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3.1 GENERAL DESCRIPTION. . . . . . . . . . . . . . . . 3-1
3.2 CONSTRUCTION . . . . . . . . . . . . . . . . . . . 3-1
3.2.1 Double-Width CAMAC Module . . . . . . . . . . . 3-1
3.2.2 Front Panel with the following items: . . . . . 3-1
3.3 CAMAC COMMANDS . . . . . . . . . . . . . . . . . . 3-2
3.4 X AND Q RESPONSE . . . . . . . . . . . . . . . . . 3-3
3.5 MANUAL MODE . . . . . . . . . . . . . . . . . . . 3-3
3.6 DRAWING PACKAGE NUMBER . . . . . . . . . . . . . . 3-3
3.7 RESPONSIBLE ENGINEERS . . . . . . . . . . . . . . 3-3 CHAPTER 3 BEAM POSITION MONITOR (BPM)
3.1 GENERAL DESCRIPTION. The BPM is a CAMAC module that is used to process the four signals from a directional-coupler type of beam position monitor, and provide digitized outputs of the vertical difference, the horizontal difference and the half sum signals. This is done by first splitting each signal, one part of each going to a power combiner to provide a "fast sum" signal. The other part is passed through a Gaussian filter and then to one of two hybrid junctions, to obtain the required differences and a "slow sum" signal. These three signals then pass through variable attenuators to "track & hold" circuits, through fast switches. These switches are closed by the simultaneous presence of the fast sum signal and an external beam gate. This external beam gate allows the measurement to be made on a particular bunch. The track & hold circuit voltages are digitized by 10-bit ADCs, which can be read through the CAMAC dataway. The beam gate is supplied from a PDU via the upper backplane connector. The diode variable attenuators are all set to the same nominal attenuation by means of a DAC. The attenuators have a means for reversing the signal polarity, for operation with positrons. The unit is calibrated by applying the slow sum signal to the two difference channels, thus showing up any difference in gain between the three. In the absence of beam, a special trigger can be used to close the track & hold switches, thus measuring the pedestal levels.
3.2.1 Double-Width CAMAC Module
3.2.2 Front Panel with the following items: o 4 SMA sockets for signals from BPM o 1 Lemo input for test gate signal ______________________________ For further details on the BPM, see SINGLE PASS COLLIDER MEMO CN-217.
BEAM POSITION MONITOR (BPM) Page 3-2 o 4 Lemo outputs - Beam generated trigger - Horizontal difference signal - Sum signal - Vertical difference signal o 4 LEDs - CAMAC X response - Coversion being done - Electron bunch - self triggering - Positron bunch - " " " o Push-button for manual operation.
3.3 CAMAC COMMANDS o F0 A0,A1,A2: READ ADCs X is returned to the dataway and Q also, but only when the data from the ADCs is ready, that is, after the completion of a conversion. The command for a conversion is generated by the beam gate or, in its absence, by the beam derived "hold" signal. o F1 A0: READ DAC o F1 A1: READ OFFSETS The x and y offsets are two 8 bit words which are stored for eventual corrections of the measured data. The 8 least significant bits contain the x offset, the y offset being written in the next 8 higher order bits. o F3 A0: READ MODULE TYPE AND SERIAL NUMBER The serial number is presented on the lower 10 bits and the type code on the next 6 bits. o F9 A0: CLEAR MODULE o F16 A0: WRITE DAC The attenuation (not the dB figure) is approximately linear with the count number as follows: o 0 Minimum attenuation for the e- bunch o 127 Maximum attenuation for the e- bunch o 128 Maximum attenuation for the e+ bunch o 255 Minimum attenuation for the e+ bunch
BEAM POSITION MONITOR (BPM) Page 3-3 These values are not affected by an Initialize (Z and S2) or a Clear (C and S2). o F24 A0: CALIBRATE A beam and a beam gate are required. This function is latched and is reset by an Initialize, a Clear, F9 or F26. o F25 A0: PEDESTAL No beam required, only a beam gate or a substitute gate. This function is latched and is reset in the same way as the Calibrate mode. o F26 A0: CLEAR CALIBRATE AND PEDESTAL o F27 A0: BEAM GATE SUBSTITUTE ON This function is reset by an Initialize, a Clear, F9 or F28. o F28 A0: BEAM GATE SUBSTITUTE OFF.
3.4 X AND Q RESPONSE X and Q are returned true for all the above commands; Q is not returned true, however, when the data is not ready. The data is made not ready following an Initialize, a Clear, F9, F0 A3 or when the substitute gate has been turned on by depressing the front panel push-button.
3.5 MANUAL MODE This feature is implemented for test purposes. Depressing the push-button switch once sets the module with a substitute gate and a minimum attenuation for the e- bunches; depressing the button a second time sets the circuit in the same mode but for the e+ bunches; a third actuation of the button will return the module to its original state. The manual mode is of course reset by any valid command.
3.6 DRAWING PACKAGE NUMBER 123-605
3.7 RESPONSIBLE ENGINEERS G. Oxoby, J.-L. Pellegrin, and V. Smith