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Electron cloud studies for the HL-LHC: where do we stand and the next steps. G. Iadarola , G. Rumolo. Many thanks to: H. Bartosik , R. De Maria, O. Dominguez, L. Mether , R . Tomas. 11th HiLumi WP2 Task 2.4 meeting - April 30, 2014. Outline. Studies for the arc main magnets - PowerPoint PPT Presentation
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Electron cloud studies for the HL-LHC: where do we stand and the next steps
G. Iadarola, G. Rumolo
11th HiLumi WP2 Task 2.4 meeting - April 30, 2014
Many thanks to:H. Bartosik, R. De Maria, O. Dominguez, L. Mether, R. Tomas
Outline
• Studies for the arc main magnets
o Scaling with bunch intensity
o 200 MHz option
o 8b+4e scheme
o “Doublet” scrubbing beam
• Studies for the inner triplets
o New triplets in IP1/5
o Present triplets in IP1/8
• Studies for the matching sections – preliminary considerations
Outline
• Studies for the arc main magnets
o Scaling with bunch intensity
o 200 MHz option
o 8b+4e scheme
o “Doublet” scrubbing beam
• Studies for the inner triplets
o New triplets in IP1/5
o Present triplets in IP1/8
• Studies for the matching sections – preliminary considerations
Bunch intensity dependence for the arc main magnets
0 0.5 1 1.5 2 2.50
10
20
30
40
50
60
Intensity [x 1e11 ppb]H
ea
t lo
ad [
W/m
]
quad_2x2808b_heatload_vs_int_lin
0 0.5 1 1.5 2 2.50
5
10
15
20
25
Intensity [x 1e11 ppb]
He
at
load
[W
/m]
dip_2x2808b_heatload_vs_int_lin
0 1 2 310
-6
10-4
10-2
100
102
Intensity [x 1e11 ppb]
Scr
ubb
ing
dos
e (
50e
V)
[mA
/m]
quad_simulated_beam_scrubdose_vs_int_log_legend
sey = 1.00sey = 1.20sey = 1.40sey = 1.60sey = 1.80sey = 2.00
Dipole Quadrupole
Bunch intensity dependence for the arc main magnets
0 0.5 1 1.5 2 2.50
10
20
30
40
50
60
Intensity [x 1e11 ppb]H
ea
t lo
ad [
W/m
]
quad_2x2808b_heatload_vs_int_lin
0 0.5 1 1.5 2 2.50
5
10
15
20
25
Intensity [x 1e11 ppb]
He
at
load
[W
/m]
dip_2x2808b_heatload_vs_int_lin
0 1 2 310
-6
10-4
10-2
100
102
Intensity [x 1e11 ppb]
Scr
ubb
ing
dos
e (
50e
V)
[mA
/m]
quad_simulated_beam_scrubdose_vs_int_log_legend
sey = 1.00sey = 1.20sey = 1.40sey = 1.60sey = 1.80sey = 2.00
Dipole Quadrupole
Underlying mechanism:• When the SEY decreases the energy window for
multipacting becomes narrower
0 1 2 310
-6
10-4
10-2
100
102
Intensity [x 1e11 ppb]
Scr
ubb
ing
dos
e (
50e
V)
[mA
/m]
quad_simulated_beam_scrubdose_vs_int_log_legend
sey = 1.00sey = 1.20sey = 1.40sey = 1.60sey = 1.80sey = 2.00
Quadrupole – SEY=1.3
• For high bunch intensity the e- spectrum drifts to higher energies
Bunch intensity dependence for the arc main magnets
0 0.5 1 1.5 2 2.50
10
20
30
40
50
60
Intensity [x 1e11 ppb]H
ea
t lo
ad [
W/m
]
quad_2x2808b_heatload_vs_int_lin
0 0.5 1 1.5 2 2.50
5
10
15
20
25
Intensity [x 1e11 ppb]
He
at
load
[W
/m]
dip_2x2808b_heatload_vs_int_lin
Dipole Quadrupole
0 1 2 310
-6
10-4
10-2
100
102
Intensity [x 1e11 ppb]
