simulated and measured loss maps with lhc collimators at the

Simulated and Measured Loss Maps with LHC collimators at the SPS and LHC

CARE-HHH-APD BEAM’07 workshopOctober 1st-5th, 2007

CERN, Geneva, Switzerland

S. Redaelli, R. Assmann, C. Bracco, T. Weiler and G. Robert-Demolaize

CERN, AB department

S. Redaelli, BEAM’07, 02-10-2007 2

• Introduction• Loss studies for the LHC Simulation tools Performance of a perfect system Energy deposition studies• Imperfection models Jaw surface deformations Aperture alignment errors• Loss studies at the SPS Experimental layout Simulated versus measured losses• Conclusions

Outline of my talk

S. Redaelli, BEAM’07, 02-10-2007

Introduction

3

x 200!!

Stored energy ~ 2 x 360 MJQuench limit ~ 10 mJ / cm3

Damage (metal) ~ 50 kJ / mm2

➙Control losses 1000 time better than the state-of-the-art!

➙Need collimation at all machine states: injection, ramp, squeeze, physics

➙Important role of collimation system for machine protection

Cleaning

Protection

Eb = 7 TeV - Ib = 3.4x1014

R. Assmann


Introduction

3

x 200!!

LHC enters in a new territory for handling ultra-intense beams in a super-conducting environment!Correspondingly, we need appropriate tools to understand the system performance!

Stored energy ~ 2 x 360 MJQuench limit ~ 10 mJ / cm3

Damage (metal) ~ 50 kJ / mm2

➙Control losses 1000 time better than the state-of-the-art!

➙Need collimation at all machine states: injection, ramp, squeeze, physics

➙Important role of collimation system for machine protection

Cleaning

Protection

Eb = 7 TeV - Ib = 3.4x1014

R. Assmann


The Phase I LHC collimation system

4

Picture by C. Bracco



4

Two warm cleaning insertions IR3: Momentum cleaning 1 primary (H) → TCP [C] 4 secondary (H,S) → TCS [C] 4 shower abs. (H,V) → TCLA [W] IR7: Betatron cleaning 3 primary (H,V,S) 11 secondary (H,V,S) 5 shower abs. (H,V) 3 beam scrapers (H,V,S)




4


Local cleaning at triplets 8 tertiary (2 per IP)→ TCT [W]




4

Mul

ti-st

age

halo

cle

anin

g Two warm cleaning insertions IR3: Momentum cleaning 1 primary (H) → TCP [C] 4 secondary (H,S) → TCS [C] 4 shower abs. (H,V) → TCLA [W] IR7: Betatron cleaning 3 primary (H,V,S) 11 secondary (H,V,S) 5 shower abs. (H,V) 3 beam scrapers (H,V,S)





4

Mul

ti-st

age

halo

cle

anin

g Two warm cleaning insertions IR3: Momentum cleaning 1 primary (H) → TCP [C] 4 secondary (H,S) → TCS [C] 4 shower abs. (H,V) → TCLA [W] IR7: Betatron cleaning 3 primary (H,V,S) 11 secondary (H,V,S) 5 shower abs. (H,V) 3 beam scrapers (H,V,S)


Physics debris absorbers [ Cu ] 2 TCLP’s (IP1/IP5)

Protection (injection/dump) 10 elements →TCLI/TCDQ [ C ]

Transfer lines 13 collimators → TCDI [ C ]

Passive absorbers for warm magnets




4

Mul

ti-st

age

halo

cle

anin

g

44 movable ring collimators per beam

for the Phase I system!



Physics debris absorbers [ Cu ] 2 TCLP’s (IP1/IP5)

Protection (injection/dump) 10 elements →TCLI/TCDQ [ C ]

Transfer lines 13 collimators → TCDI [ C ]

Passive absorbers for warm magnets



Multi-stage collimation at the LHC

5

Cold aperture

Circulating beam

Warm cleaning insertion Arc(s) IP

(An illustrative scheme)



5

Cold aperture

Circulating beam

Primary beam halo





5

Cold aperture

Circulating beam

Primary beam halo

Primarycollimator

Secondarycollimators

Tertiary beam halo + hadronic showers

Secondary beam halo + hadronic showers





5

Cold aperture

Circulating beam

Primary beam halo

Primarycollimator




Shower absorbers





5

Cold aperture

Circulating beam

Primary beam halo

Primarycollimator




Shower absorbers

Warm cleaning insertion

SCTriplet

Arc(s) IP




5

Cold aperture

Circulating beam

Primary beam halo

Primarycollimator




Shower absorbers


Tertiarycollimators

SCTriplet

Arc(s) IP




5

Cold aperture

Circulating beam

Primary beam halo

Primarycollimator




Shower absorbers


Tertiarycollimators

SCTriplet

Arc(s) IP

Protection devices




5

Cold aperture

Circulating beam

Primary beam halo

Primarycollimator




Shower absorbers


All cleaning + protection devices must be included in simulations!

