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18 MHz to 40 MHz sweep-tuneable RF system

18 MHz to 40 MHz sweep-tuneable RF system. Christine Völlinger , Erk Jensen Introduction. Why?. The chopper allows for longitudinal “painting” to obtain any desired bunch spacing and pattern; Complicated “longitudinal gymnastics ” with many RF systems would no longer be required;

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18 MHz to 40 MHz sweep-tuneable RF system

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  1. 18 MHz to 40 MHzsweep-tuneable RF system Christine Völlinger, Erk Jensen Introduction

  2. Why? • The chopper allows for longitudinal “painting” to obtain any desired bunch spacing and pattern; • Complicated “longitudinal gymnastics” with many RF systems would no longer be required; • This allows to work with one single RF system, making the machine relatively “clean” of spurious impedances. • For LHC bunch spacings of multiples of 25 ns, 40 MHz is the lowest possible frequency. • For ion acceleration, a sweep-tuneable system of 18.5 MHz to 40 MHz would be required.

  3. The challenge: • > 1 octave, sweep-tuneable RF system in this f-range has never been built before. Can it be done? • Conventional ferrite RF systems cover the f-range of up to about 20 MHz – above this, losses become prohibitive; • A possible way out is to use “perpendicular bias” with “microwave ferrites” – similar to what has been tried before at LANL, SSC, FNAL, TRIUMF.

  4. Issues being addressed: • Ferrite material & manufacturer (custom made?) • Cavity geometry? • Loss density and cooling? • Non-linearities in the ferrites; • Magnetic bias system – sweep tuning speed? • Impedance; • HOM’s? • RF amplifier? • LLRF.

  5. How many gaps? • More gaps lead to less total power – but to more impedance. There is a trade-off, here shown for assumed shunt impedance of 10 kΩ and a total voltage of 1.5 MV: • To allow a moderate RF power, one would plan for many “small” systems and provide for fast RF feedback to reduce the impedance. Optimum to be found!

  6. For reference, see also: http://indico.cern.ch/conferenceDisplay.py?confId=31855 ... and now over to Christine for the real work!

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