 mW continuous.

1. If desired, attach a user-supplied connector to theunterminated end of the cable which has one exposed
conductor and the outside at ground.

2. Position the Faraday cup in the target area inside thevacuum chamber.

3. Connect the Faraday cup cable to a user-suppliedfeedthrough on the vacuum chamber.

4. Connect the feedthrough to a suitable user-suppliedpico-ammeter. NEVER collect beam current in theFaraday cup unless the cup output is connected toan ammeter or grounded. Without proper termination,
the Faraday cup terminal will charge up to full beamenergy and electrical discharging will result.

5. Calculate the expected power input into the Faraday cup
and check that it is within the acceptable range. See thediscussion of power input cautions.

6. Measure electron or ion current with the pico-ammeter.
7. If desired, the cable can be removed from the Faraday
cup by loosening the outer 0-80 screw on the back of thebody. When replacing cable, insert its end fully andtighten screw. Check continuity between cup and cableend.
FC-70C info.02
FC-70 drawing #173F020

Loosen one screw
to remove cable
Figure 2 Back of FC-70C assembly

311 KIMBALL HILL ROAD, WILTON, NH 03086-9742 USA
Tel: (603) 878-1616 1-888-546-7497 Fax: (603) 878-3700
e-mail: info@kimphys.com Web: www.kimballphysics.com