A Study of Ion Trapping and Instability in the Fermilab Antiproton Accumulator
- Northwestern U.
In particle accelerators, electron-ion pairs are constantly created by beam particle collision with residual gas molecules. The beam may trap opposite charged ions. If uncorrected, trapped ions may cause beam instability and beam loss, and limit accelerator performance. The ion trapping problem especially related to the Fermilab antiproton accumulator, where the beam is unbunched and negatively charged, is studied here. The old clearing electrode system is found to be insufficient for complete ion clearing. The proposed upgrade to the clearing electrode system greatly improved the performance of the machine. Incomplete ion clearing is found to directly contribute to beam coherent oscillation and therefore beam coherent instability. A model has been developed which includes the effect of trapped ions in the normal beam coherent instability treatment with conventional machine impedance. It is found that the effect of trapped ions on the beam coherent instability can be described as a form of impedance. Together with physical arguments, it can be used to explain some of the behavior of the beam coherent instability observed in the accumulator. An Ion Detector and Energy Analyzer system was developed which provides the ability to directly monitor the ions coming out of the beam and measure their energy spectrum. Ions are observed to interact with explosive coherent oscillations that lead to emittance blowups. The ion energy distribution extends to much higher energy than expected. The flux of ions escaping with cool, stable beam is also higher than previously thought. The main subject of the study is related only to ion trapping in a DC beam, although a few issues are illustrated with a case study on the Tevatron with separated orbits of proton and antiproton beams.
- Research Organization:
- Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), High Energy Physics (HEP)
- DOE Contract Number:
- AC02-07CH11359
- OSTI ID:
- 1425589
- Report Number(s):
- FERMILAB-THESIS-1993-40; UMI-94-15841; 369861
- Country of Publication:
- United States
- Language:
- English
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