Collimation needed from injection to collision!

Tertiarycollimators

SCTriplet

Arc(s) IP

Protection devices



Simulation tools for loss maps

6



6

Accurate tracking of halo particles6D dynamics, chromatic effects, δp/p, high order field errors, ...

SixTrack



6


SixTrack

Scattering routineTrack protons inside collimator materials K2



6


SixTrack


Detailed collimator geometryImplement all collimators and protection devices, treat any azimuthal angle, tilt/flatness errors



6


SixTrack



Detailed aperture model of full ringPrecisely find the locations of losses BeamLossPattern



6


SixTrack



Detailed aperture model of full ringPrecisely find the locations of losses BeamLossPattern

20 20.5 21 21.5 22 22.5 23 23.5 24-0.2

-0.16-0.12-0.08-0.04

00.040.080.120.16

0.2

s [ km ]

Aper

ture

/ be

am p

ositio

n [ m

]

23.05 23.1 23.15 23.2 23.25 23.3 23.35-0.06

-0.04

-0.02

0

0.02

0.04

0.06

s [ km ]

Aper

ture

/ be

am p

ositio

n [ m

]

IR8

Magnet locations : ∆s ≤ 100m

Interpolation: ∆s=10cm(270000 points!)

0.02

0.03

0.04

Trajectory of a halo particle


Example - one particle’s trajectory

• Scattering routine called within tracking at each collimator• If particle touches jaw, calculate absorption, offsets,

scattering angles and energy error• Trajectories of halo particles saved for off-line aperture

analysis (∆s < 10 cm)

19.78 19.8 19.82 19.84 19.86 19.88-80

-60

-40

-20

0

20

40

60

s [ km ]

X [ m

m ]

D3 D4 Q5.L7TCP TCS

LHC betatron cleaning (IR7)

(δx,δx’,δy,δy’,δE)

IR7→

Beam 1


Incoming halo particle

Loss location






R.Assmann at al., LHC-PR 639 (2003)

TOOLS FOR PREDICTING CLEANING EFFICIENCY IN THE LHC

R. Aßmann, M. Brugger, M. Hayes, J.B. Jeanneret, F. Schmidt, CERN, Geneva, Switzerland

I. Baichev, IHEP, Protvino, Russia

D. Kaltchev, TRIUMF, Canada

Abstract

The computer codes Sixtrack and Dimad have been

upgraded to include realistic models of proton scattering

in collimator jaws, mechanical aperture restrictions, and

time-dependent fields. These new tools complement long-

existing simplified linear tracking programs used up to now

for tracking with collimators. Scattering routines from

STRUCT and K2 have been compared with one another

and the results have been cross-checked to the FLUKA

Monte Carlo package. A systematic error is assigned to

the predictions of cleaning efficiency. Now, predictions

of the cleaning efficiency are possible with a full LHC

model, including chromatic effects, linear and nonlinear er-

rors, beam-beam kicks and associated diffusion, and time-

dependent fields. The beam loss can be predicted around

the ring, both for regular and irregular beam losses. Exam-

ples are presented.

INTRODUCTION

The collimation system of the LHC [1] requires an excel-

lent cleaning efficiency in order to avoid quenches of the

super-conducting magnets. Various numerical tools used

for prediction of cleaning efficiency were compared. The

programs include generation of a primary beam halo, scat-

tering of high energy protons through material and tracking

of beam halos in the storage ring. The degree of agreement

between different codes is discussed. Differences are used

to assess possible systematic errors.

SCATTERING CODES

The physics of proton scattering in the material of col-

limator jaws has been implemented in various computer

codes. The scattering routines track the protons through

some length of a given material having them interacting

with the proper cross-sections. The protons receive trans-

verse kicks ∆θx, ∆θy and offsets ∆x, ∆y and some mo-mentum loss δ = ∆p/p0. Note that a full shower calcula-

tion is not required for predicting the cleaning of ”primary”

beam protons.

