Collimation MD’s and Preparation of Review

Collimation MD’s and Preparation of Review

R. Assmann et al

Collimation Study Group, 23.5.2011

CWG 23.5.2011R. Assmann

MD Sat – Mon

Day Time MD

Sat 10:00 0.45 TeV: ATS (including cycle to new injection settings)

20:00 0.45 – 3.5 TeV: Nominal collimation, single bunch tune shift

04:00 Ramp down, cycle

Sun 06:00 0.45 TeV: RF multi-bunch instabilities

10:00 0.45 3.5 TeV: Coupled-bunch instability rise times

18:00 Ramp down, cycle

20:00 0.45 3.5 TeV: Quench test in the DS of IR7

Mon 06:00 Technical Stop

Lost 6h3.5 TeV: Tune scan – beam-beam optimization, lifetime, losses

CWG 23.5.2011

Status 9.5.2011, 08:00

R. Assmann

Nominal collimation, single b tune shift (Coll, Imp.)

Initial blow-up tests with transverse damper. Injection scraping during short delay from injectors. Nominal 3.5 TeV collimation settings achieved for b1 &b2:

TCP = 5.7 sigma (nom), TCSG = 6.7 sigma (nom) TCLA = 9.7 sigma (nom), IP6 = 7.2/7.7 sigma (nom)

Octupoles trimmed to 350A for beam 1. For b1 moved towards nominal 7 TeV settings. Limited by

TCSG losses close to IP7. Valid setup reached: TCP = 4.0 sigma (nom), TCSG = 6.0 sigma (nom) TCLA = 8.0 sigma (nom), IP6 = 7.0/7.5 sigma (nom) Smallest gap: 2.2 mm Beam lifetime: > 100 hours Tune shift measured: ~2e-4 Efficiency measured: 3e-5 – 1e-4


Settings b1 first loss-maps


Vertical tune shift – collimator movement


Clearly seen in vertical plane when moving collimtors out by 4 sigma and back in, etc…

Magnitude: ~0.0003

Efficiency measured – here b1, horizontal


4e-5

Losses in Dispersion-Suppressor (Coll+BLM+MP)

BLM thresholds adjusted on 120 BLM’s, based on old data. Created fast (~2 s) beam losses at primary collimators. 3 bunches, b2 loss

Loss rate: 1.5e11 p/s 20 times below BLM limits, 10 times below assumed quench limit,

16 bunches, b2 loss Loss rate b2: 2.5 – 3e11 p/s, 6e11 p/s Reached 505 kW loss Beam dump after damper switched on, b2 still on 1/3 resonance.

16b (b1) and 21b (b2):


Beam Loss with 16 bunches, 3.5 TeV


Loss rate:

9e11 p/s @ 3.5 TeV 505 kW

Losses into DS (beam 2): No quench!


505 kW – Primary beam loss

336 W – Q8

35 W – Q11

5 W – Q19

Po

we

r lo

ad [k

W]

peak in 1 sno correction BLM response

IR7

IR6

Update Performance Reach: 3.5 TeV

3.5 TeV

ineff Efficiency Rq Ldil [p/s] min [h] Nmax [p] Nlim @BLM [p] Nlim/Nnom

2010 5.20E-04 99.95% 8.40E+07 0.6 3.7E+14 1.2E+14 41%

MD 1.20E-04 99.99% 1.20E+09 1.2 4.1E+16 1.4E+16 4600%


Cleaning

efficiency:

Gain factor 4.3

(MD result)

Quench limit times

dilution length:

Gain factor 14.3

(MD result)

Min. lifetime:

Gain factor 2

(2011 operation)

Update Performance Reach: 7 TeV


Extrapolation to 7 TeV


2010 1.30E-03 99.87% 2.71E+07 0.6 4.8E+13 1.6E+13 5%

MD 3.00E-04 99.97% 3.87E+08 1.2 5.3E+15 1.8E+15 594%

Cleaning

efficiency:

