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Frequency characteristics of damper versus growth rates 450 GeV – part 1

Frequency characteristics of damper versus growth rates 450 GeV – part 1. W. Hofle. Acknowledgements: N. Mounet , E. Metral , D. Valuch. Rise-times computed for full machine @50 ns bunch spacing. 10 MHz. N. Mounet. Damper gain versus frequency (1).

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Frequency characteristics of damper versus growth rates 450 GeV – part 1

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  1. Frequency characteristics of damper versus growth rates 450 GeV – part 1 W. Hofle Acknowledgements: N. Mounet, E. Metral, D. Valuch W. Hofle @ LBOC 31.05.2011

  2. Rise-times computed for full machine @50 ns bunch spacing 10 MHz N. Mounet W. Hofle @ LBOC 31.05.2011

  3. Damper gain versus frequency (1) Capacitances and resistor determine 3 dB point power amplifier / kicker simplified model, PAC 2001 detailed simulations see LHC Project-Note-259, 2001 W. Hofle @ LBOC 31.05.2011

  4. Damper gain versus frequency (2) • 1-pole roll-off at 1 MHz, with phase compensated by a digital filter • 30% less gain at 1 MHz than at 3 kHz … • some tuning of phase compensation needed when we go to 25 ns spacing, i.e.  20 MHz • quality of compensation of cable losses by analog filter recently checked (D. Valuch) • further checks can be done in next technical stop, no surprises expected kick @ 10 MHz, 10% left measured on power amplifier (blue curve on kicker, green on anode of tetrode) LHC-PROJECT-REPORT-1148 W. Hofle @ LBOC 31.05.2011

  5. 40 turns, 1/40 = 0.025 W. Hofle @ LBOC 31.05.2011

  6. Conclusions (450 GeV) sufficient damper gain available at 450 GeV to damp all coupled bunch dipole modes growth-rate of instabilities has zero @10 MHz (half bunch repetition frequency) should we put a notch here for the damper gain, too ? computed growth rates do not support increase of “damper gain versus frequency” concerning observation: individual bunches seem to be not stable sometimes:  here a flat gain of the damper with frequency might help, but the implementation is only possible at an expense of signal/noise ratio possible should we pursue this in a test/MD ? W. Hofle @ LBOC 31.05.2011

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