Collective Effects and Beam Measurements in Particle Accelerators

1
Collective Effects and Beam Measurements in
Particle Accelerators

• beam diagnostics and fundamental limitations to
  the performance of high-intensity accelerators

http//ab-abp-rlc.web.cern.ch/ab-abp-rlc/
See also slides on Measurements, ideas,
curiosities
2
Wakefield for a pill-box cavity

• Animation showing a bunch of charged particles
  moving on the cavity axis and the corresponding
  electric field lines computed by the program ABCI
• Courtesy Andreas Wagner http//awagner.home.cern.c
  h/awagner/

3
TRISIM3D simulation of a LEP bunch E 22 GeV,
Qs 0.092, I 0.3 mA

• 3-dimensional computer simulation of single bunch
  collective effects in particle accelerators
• top and side view of the particle distribution
  turn by turn, over 60 turns
• Courtesy Andreas Wagner http//awagner.home.cern.c
  h/awagner/

4
CERN Linac4layout and parameters
160MeV
3MeV
40MeV
90MeV
3MeV
95keV
DTL
CCDTL
SCL
CHOPPER
RFQ
H-
Drift Tube Linac 352 MHz 13.4 m 3 tanks 5
klystrons 4 MW
Side Coupled Linac 704 MHz 28 m 20 tanks 4
klystrons 12 MW
Cell-Coupled Drift Tube Linac 352 MHz 25.3 m 24
tanks 8 klystrons 6.5 MW
Chopper 352 MHz 3.6 m
Radio Frequency Quadrupole 352 MHz 6 m 1
Klystron 1 MW
Duty cycle 0.1 phase 1 (Linac4) 3-4 phase 2
(SPL) (RF design 15)
4 different structures, (RFQ, DTL, CCDTL, SCL) 2
frequencies
Total Linac4 80 m, 18 klystrons
current 40 mA (avg. in pulse), 65 mA (bunch)
Courtesy A. Lombardi
5
Instabilities in a Linac
Transverse tune depression
Longitudinal to transverse phase advance

• Courtesy A. Lombardi

6
Intra-Beam Scattering (simplified formulae by K.
Bane, EPAC 2002)

• For the LHC, the average dispersion invariant is
  ltHxgt0.03 m, bav100 m, and the Coulomb logarithm
  (log)24
• Note that the transverse IBS growth rate is about
  proportional to the particle density in the 6D
  phase space Nb/(e2szsd)

IBS growth times for long super-bunches
in the LHC as a function of the rms momentum
spread sd