BCM1F Performance in 2012

The Fast Beam Condition Monitor BCM1F consists of 8 single-crystal CVD 5 mm x 5 mm diamonds positioned 1.8 m on either side of the interaction point at a radius of 4.5 cm from the beam pipe. The signal is read out, shaped by a frontend ASIC, and converted to an optical signal which is then transmitted to the backend electronics in USC55. The data travels parallel paths: a discriminator path registers the time of signal pulses and transfers this information to the readout electronics, while an ADC captures full orbits for monitoring studies but is prevented from acting as data readout by a high deadtime. BCM1F provides information on the condition of the beam and ensures that the inner detector occupancy is sufficiently low for data-taking. In addition to providing beam information, BCM1F also detects collisions and as such can be used as a luminometer. Effort was made to commission BCM1F as an online luminometer in 2012. In 2012 the Real-time Histogramming Unit (RHU) for BCM1F readout was introduced. The board provides 8 channels of deadtimeless full-orbit histograms with a configurable accumulation interval, with bins in 6.25-ns intevals, or four bins per bunch bucket. Also during Run I, the effects of radiation damage to various parts of the BCM1F system became apparent. The diamond sensors themselves were subject to a high amount of radiation, which cause charge traps to form within the material, reducing the efficiency of hit detection in BCM1F. In addition, the optical driver was integrated into the sensor module and therefore subjected to the same amount of radiation. Deterioration was observed in various ways, including the decreasing range of signal heights transmitted.