Scr
ubb
ing
dos
e (
50e
V)
[mA
/m]
quad_simulated_beam_scrubdose_vs_int_log_legend
sey = 1.00sey = 1.20sey = 1.40sey = 1.60sey = 1.80sey = 2.00
Bunch intensity dependence for the arc main magnets
0 0.5 1 1.5 2 2.50
10
20
30
40
50
60
Intensity [x 1e11 ppb]H
ea
t lo
ad [
W/m
]
quad_2x2808b_heatload_vs_int_lin
0 0.5 1 1.5 2 2.50
5
10
15
20
25
Intensity [x 1e11 ppb]
He
at
load
[W
/m]
dip_2x2808b_heatload_vs_int_lin
Dipole Quadrupole
0 1 2 310
-6
10-4
10-2
100
102
Intensity [x 1e11 ppb]
Scr
ubb
ing
dos
e (
50e
V)
[mA
/m]
quad_simulated_beam_scrubdose_vs_int_log_legend
sey = 1.00sey = 1.20sey = 1.40sey = 1.60sey = 1.80sey = 2.00
• In dipoles the multipacting region becomes wider for higher intensities
Bunch intensity dependence for the arc main magnets
• Warning: dependencies rely on assumptions on Emax and uniform SEY on the wall
• Provided that we manage to access a low SEY regime, increased bunch intensity should be acceptable for heat load, effect on the beam still to be assessed
0 0.5 1 1.5 2 2.50
10
20
30
40
50
60
Intensity [x 1e11 ppb]H
ea
t lo
ad [
W/m
]
quad_2x2808b_heatload_vs_int_lin
0 0.5 1 1.5 2 2.50
5
10
15
20
25
Intensity [x 1e11 ppb]
He
at
load
[W
/m]
dip_2x2808b_heatload_vs_int_lin
0 1 2 310
-6
10-4
10-2
100
102
Intensity [x 1e11 ppb]
Scr
ubb
ing
dos
e (
50e
V)
[mA
/m]
quad_simulated_beam_scrubdose_vs_int_log_legend
sey = 1.00sey = 1.20sey = 1.40sey = 1.60sey = 1.80sey = 2.00
Dipole Quadrupole
200 MHz option: effect on e-cloud in the dipoles
• If option with 200 MHz main RF is adopted, longer bunches will have a positive impact also on electron cloud
• Impact of bunch length on e-cloud to be studied experimentally in Run 2 (e.g. to mitigate degradation at low energy)
Thanks to O. Dominguez
8b+4e fallback scenario
• Filling pattern with 25 ns spacing interleaving batches of 8 bunches with gaps of 4 slots, showed a significantly increased multipacting threshold compared the standard scheme
o backup scheme in case safe operation with 25 ns beam is hampered by e-cloud (still 50% more bunches wrt 50 ns)
• The effectiveness of this scheme will have to be confirmed during Run 2
Thanks to O. Dominguez
25 ns (72b. per PS batch)8b + 4e (48b. per PS batch)8b + 4e (56b. per PS batch)
Measured in 2012 (Fill 3429)
“Doublet” scrubbing beam
• Operation with 25 ns will rely on SEY reduction by beam induced scrubbing
• To operate with 25 ns beams (~2800b.) it is mandatory to achieve lower values in SEY compared to what was achieved in Run
o Dedicated scrubbing beams with hybrid bunch spacing (5+20 ns) are presently under study (e-cloud enhancement shown experimentally at SPS)
o If possible to be used for scrubbing already during Run 2 (SPS and LHC)
1.1 1.2 1.3 1.4 1.510
-6
10-4
10-2
100
102
SEY
Scr
ubb
ing
dos
e (5
0eV
) [m
A/m
]
0.50e11ppb0.60e11ppb0.70e11ppb0.80e11ppb0.90e11ppb1.00e11ppb1.10e11ppbStd. 25 ns
10 20 30 40 50 60 700
2
4
x 1011
Bea
m p
rof.
