PCT general information

General Information and Installation

The Parametric Current Transformer (PCT) is a device intended to continuously integrate an alternating current flowing in the ESRF storage ring (SR) or in the booster section (SY). Since the device is an integrating system, its behavior is insensitive to the shape of the current. That is to say, whatever the operating mode, single bunch, multibunch etc.., the PCT delivers a clean DC voltage, ranging from - 10 to 10 V.

The PCT, in its current form, was originally developed at CERN by Klaus UNSER and later manufactured by BERGOZ, a French company located at Saint Genis Pouilly, France. Basically, it can be split into three parts: the sensor, the front-end electronic black box and the control system. The sensor is the most sensitive part. It must not be bumped nor overheated.

The sensor straddles the vacuum chamber, as depicted by figure 1. The vacuum chamber welcomes a cut-off part in order to re-route the image current outside the torrus, otherwise the algebraic sum of these currents would nullify the measurement.

Moreover, the CT is disturbed by the parasitic magnetic fields provided by the adjacent quadrupoles, the feedback steerers and the power cables. However, in operation, the feedback steerers are the only really disturbing factor because the other magnets, which provide constant fields, are taken into account in the calibration. They provide a beam intensity noise which can reach a few uA peak to peak.

The lifetime is deduced from the beam intensity with a resolution that depends on the beam intensity. The computation algorithm uses the least square method. At present, the lifetime resolution is about three hours peak to peak in normal conditions (Ibeam = 50 mA and life time = 40 h).

Its working principle is a zero-flux transformer. The main drawback of the system lies in the presence of a strong clocking signal in the output (# 7kHz) which the user must remove to obtain viable clean measurements.

The front-end electronic black box houses all the necessary low-noise electronics that controls the sensor and finally transports the demodulated signal to the control box, located in the technical gallery. This box has to be properly shielded by lead against the radiations. The output of the control box goes via a passive low-pass filter and provides a strong attenuation to the previous 7kHz. The voltage is measured by an HP34401A IEEE-488 voltmeter driven by from C-PCI crate.