The primary protons in the LHC have energies from

450 GeV at injection to 7 TeV at top. The scattering rou-

tines must correctly describe the interactions over the full

range of energies, allow for different jaw materials, and in-

clude the correct jaw geometry, as protons impact at very

close distance from the edge of the jaw.

Three different scattering routines were compared:

1. K2 was developed in the 1990’s by Jeanneret and

Trenkler for studies of LHC collimation [2].

2. STRUCT was developed in the 1980’s by Baichev

et al, amongst others for studies of lHC and SSC collima-

tion [3].

3. FLUKA is a general purpose scattering and showering

code [4].

1e-006

1e-005

0.0001

0.001

0.01

0.1

-100 -80 -60 -40 -20 0 20 40 60 80 100

dN

/ (

dx

N0)

[µm

-1]

∆x [µm]

FLUKA

K2

STRUC

1e-006

1e-005

0.0001

0.001

0.01

-100 -80 -60 -40 -20 0 20 40 60 80 100

dN

/ (

dθ

x N

0)

∆θx [µrad]

FLUKA

K2

STRUC

[µ

rad

-1]

0.001

0.01

0.1

1

10

100

1000

0.001 0.01 0.1

dN

/ (

dδ N

0)

δ

K2FLUKA

STRUCT

Figure 1: Scattering probabilities for one 7 TeV proton im-

pacting on a 0.5 m long Cu jaw. Change in position (top),

angle (middle) and energy (bottom).

A test case was defined for the three routines: A 7 TeV

pencil beam with zero angle (y′ = 0) impacting y = 1µmfrom the edge of a 0.5 m long vertical collimator, made of

Cu. The changes in particles offsets, angles, and momen-

tum were recorded. The comparison of the different scat-





Abstract
















ples are presented.

INTRODUCTION










SCATTERING CODES








beam protons.












tion [3].


code [4].

1e-006

1e-005

0.0001

0.001

0.01

0.1

-100 -80 -60 -40 -20 0 20 40 60 80 100

dN

/ (

dx

N0)

[µm

-1]

∆x [µm]

FLUKA

K2

STRUC

1e-006

1e-005

0.0001

0.001

0.01

-100 -80 -60 -40 -20 0 20 40 60 80 100

dN

/ (

dθ

x N

0)

∆θx [µrad]

FLUKA

K2

STRUC

[µ

rad

-1]

0.001

0.01

0.1

1

10

100

1000

0.001 0.01 0.1

dN

/ (

dδ N

0)

δ

K2FLUKA

STRUCT












Abstract
















ples are presented.

INTRODUCTION










SCATTERING CODES








beam protons.












tion [3].


code [4].

1e-006

1e-005

0.0001

0.001

0.01

0.1

-100 -80 -60 -40 -20 0 20 40 60 80 100

dN

/ (

dx

N0)

[µm

-1]

∆x [µm]

FLUKA

K2

STRUC

1e-006

1e-005

0.0001

0.001

0.01

-100 -80 -60 -40 -20 0 20 40 60 80 100

dN

/ (

dθ

x N

0)

∆θx [µrad]

FLUKA

K2

STRUC

[µ

rad

-1]

0.001

0.01

0.1

1

10

100

1000

0.001 0.01 0.1

dN

/ (

dδ N

0)

δ

K2FLUKA

STRUCT








19.78 19.8 19.82 19.84 19.86 19.88-80

-60

-40

-20

0

20

40

60

s [ km ]

X [ m

m ]

D3 D4 Q5.L7TCP TCS



IR7→

Beam 1



Loss location






R.Assmann at al., LHC-PR 639 (2003)





Abstract
















ples are presented.

INTRODUCTION










SCATTERING CODES








beam protons.












tion [3].


code [4].

1e-006

1e-005

0.0001

0.001

0.01

0.1

-100 -80 -60 -40 -20 0 20 40 60 80 100

dN

/ (

dx

N0)

[µm

-1]

∆x [µm]

FLUKA

K2

STRUC

1e-006

1e-005

0.0001

0.001

0.01

-100 -80 -60 -40 -20 0 20 40 60 80 100

dN

/ (

dθ

x N

0)

∆θx [µrad]

FLUKA

K2

STRUC

[µ

rad

-1]

0.001

0.01

0.1

1

10

100

1000

0.001 0.01 0.1

dN

/ (

dδ N

0)

δ

K2FLUKA

STRUCT












Abstract
















ples are presented.