[p/m
]
10 20 30 40 50 60 701
1.5
2
2.5
3
3.5
Time [ns]
Ne /
Ne(0
)
PyECLOUD simulations
LHC dipole
Ele
ctro
n de
nsity
[a.
u.] Scrubbing beam (5+20) ns
Standard beam 25 ns
Outline
• Studies for the arc main magnets
o Scaling with bunch intensity
o 200 MHz option
o 8b+4e scheme
o “Doublet” scrubbing beam
• Studies for the inner triplets
o New triplets in IP1/5
o Present triplets in IP1/8
• Studies for the matching sections – preliminary considerations
Q1 (A/B)
Q2 (A/B)
Q3 (A/B) D1
Q1
Q2 (A/B)
Q3 D1Present
HiLumi
IP1, 4 TeV, β* = 0.6 m
IP1, 7 TeV, β* = 0.15 m
Inner triplets for HL-LHC upgrade
More details on electron cloud studies for the inner triplets can be found in:
• For the present triplets:
http://indico.cern.ch/event/270441/
• For the HL LHC triplets (including IP2 and IP8):
https://indico.cern.ch/event/278323/
https://indico.cern.ch/event/303742/
A look to the EC buildup – HL-LHC triplets
Few snapshots of the electron distribution HL-LHC triplets develop thicker stripes along field lines farther from the center of the chamber
HL-LHC (2.20 x 1011 ppb)
Present (1.15 x 1011 ppb)
Distribution of heat load – HL-LHC triplets
Heat load distribution along HL-LHC triplets + D1 • Build up more or less efficient at different locations mainly due to the different
hybrid bunch spacings• The least efficient build up, i.e. lower heat load, at the locations of the long-range
encounters (vertical dashed lines)• Values in D1 are comparable or higher than values in the quads
Total heat load per element – HL-LHC triplets
Total heat load per element in HL-LHC triplets + D1 • Similar thresholds for quads and D1• Values in D1 higher than values in the quads for high SEY values
1 1.2 1.4 1.6 1.8 20
200
400
600
800
1000
1200
1400
1600
SEY
Hea
t lo
ad
[W]
25 ns - 2800 bunches
1 1.2 1.4 1.6 1.8 20
200
400
600
800
1000
1200
1400
1600
SEY
Hea
t lo
ad
[W]
25 ns - 2800 bunches
Effect of larger bunch population and chamber size. For the same SEY:- Similar energy of multipacting electrons- Larger number of impacting electrons
⇒ Total heat load about x3 largere-cloud suppression can be obtained using low SEY coatings and/or clearing electrodes
Total heat load on the triplet beam screen
Present triplets(1.15 x 1011 ppb)
HiLumi triplets(2.20 x 1011 ppb)
Cu beam scr.
SEY like 2012
Cu beam scr.
