heat load due to e-cloud in the hl-lhc triplets

Heat load due to e-cloud in the HL-LHC tripletsG. Iadarola, G. Rumolo

19th HiLumi WP2 Task Leader Meeting - 18 October 2013

Many thanks to: H.Bartosik, R. De Maria, R. Tomas, L. Tavian

Outline

• Present inner triplets

o Layout and optics

o PyECLOUD simulations

o Heat load measurements and estimate of the SEY

• Inner triplets for the HL-LHC upgrade

o Layout and optics

o Heat load estimates from PyECLOUD simulations

B2L1 A2L1

3L1 1L1

Machine layout and optics near IP1

IP1, 4 TeV, β* = 0.6 m

IP1

1R1

A2R1 B2R1

3R1

Machine layout and optics near IP1

IP1, 4 TeV, β* = 0.6 m

IP1 1R1

A2R1 B2R1

3R1

The longitudinal direction

The delay between two following bunch passages changes along the machine elements

• Locations of long range encounters spaced by half the bunch spacing

7.5 m

Beam 2

Beam 1 IP1

25 ns spac.




7.5 m

Bea

m 1

25 ns 3R1 sey = 1.40

10 20 30 40 500

5

10x 10

9

e- per

uni

t len

gth

[m-1

]

Time [ns]

10 20 30 40 50

Bea

m 2

Time [ns]

Beam 2

Beam 1 IP1

25 ns spac.

Outline


o Layout and optics




o Layout and optics


PyECLOUD simulations for the inner triplets

Quite a challenging simulation scenario:

• Two beams with:

o Different transverse position (off center)

o Different transverse shape

o Arbitrarily delayed with respect to each other (no real bunch spacing)



• Two beams with:




• Quadrupolar magnetic field

• Non elliptical chamber



• Two beams with:






Required the introduction of new

features in PyECLOUD



• Two beams with:








Beam properties (delay, position, size) changing along the structure:

• Simulated 10 slices per magnet

• SEY = 1.0, 1.1, … , 2.0

• 50 ns and 25 ns



• Two beams with:








Beam properties (delay, position, size) changing along the structure:

• Simulated 10 slices per magnet

• SEY = 1.0, 1.1, … , 2.0

• 50 ns and 25 ns

~1000 simulations,~48 h for two bunch trains,

~120 GB of sim. data

Simulated scenarios

8 72 8 7272 8 72

25 ns beam – 1.15 x 1011 ppb38 8 72 8 7272 8 72 38

4 36 4 3636 4 36

50 ns beam – 1.65 x 1011 ppb19 4 36 4 3636 4 36 19

Other beam parameters:

• Beam energy: 4 TeV

• Transverse emittance: 2.4 μm

• Bunch length: 1.3 ns

• Optics with β* = 0.6 m

Few snapshots of the electron distribution (50 ns spacing)

Beam 1

A look to the EC buildup

The presence of two beams enhances the multipacting efficiency, especially far enough from the locations of the long range encounters

A look to the EC buildupB

eam

1

25 ns 3R1 sey = 1.40

0.5 1 1.5 2 2.5 30

5

10x 10

9

e- per

uni

t len

gth

[m-1

]

Time [us]

0.5 1 1.5 2 2.5 3

Bea

m 2

Time [us]

1 1.2 1.4 1.6 1.8 210

-3

10-2

10-1

100

101

102

SEY

Scr

ubbi

ng d

ose

(50e

V) [

mA

/m]

25 ns 3R1

s = 47.90 ms = 48.54 ms = 49.19 ms = 49.83 ms = 50.47 ms = 51.12 ms = 51.76 ms = 52.40 ms = 53.05 m

Bea

m 1

25 ns 3R1 sey = 1.40

0.2 0.4 0.6 0.8 1 1.2 1.40

5

10x 10

9

e- per

uni

t len

gth

[m-1

]

Time [us]

