Transcript Pergine Slides

Measurements, ideas, curiosities
beam diagnostics and fundamental limitations to
the performance of high-intensity accelerators
Complement to the lecture on Collective Effects & Beam Measurements
F. Ruggiero
CERN
Univ. “La Sapienza”, Rome, 20–24 March 2006
Transverse head-tail modes at the CERN PS
(E. Metral, 1999, 20 revolutions superimposed)
m q4
m q 5
m q7
m q6
m  q 8
m  q  10
Time (20 ns/div)
F. Ruggiero
CERN
Collective Effects and Beam Measurements
Fast vertical single-bunch instability with
protons at the PS near transition in 2000
(Courtesy E. Metral)
E  6 GeV Nb  4 1012 p/b
, R, V signals
Tail unstable
Head stable
~ 700 MHz
Time (10 ns/div)
 Instability suppressed by increasing the longitudinal emittance
F. Ruggiero
CERN
Collective Effects and Beam Measurements
Fast vertical single-bunch instability
with protons at injection in the CERN SPS
(E. Metral, 2003)
Synchrotron period 7 ms
p  26 GeV/c Nb  1.21011 p/b
 l  0.2eVs   lLHC  0.35 eVs
 Instability suppressed
by increasing
the chromaticity
y  0
F. Ruggiero
CERN
 y  0.8
Collective Effects and Beam Measurements
LONGITUDINAL – HIGH INTENSITY EFFECTS
Experiment with a CERN PS proton beam in 1999
 Longitudinal Schottky scan spectrogram during debunching
~ 200 ms
Low-intensity beam
F. Ruggiero
CERN
High-intensity beam
Courtesy R. Garoby
Collective Effects and Beam Measurements
Longitudinal Solitons in RHIC
•
•
Wall Current Monitor data for a proton bunch freshly
injected into RHIC (left) and for the same bunch after
17 minutes (right)
Injection is at g = 25.9, i.e. above transition gt = 23.8
Longitudinal phase
space distribution
obtained by a selfconsistent solution of
the Vlasov equation
• These oscillations should be Landau damped
• When nonlinear effects are included, long lived,
stable coherent oscillations become possible for
low-intensity beams
• Long-lived beam “holes” have been observed
below transition in the CERN PS Booster
“Longitudinal Solitons in RHIC”, M. Blaskiewicz, J.M. Brennan,
P. Cameron, W. Fischer, J. Wei, A. Luque, H. Schamel, PAC’03
F. Ruggiero
CERN
Collective Effects and Beam Measurements
Vertical growth rate of head-tail modes in the
LHC as a function of chromaticity at injection
energy, for ~3000 bunches of nominal intensity
Instability growth rates sec
20
1
Mode 0
15
Mode 1
10
Mode 2
5
10
5
Mode 3
5
10
Qy'
At injection head-tail modes with growth rates up to about 4 sec-1 are stabilized
by lattice nonlinearities (assuming an amplitude detuning of 0.002 at 6 sigma).
The rigid mode m=0 has to be stabilized by the transverse feedback.
F. Ruggiero
CERN
courtesy E. Metral and F. Zimmermann
Beam Echo Measurements at CERN
•
•
•
An echo is formed by the interference of two consecutive RF pulses with slightly
different frequencies. Each RF excitation induces a well defined pattern of particle
energy along the machine circumference, rapidly destroyed by the revolution
frequency spread. However, the long lasting memory of the proton beam allows the
re-appearance of an ordered structure long after the initial excitations.
The timing of the echo response depends on the frequency of the kicks and their
separation; the longer the separation, the later the echo: in the SPS we have
observed echo delays up to two minutes (i.e., more than 5 millions turns).
The picture shows the superposition of 22 echo measurements with different time
separations between the two RF-kicks, ranging from 5 to 220 ms. The vertical axis
shows the absolute value of the echo amplitude on a linear scale and the horizontal
axis shows the time measured from the first RF-kick. The horizontal scale is 50 s.
The solid line shows the analytical estimate for the echo envelope assuming a
diffusion coefficient of 10-13 s-1: in order to observe such a small diffusion with the
Schottky signal, one would have to wait more than one day.
F. Ruggiero
CERN
Collective Effects and Beam Measurements
Collective Effects: web links & references
http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/
(web site of the R&D and LHC Collective Effects team at CERN)
“Physics of Collective Beam Instabilities in High Energy Accelerators”,
A. Chao, (Wiley, 1993)
“Impedances and Wakes in High-Energy Particle Accelerators”,
B.W. Zotter and S. Kheifets, (World Scientific, 1998)
“Longitudinal holes in debunched particle beams in storage rings,
perpetuated by space-charge forces”, S. Koscielniak, S. Hancock, and
M. Lindroos, Phys. Rev. ST Accel. Beams 4, 044201 (2001)
“Beam dynamics studies for uniform (hollow) bunches or super-bunches in the
LHC: beam–beam effects, electron cloud, longitudinal dynamics, and intra-beam
scattering”, F. Ruggiero, G. Rumolo, F. Zimmermann, Y. Papaphilippou, CERN LHC
Project Report 627 (2002)
“Intrabeam Scattering with Non-Ultrarelativistic Corrections and Vertical Dispersion
for MAD-X”, F. Zimmermann, CERN-AB-2006-002 (2006)
F. Ruggiero
CERN
Collective Effects and Beam Measurements