hh 1082015 FCChh RF and Transverse Feedback System W Hofle 08 October 2015 1 As presented at the FCC Week With some additional remarks Wolfgang Hofle BERFFB Start with where we stand ID: 780205
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Slide1
Transverse Feedback FCC-hh
10/8/2015
FCC-hh RF and Transverse Feedback System / W. Hofle 08 October 2015
1
As presented at the FCC Week
With some additional remarks
Wolfgang Hofle
BE-RF-FB
Slide2Start with where we stand LHC10/8/2015
FCC-hh RF and Transverse Feedback System / W. Hofle 08 October 2015
Key FCC-
hh parameters very similar to LHC
25 ns and
5 ns
bunch spacing options
Beam current similar to LHC, 1x10
11 protons per bunch for 25 ns FCC-hh transverse feedback design follow same design path as for the LHC Design:strong transverse feedback for coupled bunch instability mitigation driven by resistive wall impedance of beam screen and machine elementsknowledge of impedance key to define parameter space for RF system and transverse feedbackFCC-hh will have significant synchrotron radiation damping; emittance control important both longitudinal and transverse (blow-up may be needed)
2
Slide3Transverse Feedback: LHC10/8/2015
FCC-hh RF and Transverse Feedback System / W. Hofle 08 October 2015
Injection damping
high gain, low bandwidth, large kick strength
Instability damping
gain adapted to instabilities, bandwidth can be tailored by signal processing
Preservation of
emittance
low noise, detection of mm oscillationTool for transverse blow-up loss maps, quench tests, aperture measurementsLHC Transverse Feedback operation with colliding beams well established using a digital system, a first in a Hadron Collider, it is also needed with colliding beams (non colliding bunches, offsets)Full exploitation of ADT data for beam diagnostics and tune measurement being prepared for Run 2
Improvements prepared in LS1 (number of pick-ups, electronics, software upgrade), reduction of noise, to come on gradually in run 2
ADT - LHC Transverse Feedback (Damper)
3
Slide4FCC-hh Requirements10/8/2015FCC-hh RF and Transverse Feedback System / W. Hofle 08 October 2015
4
Do we require to damp single bunch instabilities ?
Do we require to damp internal bunch motion (TMCI like) ?
Are there narrow band transverse impedances that require damping with high gain up to half the bunch repetition frequency (see for example the issue with HOMs of High
Lumi
LHC crab cavities) ?
Injection damping
high gain, low bandwidth, large kick strengthInstability damping coupled bunch instabilities driven by resistive wall impedance of beam screen / beam pipePreservation of emittance low noise, detection of
m
m oscillation
Maintaining
emittance
noise injection to counteract
emittance
shrinking by radiation damping at top energy and during ramp ?
Advanced diagnostics potential and compatibility with tune measurement needs to be given attention from the beginning
learn from LHC and High
Lumi
LHC experience
Slide5LHCADT Power and Kicker System 10/8/2015FCC-hh RF and Transverse Feedback System / W. Hofle 08 October 2015
5
K
icker length: each kicker 1.5 m
M
ax voltage: 10.5 kV
2
m
rad kick to 450 GeV beamGain up to beyond 20 MHz16 kickers, 32x30 kW tetrode amplifiersBandwidth up to 20 MHzs
caled from SPS system
LHC transverse Feedback (ADT) kickers and amplifiers in tunnel point 4 of LHC, RB44 and RB46
M
easured ADT frequency response. Green: bare power amplifier, blue: power amp + kicker.