SEY like 2012
SPS like a-C coating
Full suppression(SEY≈1 or clearing
electrodes)
Scaling with bunch population - IP2 and IP8
1.1e11 ppb 2.1e11 ppb
Electron cloud in present inner triplets, scaling with bunch population for one cut:• Wider multipacting region for high bunch intensity
Scaling with bunch population - IP2 and IP8
Electron cloud in present inner triplets, scaling with bunch population for one cut:• Wider multipacting region for high bunch intensity • Doubling bunch population leads to about x3 larger heat load • e-cloud suppression strategies needed also for these magnets
Detailed study for precise heat load estimation still needs to be performed
0 0.5 1 1.5 2 2.50
20
40
60
80
100
120
140
Intensity [x 1e11 ppb]
Hea
t lo
ad
[W/m
]
B2R1_cut_8_2808b_heatload_vs_int_lin
Section far from long range encounter
0 1 2 310
-4
10-3
10-2
10-1
100
101
102
Intensity [x 1e11 ppb]
Scr
ubb
ing
dos
e (5
0eV
) [m
A/m
]
B2R1_cut_8_simulated_beam_scrubdose_vs_int_log_legend
sey = 1.00sey = 1.10sey = 1.20sey = 1.30sey = 1.40sey = 1.50sey = 1.60sey = 1.70sey = 1.80sey = 1.90
Outline
• Studies for the arc main magnets
o Scaling with bunch intensity
o 200 MHz option
o 8b+4e scheme
o “Doublet” scrubbing beam
• Studies for the inner triplets
o New triplets in IP1/5
o Present triplets in IP1/8
• Studies for the matching sections – preliminary considerations
Matching section IP5 - Present LHC
ab
BS1a=22.5, b=17.6
BS2a=28.9, b=24
BSArca=22, b=17.15
BSD2a=31.3, b=26.4
Beam screens can be rotated
Q4BS2
Q5BS1
Q7BSArc
Q6BS1
D2 - BSD2
Beam off center
Matching section IP5 – HL-LHC
ab
BS1a=22.5, b=17.6
BS2a=28.9, b=24
BSHLa=37, b=32
BSArca=22, b=17.15
BSHLD2a=41, b=36
Q4BSHL
Q5BS2
Q7BSArc
Q6BS1
D2 - BSHLD2
Matching section IP2 – Present LHC
ab
Q4BS2
Q5BS1
Q7BSArc
Q6BS1
D2 - BSD2
Q4BS2
Q5BS2
Q7BSArc
Q6BS1
D2 - BSD2
BS1a=22.5, b=17.6
BS2a=28.9, b=24
BSArca=22, b=17.15
BSD2a=31.3, b=26.4
Beam screens can be rotated
Inj. beam
Matching sections
abBS1
a=22.5, b=17.6BS2
a=28.9, b=24BSArc
a=22, b=17.15BSD2
a=31.3, b=26.4
BSHLa=37, b=32
BSHLD2a=41, b=36
In total 6 beam screen shapes (all rect-ellipse):
Many, many, many configurations in terms of B field/gradient, beam size and beam position considering energy ramp, squeeze, separation, β*-leveling etc…
Need for parametric scans to asses which of these dependencies strongly impact the EC buildup
Matching sections
abBS1
a=22.5, b=17.6BS2
a=28.9, b=24BSArc
a=22, b=17.15BSD2
a=31.3, b=26.4
BSHLa=37, b=32
BSHLD2a=41, b=36
In total 6 beam screen shapes (all rect-ellipse):
Many many many configurations in terms of B field/gradient, beam size and beam position considering energy ramp, squeeze, separation, β*-leveling etc…
Need for parametric scans to asses which of these dependencies strongly impact the EC buildup1 1.1 1.2 1.3 1.4
10-4
10-3
10-2
10-1
100
101
SEY
He
at l
oa
d [W
/m]
QF nemitt=2.50 um
0.45TeV1.34TeV2.22TeV3.11TeV4.00TeV
1.3 1.35 1.4 1.45 1.510
-4
10-3
10-2
10-1
100
SEY
He
at l
oa
d [W
/m]
MB2 nemitt=2.50 um
0.45TeV1.34TeV2.22TeV3.11TeV4.00TeV
Some preliminary indication: effect of beam size and B field variation during the energy ramp (nominal intensity)
Arc quadrupoleArc dipole
Thanks to L. Mether
Preliminary
Uniform train of 600b.
Matching sections
abBS1
a=22.5, b=17.6BS2
a=28.9, b=24BSArc
a=22, b=17.15BSD2
a=31.3, b=26.4
BSHLa=37, b=32
BSHLD2a=41, b=36
In total 6 beam screen shapes (all rect-ellipse):
Many many many configurations in terms of B field/gradient, beam size and beam position considering energy ramp, squeeze, separation, β*-leveling etc…
Next steps:Effects of beam sizeEffect of B gradient
Effect of beam position
Arc quadrupole (practically also matching quad with BS1)
Q4 IP2 (where the effect is stronger)
Thanks for your attention!
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