Accumulation in the LEIR Ring

November 28th, 2005 LEIR Commissioning – AB/LII section meeting 1/6

Accumulation in the LEIR Ring

E-Cooling D=0m

Ejection

Ejectionkicker

RF

Injection

D=10m

LEIR ring during installations (spring 2005)

Cooler not yet in place,tripletts in cooler section and oppositedoublets in injection section and opposite

Electron cooler on

0 time (s) 3.6

mom

entu

m (

or fi

eld)

Injections

Bunching, acceleratio

n

Extraction

Accumulation alternates : - Multiturn injection with horizontal,

vertical and longitudinal stacking : 70 turns with >50% efficiency every 200 ms to 400 ms,- Fast electron cooling with a new state-of-the-art cooler constructed by a BINP team.Aim of commissioning : provide Pb54+ beam for the first LHC ion run(s).

November 28th, 2005 LEIR Commissioning – AB/LII section meeting 2/6

Overview of LEIR ring commissioning

• Situation at the beginning of October :– Lines already commissioned until beginning of July,– Hardware ready to start commissioning (but not all installations completed)

• At the beginning quite some control problems, amongst them :– Sometimes (in a rather erratic manner) working sets and knobs (our main interface

for remote control) became filled with error messages,– Persistency problems,– Some equipments not yet controllable remotely (not the most annoying), GFA

problems.

• Polarity tests :– Proved to be very useful (a few hardware errors, e.g. wrong polarity of two

quadrupoles) have been found),– Perturbed as well by controls problems,– Heavily perturbed by new security rule which are not clear (contradictory

informations) and without official transition scheme.

• First injections (expected to be a critical milestone) on October 11th :– Little adjustments (one day between one turn and stable beam) for first injection,

but skew quads for reproducibility !

November 28th, 2005 LEIR Commissioning – AB/LII section meeting 3/6

Overview of LEIR ring commissioning

Members of the commissioning team with first Longitudinal Schottky Spectra

(Photo published on the first page of the bulletin announcing first beam in LEIR)

Circulating intensity (blue), injection bumper (red) and arriving beam (green)

Transverse Schottky spectrum

November 28th, 2005 LEIR Commissioning – AB/LII section meeting 4/6

Overview of LEIR ring commissioning

• Commissioning resumed on October 26th :– Again rather quickly circulating beam

(low intensity !) was established

• Bunching and first orbit measurements :– First bunching on October 27th– Orbit acquisitions right from the

beginning (corrections worked, but due to doubts on the orbits, we did not send them

• Momentum ramping set up on Nov 1st :– Needed to obtain good injection

efficiencies,– Clear increase of intensity with

nominal settings,– Nearly 50 % injection efficiency

after few adjustments.

• First Orbit response measurements :– Lattice without cooling -> some losses due to measurements– LEIR optics reasonably close to expectations (all gradients found with orbit response smaller

than expected).

November 28th, 2005 LEIR Commissioning – AB/LII section meeting 5/6

Overview of LEIR Ring Commissioning

• Position Pick-up cable problem (discovered on November 2nd) :

– C-shaped bending magnet -> electric fields induced during the ramp,

– Current on cable (on outer conductor) between pick-up and amplifier damaged the cable !!

– Only ideas on cures.

• First “start-up” (after week-end & Linac failure) without local intervention on November 15th.

• First acquisitions by Tomoscope on November 16th (see image).

• Surprising chromaticity measurements (vertical not as expected)

• Electron cooler preparations :– Quite some installations during commissioning,– First electron beam on November 15th (after long

technical difficulties),– First signs of cooling on November 16th,

• Magnetic cycle with corrections (and long plateaus) for cooling more or less ready.

November 28th, 2005 LEIR Commissioning – AB/LII section meeting 6/6

LEIR Commissioning Status

• Despite some problems (vacuum problem, controls problems -situation improved-, many installations for the cooler, RFQ problem), a lot of progress since beginning of October :

– Injection with good efficiency (-> injection line setting that works),

– A lot of beam diagnostics (TVs, MTRs, Schottky, Tunes …) works,

– Bunching and orbit works,

– Lattice : reasonably close to theory, cooler compensations work.

• Next steps to come :– Systematic investigations on cooling (very soon, Ionization Profile Monitors needed),

– Acceleration up to nominal field (latticeproblems expected),

– Switch to Pb54+ (putting the vacuum system and the collimation to a test),

– Ejection (not before February),

– Transfer towards the PS (and check of performance).

