Checks of LBDS for new IR6 optics

B.Goddard, with input from C.Bracco, R.Bruce, S.Fartoukh,

V.Kain, R.Tomas-Garcia, J.Uythoven

Phase advance MKD to TCDQ/TCSG

Motivation

• Present nominal phase advance MKD (kick centre) to TCSG6 is ~94.7 deg

• Idea from S.Fartoukh during discussions on ATS to rematch IR6 to exactly 90 deg.– Improves protection in terms of amount of beam

transmitted above a certain amplitude.– Effective gain depends on particle amplitude from the

bunch core (with 2 um ex and 8.5 sigma tight setting, gain 0.2 s for 3 s particles, 0.03 s for on-axis) small but useful

Considerations for dump system

• Possible gains • Trajectories and apertures in dump region• Beta functions in TD lines• Operational limits of TDE, VDWB, BCTDD, TCDQ,

TCDS• Setting-up of TCSG/TCDQ• Asynchronous dumps and TCTs• Measured values• Extra checks and commissioning time needed

Gains• Gain about 0.2 sigma for particles with 3 (real) sigma

amplitudes (for 2 um emittance)• Could reduce margins needed from TCSG/TCDQ to

TCT, to shadow TCTs

8.40

8.60

8.80

9.00

9.20

9.40

9.60

9.80

-4 -3 -2 -1 0 1 2 3 4

Tran

smitt

ed a

mpl

itud

e (n

omin

a si

gma)

Amplitude from core (nominal sigma)

B1 old

B1 new

beam core

Trajectories and apertures in dump channel

• Strengths of Q4 L6 for B1 and R6 for B2 are unchanged– Trajectories identical to nominal

• Changes in beta functions in extraction region– 8% larger at TCDS – 4% larger beam size (1.096 1.140 mm)

• N1 already at 6.5 – would be reduced to about 6.25 at TCDS entrance• 16.3 mm aperture – lose 0.55 nominal sigma here in H plane.

– 14% smaller at TCDQ – 7% smaller beam size– Beam size 3% larger at MSDA1, 2.5% smaller at MSDC15

• Protection by TCDS OK (up to 17% change in betas)

• No major issues for trajectory or local aperture – Only question is about n1 = 6.25 at TCDS, at 450 GeV (calculated

for 3.75 um beams).

Beta functions in TD lines• No change to vertical beta functions• Smaller H values for both beams at TDE (5000 4300

m)– No aperture issues– Reduction in beam sigma from 1.59 to 1.47 mm ( 7 TeV)– Increased p+ density on VDWB, BTVDD, TDE

Optics functions in TD linesB1 nominal optics

B1 90.0 deg

B2 nominal optics

B2 90.0 deg

Operational limits: TDE/VDWB/BTVDD

• Regularly solicited (each fill)• Designed for ultimate beam intensity (2808b of 1.7e11 p+ at 7

TeV with 3.75 um exy)• Assuming (pessimistic) that limit scales with peak energy

density, for constant by have as safe limit (25 ns)

75.3

0.7107.1

_

_11 m

TeVEN new

oldx

newxb

Scaling of limit intensities: TDE/VBWD, BTVDD

• New optics reduces ‘safe’ intensity limits by ~0.1e11– Not an issue for 50 ns– Main effect from emittance much lower than nominal

1.00

1.20

1.40

1.60

1.80

2.00

2.20

2.40

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

Lim

it pe

r bun

ch [e

11 p

+]

Emitt ance [um]

Nb new 6.5 TeV

Nb old 6.5 TeV

Nb new 4 TeV

Nb old 4 TeV

TCDS, TCDQ operational limits• Only asynchronous dumps of which one for 3.5 TeV 2010-11, with 1

pilot (expected to be worse for 7 TeV...)• 47 bunches on TCDS, 34 bunches on TCDQ (depending on failure)• TCDS beta function is larger with the new optics

– Situation is slightly better – more margin• TCDQ beta function is 14% smaller

– 7% smaller beam size may have an impact on the TCDQ performance limit for small emittance

