2.5 MHZ FEEDFORWARD BEAM LOADING COMPENSATION IN THE

MHz feedforward beam loading compensation is crucial to all operations of the Main Injector. Recently a system using a fundamental frequency down converter mixer, a digital bucket delay module and a fundamental frequency up converter mixer were used to produce a one- turn-delay feedforward signal. This signal was then combined with the low level RF signal to the cavities to cancel the transient beam induced voltage. During operation we have shown consistently over 20 dB reduction in side-band voltage around the fundamental frequency during Proton coalescing and over 14 dB in multi-batch antiproton coalescing. HARDWARE The purpose of the hardware (Fig. 1) is to take the Main Injector resistive wall current monitor and delay it by one turn and combine it with the 53 MHz low level RF (VCO) fan-out sent to the cavities. This signal is down converted and up converted (In-Phase) because the Digital Bucket Delay A/D clock is operated at the VCO frequency. After the down convert, the fundamental frequency (DC component) is removed with a capacitor leaving the 90 kHz spaced transient mode lines to be digitized and delayed. The Digital Bucket Delay consists of an A/D converter, a FIFO, and a D/A converter that all operate off of the VCO frequency. The A/D and D/A are both 14-bit and operate between ± 1 volt. With the FIFO, the signal is delayed by an integer numbers of rf cycles. The Main Injector harmonic number is 588 and taking into account cable delays and component positions we use the FIFO to delay the signal 531 buckets. Once delayed, the signal is cleaned up with a 30 MHz low pass filter and up converted with the VCO. In order to run this system from 52.8 MHz to 53.1 MHz up the ramp, 6 ns of phase shift is used of the 180 degree 53 MHz phase shifter. A mixer was used to electronically attenuate the signal for different gains and number of bunches. A Mini-Circuits ZFSC-24- 11 24 way-0° splitter was used to fan-out the signal to each of the 18 Main Injector stations. This signal was then combined with the low level rf just after the limiter (1) in the solid state metering chassis using a Mini- Circuits ZFSC-2-1 2 way combiner. In doing fan-out and fan-back for Feedforward BLC, one must take into account the time of flight for the particles to pass each station. The fan-back also uses the Mini-Circuits ZFSC-24-11 to vectorialy sum up all of the Main Injector Cavity gap monitors. Since the Pbars spin in the opposite direction, Station 18 now becomes the first cavity, a whole separate time of flight fan-out and fan-back system was created for Pbar Feedforward BLC.