INTRODUCTION










SCATTERING CODES








beam protons.












tion [3].


code [4].

1e-006

1e-005

0.0001

0.001

0.01

0.1

-100 -80 -60 -40 -20 0 20 40 60 80 100

dN

/ (

dx

N0)

[µm

-1]

∆x [µm]

FLUKA

K2

STRUC

1e-006

1e-005

0.0001

0.001

0.01

-100 -80 -60 -40 -20 0 20 40 60 80 100

dN

/ (

dθ

x N

0)

∆θx [µrad]

FLUKA

K2

STRUC

[µ

rad

-1]

0.001

0.01

0.1

1

10

100

1000

0.001 0.01 0.1

dN

/ (

dδ N

0)

δ

K2FLUKA

STRUCT












Abstract
















ples are presented.

INTRODUCTION










SCATTERING CODES








beam protons.












tion [3].


code [4].

1e-006

1e-005

0.0001

0.001

0.01

0.1

-100 -80 -60 -40 -20 0 20 40 60 80 100

dN

/ (

dx

N0)

[µm

-1]

∆x [µm]

FLUKA

K2

STRUC

1e-006

1e-005

0.0001

0.001

0.01

-100 -80 -60 -40 -20 0 20 40 60 80 100

dN

/ (

dθ

x N

0)

∆θx [µrad]

FLUKA

K2

STRUC

[µ

rad

-1]

0.001

0.01

0.1

1

10

100

1000

0.001 0.01 0.1

dN

/ (

dδ N

0)

δ

K2FLUKA

STRUCT








19.78 19.8 19.82 19.84 19.86 19.88-80

-60

-40

-20

0

20

40

60

s [ km ]

X [ m

m ]

D3 D4 Q5.L7TCP TCS



IR7→

Beam 1


1 case study: Three halo planes (Hori., vert. and skew); both beams.Track 5000000 particles for 200 turns.

Scattering in 44 collimators at each turn. Check the trajectory in 270000 aperture locations!


Loss location


Cleaning performance at 7 TeV

8

Beam1

Losses in collimators Losses in cold apert.

Beam2

Legend:Black = okayControlled losses at the collimators

Blue = BAD!Losses in cold aperture →quench

Only a few loss locations outside the collimators (ideal performance)

Betatron cleaning

(Nominal intensity, ideal performance, τb=0.2h)


Details of beam 1 losses, 7 TeV

9

0 5 10 15 20 25 30

106

107

108

109

1010

1011

Longitudinal coordinate, s [ m ]

Loss

rate

per

uni

t len

gth

[ p/m

/s ]

IP2 IP3 IP4 IP5 IP6 IP7 IP8 IP1

Beam 1


By design, losses are concentrated in the warm insertion.

However, there is some leakage (~10-4): losses in the dispersion suppressor from single diffractive interaction with primary collimators.

This limits the Phase I performance.


Details of beam 1 losses, 7 TeV

9

0 5 10 15 20 25 30

106

107

108

109

1010

1011


Loss

rate

per

uni

t len

gth

[ p/m

/s ]


Beam 1

-20 -10 0 10 20

-20

-10

0

10

20

Y [

mm

]

X [ mm ]

Sloss: s1=20290m; s2=20300m.Nloss = 304


By design, losses are concentrated in the warm insertion.

However, there is some leakage (~10-4): losses in the dispersion suppressor from single diffractive interaction with primary collimators.

This limits the Phase I performance.


Cleaning performance at 450 GeV

10

0 5 10 15 20 25 30106

107

108

109

1010

1011

s [ km ]

Loss

rate

per

uni

t len

gth

[ p/m

/s ]

Assumed quench limit



Larger losses (larger betatron amplitudes at lower energy) but also larger quench limits.

Below the assumed quench limits!


Cleaning during energy ramp

11

Beam cleaning needed throughout the ramp! Collimator settings: trade off between- Optimum cleaning Maintain canonical 6/7σ settings! σInj ≈ 1 mm → σ7TeV ≈ 0.25 mm- Ease operation in early commissioning Keep injection settings until β-squeeze!



11

C. Bracco




11

C. Bracco


Proposed optimized setting during energy ramp: Constant retraction in millimeters: easy tolerances + sufficient cleaning at startup with reduced intensities.Detailed commissioning scenarios worked out by C. Bracco (PhD work).