0.2 0.4 0.6 0.8 1 1.2 1.4

Bea

m 2

Time [us]

Heat load density along the triplet - 50 ns

20 25 30 35 40 45 50 550

0.5

1

1.5

2

2.5

3

s [m]

Ave

rage

hea

t loa

d [W

/m]

50 ns - 288 bunches

sey = 1.00sey = 1.20sey = 1.40sey = 1.60sey = 1.80sey = 2.00

Locations of long range encounters

Remarks:

• EC much weaker close to long range encounters

• Modules with the same beam screen behave very similarly

20 25 30 35 40 45 50 550

0.5

1

1.5

2

2.5

3

s [m]

Ave

rage

hea

t loa

d [W

/m]

50 ns - 288 bunches


1R1 A2R1 B2R1 3R1


20 25 30 35 40 45 50 550

0.5

1

1.5

2

2.5

3

s [m]

Ave

rage

hea

t loa

d [W

/m]

50 ns - 288 bunches


1R1 A2R1 B2R1 3R1

Remarks:



20 25 30 35 40 45 50 550

0.5

1

1.5

2

2.5

3

s [m]

Ave

rage

hea

t loa

d [W

/m]

50 ns - 288 bunches


1 1.2 1.4 1.6 1.8 210

-3

10-2

10-1

100

101

102

SEY

Hea

t loa

d [W

/m]

50 ns 1R1

1 1.2 1.4 1.6 1.8 210

-3

10-2

10-1

100

101

102

SEY

Scr

ubbi

ng d

ose

(50e

V) [

mA

/m]

25 ns 1R1


The presence of the two beams leads to an important lowering of the multipacting threshold w.r.t. the single beam case (dashed)


20 25 30 35 40 45 50 550

0.5

1

1.5

2

2.5

3

s [m]

Ave

rage

hea

t loa

d [W

/m]

50 ns - 288 bunches


1R1 A2R1 B2R1 3R1

Remarks:



20 25 30 35 40 45 50 550

0.5

1

1.5

2

2.5

3

s [m]

Ave

rage

hea

t loa

d [W

/m]

50 ns - 288 bunches



1 1.2 1.4 1.6 1.8 210

-3

10-2

10-1

100

101

102

SEY

Hea

t loa

d [W

/m]

50 ns A2R1

1 1.2 1.4 1.6 1.8 210

-3

10-2

10-1

100

101

102

SEY

Scr

ubbi

ng d

ose

(50e

V) [

mA

/m]

50 ns A2R1



20 25 30 35 40 45 50 550

0.5

1

1.5

2

2.5

3

s [m]

Ave

rage

hea

t loa

d [W

/m]

50 ns - 288 bunches


1R1 A2R1 B2R1 3R1

Remarks:



20 25 30 35 40 45 50 550

0.5

1

1.5

2

2.5

3

s [m]

Ave

rage

hea

t loa

d [W

/m]

50 ns - 288 bunches



1 1.2 1.4 1.6 1.8 210

-3

10-2

10-1

100

101

102

SEY

Hea

t loa

d [W

/m]

50 ns B2R1

1 1.2 1.4 1.6 1.8 210

-3

10-2

10-1

100

101

102

SEY

Scr

ubbi

ng d

ose

(50e

V) [

mA

/m]

50 ns B2R1


20 25 30 35 40 45 50 550

0.5

1

1.5

2

2.5

3

s [m]

Ave

rage

hea

t loa

d [W

/m]

50 ns - 288 bunches



1R1 A2R1 B2R1 3R1

Remarks:



20 25 30 35 40 45 50 550

0.5

1

1.5

2

2.5

3

s [m]

Ave

rage

hea

t loa

d [W

/m]

50 ns - 288 bunches



1 1.2 1.4 1.6 1.8 210

-3

10-2

10-1

100

101

102

SEY

Hea

t loa

d [W

/m]

