Main A ctivities and News from LHC e-Cloud Simulations
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Transcript of Main A ctivities and News from LHC e-Cloud Simulations
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Main Activities and News from LHC e-Cloud Simulations
Frank Zimmermann
ICE Meeting 8 June 2011
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e-cloud simulation meetings• 12 meetings since 26 November 2010• summary notes (thanks to Octavio) and all
presentations available at
https://project-ecloud-meetings.web.cern.ch/project-ecloud-meetings/meetings2010.htm
• regular participants: Gianluigi Arduini, Chandra Bhat, Octavio Dominguez, Kevin Li, Humberto Maury, Elias Metral, Tatiana Pieloni, Giovanni Rumolo, Frank Zimmermann, + Alexey Burov
• special guests: Giuliano Franchetti, Wolfgang Hoefle, Ubaldo Iriso, Kazuhito Ohmi, EPFL team
• AccNet CERN-GSI e-cloud workshop, 7-8.03.2011
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main focus / mission• understand LHC electron-cloud observations• determine LHC surface parameters at different locations
by benchmarking simulations and observations:– measured relative pressure rise in the straight
section for different filling schemes – measured heat load in the arcs – synchronous phase shift (with RF & GSI)– (non-)observation of instabilities → constrain re
• scrubbing and running scenarios for 2011 & 2012• longer-term operation modes & upgrade path • beam instabilities & emittance growth due to e-cloud
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example studies
• benchmarking surface parameters with pressure rise at LSS gauges (Octavio Dominguez)
• benchmarking surface parameters with arc heat load (Humberto Maury)
• upgrade scenarios (Humberto Maury)• instability thresholds & tune shifts (Kevin Li)• PS e-cloud simulations for experimental test of
LHC LPA upgrade scheme (Chandra Bhat)
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• dmax: maximum secondary electron yield• emax: electron energy at which yield is maximum = dmax
• R: reflection probability for low-energy electrons
emax
R
• dmax, emax (q)!
• R is assumed to be independent of q
• plot assumes =90°q
secondary emission parameters
O. Dominguez
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example 2010 observationpressure increase versus batch spacing
Pilot bunch + Batch 1 (12 bunches) + 1950 ns + Batch 2 (24 bunches) + batch spacing (variable according to measurement) + Batch 3 (24 bunches)
b
a
b
aii P
PP
pressure increase related to electron flux @ wall:
O. Dominguez
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O. Dominguez
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O. Dominguez
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O. Dominguez
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dmax=1.86R=0.25
O. Dominguez
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Approximately same SEY but much lower R
3rd order fit
dmax~1.84R~0.1
O. Dominguez
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taking an arbitrary 10% error in the pressure
3rd order fit
O. Dominguez
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1.35, 1.85, 8.85, 28.85ms
taking an arbitrary 10% error in the pressure
Should the solution be here?
3rd order fit
O. Dominguez
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2011 Scrubbing run – First night
6ms 4ms 2ms 1ms
Injection interlock due to BIC sanity checks not performed in the last 25 hours
Pressure close to the thresholds
We wanted:
O. Dominguez
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6ms
4ms
2ms
2ms
DP1DP2
2011 Scrubbing run – First night
O. Dominguez
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2011 P vs. batch spacing experiment
O. Dominguez
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2011 P vs. batch spacing experiment
[1.86, 0.12][1.70, 0.11]
[1.86, 0.12] 3rd order fitto simulated fluxes in orderto reduce local effect of statistical fluctuations
O. Dominguez
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2011 P vs. batch spacing experiment