S. Redaelli, BEAM’07, 02-10-2007 12

Overview of energy deposition studies

Energy deposition studies play a major role in the system design!➙ Energy in the super-conducting magnets versus quench limit➙ Determine the BLM locations for optimum response (BI team)➙ Estimate life time of warm magnets/electronics (passive absorbers)➙ Quantify dose to personnel and impact on the environment➙ Optimize layout of insertion (shielding design)➙ Calculate heating of critical components➙ Beam halo loads in specific locations (e.g., LHC beam dump)➙ Detector background from tertiary collimators (IHPE + US-LARP)All these studies for the LHC rely on the results of our simulations!

Distribution of inelastic interactions within collimator jaw material is used as an input for energy deposition studies (collaboration with the CERN FLUKA team).

Impact distribution at

the TCP

See overview talk by M. Brugger at the recent Collimator Material workshop at CERN.


Radiation doses in IR7

13

- 8 -

Figure 3 Dose rate distributions along the tunnel in Gy/year. The values shown are the

average of ±1m vertically from the beam line. In the upper figure the dose rate

distribution is plotted as a histogram and in the lower figure the same values are

shown in a contour plot together with the geometry. The regions of interest (RR73,

UJ76, RR77 – from left to right on the figure) are marked with the blue vertical

lines.

IR7

WARMCOLDCOLD

K. Tsoulou et al

Radiation is confined within the warm insertions!


Radiation doses in IR7

13

- 8 -

Figure 3 Dose rate distributions along the tunnel in Gy/year. The values shown are the

average of ±1m vertically from the beam line. In the upper figure the dose rate

distribution is plotted as a histogram and in the lower figure the same values are

shown in a contour plot together with the geometry. The regions of interest (RR73,

UJ76, RR77 – from left to right on the figure) are marked with the blue vertical

lines.

IR7

WARMCOLDCOLD

5 or

ders

of m

agni

tude

!!

K. Tsoulou et al

Radiation is confined within the warm insertions!


Optimization of the BLM locations

14

Courtesy of L. Ponce

Detailed loss maps around the ring used to determine the location of the beam loss monitors (BLM’s)

Critical elements for active machine protection: trigger dump in case of abnormal losses

Final layout: 6 monitors per quadrupole + dedicated monitor (dispersion suppressor downstream of IR7)


Outline of my talk

15

• Introduction• Loss studies for the LHC Simulation tools Performance of a perfect system Energy deposition studies

• Imperfection models Jaw surface deformations Aperture alignment errors• Loss studies at the SPS Experimental layout Simulated versus measured losses• Conclusions


Imperfection models - what can be wrong?

16



16

Optics errorsClosed orbit distortion, coupling, static and dynamic beta-beat (on- and off-momentum), non-linear field errors, feed-down from alignment errors, ...



16


Collimator errorsAlignment (set-up) errors, tilts, surface flatness



16



Aperture imperfectionsStatistical errors, manufacturing errors, measured alignment, ...



16




Full MADX optics model implemented

in SixTrack



16





in SixTrack

Detailed collimator geometry in our

scattering routine



16





in SixTrack

Detailed collimator geometry in our

scattering routine

Dedicated tools in aperture program


0 2.0 4.0 6.0 8.0 15.1

2

5.2

3

5.3

4

5.4

5

] m [ Z ,etanidrooc lanidutignoL

Tran

sver

se c

oord

inat

e, X

[ m

m ]

Jaw flatness errors

17

Effect of flatness errors: - Halo particles interact with less material: → Reduced absorption!- More losses close to the downstream edge → More particles/showers escape- Higher deposited energy density

Collimator jaw bulk material

Beam

1m jaw (TCSG)

Perfect surface

0 2.0 4.0 6.0 8.0 15.1

2

5.2

3

5.3

4

5.4

5

Tran

sver

se c

oord

inat

e, X

[ m

m ]

] m [ Z ,etanidrooc lanidutignoL

Collimator jaw bulk material

“Banana” shape

Simulations: can slice each collimator and assign any shape (polynomial fit)Sensitivity studies + measured flatness from production

Error:250 μm


Sensitivity on flatness errors

18

Based on these studies, the production tolerance was set to 40 μm.

Tolerance achieved in production. Database of flatness data being prepared to study the performance of the “as-built” system.

(parabolic “banana” deformation of all secondary collimators)

50 % lost of cleaning efficiency for errors of ~ 50 μmFactor 2-3 for errors above 250 μm


Random aperture alignment errors

19

- Alignment errors in the aperture model: many “machines” for one tracking run!

