Analysis of Beam-Based Measurements in Recycler and Accumulator

1
Analysis of Beam-Based Measurements in Recycler
and Accumulator

• Alexey Burov
• Nov 13 2003

2
Sources of Energy Evolution

• Beam energy distribution evolves because of
• Impedance
• IBS
• Gas ionization
• Radiation
• For RR and AA, the first 3 mechanisms are
  normally responsible for observed evolution of
  the beam energy distribution.
• Is it possible to extract from measurements
  separate contributions of impedance, IBS and gas
  ?

3
Evolution in RR

• Evolution of 9E10 coasting proton beam in the RR
  for 1 hr. Initial is red, final is blue
  (digitized filtered data).
• Impedance shifts the distribution as a whole
• IBS widens it, preserving the mirror symmetry
• Gas shifts and creates low-energy tail,
  asymptotically
• This asymptotic and IBS symmetry allows to
  separate IBS and gas.

4
Asymptotic Fit Gives Electron Density

• When the low-energy tail is well-seen, the IBS
  and impedance contributions disappear for
  anti-symmetric combination
• Figure shows this anti-symmetrized tail (red) and
  its fit. This fit gives density of
  electrons of the residual gas
• For this fit
• Impedance losses
• leading to impedance estimate
• at frequency range 10-40 GHz

5
Emittance Growth and Gas Composition

• Gas scattering gives rise to emittance growth
  (95 normalized)
• Measurements give .
  Combined with the energy evolution measurements,
  this allows to find
• Assuming that there is only H2 and water/methane
  molecules. It leads to
• More measurements can give more precise and
  definite conclusions.

6
Low Current AA Measurements

• Figure shows energy distributions
• measured (P. Derwent) initial (red), final
  (blue) and calculated with the Landau
  distribution (brown).
• Current 1.8 mA, emittance 10 um. Calculated
  electron density
• Energy losses are all impedance-related

7
Emittance Growth and Lifetime in AA

• Assuming measured gas composition with
  , it allows to calculate gas-driven emittance
  growth
• and the total beam lifetime and pressure
  ,
• Measured values
• The difference can be explained by higher
  contribution of C, N, O and Ar.
• Conclusions
• Beam-based measurements is a powerful tool for
  vacuum diagnostic.
• More measurements at RR at various intensities
  would bring more light and allow more definite
  and accurate conclusions.