1. Upgrading the Digital Component of the Bunch Current Monitors
Josh Kline
Mentor: Alan Fisher

3. Where? What? Why?
The PEP II storage rings at the Stanford Linear Accelerator Center.
The digital portion of the bunch current monitor interface system.
The original components are from 1995 and have become difficult to replace.

4. How the ring works
Electrons/positrons are fed to the ring from the linear accelerator.
The ring pushes bunches of electrons/positrons around the ring using microwave radiation.
Buckets are phases of the standing microwave that supplies the bunch with the energy equal to what it radiates.

5. How the detectors work
The detector measures the electric field of a passing charge bunch.
The charge bunches are moving with relativistic speed, causing the electric field to flatten so the detector sees a fast pulse. v

6. The analog electronics
The analog system turns the fast pulse of the bunch current detector into two periods of a sinusoid using a comb filter with a reference frequency of 1428 MHz the then signal goes through a low pass filter and is then digitized.

7. BLOCK DIAGRAM Detector Current system Comb filter Digitizer Decimator
6 FPGAs
Digital to
Analog
Digitizer
Decimator
6 FPGAs
Detector
Proposed system
Comb
filter
Digitizer
FPGA
Digital to
analog
Main control

8. The current system
Big problem, some of the electronics have become to old to be replaced.
Little problem, the system is too slow to handle the full data rate, so 7/8 of the data is thrown away.

9. The proposed system Big solution, modern components.
Little solution, the new system is fast enough to sample at the full data rate.

10. Details Current Proposed VXI crate processor Linux computer
Two Digitizers
Two Decimators
Twelve FPGAs
One digital to analog I/O bus
Linux computer
One digitizer
One FPGA
One digital to analog I/O bus

11. The First Step
Testing the prototype using software simulator, signal generator, and the last test will be connecting the prototype in parallel with the current system.

12. ModelSim

13. Test Bench

14. Conclusion The prototype has been simulated using ModelSim.
The prototype has been tested using a saw tooth signal generator.
The final test is yet to be preformed.