– TCDQ anyway not OK for full intensity beam - being redesigned now (for LS1)– Needs detailed FLUKA and thermomechanical simulations for each case -

very time consuming...– Plan sensitivity analysis to beam size in present TCDQ upgrade study– Present situation already not comfortable) – new optics will make this

slightly worse – difficult to quantify as present limits unknown

Setting up of TCSG/TCDQ

• 7% smaller beam size for given emittance; will reduce slightly the accuracy (in terms of sigma/setting up step)

• Not expected to be a problem

Asynchronous dumps• Phase advances MKD to TCTs with the new IR6 optics hardly

change at all (max 0.2 deg)

dq to MKD (deg) Beam1 old Beam1 new Beam2 old Beam2 newTCTHP1 348.4 348.5 215.8 215.7TCTHP2 186.9 187.0 108.3 108.3TCTHP5 52.4 52.6 193.5 193.4TCTHP8 348.4 348.5 168.2 168.2

TCTHP1 TCTHP2 TCTHP5 TCTHP80.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Beam1 old

Beam1 new

TCTHP1 TCTHP2 TCTHP5 TCTHP80.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Beam2 old

Beam2 new

|sin(q)| |sin(q)|

Measured values• Rogelio has checked measurements made at 3.5 TeV with

1m_10m_1m_3m (with 1.5 m b* corrections in), and calculated MKD-TCSG phase advance– B1: essentially no difference to nominal (0.001) within the error of the

measurement (±0.001)– B2: measure 0.254 ±0.001, compared to nominal 0.263.

• For B2 correction of phase by -0.013 would make things worse, if the beta-beating remains unchanged

• Expect new beta-beating pattern for new b* and new energy– Correct strategy would be to deploy new ‘90 deg’ optics and then constrain

beta-beat correction to conserve this phase advance in IR6...

• Also note: may have much larger loss of protection (0.5 s) from beam size variation at TDDQ/TCSG and TCTs – should use measured betas for calculating settings of these devices!

Extra setting up and checks for 2012 startup, if new IR6 optics?

• No changes to Q4, MKD, MSD strength – LBDS energy tracking does not need extra checks

• Will anyway need to carry out substantial range of LBDS checks– TCDQ setup, interlock BPM setup and checks, dump sweeps

• Should foresee extra aperture checks in IR6 at TCDS, Q4/5– Maybe few hours per beam at 450 GeV

• New TCSG/TCDQ settings – probably anyway the case• Maybe some more time for beta-beat corrections• Realistically, maybe 1-2 shifts for ‘extra’ tests

SummaryNew optics can reduce transmission amplitudes into LHC by 0.03 - 0.20

sigma, for 0 to 3 sigma particle amplitudes respectively (with 2 um emittance).

Trajectories in dump channel unchanged

Lose about 0.5 sigma at TCDS entrance: n1 reduced to 6.25 at injection.

Slightly smaller beam size on dump block: sticking to design p+ density means reduce intensity ‘reach’ by 0.1e11, for any given emittance.

Slightly better for TCDS (larger beam), but slightly worse for TCDQ, with 7% smaller beam, already known to be potential limit…

Setting up accuracy/speed should not be affected

Phase advances to TCTHs basically unchanged: no issues for asynch dumps

2011 phase advances: B1 = 0.263, B2 = 0.25. New beta-beat expected in 2012, but will need to include in correction strategy, after measurement.

Extra testing and validation maybe 1, maximum 2 shifts

Conclusion• No major issues identified• Potential gain is real but small

– Risk making things worse unless included in b-beat correction strategy

• Some unknowns, especially TCDQ robustness– Goes in wrong direction– Already not OK for nominal beam at 3.5 TeV

• Propose to keep new optics “in pocket” for future (>LS1), especially when approaching nominal settings at 6.5-7.0 TeV

• Use 2012-13 to investigate key points, especially TCDQ robustness (include in new design study), TDE limits as function of sigma, correction of beta-beat to nominal, ...

• In any case beta-beat correction and collimator setting definition need to take account of these issues