ADT kicker. The beam is kicked by electric field
Power
beam
observation
FCC-
hh
requires more bandwidth
(5 ns option bunch spacing option)
Slide6Injection Oscillations – Batch View10/8/2015FCC-hh RF and Transverse Feedback System / W. Hofle @FCC Week, Washington D.C. 22-27 March 2015
6
50 ns bunch spacing
standard + hold
144 bunches (4x36)
25 ns bunch spacing
e
nhanced bandwidth
144 bunches (2x72)
Injection
oscillation
damping
IPAC’13, WEPME43
6
d
amping at edges of batch slower
t
ime domain ADT response
LHC
V-plane
Slide7LHC 2012 Run achievements10/8/2015FCC-hh RF and Transverse Feedback System / W. Hofle @FCC Week, Washington D.C. 22-27 March 2015
Beam 1
H: 16 turns
V: 27 turns
Beam 2
H: 13 turns
V: 26 turns
H
HVVLHC, curtesy A. MacphersonSee also IPAC’13, FRXCA017
Damping times as measured on first bunch of batch
Slide8LHC Damping10/8/2015FCC-hh RF and Transverse Feedback System / W. Hofle 08 October 2015
8
8 turns damping achieved in LHC (H-plane)
first bunch of train of 12 injected is displayed
H-plane not affected by ripples of vertical injection kicker
Important: gain can be as high as needed to achieve 8 turns damping
LHC 6.10.2015
Slide9LHC ADT Design parameters10/8/2015FCC-hh RF and Transverse Feedback System / W. Hofle 08 October 2015
9
r
elative
emittance
i
ncrease at injection
b
low-up factor
injection
value
energy
E
450
GeV
emittance
(norm)
e
3.5
m
m
injection error
a
inj
4 mm @
b
=185 m
increase w/o FB
a
inj
2
/(2
s
2
)
(5.92)
max increase of
e
(De
/
e)max
0.025
blowup
factor
F
e
< 4.22 x10
-3
d
e-coherence time
(in design report due to Q’)
Full tune spread 1.3x10
-3
Damping time
u
ltimate LHC
1.7e11 ppb
nominal LHC
1.0e11 ppb
EPAC’08, THPC121
LHC Design Report CERN-2004-003
LHC Run 1: in practice smaller
emittances
available from injectors
Slide10FCC-hh RF and Transverse Feedback System / W. Hofle 08 October 2015R&D: intra-bunch feedback (SPS)10/8/2015
Analog
Front
End
Analog
Back
End
Signal
ProcessingBPM
Kicker
Power Amp
ADC
DAC
Beam
Active closed loop
Feedback
transverse
position
pre-processed
sampled
position
“
slices
”
calculated
correction data
correction
signal
pre-distortion
drive signal
10
capacity to damp intra-bunch instabilities, 4-8 GS/s digital feedback
o
riginally started as e-cloud instability
a
lso shown to damp TMCI in simulation if synchrotron tune low
c
losed loop experiments in SPS started
m
ilestone to demonstrate feasibility: mid 2016
t
argeted bandwidth
1
GHz, needed BW scales with
bunchlength
g
ood
to cover large range of bandwidth, two kicker designs
short
stripline
(completed) and
slotline
(under development)
s
upported by US-LARP
and SPS-LIU
J.D. Fox et. al
Slide11US LARP Feedback Kicker Design10/8/2015FCC-hh RF and Transverse Feedback System / W. Hofle 08 October 2015
11
Need for high Bandwidth requires new kicker for the SPS:
Inspired by Stochastic
C
ooling
Systems
Faltin type kickerconsidered (strip-line withslotted shield to beam pipe)J. Cesaratto et al. (SLAC)WEPME061, IPAC’2013Develop for test of prototype in SPSSmaller vacuum chamberEasily permits higher frequency(LHC and FCC)
Slide12FCC-hh TFB: 25 ns -100 km option
10/8/2015FCC-hh RF and Transverse Feedback System / W. Hofle 08 October 2015
12
r
elative
emittance
i
ncrease at injection
b
low-up factor
injection
value
energy
E
3300
GeV
emittance
(norm)
e
2.2
m
m
injection error
a
inj
1 mm @
b
=185 m ?
increase w/o FB
a
inj
2
/(2
s
2
)
(4.32)
max increase of
e
(De
/
e)
max
0.05
blowup
factor
F
e
< 11.6 x10
-3
d
e-coherence time
(needs determination)
Damping time
FCC versus LHC:
smaller injection error
s
lower de-coherence ?
but faster instability
?
4 turns
?
5
turns
6.7 turns
10 turns
develop feedback algorithms for fast damping
Slide13Summary FCC-hh TFB10/8/2015FCC-hh RF and Transverse Feedback System / W. Hofle 08 October 2015
Impedance estimates key to TFB design
TFB
design
:
coupled bunch feedback with options for 5 ns and 25 ns bunch spacing (driven by resistive wall instability
fast instability rise times)bandwidth up to 100 MHz for 5 ns option to cover all CBMs injection damping kicker waveform a challenge (ripple)TMCI instability: Potential of intra-bunch GHz feedback is being investigated with US-LARP supported work for the SPS
needed R&D for FCC covers the technology of kicker, power systems, signal processing electronics and algorithms
Leverage on US LARP work for SPS Feedback !
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Slide14Tentative options FCC-hh TFB10/8/2015FCC-hh RF and Transverse Feedback System / W. Hofle 08 October 2015
System like LHC System to cover low frequency coupled bunch modes and injection damping,
cost scales with
energy
for constant injection error
tetrodes/ like LHC system,
or very long
strip-lines (10 m ?) + solid stateInstability rise-times of faster than 10 turns call for a distributed system (bandwidth 100 kHz – 1 MHz), simulations needed:5-10 turns: two locations in ring symmetrically placed2-5 turns: four locations symmetrically placed
1-2 turns: eight locations symmetrically placed
Strip-line system to cover frequency range up to 40 MHz or 100 MHz
Frequency range depends on bunch spacing option, perhaps further split in two systems (5 ns or 25 ns)
Intra-bunch systems
Band-by-band approach at n x RF (400 MHz, 800 MHz …)
Combination of strip-line of 400 MHz and slot lines(s)
Important work that needs to start
Kicker electromagnetic design
Beam Simulations with
feedback
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