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The PS Wideband Electrostatic Pick-Up |
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 shaped to obtain
a linear characteristic w.r.t. displacement.
The table below summarises
the properties of the PU as installed in the PS elliptical chamber.
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Three WBESPUs are installed in the PS complex: One in the
PS ring
and two in the
TT2 tunnel.
The one in the PS ring is in
straight section 94).
See the
cabling diagram.
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Also during the 2003-2004 shutdown, the pre-amplifiers based on YD1060 triode cathode followers have been replaced by semiconductor amplifiers. The lifetime of semiconductors in this location is expected to be similar to the lifetime of the triodes, but their cost is much lower. The new amplifiers load the electrodes with a 500Ω resistive load impedance, thus setting the lower cut-off frequency to 2.25MHz. Frequency-dependent feedback around the operational amplifier recovers the low frequencies down to 200kHz. The upper cut-off frequency is determined by the properties of the THS3061 op-amps used and ends up at about 250MHz. The transfer ratio w.r.t. the open electrode works out as -11dB in the flat portion of the pass band. The amplifiers can handle about 2Vp at their inputs. This corresponds to a 3Vp sum output. |
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| Pre-amplifier electronics |
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After the pre-amplifiers, the four electrode signals are combined in a hybrid circuit to produce the horizontal and vertical difference and an overall sum. The Q signal is dumped into a terminator. This circuit is based on Anzac's (now M/A-COM) model HH109 hybrids. These have a useful frequency range of 500kHz to 200MHz. The hybrid combiner presents a 75Ω input impedance, but expects a 50Ω load. |
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| The hybrid combiners |
