Injection protection with TDI-TCLI

• Introduction and scope

• Parameters and Assumptions

• Simulation methodology

• Simulation results

• Implications for TCLI design

• Future work

• Summary

Introduction and scope • Failures of LHC injection kickers are protected against

with TDI and TCLI collimators (with TCDD mask).• TDI and TCLI are 2-sided moveable objects.

• TCLI locations already defined by phase advance

• TCLI spec. required (robustness, tolerances, settings)

• Simulated protection level as a function of system (TDI + TCLI) aperture.

• Checked utility of TCLIs (simulated with, without)

• Treated IR8 only (but should hold for IR2)

Overview of injection region (IR8)MSI

TDI

TCDD

TCLI2TCLI1

MKI

Which failures…?

• Most dangerous case is where whole beam grazes TDI face….

• This can happen in several ways:– Wrong settings (kicker, TDI, correctors, …):

• can in principle be ‘prevented’ by interlocks and/or adequate procedures.

– MKI flashover • no defence – rely on passive protection AND

rareness of the event.

Taken as worst case for simulation

Derive particles outside aperture for quoted errors and failure case, as a function of system (TDI plus TCLI) aperture

• Beam2 particles are tracked with MADX through TI 8 and injection region of LHC• TDI (4 slices), TCLI1 and TCLI2 included.• Generate typical random TL error pattern with ‘max’ y offset at MKI • Introduce phase errors in Q4 • Scan aperture over range of interest (define TDI, TCLI settings)

• Scan MKI kick over range of interest (for scan: MKI as single kicker)

• Track particles through, counting losses at TDI and TCLIs• Calculate number of particles in LHC above aperture limit

• Calculate max. p+ into LHC vs. aperture• Calculate risk of damaging flashover vs. aperture• Calculate load on TLCI vs. aperture

• Simulated with 1000 p+ (interested in 5% statistics)• Gaussian beam in y, y’

Simulation methodology

Simulation ranges

MKI-TDI phase error TCLIs IN TCLIs OUT

+20 deg X X

0 deg* X X

-20 deg X X

*the quoted (OB) tolerance on k Q4 is 20 units = 2 x 10-3, which translates to a phase error of about 3 x 10-3 rad, or an offset of about 3 x10-2 y – hence this was neglected in the analysis (given the ~0.1 step sizes)

6 10Aperture setting41 steps

+0.13 mrad

-0.13 mradM

KI

kick

241

step

s

What was included….• Assumed normal distribution of various errors, derived 95% confidence

limit (2rms) as representing max. level for the combination of these errors at the moment of the rare kicker failure

• Injection error (y) ±0.45 mm at injection point• SPS orbit errors (0.1 mm / 1 rad rms in SPS)• Transfer line magnet ripples (used quoted PC tolerances in MAD)• Transfer line drifts (assumed 0.2 mm rms at injection point)

• TDI mechanical ±0.2 mm• TCLI mechanical ±0.075 mm• Orbit precision ±0.05 mm (setup with intermediate beam)

• Coldbore aperture 8.2 (for n1 = 6.8)• Damage limit 2.4 x 1012 p+ (5% of full batch)• MKI-TDI phase error 20˚ (made by change of ~20% in Q4

kick!)

• 288 x 1.7 x 1011 p+ injected• Gaussian beam in y, y’

Values from J.Wenninger, M.Lamont, L.Bruno, V.Maire, O.R.Jones and O.Brüning

What was neglected…• Sweep effect of MKI kicker

• Will slightly (few %) improve situation as regards beam into LHC above aperture limit, and load on TCLI.

• Will be much more important when looking at losses in LHC at aperture limits at injection.

• Apertures (but checked > ~9 in IR 8)• Transfer line failures (magnet trips – MSI, MCIAV, …).