Gain factor 4.3

(MD result)

Quench limit times

dilution length:

Gain factor 14.3

(MD result)

Min. lifetime:

Gain factor 2

(2011 operation)

Request for Checks Important estimates for the June review! Please check! Conditions apply (are they reasonable?):

Same minimum beam lifetime at 3.5 TeV and 7 TeV. Minimum beam lifetime independent from intensity. No disturbing effect from much larger impedance. Theoretical scaling of cleaning efficiency and quench limit. Same spatial distribution of losses in SC magets at 3.5 TeV and

7 TeV: Loose factor 1.4 due to smaller beam emittance (single diffractive losses

form line with vertical extent given by vertical beam size)… Any other effects for losses with higher density at 7 TeV?

Peak MD performance achievable in routine operation and at 7 TeV. No disturbing effect from smaller impact parameters at 7 TeV. Both beams behave the same. Same locations for peak loss into SC magnets. No other performance limits included (IR1/5, ions, …).


Assign Margins

For the first time room for some small margins! Margins and effect on predictions:

Smaller V beam size: factor 1.4 Stability efficiency: factor 2 Lower beam lifetime: factor 2

With these margins would loose factor 5.6 in predicted performance…

These margins are somewhat arbitrary, still small and not complete (no margin for uncertainties in theoretical scaling to 7 TeV).

Still better than nothing… Also note: we did not quench, so we have determined a

lower limit (quench margin might still be higher).


Performance Reach with Margins: 7 TeV


Extrapolation to 7 TeV


2010 1.30E-03 99.87% 2.71E+07 0.6 4.8E+13 1.6E+13 5%

MD 3.00E-04 99.97% 3.87E+08 1.2 5.3E+15 1.8E+15 594%

use 6.00E-04 99.94% 2.76E+08 0.6 9.9E+14 3.3E+14 110%

Margin factor 2 factor 1.4 factor 2 n/a n/a n/a

Cleaning

efficiency:

Gain factor 4.3

(MD result) Quench limit times

dilution length:

Gain factor 14.3

(MD result)

Min. lifetime:

Gain factor 2

(2011 operation)

Why Large Changes in Prediction?

This is a complicated prediction. It involves: Beam loss rate. Cleaning efficiency of a 4 stage collimation system. Spatial and temporal distribution of leakage losses in super-

conducting magnets. Quench limit of super-conducting magnets, versus time and energy.

That is why we always pointed out large error bars and need for experimental data. Last memo included the request for MD’s to get more reliable data. Biggest concerns: achievable cleaning efficiency, distribution of

losses in DS and quench limit in DS

That is why we refused a decision before the June review! Now with the new experimental data we have for the first

time sufficient data base for a decision. Ions are assumed to be behave similarly.


What Do We Conclude?

LHC collimation is working very well, close to the predicted theoretical limits excellent work by all of you.

Outstanding success: factor 200 beyond WR in one go!

We seem to have sufficient cleaning efficiency but setup accuracy and stability are found to be limited Seen in operation and MD Limits seen with tolerances relaxed by factor 4 compared to what is

used for performance reach estimates

The job is not over: Large amount of work to keep system working like in MD for years Must still improve various aspects of the system to achieve goals


Review https://indico.cern.ch/event/collreview2011


https://indico.cern.ch/event/collreview2011



Review https://indico.cern.ch/event/collreview2011



Review Committee

Chair: Mike Seidel (PSI) Committee: T. Camporesi (CERN)

W. Fischer (BNL)M. Lamont (CERN)T. Markiewicz (SLAC)N. Mokhov (FNAL)

plus a few to be confirmed


New Memo under Preparation Sufficient data with the LHC beams has been recorded and the

requested beam tests for LHC collimation have been performed. The results allow an update of the LHC performance reach calculation. This calculation is still affected by uncertainties but for the first time provides reasonable certainty for being used as a basis for decisions.

