# Presentation: 206664

## Status of the Third RF Cavity Upgrade for the IPNS RCSJ. C. Dooling, F. R. Brumwell, M. K. Lien, G. E. McMichael, M. E. Middendorf, and M. R. MoserArgonne National Laboratory, Argonne, IL 60439, USA presented at the Second-Harmonic/Low-Impedance Amplifier Collaboration MeetingJuly 4, 2003ISIS, Rutherford Appleton Laboratory, Chilton, UK 

## RCS Third Cavity Upgrade—Rationale

- Provide a backup rf cavity—improve reliability.
- Increase current limit—more neutrons
- More and/or faster experiments
- Better resolution

## Rapid Cycling Synchrotron

- Circumference=42.9 m
- Two cavities
- 21 kV, rf accel. voltage
- 3rd cavity planned in L6
- 30 Hz
- Began operation in 1981

##  IPNS RCS

## Physical Description RCS Voltage and Magnetic Field Programs

## Physical Description, con’t

- 50 MeV, injection
- 3.7x1012 protons injected
- 450 MeV, 3.2x1012 protons extracted
- Combined function magnets
- Pulsed quads
- Sextupoles
- Tunes:
- 2.20 horizontal
- 2.35 vertical

## Physical description, con’tCavity-cavity phase modulation (PM) adds stability

## Simulation results with second harmonic (SH)

- Simulation with fund. only and SH, zero phase
- Comparison of predictor-corrector model and CAPTURE_SPC† (also second order) with no space-charge yields essentially identical results.
- †Y. Cho, E. Lessner, K. Symon, Proc. EPAC, 1228(1994).

## Loss and Efficiency capture and early acceleration

- Initial testing with SH, try SH early then switch to fundamental frequency program
- J. Norem, et al., IEEE Trans. NS, _30_, 3490(1983).
- CB PS rise time 2.5 ms
- Initial phasing tied to fundamental
- New ferrite not needed for this
- For simulations:
- Einj=0.4 MeV
- p/p=0.4%

## J. Norem’s proposal

- PM not included!

## Comparison of CAPTURE_SPC and HP elliptical line densities

## With new ferrite, can extend SH for the full acceleration cycle (4.4-10.3 MHz)possible phasing strategies--

## Simulation suggests current increase as much as 60 percent with full SH

## CAPTURE_SPC simulation for full SH and phase ramp

## 3rd cavity operational issues

- How far can present ferrite be pushed (~6 MHz)?
- Cavity response time (relatively slow CB PS) for frequency switch over
- Idling—once 3rd cavity is in, can we turn it off without too much parasitic losses
- Stability—with SH, will the PM scrambler still be necessary?
- Phasing—determine the optimum phase vs. t
- Hopefully we can glean some of this from ISIS studies

## Recent results

- Good news—Pre-driver and driver are working up to design power levels~15 kW into 50- loads.
- Bad news is the final is not completed yet
- Good news is that the final is almost complete as later pictures will show
- Still need crowbar (talking to DTI—fast opening sw.)
- Filament choke using ferrite design is presently being constructed in our shop

## Driver Schematic

## Driver Data–amplitude vs. frequency

## Driver Data–amplitude vs. time

## Final schematic

## Final Cabinet is now in the RF Test Stand Area

## Two-turn ferrite filament choke

## Filament choke prototype data

## Ferrite filament choke—impedance stays inductive, is not as peaked, and has a significant resistive component

## RF Test Stand Cabinets

- SS, PreDriver, and Driver Amplifiers

- Final Grid and Filament PS

## RF Test Stand—inside the ZGS tunnel 

## RF Final Diagnostics

- Plate current on each tube (shunt resistor, 0.1 , 50 W)
- Total plate current return to the NWL PS (shunt resistor, 0.1 , 100 W)
- Fast current on each side of the gap (Pearson CTs)
- Gap voltage (cap. divider)
- Thermocouples on both 10 kW, 50- loads at the final input for calorimetry (RTDs)

## Acknowledgement

- This work would not be possible without the dedication and hard work of the IPNS Accelerator Operations Group; as well as support from the ANL IPNS and MSD Divisions, and the DOE.