LEIR Commissioning

LHC-MAC, 15th June, 2006 LEIR Commissioning C. Carli 1/15

LEIR Commissioning

• Introduction– Recap on LEIR

– General comments

– Situation at the time of the first MAC presentation (15th December 2005)

• Completion of LEIR Commissioning :– January 2006 “shutdown”,

– Summary,

– Expected and unexpected Problems,

• LEIR Status

• Conclusions and Outlook

C. Carli on behalf of the LEIR commissioning team


Many people have contributed to construct LEIR and in LEIR commissioning:

• I-LHC project leader(s) : S. Maury (and before K. Schindl)• LEIR project leader : M. Chanel• Commissioning team : P. Belochitskii, L. Bojtar, C. Carli,

M. Chanel, K. Cornelis, B. Dupuy, J. Duran, T. Eriksson, S. Gilardoni, D. Manglunki, E. Matli, C. Oliveira, S. Pasinelli, J. Pasternak, F. Roncarolo, G. Tranquille

• Many people from several departments and many groups have constructed and installed all the equipment we use:– despite a lot of pressure mostly in time,– Impossible to compile a list of all contributors (more than 100

contributors are on the I-LHC mailing list).


IntroductionRecap on LEIR

• Pre-LHC ion accelerator chain cannot be provided the bright LHC beams needed.

Upgrades of the ion chain:– New ion source, Low Energy Ion Ring LEIR

accumulating ions: Elaborate multiturn

injections:(70 turns > 50% efficiency),

Electron cooling (BINP):(cools within 200 to 400ms)

Transforms long (200 µs) Linac 3 pulses to short(200 ns) bright bunches.

– RF gymnastics in PS …… .LEIR in autumn 2005

(few days after first circulating beam)

Ejection

RF

InjectionElectron Cooler

(from BINP)


IntroductionGeneral comments

• Aim of LEIR Commissioning :– Provide beam needed for first LHC runs with less bunches and

luminosity (less demanding for injectors and LHC) : Shorter cycle lasting 2.4 s each one delivering one bunch with 2.25 108 ions, Transverse (normalized RMS) emittances 0.7 µm, Longitudinal emittance 0.025 eVs/u.

• Commissioning in Phases :– Lines in May and June 2005,

– LEIR ring in autumn 2005 and beginning of 2006.

• First Phase of LEIR Ring Commissioning with O4+ :– Beam rigidity very close to Pb54+,

– Longer life-time expected (is that true ?) and cooling times, Simpler for diagnostics.

• Early LHC ion beam in PS and SPS in 2006 and 2007, respectively.


IntroductionSituation at the time of the last MAC

presentation

• Successful commissioning of:– Injection line,– Injection, lattice, many beam diagnostics instruments, RF ….

• Difficulties with first cooling and accumulation:– Short life-times, explainable by high pressure in some regions

(problems with recuperated bellows (?) and an ionization profile monitor),

– Barely no increase in local density.

• Recommendation of the MAC:– Consider O8+ for first commissioning,– After some reflections, we decided to continue with Pb54+

Risky, but still the possibility to switch to O8+ in case of problems, Only way to keep a chance to complete LEIR commissioning on time, Faster cooling makes life-time less critical, Turned out to be the right choice.


Completion of LEIR Commissioning

January 2006 “shutdown”

• LEIR Commissioning on hold in January 2006 (access system …) Opportunity to open vacuum sector 5

(known difficulties, broken ionization profile monitor):– Traces of ion impact on ionization profile monitor (-> addition of Au coated plates)

• Definite cure of pick-up cable problem: insulate head amplifier box from bending

• Everything ready to restart at mid of February

Wire reducing the aperture

Traces from ion impact

Au coated plates

Looking opposite to beam direction



Summary

• Restart at middle of February 2006– Problems (expected) again with controls (magnetic cycle):

good collaboration with controls experts.

– Circulating Pb54+ beam obtained quickly, Improved beam life-time !!– Again serious difficulties with injection line.

• Electron Cooling without particular difficulties on 3rd March 2006:– Accumulation very soon afterwards.

• First synchronization and ejection on 11th April• Short life-time (1s to 3s instead of up to 14s) observed on 20th April:

– No reason identified, disappeared over a ~1 week for PS interventions.

• Beam in front of PS injection on 24th April 2006• Last phase (extension) perturbed by PS (and SPS) restart• Commissioning completed on 12th May 2006:

– Profile monitors in ejection line available during last week only,– “Early LHC ion beam” by accumulation of two Linac 3 (low beam current traded for

stability) shots.



Expected and unexpected Problems

• Controls:– LEIR as testbed for LHC controls,

Difficulties –often recurrent- as expected (magnetic cyle generation …),

– Good collaboration with controls experts, Working (not yet perfect) control system, No migration to another control system in near future.

• Injection line matching:– Problems with Pb54+ similar to O4+,

Updated optics model based on measurements.

• Electron cooling and accumulation:– Some worries after experience at the end of 2005,

No particular difficulty to set up cooling and accumulation in 2006. Difficulties cured by upgrades during January shutdown ?,




Transverse beam dynamics on

ramp:• Reason:

– C-shaped bending magnets & chamber connected to ground at several locations,

Ramp induces net Eddy current & gradient,

Optics perturbations

• Cure:– Compensation by adding

currents to five main quad families,

– One parameter (conversion of ramp to gradient) optimized,

Good acceleration efficiency.