A 9-point plan for LHC collimation is proposed, including important adjustments in the foreseen work. Based on present best knowledge and understanding, this 9-point plan is compatible with nominal LHC performance at 7 TeV in 2014 and ultimate LHC performance in 2017. At the same time the workload is reduced (e.g. no IR3 upgrade of dispersion suppressors in 2013) and collimation work is reoriented at the directions that are most efficient for optimizing LHC performance.

It is noted that a small performance risk for the LHC cannot be fully excluded. However, this risk is deemed acceptable. Lower risks can only be achieved by upgrading the LHC dispersion suppressors as soon as possible, i.e. IR3 during the first long shutdown.


DRAFT

9 Point Plan: 1 – 3

1. Action: Cancel the collimation upgrade for the IR3 dispersion suppressors during the first long shutdown in 2014. Complete ongoing prototyping work.Justification: Within reasonable uncertainties it is expected that nominal LHC luminosity can be reached without this work. This conclusion is based on the new results from the May 2011 machine studies.

2. Action: Cancel the temporary installation of vertical collimators into IR3.Justification: The need for temporary relocation of betatron cleaning into IR3 due to SEU issues in IR7 was not demonstrated by beam experience so far.

3. Action: Review priority and direction for work on crystal collimation for the LHC.Justification: Setup of crystal collimators is more complicated than for standard collimators, where limits are seen. The improvement in cleaning efficiency in IR3/7 is not required. Crystal collimators cannot help to reduce losses into DS’s of IR1/2/5.


DRAFT

R2E Input?

Do we need the IR3 temporary cleaning upgrade? Limits in IR7 electronics confirmed or not? No problem for 500 kW loss but what about extrapolation to

long-term? Does R2E agree with the action no. 2?



4. Action: Start an overall study for the upgrade of the LHC DS’s with collimators in IR1/2/3/5/7, developing a coherent approach. Develop and prototype adequate collimator hardware for readiness in 2016, in close contact with GSI. Justification: The urgency in IR3/7 DS’s is lower than anticipated and upgrades of other DS’s might become more urgent.

5. Action: Reinforce the work towards second generation collimators with beam position buttons in their jaws, aiming for first installations in 2014.Justification: Overcome the limitations in collimator setup. Allow for best efficiency and small b* at 7 TeV. Avoid lengthy collimator setup periods and win in integrated luminosity.

6. Action: Reinforce the work towards second generation collimators with robust collimator materials or damage handling concepts, with EuCARD + LARP collaborators. Readiness goal is 2016.Justification: Prepare for LHC beams with higher than ultimate brightness.


DRAFT


7. Action: Accelerate work on radiation measures with first installations in 2013 and readiness for 2016.Justification: The success of the LHC leads to a faster intensity ramp up and activation of collimators.

8. Action: Start work on design and development of hollow e-beam scrapers for the LHC. Readiness goal is 2016.Justification: Hollow e-beam scrapers are an inexpensive and safe way to reduce the magnitudes of peak beam loss. Provides insurance against risks taken in action 1, in particular against possible surprises when going from 3.5 TeV to 7 TeV.

9. Action: Assign additional dedicated CERN staff resources to the setup and optimization of the existing collimation system. Justification: Not implementing the IR3 upgrade in the DS’s implies that the associated efficiency gain of a factor 10-30 will not come. The existing system must then be operated much longer than foreseen, at the limits of its capabilities. This imposes heavy additional workload for manual setup and optimization.


DRAFT

Other Work

It is noted that the nine points proposed do not describe the full collimation work plan. Additional work packages exist on various topics: collimation setup in the control room modeling of performance optimization of setup accuracy and speed various small collimation upgrades (e.g. IR2) IR upgrades within HL-LHC design study

These work packages are not affected by the proposed changes in work plan and it is assumed that they are continued as planned.


DRAFT

Next Steps

Check technical results for review meeting. Any additional info to be included? Define program of talks and presentations:

Please send proposals to me…


Documents

Collimation MD’s and Preparation of Review