- Random errors (H+V) applied to relevant elements per type: MB’s, MQ’s, MQX’s, BPM’s, ...

Ex.: 2250 elements moved; 20 random seeds

-4 -2 0 2 40

10

20

30

Offset [ mm ]

N

BLMx: 0.5 mm

-4 -2 0 2 40

10

20

30

Offset [ mm ]

N

BLMy: 0.5 mm

-4 -2 0 2 40

20

40

60

Offset [ mm ]

N

"MB."x: 2.4 mm

-4 -2 0 2 40

20

40

60

Offset [ mm ]

N

"MB."y: 1.56 mm

-4 -2 0 2 40

5

10

15

Offset [ mm ]N

"MQ."x: 2.0 mm

-4 -2 0 2 40

5

10

15

Offset [ mm ]

N

"MQ."y: 1.2 mm

Vertical dipole error distribution



19




-4 -2 0 2 40

10

20

30

Offset [ mm ]

N

BLMx: 0.5 mm

-4 -2 0 2 40

10

20

30

Offset [ mm ]

N

BLMy: 0.5 mm

-4 -2 0 2 40

20

40

60

Offset [ mm ]

N

"MB."x: 2.4 mm

-4 -2 0 2 40

20

40

60

Offset [ mm ]

N

"MB."y: 1.56 mm

-4 -2 0 2 40

5

10

15

Offset [ mm ]N

"MQ."x: 2.0 mm

-4 -2 0 2 40

5

10

15

Offset [ mm ]

N

"MQ."y: 1.2 mm


0 5 10 15 20 25 30106

107

108

109

s [ km ]

Loss

rate

per

uni

t len

gth

[ p/m

/s ]

Quench limit

Lowb - Coll - HORI - Perfect Aperture

0 5 10 15 20 25 30106

107

108

109

s [ km ]

Loss

rate

per

uni

t len

gth

[ p/m

/s ]

Quench limit

Alignment seed = 9

Beam 1

Perfect machine(no alignment errors)

Example of a machine with errors

IR2 IR3 IR4 IR5 IR6 IR7 IR8 IR1 IR2 IR3 IR4 IR5 IR6 IR7 IR8 IR1



19




-4 -2 0 2 40

10

20

30

Offset [ mm ]

N

BLMx: 0.5 mm

-4 -2 0 2 40

10

20

30

Offset [ mm ]

N

BLMy: 0.5 mm

-4 -2 0 2 40

20

40

60

Offset [ mm ]

N

"MB."x: 2.4 mm

-4 -2 0 2 40

20

40

60

Offset [ mm ]

N

"MB."y: 1.56 mm

-4 -2 0 2 40

5

10

15

Offset [ mm ]N

"MQ."x: 2.0 mm

-4 -2 0 2 40

5

10

15

Offset [ mm ]

N

"MQ."y: 1.2 mm


0 5 10 15 20 25 30106

107

108

109

s [ km ]

Loss

rate

per

uni

t len

gth

[ p/m

/s ]

Quench limit


0 5 10 15 20 25 30106

107

108

109

s [ km ]

Loss

rate

per

uni

t len

gth

[ p/m

/s ]

Quench limit

Alignment seed = 9

Beam 1



IR2 IR3 IR4 IR5 IR6 IR7 IR8 IR1 IR2 IR3 IR4 IR5 IR6 IR7 IR8 IR1

- 10cm level: higher loss spikes!

- Total losses in single cryostat 15-20% higher

- New loss locations!


Measured alignment errors

20

Work in progress: apply measured alignment error along magnet cold bore (~10 cm level) → “as-built” aperture modelDatabase of measured alignment errors being setup/interfaced to code (ABP/LCU+AT/MCS)Example: Q9 downstream of betatron cleaning at injection (data from M. Giovannozzi)

20.33 20.335 20.34 20.345 20.35-1.5

-1

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x,y

[ mm

]

s [ km ]

H and V alignment error


Measured alignment errors

20

Work in progress: apply measured alignment error along magnet cold bore (~10 cm level) → “as-built” aperture modelDatabase of measured alignment errors being setup/interfaced to code (ABP/LCU+AT/MCS)Example: Q9 downstream of betatron cleaning at injection (data from M. Giovannozzi)

20.33 20.335 20.34 20.345 20.35-1.5

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x,y

[ mm

]

s [ km ]