• More complete analysis to be made with same tool• Will also include TCDI (performance quantification)

0

10

20

30

40

50

60

70

80

90

-0.4

0

-0.3

5

-0.3

0

-0.2

5

-0.2

0

-0.1

5

-0.1

0

-0.0

5

0.0

0

0.0

5

0.1

0

0.1

5

0.2

0

0.2

5

0.3

0

0.3

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0.4

0

Amplitude (sigma)

Nu

mb

er

of

bu

nch

es

0.9900

0.9925

0.9950

0.9975

1.0000

1.0025

1.0050

1.0075

1.0100

0 1 2 3 4 5 6 7 8 9 10

time (s)

no

rmal

ised

kic

k

ResultsLoad on TDI slices 1 and 4 for +20 deg phase error

ResultsLoad on TCLI1 and TCLI2 for +20 deg MKI-TDI phase error

ResultsLoad on TCLI1 and TCLI2 for -20 deg MKI-TDI phase error

ResultsBeam above 8.2 y in LHC for +20 deg MKI-TDI phase error, with and without TCLIs

With TCLIs Without TCLIs

ResultsMaximum beam above 8.2 y in LHC, for cases considered

0 deg +20 deg -20 deg

TDI only 7.56 6.70 6.70

With TCLI 7.78 7.92 7.73

Vertical aperture in for 5% protection limit

Attempt at risk ‘quantification’

• Consider only MKI flashover case (probability of settings error??)• Assume same results apply for IR 2• Assume 1 MKI flashover per 8 magnets per year ±0.2 mrad kick per MKI

Results

Max. load on TCLIs

Results

TCLI1 TCLI2

• Even for zero phase error, TCLIs help (better tolerances…)- intercept 10-18% for TCLI1- intercept 2-6% for TCLI2 (location not v. good ~15m y)

• For 20 deg phase error, can intercept ~40% of beam

Proposed TCLI specification

• 1.2 m long jaw of C (hBN, …?)• Surface flatness 0.1 mm• Positioning accuracy ±0.025 mm• Cooling? Depends on beam heating…• Bakeable

• TCLI2 at Q6 – looks identical to TCS… check integration• TCLI1 at D1 - common beampipe (maybe looks like

proposed D1 TCT, but with low-Z jaw on other beam?)

Errors giving min. H separation between beams

Looks close (TCLI collimates but beam 2 close to jaw)- can reduce jaw width by 5mm in direction of beam 1…- make more detailed study to check aperture (mech. tolerance etc.)

IP2 (V6.4)

-40

-30

-20

-10

0

10

20

30

40

-50 -40 -30 -20 -10 0 10 20 30

beam1

Errors giving min. H separation between beams

IP8 (V6.4)

Looks OK (TCLI collimates and beam 2 does not interfere)

-40

-30

-20

-10

0

10

20

30

40

-50-40-30-20-100102030

beam1

Summary• With TDI and TCLIs, 0.05 dangerous events per y, for aperture of ~7.75 y

• TCLIs improve the protection even without MKI-TDI phase errors gain ~0.25 y in aperture for same protection level

• For large (20˚) MKI-TDI phase errors, with TCLIs gain ~1.0 y in aperture for same protection

– TCLIs may allow some tuning of the injection optics, e.g. if need MKI-TDI phase advance ≠ 90˚….

• TCLIs desirable, to cover specified errors and to allow flexibility in operational protection strategies

• Recommend robust (C, hBN, …) 1.2m long TCLIs– Maximum beam loads on TCLIs can be 10-40% of a full batch.– Protection with 1.2m C adequate (TCDI analysis: attenuation + emittance dilution)– No worries about beam loads if protection strategy changes – e.g. if TDI has to be

retracted more due to unacceptable load from secondary halo…– Vacuum - feasibility seems OK (TCLI1 better than TDI, retracted after injection)

• Settings strategy and operational procedures also start to be considered

Future work• Completing the MKI flashover analysis

– IR 2– Expected level of load on TCLIs and risk for flashover with ‘real’ pattern

of random effects– Secondary halo load on TDI and possible implications…– Evaluation of possible optimised positions (higher y for TCLI2, separate

beampipes for TCLI1, …)

• Extension to other ‘injection’ error scenarios– Single failures in SPS / transfer lines / injections (septa, dipole families)

(especially horizontal plane…)– Check worst-case combination of random effects without any failure– Losses at other apertures (line + LHC aperture models)– Evaluation of mismatch into LHC from tilted line, plus expected

mismatch (with errors) after correction

• Losses at LHC aperture limits during first turns at injection– Include kicker waveforms