Measured Quadrupole currents along the

machine cycle with compensation of gradients in bends during ramp

Compensation increasescurrent




• “Dynamic vacuum” and collimation:– Vacuum degradation due to lost ions limited proof experiment in 1997, Upgrades based on systematic measurements at Linac 3:

Au (low outgassing) coated Collimators (fixed and movable), Additional pumping (NEGs wherever possible).

Sufficient life-time (up 14 s – interaction with rest gas and cooler) without difficulties and movable collimators in “parking position”.

• Short life-time (1s to 3s instead of up to 14s):– Suddenly observed on 20th April 2006, no reason identified,

– Disappeared over a ~1 week stop for PS interventions – Unfortunately not understood !!!


LEIR status

Circulating beam intensity (yellow) and magnetic field (purple) vs time.“Early LHC ion beam” produced on a 2.4 s machine cycle

Injection withefficiencies up

to 50% (~design)(17 μA from

Linac-> two injections)

Longer plateau & accumulation of two shots

needed

~2.3E8 ions at ejection

Acceleration within 0.8 s

(instead of 1s)


LEIR statusElectron cooling and accumulation

Time evolution of longitudinal Schottky spectra -> time evolution of long. distribution -> observation of long. cooling and accumulation

white …… zero density red …… highest densities

t (s)

0.6

0.4

0.2

0 -2 0 2 ∆p/p (10-

3)

1st injection

2nd injection

accumulated stack(ready for bunching)

cooledstack

0 20-20

0

0.3

0.6

0.9

1.2

Sin

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Raw

Pro

f ile

Sin

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Sm

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rof il

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0.2

0.4

0.6

0.8

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Horizontal beam size evolutionmeasured with an ionization profile monitor(long cycle with 400ms between injections)

Injections

Start acceleration

Bunching


LEIR statusEjection and Transfer

Last TV of the ejection line(~5m before PS injection region)

SE (wires) profile monitors in the ejection line: - transverse emittances (rms normalized) : ~0.26μm - matching: (almost) no horizontal mismatch, vertical mismatch should be corrected.

- Ejection kicker (green), - Sum (yellow) and difference (purple) of ring PU, - Ejection line beam curremnt transformer (blue)

Ejection:

Vertical mismatch (at ejection point)


LEIR statusTowards the nominal LHC ion beam

Towards nominal LEIR beam :• No systematic investigations:

– not aim of commissioning and no time available.• Accumulation tests with very long plateaus (yellow trace shows

intensity):– Intensities well above the nominal ones (after very long accumulation),– Dynamic beam life-time after accumulation (and losses) ~14s,– Good sign for “nominal LEIR beam”.


Summary, Conclusions and Outlook

• The required “early LHC ion beam” has been produced:– Two injections needed (-> acceleration in 0.8s instead of 1s),– Parameter of ejected beam well within specifications,– Successful tests of Controls developed for LHC.

LEIR construction and commissioning completed:– (almost) on time -> big success of the whole LEIR team,– LEIR can provide the “early LHC ion beam”,– Cures for all difficulties implemented.

• Outlook:– Still some work to make LEIR fully operational (Schottky diagnostics, final

version of digital low level RF, broken ionization profile monitor, controls …),– LEIR Re-start (from the “CERN Control Centre” CCC ?) in autumn 2006,– Provide beam for “Early LHC Ion Beam” Commissioning of the PS in autumn

2006,– Provide beam for “Early LHC Ion Beam” Commissioning of the SPS in 2007– Prepare the Nominal LHC Ion Beam in LEIR and further downstream.


Linac 3

ETL line

PS ring

Injection

Ejec

tion

LEIR

rin

gITE loop

ETL.

MTV

10

ETL.

MTV

40

ER

.MTV

12


LHC ion injector chain overview

Pb27+

Pb54+

LEIR

Repetition rate up to 5 Hz After acceleration and stripping :- 200 A Pb54+ at 4.2 MeV/n- >120 s long pulses

Energy ramping cavity p/p ~0.4%(needed for LEIR injection)

Accumulation of ~4 Linac pulses : - Multiturn injection (transverse+longit.) (70 turns with 50 % eff). - New electron cooler constructed by BINP. Bunching, acceleration and transfer to PS.Two bunches corresponding to 4 LHC bunches at 72 MeV/n every 3.6 s.

-RF gymnastics to obtain 4 LHC bunches spaced by 100 ns.- 4 LHC bunches at 5.9 GeV/n every 3.6s.Al Stripper Pb54+ to Pb82+:

low-beta insertion

- Accumulation of up to 13 LEIR/PS batches on a ~40s plateau.- “Variable (non-integer) harmonic” acceleration.- Direct space charge and IBS limit ?- Up to 52 LHC bunches per cycle at 177 GeV/n

200 A Pb25+ at 2.5 keV/n

200 A Pb25+ at 2.5 keV/n

- Each ring filled (during ~10 min): * with 12 SPS batches, * total 592 bunches per ring.-Design : * Luminosity 1027 cm-2s-1, * Collision energy 2.76 TeV/n.-Limited by collimation and ECPP ?


Outlook until Completion of LEIR Commissioning

Expected Problems

Loss pattern of Pb53+ ions around the LEIR ring with collimators and homogeneous gas density

Intercepted by absorbers :-Reduced outgassing with Au coating,-Efficient scrubbing due to small surface

Injection Cooler

“Dynamic life-time”

Avalanche-likepressure rise :• ions lost due to rest gas

electron capture (or loss) (Pb54+-> Pb53+),

• every lost ion desorbs some 104 molecules,

• Observed in POP in 1997.

LEIR upgrades based onmeasurement at Linac 3

NEG coatings in straight sectionsto improve vacuum there

LEIR Commissioning

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