Updates on tracking studies to study
TCT impacts during asynchronous
beam dump
R. Bruce, E. Quaranta
Acknowledgement: M. Fraser, S. Redaelli
R. Bruce, 2015.07.27
Outline
•
Introduction
•
Implementation of new kicker waveforms in simualtions
•
Merging with main SixTrack branch
•
Some results for BCMS beams with 55 cm nominal optics
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Introduction
•
β* constrained by the available triplet aperture. TCTs must
shadow triplet
•
TCTs cannot be too close to the beam – may be damaged during
asynchrounous beam dumps
– Worst case: single module pre-fire
– One or several bunches pass dump kickers during their rise and may be
kicked directly onto sensitive elements
•
Resulting limitation on β* in run 1
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Contents
•
Important to study in detail accident scenarios and quantify risk
of damage
•
Recent requests for new asynch dump simulations (HL-LHC,
BCMS beams) triggered revision of the simulation setup
•
This talk:
– Updated kicker waveform
– Merging with main branch of SixTrack using DYNK
– Some considerations for BCMS beams with nominal optics
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Simulation setup
•
Asynchronous beam dumps simulated using special version of
SixTrack (L. Lari et al., IPAC12)
•
Bunch of macro-particles tracked, receive kicks from dump
kickers (MKDs) on second turn
– Several simulations combined, where each one has a different
configuration of the MKD kicks, as seen by subsequent bunches in train
•
Full collimation system in place, scattering accounted for in
SixTrack
•
Output: loss distribution on collimators and ring aperture
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New waveforms
•
Previously used ideal kicker waveform provided by B. Goddard
– Each kicker had the same waveform, but displaced in time
– Assumed (650 + 50i ) ns retriggering time for kicker number i from the one
that mis-fired
•
New input from M. Fraser 2015: measured MKD waveforms
– Separate realistic waveform for each kicker
– Two cases studied: erratic type 1 and type 2
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Comparison of waveforms
old
Type 1
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Showing all 15 kickers
•
Much shorter re-triggering
time with type 1
Type 2
7
Total kicks (mrad)
•
Time-shifted curves for better comparison. Sum over 15 MKDs
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Total kicks (σ)
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Zoom
•
Assume TCDQ takes everything above 10-11 σ. Below ~6 σ
nothing can be hit
•
Type 2 spends more time in dangerous region. Most critical!
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Kicker A or O goes first
•
Comparing to the case where O goes first – assuming same
waveforms, but map A->O, B->N, …
•
O going first is more critical – larger β-function at kicker O
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SixTrack results with type 2
•
Implemented the type 2 waveforms in SixTrack simulation setup
•
Example result: nominal 55cm, 2σ retraction, B2, 1.5e11 p/bunch
Old, O firing
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Beam
T2, O firing
Beam
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Scan over TCT setting
•
T2: factor
~1.4-1.8
higher TCT
losses
than old
•
O firing:
up to
factor ~3.5
higher
TCT losses
than with
A firing
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Outline
•
Introduction
•
Implementation of new kicker waveforms in simualtions
•
Merging with main SixTrack branch
•
Some results for BCMS beams with 55 cm nominal optics
R. Bruce, 2015.07.27
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DYNK implementation
•
Previously, SixTrack version to simulate asynchronous dump was
a separate branch, not compatible with main SixTrack version
– Has not profited from recent upgrades to the main SixTrack branch, in
particular scattering routine
•
Recent implementation of dynamic kick module (DYNK) allows
time-dependent functions applied to almost all elements (K. Ness
Sjobak, IPAC15)
– Can be used to simulate asynch dump using the main SixTrack branch
– Not necessary to the old separate branch
•
Implementation of MKD firing with DYNK carried out using type 2
– Asynch dump simulations now includes latest updates to SixTrack
scattering models (thesis C. Tambasco)
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Results with new scattering
•
TCTPH.4L1.B1: no
change from
DYNK in primary
halo as expected
•
TCTPH.4R5.B2
sees only
secondary halo:
factor ~1.5 higher
losses with new
scattering
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Outline
•
Introduction
•
Implementation of new kicker waveforms in simualtions
•
Merging with main SixTrack branch
•
Some results for BCMS beams with 55 cm nominal optics
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Results for BCMS beams
•
•
•
Request to check the
influence on impact
distribution during asynch
dump if emittance is
changed
Study with nominal 55cm
optics, 2σ retraction coll.
settings, type 2. Checking
B1 – most critical case
Beam
Beam
No obvious difference in
loss distribution around
ring
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Losses on collimators
Macro particles
•
Losses listed for perfect
optics / collimator
settings
•
Apart from IR6, one TCSG
in IR7 sees high losses,
about 1.5e11
•
All other collimators at
least an order of
magnitude lower
•
Ring losses about 1e9
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Protons
19
TCSG.B4L7.B1, nominal 55cm
•
Bunch-by bunch impact distribution, 3.5 um
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TCSG.B4L7.B1, nominal 55cm
•
Bunch-by bunch impact distribution, BCMS 1.7 um
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TCSG.B4L7.B1, nominal 55cm
•
Number of impacts vs bunch
3.5 um
1.7 um
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TCSG.B4L7.B1, nominal 55cm
•
Summed impact distribution over all bunches
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TCSG.B4L7.B1, nominal 55cm
•
Mean impacts per bunch: smaller for BCMS
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Checks of TCT impacts
•
So far studied perfect collimator settings and optics
•
To have dangerous impacts on TCTs, need to introduce errors
(tighter setting)
•
Studying impacts on TCTPH.4L1.B1 for very pessimistic setting of
6.9 σ, still 55 cm nominal and 2σ retraction
•
Slightly fewer impacts with BCMS. In total about 1e11 impacts
3.5 um
1.7 um
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TCTPH.4L1.B1, nominal 55cm
•
Impact distribution bunch-by-bunch, 3.5 um
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TCTPH.4L1.B1, nominal 55cm
•
Impact distribution bunch-by-bunch, 1.7 um
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TCTPH.4L1.B1, nominal 55cm
•
Impact distribution summed over bunches
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TCTPH.4L1.B1, nominal 55cm
•
Mean impact distribution: ~100um deeper impact with larger
emittance
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Comparison with ATS
•
For comparison:
emittance variation
studied already for ATS
2015 optics, 55 cm (CWG
13/6/2014)
– B2, old waveform, O firing
•
No particular difference
in loss distribution around
ring
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Highest losses
Macro particles
•
Apart from TCDQ, highest losses
are about 1e11 on TCSP and the
same on TCSG.
•
Total impacts on ring aperture
about 1e9
•
Studying the IR7 TCSG more
closely
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Protons
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TCSG.B4R7.B2 with ATS 55cm
•
Impact distribution has longer tail with nominal emittance
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Mean impacts with ATS
•
Slightly smaller mean impacts with BCMS
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Conclusions
•
Updated SixTrack simulation setup for asynch dump / single
module pre-fire with type 2 waveform and merging with the
main branch
•
First application: asynch dump with BCMS beams
•
Factor ~2 smaller impact parameters found on IR7 TCSG and IR1
TCT with BCMS beams
– Not clear if this is more critical in terms of damage limit. To be studied
together with FLUKA/MME
– Longer tail without BCMS
– Maybe study TCSG impacts with imperfect setting
•
Ongoing (E. Quaranta): Updated simulations for HL-LHC and 2015
machine
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