A Faraday Cup is a conductive cup designed to catch charged particles in vacuum. A Fast Faraday Cup is used to measure the longitudinal distribution of charge density. Ideally, the device should generate signals accurately and proportional to the beam to be measured with fast response time (time resolution) and low distortion with wide bandwidth in the frequency domain– but the secondary particles escaping the “cup” result in an incorrect measurement of the primary particles from the beam. Prior solutions to this problem used a biased piece of metal to propel the secondary electrons back so as to incorporate them in the measurement.
Fermilab’s Fast Faraday Cup incorporates a “ground electrode” with a small through-hole (ID < 1mm) and a “collector electrode” with a small blind hole. As the beam to be measured falls onto the ground electrode, the through-hole cuts a small beamlet that flies into the collector hole. The diameters, depths, spacings and alignments of these two holes are controlled to enable this device to have fast time response (fine time resolution) while capturing the secondary particles as well.
The two electrodes are custom-made in coaxial cylindrical topology so that this device has wide bandwidth of 20 GHz, 50 Ohm impedance and two connection ports. The device is capable of resolving details of the longitudinal distribution of a particle beam at the level of < 0.1 ns without using any biasing circuit.
Fermilab’s Fast Faraday Cup provides fast response time (time resolution) and low distortion with wide bandwidth in the frequency domain.
Applications and Industries
- Beam diagnostics
Category: Accelerator Technologies
Tags and keywords: Beam diagnostics
Patent Status: Patent pending
Aaron G Sauers, CLP
Fermilab, MS 312 – PO Box 500
Batavia, IL 60510