• experiment could not be carried out as planned due to several reasons:- 225 ns batch spacing not available- satellite bunches in SPS (delay + 5000 RF buckets shift)- P close to thresholds for Beam 2- injection interlock (BIC sanity check)
• only three points (2 relative measurements) and solely for beam 1
• pressure did not stabilize in the time used for the first batch spacings
• simulations do not give clear agreement (a 3rd point would be needed for verification)
• Nevertheless possible solution in the same region as for 2010 experiment
• 3rd and 5th order fits have been done, showing both similar solutions
• unfortunately, experiment not repeated at the end of the scrubbing run
O. Dominguez
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2nd “experiment”: 2 ms batch spacing – P linearity
0 1 2 3 4 5 6 7 8 90.00E+00
2.00E-08
4.00E-08
6.00E-08
8.00E-08
1.00E-07
1.20E-07
1.40E-07
1.60E-07
1.80E-07
2.00E-07
f(x) = 3.17714285714288E-08 x − 7.54095238095244E-08R² = 0.997491771893218
VGI.141.6L4.B.PR
# of 36-bunch trains in the machine
P [m
bar]
Exponential growth
Linear behavior
Saturation
One could get contour plots from this points…
O. Dominguez
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2011 scrubbing - first night experiments together
Considering DP
O. Dominguez
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f2b/f1b
f3b/f1b
f5b/f1bf4b/f1b
f4us/f2us
f6us/f2us
2011 scrubbing - first night experiments together
3rd order fit
O. Dominguez
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best estimate for LSS surface :
• 2 Nov. 2010: dmax=1.85±0.05, R=0.15±0.1
• 6 April 2011: dmax=1.89±0.05, R=0.15±0.1
at same ionization gauge, b=40 mm, single beam
no evidence for dmax reduction due to surface conditioning at this location
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multipacting threshold in the LHC arcs
H. MauryDecember 2010
H. Maury
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arc heat load – some 2010 data
-1
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
4
10/3
0/10
14:
24
10/3
0/10
16:
48
10/3
0/10
19:
12
10/3
0/10
21:
36
10/3
1/10
0:0
0
10/3
1/10
2:2
4
10/3
1/10
4:4
8
10/3
1/10
7:1
2
10/3
1/10
9:3
6
10/3
1/10
12:
00
[W p
er h
alf-
cell]
, [Te
V], [
1013
p]
Qbs21L3 (calculated with T increase) Qbs33L6 (calculated with T increase)
Qbs13R7 (calculated with T increase) Qbs (IC+SR calculated with beam parameter)
Beam energy Intensity Beam1
Intensity Beam2
-1
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
4
11/1
9/10
21:
36
11/1
9/10
22:
04
11/1
9/10
22:
33
11/1
9/10
23:
02
11/1
9/10
23:
31
11/2
0/10
0:0
0
11/2
0/10
0:2
8
11/2
0/10
0:5
7
11/2
0/10
1:2
6
11/2
0/10
1:5
5
11/2
0/10
2:2
4
[W p
er h
alf-
cell]
, [Te
V], [
1013
p]
Qbs21L3 (calculated with T increase) Qbs33L6 (calculated with T increase)
Qbs13R7 (calculated with T increase) Qbs (IC+SR calculated with beam parameter)
Beam energy Intensity Beam1
Intensity Beam2
Heat load measured in the beam screen of the cells 21L3, 33L6, 13R7 during injection and ramp of 108 bunches before (left) ~30 mW/m/beam ) and after (right) the 2010 scrubbing run.
G. Arduini
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arc heat load – some 2011 dataInjection # Ring
RF bucket #
Bunch spacing [ns]
Bunches/inj
Spacing between PS trains
# PS trains/injection
1 ring_1 1 0 1 0 1 pilot1 ring_2 1 0 1 0 1 pilot2 ring_1 441 50 12 0 1 nominal2 ring_2 441 50 12 0 1 nominal3 ring_1 1581 50 72 225 2 nominal3 ring_2 1581 50 72 225 2 nominal4 ring_1 3511 50 72 225 2 nominal4 ring_2 3511 50 72 225 2 nominal5 ring_1 5441 50 72 225 2 nominal5 ring_2 5441 50 72 225 2 nominal
Fill 1704 (13/4/2011 – 12:16 to 16:47Filling scheme (for both beams): 228 bunches/beam - Average intensity 1.22 e 11 p/bunch (first ramp after scrubbing): 50ns_1164b_36x2bi_18inj_scrub (cut at 228 bunches)Emittances at injection
70-80 mW/m/beam
trains of 72 bunchesspaced alternatinglyby 225 ns and by 1.1 ms
G. Arduini
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1.6 1.8 2.0 2.2 2.4
0.1
1
10
100
1000
Hea
t lo
ad (m
W/m
)
Secondary emission yield (Max
)
R = 0.2 R = 0.3 R = 0.4 R = 0.5 R = 0.6 R = 0.7 R = 0.8 R = 0.9
Average Heat Load - Real Pattern - 3.5 TeV
H. Maury
simulated 2011 heat load versus dmax
70 mW/m
