Some Wakefield Studies

1
Some Wakefield Studies

• Roger Barlow
• \Adriana Bungau, German Kourevlev, Adam Mercer
• Cockcroft All Hands
• January 2005

2
Wake Fields

• Beam particles passing through an aperture
  produce image charges and currents
• Image charges and currents push beam particles
  around
• Wake fields in Collimators are a big concern for
  Linear Collider

• Kick depends on bunch position. Jitter in x gives
  jitter in x. Kick factor. Low luminosity
• Particles within bunch get different kick.
  Increase in emittance. Low luminosity.
• Particles in tail see bigger effect than
  particles in head. Banana bunches. Need
  particle-by-particle simulation as bunches non
  Gaussian

3
Formalism

• Kick on one particle (r, ?,0) due to another at
  (r, ?,z)
• Circular Aperture
• ?(?mrmrmWm(z)Cos m??-??)
• Wake effect can be coded as
• ?m(trailing particle)xAperture(z)x(Leading slice)
• Factorisation

z
4
Code in Merlin
Has basic formalism in code Needed extending to
include more than lowest (m1) mode. And
non-radial kicks
5
Merlin progress/plans

• Building library of functions
• Wm(z) or
• wakePotential(double s, int m)..
• For various shapes of aperture
• Resistive and Geometric wakes
• Dielectric wakes

6
The functions

• Analytic functions being extracted from
  literature
• No reason not to have numerical functions from
  tables produced by GDFIDL etc.
• Working with Lancaster on this

7
Wake fields results
Predict experimental results if 5th order used
8
More Wake Fields

• What about rectangular apertures
• (realistic!)
• Much less in the literature. Special cases/
  consider only dipole approximation
• Can they be factorised?

Complicated
9
And as well

• Using MERLIN for studies of beam halo
• Putting tapered collimator class into MERLIN
  (needed for wakefields and scattering)
• Analysis of SLAC ESA data (old and upcoming) on
  wakefields. Run in March/April