SLIDE 1
Narrow band excitation simulations
Hector Garcia Morales Royal Holloway University of London Joschka Wagner, Roderik Bruce, Stefano Redaelli
SLIDE 2 Motivation Motivation
- Experimental results (presented by Joschka) look
promising but not fully conclusive (yet).
- To fully understand the results we need to
understand the physics involved.
- Tracking codes (MADX, SixTrack) would give a more
precise description but the physics of the narrow band excitation might be difficult to extract clearly.
- A simple model with the minimum physics could give
a better understanding of the principle.
SLIDE 3
Toy Model Toy Model
Map with octupole
Map with ADT kick
SLIDE 4
Matching octupole strength Matching octupole strength
SLIDE 5 Simulation set up and limitations Simulation set up and limitations
– Allows to run an unlimited number of turns and particles.
(<1ms/turn/part)
– Allows fixed and scan – Allows frequency scan in steps or continuously – ADT amplitude ramp up and down
– No chromaticity – No other nonlinear effects – No repopulation – ...
SLIDE 6 Simulation results (fixed frequency) Simulation results (fixed frequency)
- Q(ADT) = 0.295 (as in promising result)
- Npart = 1e5
- Turns = 5e5 (45 sec in real time)
- 1sigma (nominal) and 2sigma (blown up)
bunches
SLIDE 7 0 turns 5e4 t 1e5 t 1.5e5 t 2e5 t 2.5e5 t 3e5 t 3.5e5 t 5e5 t
SLIDE 8
Final amplitude Final amplitude vs vs Initial amplitude Initial amplitude
1sigma 2sigma
SLIDE 9
Final amplitude Final amplitude vs vs Initial amplitude Initial amplitude
1sigma 2sigma
SLIDE 10
- Initial distribution
- Particles which end
beyond 5sigma
Particles lost Particles lost
SLIDE 11
Losses and emittance Losses and emittance
Emittance stays constant everywhere Not too many losses...
SLIDE 12 Simulation results (frequency scan) Simulation results (frequency scan)
- Q(ADT) = 0.290-0.295
- Npart = 1e5
- Turns = 5e3 (0.5 sec in real time)
- 1sigma (nominal) and 2sigma (blown up)
bunches
SLIDE 13
SLIDE 14
SLIDE 15
Tail depletion Still some tail population Core affected
SLIDE 16 Initial vs final distribution Initial vs final distribution
- Initial distribution
- Particles which end
beyond 5sigma
SLIDE 17
Losses and emittance Losses and emittance
Although the core is clearly affected, the core emittance stays constant
1.8% particles lost (Not far from measurement results)
SLIDE 18 Conclusions
- The model shows some of the features expected
from the narrow band excitation principle.
- Results for fixed frequency still not conclusive.
Need to explore a bit more
- Results for frequency scan look promising but
need to find a way to keep core unaffected.
- Complete simulation with toy model before using
realistic tracking codes.
