The TT2 Wideband Electrostatic Pick-Ups

General

Fig 1: Location of TT2 wideband electrostatic PUs

Fig 2: The electrode geometry

The PS-SPS transfer line FT16 in the TT2 tunnel is equipped with two wideband electrostatic position pick-ups, with a useful bandwidth of 5kHz-400MHz. The OBnames are (FT16.UES208 and FT16.UES228), and they are spaced about a quarter of a betatron wavelength apart. The pick-ups are equipped with source follower pre-amplifiers and wideband passive hybrids. The analogue signals are available in Y-building, where distribution amplifiers provide them to the OASIS system and to a pair of LeCroy LC564 oscilloscopes. Note that the OASIS system limits the usable bandwidth to some 80MHz.

To prevent the build-up of free electrons for certain beams, clearing coils can provide a pulsed solenoidal field of about 20mT in the PU volume.

Electrodes

The wideband electrostatic pick-ups consist of four electrodes that together form a cube 120mm on a side, installed in a common vacuum chamber. The electrodes are cut to obtain a linear characteristic w.r.t. displacement in both axes. The table below summarises the properties of the PU as installed in the FT16 cylindrical chamber.

Basic pick-up properties Aperture 120x120mm Length 120mm Cel 140pF (One plate) Bandwidth 5kHz-400MHz Rt 0.78Ω (Electrodes only) Rt 0.5Ω (With electronics) Sx 40mm (Note 1) Sy 40mm (Note 1)

(Note 1: Using the passive four-decade BW hybrids)

Other links

• Clearing coil wiring diagram
• Signal wiring diagram
• Pre-amplifier schematic diagram
• Pre-amplifier test set-up
• Power Supply Schematics
• Miscellaneous stuff that hasn't found its right place yet

References

• J. Belleman, A four decade bandwidth hybrid, PS/BD/ Note 99-09 (100kB)
• R. Cappi, M. Giovanozzi, E. Métral, G. Métral, G. Rumolo, F. Zimmermann, Electron cloud build-up and related instability in the CERN PS, CERN/PS 2002-006 (AE) (2.4MB)