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

1. Kick depends on bunch position. Jitter in x gives
   jitter in x. Kick factor. Low luminosity
2. Particles within bunch get different kick.
   Increase in emittance. Low luminosity.
3. 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