50 ns 3R1

1 1.2 1.4 1.6 1.8 210

-3

10-2

10-1

100

101

102

SEY

Scr

ubbi

ng d

ose

(50e

V) [

mA

/m]

50 ns 3R1


20 25 30 35 40 45 50 550

1

2

3

4

5

6

7

s [m]

Ave

rage

hea

t loa

d [W

/m]

25 ns - 576 bunches




Remarks:



20 25 30 35 40 45 50 550

0.5

1

1.5

2

2.5

3

s [m]

Ave

rage

hea

t loa

d [W

/m]

50 ns - 288 bunches


1R1

A2R1 B2R1 3R1

20 25 30 35 40 45 50 550

1

2

3

4

5

6

7

s [m]

Ave

rage

hea

t loa

d [W

/m]

25 ns - 576 bunches



Remarks:



20 25 30 35 40 45 50 550

0.5

1

1.5

2

2.5

3

s [m]

Ave

rage

hea

t loa

d [W

/m]

50 ns - 288 bunches


As in the other quardupoles in the LHC, the multipacting threshold is already quite low even for a single beam with 25 ns spacing

1 1.2 1.4 1.6 1.8 210

-3

10-2

10-1

100

101

102

SEY

Hea

t loa

d [W

/m]

25 ns 1R1

1 1.2 1.4 1.6 1.8 210

-3

10-2

10-1

100

101

102

SEY

Scr

ubbi

ng d

ose

(50e

V) [

mA

/m]

25 ns 1R1


1R1

A2R1 B2R1 3R1

20 25 30 35 40 45 50 550

1

2

3

4

5

6

7

s [m]

Ave

rage

hea

t loa

d [W

/m]

25 ns - 576 bunches



Remarks:



20 25 30 35 40 45 50 550

0.5

1

1.5

2

2.5

3

s [m]

Ave

rage

hea

t loa

d [W

/m]

50 ns - 288 bunches



1 1.2 1.4 1.6 1.8 210

-3

10-2

10-1

100

101

102

SEY

Hea

t loa

d [W

/m]

25 ns A2R1

1 1.2 1.4 1.6 1.8 210

-3

10-2

10-1

100

101

102

SEY

Scr

ubbi

ng d

ose

(50e

V) [

mA

/m]

50 ns A2R1


1R1

A2R1 B2R1 3R1

20 25 30 35 40 45 50 550

1

2

3

4

5

6

7

s [m]

Ave

rage

hea

t loa

d [W

/m]

25 ns - 576 bunches



Remarks:



20 25 30 35 40 45 50 550

0.5

1

1.5

2

2.5

3

s [m]

Ave

rage

hea

t loa

d [W

/m]

50 ns - 288 bunches



1 1.2 1.4 1.6 1.8 210

-3

10-2

10-1

100

101

102

SEY

Hea

t loa

d [W

/m]

25 ns B2R1

1 1.2 1.4 1.6 1.8 210

-3

10-2

10-1

100

101

102

SEY

Scr

ubbi

ng d

ose

(50e

V) [

mA

/m]

50 ns B2R1


1R1

A2R1 B2R1 3R1

20 25 30 35 40 45 50 550

1

2

3

4

5

6

7

s [m]

Ave

rage

hea

t loa

d [W

/m]

25 ns - 576 bunches



Remarks:



20 25 30 35 40 45 50 550

0.5

1

1.5

2

2.5

3

s [m]

Ave

rage

hea

t loa

d [W

/m]

50 ns - 288 bunches



1 1.2 1.4 1.6 1.8 210

-3

10-2

10-1

100

101

102

SEY

Hea

t loa

d [W

/m]

25 ns 3R1

1 1.2 1.4 1.6 1.8 210

-3

10-2

10-1

100

101

102

SEY

Scr

ubbi

ng d

ose

(50e

V) [

mA

/m]

50 ns 3R1


1R1

A2R1 B2R1 3R1

1 1.2 1.4 1.6 1.8 20

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

SEYH

eat l

oad

per b

unch

[W]

