Vladimir Shiltsev

1
Studies of High-Frequency Magnetic Field
Fluctuations in LHC MagnetsApril 27, 2006

• Vladimir Shiltsev
• Riccardo de Maria
• Luca Bottura

2
B-field is frozen at high frequencies
3
dB/B Fluctuations Tolerances
4
Tevatron Dipoles
LHe (turbulent)
5
No LHe flow in LHC Dipole Except Screen
6
LHC Beam Screen
LHC screen light and under action of 20 K He
flow turbulent kicks B-flux is constant at 3kHz
dB/B dR/R ? need dR lt 1A to blow horizontal
emittance gt10 dE/dt Being measured at CERN MMF
7
dB/B in Tevatron dipole
Tevatron Stand-Alone Dipole measurements (Proc.
PAC01)
8
dB/B measurements at CERN
5 coils calibrated
9
dB/dJ suppression in LHC dipole (warm)
10
dB/dJ suppression
By inductance and SS
by the screen
11
dB/B in cold Quadrupole
Coil placed off-center 8 bit Tectronix Digital
scope too noisy
12
19bit 50kHz HP3458A sent to CERN
HP?PC DAQ works, nx1kHz ringing Noise measured,
triggering issues
13
dB/B Plan of Action

• Perform dB/B measurements at CERN in
• Dipole (cold, high current)
• Quadrupole (same)
• Measure vibrations of the screen
• Will take about 1 year
• Cost
• 2-3 more trips to CERN 5k
• Low-noise pre-amp 5k
• Goal be able to conclude on dEmm/dt and need of
  FB
• Next steps designand development of low-nosie FB

14
Then , one needs a fast feedback system
requires P100W in df50kHz band BPM noise
0.5um (Tev standard BPM 5 um, special
stripline 0.2 um at Qx,y)