H and V alignment error

20.3 20.31 20.32 20.33 20.34 20.35 20.36 20.37 20.38 20.39

10-6

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s [ km ]

Loca

l cle

anin

g in

effic

ienc

y [ 1

/m ]

20.3 20.31 20.32 20.33 20.34 20.35 20.36 20.37 20.38 20.39

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s [ km ]

Loca

l cle

anin

g in

effic

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/m ]

Losses for perfect machine(no alignment errors)

Losses with measured Q9 alignment

S. Redaelli, BEAM’07, 02-10-2007 21

• Introduction• Loss studies for the LHC Simulation tools Performance of a perfect system Energy deposition studies• Imperfection models Jaw surface deformations Aperture alignment errors• Loss studies at the SPS Experimental layout Simulated versus measured losses• Conclusions

Outline of my talk


Layout of collimator tests at the SPS

22

A horizontal LHC collimator prototype (full mechanical

functionalities) installed in SS5 for beam tests.


SPS optics and aperture

23

Prototype LHC collimatorMain beam parametersβx = 24.9m ➘ σx ≈ 0.7mm

βy = 89.9m ➘ σy ≈ 1.3mm

En = 270 GeV / cε ≈ 1-3 µm

Aperture model by G. Arduini



23


βy = 89.9m ➘ σy ≈ 1.3mm

En = 270 GeV / cε ≈ 1-3 µm

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Verti

cal a

pertu

re [

mm

]

Horizontal aperture [ mm ]

QD




23


βy = 89.9m ➘ σy ≈ 1.3mm

En = 270 GeV / cε ≈ 1-3 µm

-90 -60 -30 0 30 60 90-90

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QD-90 -60 -30 0 30 60 90-90

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QF1




23


βy = 89.9m ➘ σy ≈ 1.3mm

En = 270 GeV / cε ≈ 1-3 µm

-90 -60 -30 0 30 60 90-90

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cal a

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QD-90 -60 -30 0 30 60 90-90

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QF1

⎬

-90 -60 -30 0 30 60 90-90

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MBA




23


βy = 89.9m ➘ σy ≈ 1.3mm

En = 270 GeV / cε ≈ 1-3 µm

-90 -60 -30 0 30 60 90-90

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0

30

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90

Verti

cal a

pertu

re [

mm

]


QD-90 -60 -30 0 30 60 90-90

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90

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cal a

pertu

re [

mm

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QF1

⎬

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90

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re [

mm

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MBA

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MBB

⎬Aperture model by G. Arduini


Generation and measurement of losses

24

Lifetime of SPS coasting beam: > 100h! How do we generate proton losses?

➙ Full or partial beam scraping with the collimator jaw!

Simulations were updated to include time-dependent

jaw movements: - 1 or 2 jaws can be moved at a speed of 2 mm/s - 20000 turns for the sweep across the beam


Generation and measurement of losses

24

Lifetime of SPS coasting beam: > 100h! How do we generate proton losses?

➙ Full or partial beam scraping with the collimator jaw!

• One ionization chamber per quadrupole → Total of 36x6=216 BLM’s

• QD (smaller σx) have one H monitor and vice-versa• Losses integrated over 1 super-cycle of ~ 25 s

Ionization chamber

Simulations were updated to include time-dependent

jaw movements: - 1 or 2 jaws can be moved at a speed of 2 mm/s - 20000 turns for the sweep across the beam


Comparison of overall loss pattern

25

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BLM

RIN

G re

adin

g [ b

it ]


SimulationsMeasurements

Overall loss pattern along the full ring is correctly predicted!➘Main losses immediately downstream of the collimator➘Next significant peak at an SPS collimator, >2.5km downstream!

Beam Beam

↓collimator ↓collimator

N los

s [ a

u.]

S. Redaelli, BEAM’07, 02-10-2007 26

We look at small loss peaks in regions with no collimators:

6450 6500 65500

5

10

15

Longitudinal coordinate s [ m ]

Num

ber o

f los

t par

ticle

s

Measurements Simulations

Simulations agree qualitatively with measurements also at locations without collimators!

S. Redaelli, BEAM’07, 02-10-2007 26

We look at small loss peaks in regions with no collimators:

6450 6500 65500

5

10

15


Num

ber o

f los

t par

ticle

s


Simulations agree qualitatively with measurements also at locations without collimators!