25 ns

1 1.2 1.4 1.6 1.8 20

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

SEY

Hea

t loa

d pe

r bun

ch [W

]

50 ns

Average heat load density – 50 ns vs. 25 ns

Remarks:

• Above threshold values are very similar enhancement from hybrid spacings

much stronger on the 50 ns than on 25 ns

For each triplet we get:

Outline


o Layout and optics




o Layout and optics


Machine observations – 50 ns

No big change during ramp and squeeze

Data provided by L. Tavian


Heat load much higher than in two-aperture quadrupoles


Machine observations – 25 ns (4 TeV)





Heat load similar to two-aperture quadrupoles

Comparison against simulations

1 1.2 1.4 1.6 1.8 20

50

100

150

SEY

Hea

t loa

d [W

]

25 ns - 800 bunches - short trains

Fill 3429

1 1.2 1.4 1.6 1.8 20

50

100

150

200

250

SEY

Hea

t loa

d [W

]

50 ns - 1374 bunches

Fill 3286

1 1.2 1.4 1.6 1.8 20

20

40

60

80

100

120

140

160

SEY

Hea

t loa

d [W

]

25 ns - 800 bunches

Fill 3405

50 ns, 4 TeV 25 ns, 450 GeV

25 ns, 4 TeV

1.2 < SEYmax < 1.3 is compatible with the observations

Crosscheck with single beam MDs

For the estimated SEY value we do not expect nor observe EC in the triplets

with only one beam with 50 ns spacing circulating in the LHC

1 1.2 1.4 1.6 1.8 210

-3

10-2

10-1

100

101

102

SEY

Hea

t loa

d [W

/m]

50 ns B2R1

Crosscheck with single beam MDs

For the estimated SEY value we do not expect nor observe EC in the triplets

with only one beam with 50 ns spacing circulating in the LHC

Outline


o Layout and optics




o Layout and optics


Optics, layout and apertures

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


Q1 (A/B)

Q2 (A/B)

Q3 (A/B) D1

Q1

Q2 (A/B)

Q3 D1

For the moment, only quadrupoles have been simulated

IP1, 7 TeV, β* = 0.15 m

Thanks to R. De Maria


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

Outline


o Layout and optics




o Layout and optics


Simulated scenario

8 72 8 7272 8 72

25 ns beam – 2.20 x 1011 ppb38 8 72 8 7272 8 72 38

Other beam parameters:

• Beam energy: 7 TeV

• Transverse emittance: 2.5 μm

• Bunch length: 1.0 ns

• Optics with β* = 0.15 m

A look to the EC buildup – HiLumi triplets

Few snapshots of the electron distribution much wider stripes for HiLumi triplets

HiLumi

Present

Heat load along the triplet

20 25 30 35 40 45 50 55 60 650

2

4

6

8

10

12

14

16

18

20

s [m]

Ave

rage

hea

t loa

d [W

/m]

25 ns - 576 bunches


20 25 30 35 40 45 50 55 60 650

1

2

3

4

5

6

7

s [m]

Ave

rage

hea

t loa

d [W

/m]

25 ns - 576 bunches


Present triplets

HiLumi triplets


1 1.2 1.4 1.6 1.8 20

100

200

300

400

500

600

SEY

Av.

e- e

nerg

y [e

V]

Only e- with En>50eV are considered

1R1A2R1B2R13R1

1 1.2 1.4 1.6 1.8 20

100

200

300

400

500

600

SEY

Av.

e- e

nerg

y [e

V]

Only e- with En>50eV are considered

A1R1B1R1A2R1B2R1A3R1B3R1

Bunch intensity is larger but also chamber is wider energy of multipacting electrons is quite similar

Present triplets HiLumi triplets

Heat loads

1 1.2 1.4 1.6 1.8 20

0.5

1

1.5

2x 10

13

SEY

Impa

ctin

g e

- [m-1

]

