Status of the CERN chopper.

1. Status of the CERN chopper. • Problem review • The deflector status • The old driving solution • An alternative scheme • The basic amplifier module • 2 and 4 ways combiners • The solid state driver • Measurements in 500V mode • Measurements in +/- 250V mode • Final design • Conclusion

2. Problem review (1) The RFQ operated at 352 MHz ► 2.84 ns bunch spacing, 1 ns RMS bunch length ► 2 ns available for rise/fall time 2 ns fronts require cutting no lower than 175 MHz. To overcome kicker filling time problem ► 50 W traveling wave deflector ► b=v/c~8% to match beam velocity To get the minimum extraction field ► +/- 500V on the two deflector plates (1kV differential) ► 5 kW pulsed power per plate

3. Problem review(2) For the neutrino factory beam ► Dump 3 bunches out of 8 ► 0.6 ms / 50Hz burst of 8.52 ns / 44 MHz pulses For the PSB beam ► Dump up to 133 bunches out of 355 ► 0.4 ms / 2 Hz burst of 380 ns / 990 kHz pulses With a first order high pass response cutting at 7 Hz the baseline will be displaced by 1% at the end of the burst for the first case; 11 Hz would be enough for the second case.

4. The deflector status (1) ► Due to amplifier changes system modified for coaxial connections instead of tri-axial. ► All mechanical parts for the deflectors available. ► 1st deflector tests expected for beginning of November.

5. The deflector status (2) ► Meander lines production went through various stages to achieve reasonable performances. ► Thick film technology was used with good results in previous projects (AA and AD). ► Due to the high current for the chopper, need to enhance thickness of silver layer but printed and thick film not compatible with electrochemical deposition! ► Adoption of different process: chemically etched pattern on fired molymangan followed by silver layer deposition. Intermediate Ti layer instead of Nickel (magnetic) not as solid but acceptable after firing at 800 °C under protective gas. ► Meander lines characteristics considered as reasonable but due to the many process steps production yield poor and conductivity at limit. ► 1st deflector equipped with meander lines manufactured at CERN.

6. The deflector status (3) ► In parallel contacted industry to find a possible alternative solution. ►Japanese company KYOCERA produced 10 cm samples with good performance: - DC resistance down by ~50%, - improved bonding - Comparable prize Active metallization For the 2nd structure the choice of meander lines manufacturer will depend on 1st deflector results. Cu plating (30mm) Ag plating (3mm)

7. The old driving solution (1)

8. The old driving solution (2)

9. The old driving solution (3) Analysis and measurements shown that: ► Output voltage limited by tube performance below expectations. ► Slow tails due to ferrite saturation in the wideband transformers extremely difficult to avoid or compensate. ► Matching and stability of transition times, timing and output amplitude of the LF and HF amplifier difficult to maintain on long term for proper operation.

10. An alternative scheme (1) DC component self compensates over two cycles ! But how can we make an inverter with an high frequency cut-off compatible with the 2 ns required fronts and a low frequency cut-off such that the droop is negligible?

11. An alternative scheme (2) Hybrid coupler with theoretically infinite high frequency cut-off. Udo Barabas, “On an Ultrabroad-Band Hybrid Tee”,IEEE Transactions on microwave theory and thecniques, vol.MTT-27, no.1, January 1979

12. An alternative scheme 3) Operate each amplifier with 352/16=22 MHz but one shifted by half cycle with respect to the other and modulate the duty-cycle from 18% to 50% according to the number of bunches that have to be ejected (pulse length varying from 8.52 ns to 22.72 ns). With low frequency cutoff set at 140 kHz the baseline displacement is limited to 2%. 3 out of 8 bunches ejected. All beam ejected

13. The basic amplifier module (125V on 25W) Very low frequency simplified equivalent circuit

14. 2 and 4 ways combiners

15. Solid state driver : 250V, 50W module

16. Solid state driver : 4 Way 50W Hybrid

17. Solid state driver : 500V or +/- 250V, 50W amplifier

18. Measurements in 500V mode

19. Measurements in +/-250V mode (1)

20. Measurements in +/-250V mode (2)

21. Final design (1) New mosfets increase the basic module output from 125V to 150V. New commercial gate driver improves switching time despite the higher capacitance of new mosfets. Strip-line to coaxial transitions have been minimized for a better high frequency response.

22. Final design (2) Full hybrids chain tested in splitting mode rather than sum mode. Tests suggest that full scale amplifier will achieve the specified output voltage and transition times while keeping ripple within ±3%.

23. Conclusions The 1st unit of the CERN chopper deflector is now being assembled. It uses CERN made meander lines. If required , improved industry made, meander lines might be used in the 2nd unit. A new scheme has been identified for the CERN chopper driver operation. It allows to relax the required amplifier low frequency response and the use of a single, solid-state amplifier based on identical modules. A half scale prototype proved the principle and provided information for the final version design. A final version basic amplifier module has been produced and tests suggest that the full version will satisfy all requirements. Modules for a half scale test are now in production and test are expected before the end of the year. A full scale amplifier will be produced in spring 2006.