~1/1000 of max peak

~1/5000


Simulation further downstream

27

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ber o

f los

t par

ticle

s

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read

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[ bit

]





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[ bit

]



The peak is downstream of the BLM location!



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[ bit

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Difference understood if details of BLM mounting are taken into account!

We can nicely simulate losses but, of course, cannot measure without BLM’s!



27

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[ bit

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Difference understood if details of BLM mounting are taken into account!

We can nicely simulate losses but, of course, cannot measure without BLM’s!

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-10

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Y [

mm

]

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Sloss: s1=590m; s2=610m.Nloss = 621

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mm

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Sloss: s1=450m; s2=460m.Nloss = 45

2nd peak:TIDV1st peak:TIDP

S. Redaelli, BEAM’07, 02-10-2007 28

• The simulation tools for LHC beam loss studies were presented• Codes evolved during the years to match the increasing complexity

of the LHC collimation system• Played a major role in the improvement of the final multi-stage

system from the original 2-stage cleaning• Detailed error models developed to understand the performance of

the realistic and “as-built” machine• Crucial importance for energy deposition and background studies• Tools are portable end documented on the web - extension to other

machines is straightforward!• Application to collimator induced beam loss at the SPS showed a

good agreement between simulations and measurements

Conclusions

S. Redaelli, BEAM’07, 02-10-2007 29

• AB-ABP-LCU members (M. Giovannozzi, W. Herr, S. Fartouhk)• AB/ATB members• F. Schimdt• J.B. Jeanneret• CERN BLM team• M. Jonker• SPS operation crew (G. Arduini, J. Wenninger)

Acknowledgments

S. Redaelli, BEAM’07, 02-10-2007 30

Reserveslides


Beam halo loads in the dump region

31Energy deposition studies by L. Sarchiapone

Higher loss rates at the TCDQ for beam2

- Critical loss rates for beam 2: dump region immediately downstream of betatron cleaning

- Detailed simulation campaigns to investigate commissioning scenarios with reduced collimation system (C. Bracco, T. Weiler)

- Proposed additional shielding to achieve ultimate intensities


Closed-orbit distortions

32

LHC tolerance: ± 4mm in arcs, ± 3mm in insertions.Scans of amplitude and phase of orbit errors to find critical spots. Extensive studies by G. Robert-Demolaize (PhD work).


Improvements of the system

33There are still losses above the quench limit!

Full system with TCT’s + absorbers

2 stage cleaning in IR7 (as of Jan. 2005)

Beam


TCLA + TCT➙Significant improvement in the IR’s

Before ➙many losses outside collimators!



34

0 5 10 15 20 25 30106

107

108

109

s [ km ]

Loss

rate

per

uni

t len

gth

[ p/m

/s ]

Quench limit


0 5 10 15 20 25 30106

107

108

109

s [ km ]Lo

ss ra

te p

er u

nit l

engt

h [ p

/m/s

]

Quench limit

Alignment seed = 9



20.25 20.3 20.35 20.4 20.45 20.5

106

107

108Lowb - Coll - HORI - Perfect Aperture

20.25 20.3 20.35 20.4 20.45 20.5

106

107

108Alignment seed = 9

Dispersion suppressor of IR7

Beam 1

1. Loss spikes at the 10cm level much higher (effect on quench performance to be understood)2. Total losses in single cryostat up to 15-20% higher3 .New loss locations!


Time-dependent jaw movements

35

Simulations include time-dependent jaw movements (new feature) ➘ Single or both jaws can be moved at their real speed ➘ Long tracking runs ~ 20000 turns to simulate the full sweep across the beam

Csps ≈ 6.9 km

Num

ber o

f los

t par

ticle

s


Time-dependent jaw movements

35

Simulations include time-dependent jaw movements (new feature) ➘ Single or both jaws can be moved at their real speed ➘ Long tracking runs ~ 20000 turns to simulate the full sweep across the beam

Model accurate to the < 1e-4 level

Can the BLM’s measure this wide dynamic range?

Csps ≈ 6.9 km

Num

ber o

f los

t par

ticle

s


More details of the SPS simulations

36

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10000

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m ]

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D x [ m

]

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Np



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]

11

Dynamic range of BLM’s ?

Np



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The comparison showed that the correct settings of septum collimator were missing in first simulation runs!

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Beam losses at an SPS collimator (was OUT during tests!)

Simulations

Prediction power: We found that the TPSG was OUT and not IN!

↓ LHC collimator

simulated and measured loss maps with lhc collimators at the

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