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H. Maury
simulated heat load in dmax-R plane
measuredheat load correspondsto blue region
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20 22 24 26 28 301.5
1.6
1.7
1.8
1.9
2.0
2.1
2.2
2.3
2.4
Sec
ondar
y em
issi
on y
ield
( M
ax)
Radius (mm)
Multipacting Threshold vs. Chamber Radius
H. Maury
multipacting threshold versus chamber radius,50 ns bunch spacing
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10 15 20 25 30 35 40 45 50 55
10
100
1000
10000
Hea
t lo
ad (m
W/m
)
Radius (mm)
SEY 1.7 SEY 1.9 SEY 2.1 SEY 2.3
Average heat load - 3p5 TeV - 50ns - R = 0.3 - Drift section
H. Maury
heat load versus chamber radius, 50 ns spacing
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e-cloud heat load for LHC upgrades
25-ns bunch spacing 50-ns bunch spacing
H. Maury
electron cloud contribution acceptable if dmax≤1.2
H. Maury
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e-cloud heat load also OK for 50 ns spacing plus “LHCb
satellites”
H. Maury
H. Maury
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K. Li
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K. Li
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K. Li
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K. Li
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instabilities
threshold e- density : 3-6x1011 m-3 at 450 GeV6-10x1011 m-3 at 4 TeV
tune shift: ~0.01 at injection for 2x1011 e-/m-3 (no field)~0.002 at 4 TeV for 2x1011 e-/m-3 (no field)
K. Li
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LHC arc chamber sawtooth
I. Collins,V. Baglin, et al.
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beam-screen orientation in S3-4
Beam tube 1Beam tube 2
(4.6 K, 3 bar)
(20 K, 1.3 bar)
(75 K, 19 bar)
(4 K, 16 mbar)
(50 K, 20 bar)
D Q DD D Q DD D Q
Header C
Header D
Header B
Header F
Header E
Line N, Bus-Bars
T
T
T
T
T
T T
X
T
T
Y Y
T
T
T
L
T
T
X
T
PP
PP
T
T T
P
X
P
T
TT T T T T T T T T
YY Y Y Y Y Y Y Y Y
Beam screen
Support Posts
Warm Instrumentation
Under Evaluation
Cryogenic Instrumentation, vacuum type
X Cryogenic Instrumentation, insertion type
MAGNETS
Cryogenic Distribution Line
L: Liquid Helim LevelP: PressureT: TemperatureY: Electrical Heater
Type "A" Service Module Type "B" Service Module
L L
HX HX
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V. Baglin I. Collins, O. Grobner, EPAC’98
effect of the sawtooth
assumptions agreed with Humberto Maury to model chamber w/o sawtooth:
• change distribution of reflected photons from cos2 y to uniform• increase reflectivity from 20% to 80% • increase photoelectron yield by factor 2
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e- build up with & w/o sawtooth
dmax=1.4 dmax=1.5
H. Maury
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heat load with & w/o sawtooth
H. Maury
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PS e-cloud: ion=2.9 Mbarn, SEY=1.5, R=0.6, B=0 G, sz=60-85cm, Gaussian bunch(2000 macro particles)
PS e-cloud simulations for different sz
C. Bhat
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next steps• if/once method is established map surface
parameters around the machine (>100 gauges); and track their changes
• draw conclusions for inverted sawtooth chambers• make updated predictions for LHC at 25 ns spacing,
e.g. optimize filling patterns for 25-ns scrubbing; scrubbing/commissioning scenarios
• update predictions for LHC upgrade scenarios• higher-order coupled-bunch head-tail instability
driven by e- cloud: “wake field” & growth rates
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other ongoing or planned activities• e-cloud pinch in quadrupoles, & new approach to
resonance crossing (G. Franchetti)• code development with EPFL (M. Mattes & E. Sorolla) modeling mwaves & electron cloud • e-cloud simulations for flat intense bunches in PS/SPS & corresponding MDs (Chandra Bhat) • planned studies of SPS feedback with LARP & ICE
(W. Höfle, E. Metral, G. Rumolo) • longitudinal wake field & energy loss in SPS and
LHC (collaboration with GSI (F. Yaman, O. Boine-Frankenheim, G. Rumolo, E. Shaposhnikova , F. Z.)• e-cloud at collimators, field emission, heating