• LEIR commissioning :– is in full swing now (but January will be “shutdown”),

– Aims at providing the beam first LHC ion run(s),

– and may (if progress is like during the last ) be completed on time until end of March or beginning of April

Order not yet decided

November 28th, 2005 LEIR Commissioning – AB/LII section meeting 7/6

LHC (Ion) Injector Chain

Overview of the LHC injector chains Accumulation in the LEIR Ring Electron Cooling Injector Chain for (nominal) LHC Pb Ion Operation LEIR Issues :

Increase accumulation rate (missing factor 3) w.r.t. 1997 experiment,

Control beam induced vacuum degradation, Keep reasonable lattice during acceleration

November 28th, 2005 LEIR Commissioning – AB/LII section meeting 8/6

Overview of the LHC Injector chains

(for Protons and Ions)LHC – operated with

Protons (red) and ions (green)

• LHC will run with protons and ions (Pb approved ),

• Injectors chains for both beams needed :– Start with a source and a linear

accelerator :• fast acceleration,• Little time with problems due to direct

space charge, ….. .

– Several Synchrotrons : • To reach higher and higher energies,• Avoid very small magnetic fields,• Focussing structure and aperture

adapted to energy (beam shrinks with energy)

• No Ion Beam useful for LHC with Previous chain (without LEIR),

Add Low Energy Ion Ring LEIR :– Transforms several long Linac

pulses into short and dense bunches

– Elaborate multiturn injection, electron cooling

November 28th, 2005 LEIR Commissioning – AB/LII section meeting 9/6

Electron Cooling

Basic Principle (Analogy withmixing of gases) :• In co-moving coordinates:

chaotic motion of ions = temperature.

• Mixture (“hot” ion beam and “cold” electrons) tends to an equilibrium temperature,

• Continuous renewal of electrons -> electron beam “stays cold”.

Cooling reduces : Reduces Emittance

(accelerator jargon), Reduces transverse beam

sizes, Increases density

Cooler constructed at INP Novosibirsk

electron gun (up to 40 kV) solenoid 6 kG

collector

November 28th, 2005 LEIR Commissioning – AB/LII section meeting 10/6

Injector Chain for (nominal) LHC Pb Ion Operation

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 ?

November 28th, 2005 LEIR Commissioning – AB/LII section meeting 11/6

LEIR Issues (1/2)

• Increase accumulation rate (missing factor 3) w.r.t. 1997 experiment:– New ion source,– Multiturn injection with

stacking in vertical phase space as well,

– Faster cooling (new cooler from BINP) and higher Linac repetition,

Confidence to meet requirements thanks to a safety factor.

2 4 6 8 10 12

Time [s]

0

2

4

6

8

Beam

Inte

nsity [

E8 ions]

beam lifetime : 6.5s

Linac III rep rate : 2.5 HzIon beam energy : 4.2 MeV/uElectron energy : 2.35 keVElectron current : 105 mA

Average accumulated intensity : 6E8 ionsPeak intensity : 7.1E8 ions

2 4 6 8 10 12

Time [s]

0

2

4

6

8

Beam

Inte

nsity [

E8 ions]

beam lifetime : 6.5s

Linac III rep rate : 2.5 HzIon beam energy : 4.2 MeV/uElectron energy : 2.35 keVElectron current : 105 mA

Average accumulated intensity : 6E8 ionsPeak intensity : 7.1E8 ions

8 108

ions

6

4

2

00 2 4 6 8 10 sec 12

Intensity accumulated in LEAR versus time during a proof of principle experiment in 1997

1/3 of the intensity

needed after 4 Linac pulses

Poor life-time with beam:

mainly due to beam-loss induced outgassing

Nominal intensity to be provided by LEIR

November 28th, 2005 LEIR Commissioning – AB/LII section meeting 12/6

LEIR Issues (2/2) :(Beam induced Vacuum Degradation)

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

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

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

• every lost ion desorbs some 104 molecules .

LEIR upgrades based on

measurement atLinac 3:• Au (low outgassing yield)

absorbers to intercept.• NEG coatings reduce

pressure rise,• “Scrubbing” (continuous

bombardment reduces outgassing) if needed.

NEG coatings in straight sectionsto improve vacuum there

November 28th, 2005 LEIR Commissioning – AB/LII section meeting 13/6

LHC Ion Injector Chain Status

• New source and Linac 3 : operational• LEIR :

– Construction completed,– Commissioning underway (Injection line and injection o.k.) until April 2006 (beam for first LHC ion

run).

• Commissioning of the LHC ion beam in the PS and SPS in 2006 and 2007, respectively• First LHC Pb ion run at beginning 2008

LEIR construction(Photo taken

in spring 2006)