25 ns - 576 bunchesOnly e- with En>50eV are considered

A1R1B1R1A2R1B2R1A3R1B3R1

1 1.2 1.4 1.6 1.8 20

0.5

1

1.5

2x 10

13

SEY

Impa

ctin

g e

- [m-1

]

25 ns - 576 bunchesOnly e- with En>50eV are considered

1R1A2R1B2R13R1

Bunch intensity is larger but also chamber is wider energy of multipacting electrons is quite similar number of impacting electrons about x2 larger

Heat loads


1 1.2 1.4 1.6 1.8 20

200

400

600

800

1000

1200

SEY

Hea

t loa

d [W

]


1 1.2 1.4 1.6 1.8 20

200

400

600

800

1000

1200

SEY

Hea

t loa

d [W

]


Bunch intensity is larger but also chamber is wider energy of multipacting electrons is quite similar number of impacting electrons about x2 larger Total heat load about x2 larger

Heat loads


D1 and correctors not included!

SEYmax in the present triplets at the end of 2012

Summary and conclusions

• Simulations show a strong enhancement of the EC due to the presence of the two

beams extremely low multipacting thresholds (SEYth<1.1 for 25 ns beams)

• Comparing measured heat load against simulation we infer SEYmax = ~1.3 for the

present triplets (crosschecked in different beam conditions )

• Simulations for the HiLumi scenario show x2 stronger heat load w.r.t. the present

scenario (SEYmax = ~1.3 HL = ~500 W – D1 and correctors to be added)

• Heat load could be strongly reduced by EC mitigation strategies:

o Low SEY coating (but we need SEYmax<1.1 to have full suppression)

o Clearing electrode (EC localized in a region where there should be enough

aperture to place a polarized plate/wire)

Thanks for your attention!

Machine layout and optics near IP1 - present

Common beam pipe Separated beam pipesSeparated beam pipes

IP1

IP1, 4 TeV, β* = 0.6 m

Machine layout and optics near IP1 - HiLumi

Common beam pipe Separated beam pipesSeparated beam pipes

IP1

IP1, 4 TeV, β* = 0.6 m

B2L1 A2L1

3L1 1L1

IP1, 4 TeV, β* = 0.6 m

IP1

1R1

A2R1 B2R1

3R1

Machine layout and optics near IP1 - present

B2L1 A2L1

3L1 1L1

IP1, 4 TeV, β* = 0.6 m

IP1

1R1 (A/B)

2R1 (A/B)

3R1 (A/B)

Machine layout and optics near IP1 - HiLumi

Bea

m 1

50 ns 3R1 sey = 1.40

20 40 60 800

2

4

x 109

e- per

uni

t len

gth

[m-1

]

Time [ns]

20 40 60 80

Bea

m 2

Time [ns]




15 m

Beam 2

Beam 1 IP1

50 ns spac.

Average heat load density – 50 ns vs. 25 ns

1 1.2 1.4 1.6 1.8 20

1

2

3

4

5

6

7

8

9

10

SEY

Ave

rage

hea

t loa

d pe

r bun

ch [m

W/m

]

25 ns

1R1A2R1B2R13R1

1 1.2 1.4 1.6 1.8 20

1

2

3

4

5

6

7

8

9

10

SEY

Ave

rage

hea

t loa

d pe

r bun

ch [m

W/m

]

50 ns

1R1A2R1B2R13R1

Remarks:

• Above threshold values are very similar enhancement from hybrid spacings

much stronger on the 50 ns than on 25 ns


Few snapshots of the electron distribution much wider stripes

Few snapshots of the electron distribution

Beam 1

A look to the EC buildup – present triplets


Few snapshots of the electron distribution much wider stripes

heat load due to e-cloud in the hl-lhc triplets

Documents

ip1 ip1

different transverse

seyinner triplets

pyecloud14pyecloud simulations

ns15pyecloud simulations

opticsheat load estimates

following bunch passages

lhc upgradelayout