requirements of the lhc on its injectors what are the nominal & already achieved beams at ps...

E.M, PS-OP shut-down lectures, 20/02/2001 1

Requirements of the LHC on its injectors What are the nominal & already achieved beams at PS exit? How is it obtained in the PS complex?

General aspects Linac2 PSB PS

Future work SPS and LHC filling

THE LHC NOMINAL PROTON BEAM

IN THE PSB AND PS MACHINES

M. Benedikt & E. MetralM. Benedikt & E. Metral

PS-OP shut-down lectures, MCR glassbox, 20/02/2001PS-OP shut-down lectures, MCR glassbox, 20/02/2001


Requirements of the LHC on its injectors (1/3)Requirements of the LHC on its injectors (1/3)

2 main challenges involved in the design of the LHC

Very high magnetic field to reach the collision energies in the TeV range

Very high luminosity necessary to provide significant event rates at this

energy

It is limited by :- Space-charge effects in the injectors...- Head-on beam-beam interaction at collision

It is limited by :- Collective instabilities- Cryogenic load (synchrotron radiation and wall current)- S.C. magnet quench

revbbnormyx

b fekNN

L

1,

,

Brightness = transverse bunch densityBeam current



Choice of the nominal LHC parameters

Energy E [TeV]

7

Dipole field B [T]

8.3

Luminosity L [cm-2 s-1]

1034

Harmonic number h

35640

Number of bunches kb

2808

Protons / bunch Nb

1.11011

Bunch spacing b.s [ns]

25

x&y emittances

1norm,,yx [m]

3.75

Long. emittance

2l [eVs]

0.5 1


LHC project leader L. Evans

Project leader to prepare the PS complex to be a pre-injector (started in 1995) K. Schindl (Deputy M. Benedikt)


Major upgrade needed

all along the injector chain


What are the nominal & already achieved beams at PS exit?What are the nominal & already achieved beams at PS exit?

The specifications are met in the PS complex

Achieved Nominal Energy E [GeV]

25 25

Harmonic number h

84 84

Number of bunches kb

72 72

Protons / bunch Nb

1.11011 1.11011

Bunch spacing b.s [ns]

25 25

x&y emittances

1norm,,yx [m]

2.5 3

Long. emittance

2l [eVs]

0.35 0.35

Total bunch length b [ns]

4 4

Momentum spread 2p/p

2.210-3 2.210-3


How is it obtained in the PS complex?How is it obtained in the PS complex?

General aspectsGeneral aspects

2 main challenges had to be faced

High brightness production (2 as before) and conservation

Production of the train of very short bunches with the LHC spacing

Solutions

Double-batch filling of the PS (2 1.2 s)

Lowers the space charge effects at PSB injection (50 MeV)

Increase of the PSB ejection kinetic energy (PS injection) : 1 1.4 GeV

Lowers the space charge effects at PS injection

1 triple + 2 double splittings to produce the desired number of bunches,

longitudinal emittance and bunch spacing

Bunch rotation to produce the desired bunch length


Linac2Linac2

The initial transverse emittance is given by the duoplasmatron source

The beam is then adiabatically bunched and accelerated in a Radio Frequency

Quadrupole (RFQ2) under high space charge conditions

Fine-tuning of the 50 MeV Drift Tube Linac (DTL) and of the transfer line to the

PSB

m4.0

m6.0

m2.1

Depends on extraction aperture, electrode shape and space charge

Normalised, at 1


PSB (1/5)PSB (1/5) General aspects

PSB delivers 2 batches to PS (2 consecutive 1.2 s cycles)

3 PSB rings per batch (3,4 and 2)

1 bunch per ring (H1)

Injection at 50 MeV

Horizontal plane

Multi-turn injection : 3 turns exactly more stability and reproducibility (most homogeneous

longitudinal distribution of the unbunched beam)

Adjustment of the horizontal injection steering and injection bump timing to minimise the

horizontal emittance BIX.SKSW2,3,4

Special tune because of large tune shift Qh = 4.28

Tiny shaving ~ 30 ms after injection

C275, Bdot = 5 Gauss/ms

This is what sets the brightness


Vertical plane

Injection on orbit

Minimisation of vertical oscillations at injection (1/2 turn pick-up) to minimise vertical emittance

BI.DVT 50 and 70

Special tune because of large tune shift Qv = 5.44

Shaving vertical to have a well-defined emittance

Acceleration from 50 MeV to 1.4 GeV

Double harmonics operation to increase the bunching factor (bunch flattening) and thus decrease the

space charge tune shift at injection

C02 (H1, 1/ring) and C04 (H2, 1/ring). C04 voltage slowly reduced to zero at synchronisation/ejection

Available controlled blow-up C16 (H9, 1/ring)

No coupling between the transverse planes

Standard settings of multipoles for resonance compensations

C275 C765

PSB (2/5)PSB (2/5)


Synchronisation

Non-standard bunch spacing at ejection to fit the PS H7 RF system

adjustment with the phase offsets : BA3,4,2.PSYNCOFFSET (ring 3 is

always used as the reference)

Ejection at 1.4 GeV

fast extraction towards the PS through the BT/BTP transfer line

ns327ns2867

8t

7

8t 8h7h

PSPS

C805

PSB (3/5)PSB (3/5)


X & Y shavers

[ms]Time

)10(ringIntensity/ 10

PSB (4/5)PSB (4/5)


Achieved Nominal Protons / bunch 12104.1 121032.1

Hor. emittance 1norm,

x [m] 2.2 5.2

Ver. Emittance

1norm,y [m]

8.1 5.2

Long. emittance

2l [eVs]

9.0 5.1

Tot. bunch length

b [ns] 150 195

Momentum spread

pp /2 (10-3) 2 45.2

PSB (5/5)PSB (5/5)

Beam parameters at PSB extraction

Without blow-up


PS (1/10)PS (1/10) General aspects

Double-batch injection : 1 batch of 3 bunches + 1 batch of 3 bunches 1.2 s later 6 bunches out of 7

buckets

Longitudinal beam slicing complicated RF gymnastics

High brightness conservation careful control of collective effects, injection oscillations, working point,

chromaticities, non-linearities at extraction…

PSB exit

PS exit

~ 300 ns


At low energy (1.4 GeV kinetic energy)

1st injection => 3 bunches (H7)

Transverse matching between PSB and PS, orbit correction...

Careful control of the working point to avoid blow-up during the long flat-bottom Qh ~ 6.21 and Qv ~

6.23

A single-bunch head-tail instability (due to the resistive wall-impedance) develops during the long

flat-bottom => it is cured by x-y coupling (skew quadrupoles)

2nd injection => 3 bunches (H7) => 3 + 3 = 6 bunches (H7)

Momentum adaptation PSB-PS => PSB synchro. made with PS beam Triple splitting => 6 × 3 = 18 bunches (H21)

Acceleration from 1.4 to 25 GeV

on H21

At transition : -jump + change of the chromaticities sign

Inj 42 at C170

Inj 42 at C1370

3 groups of C10 cavities on H7,14,21

C1380

C1560 C145022 Gauss/ms

PS (2/10)PS (2/10)


Time (20 ns/div)

R signal

Beam-Position Monitor(20 revolutions superimposed)

6m

PS (3/10)PS (3/10)

)10(Intensity 10

[ms]Time

Head-Tail resistive-wall instability

A33.0skewI

A4.0skewI


Longitudinal coupled-bunch instabilities between 6 and 20 GeV/c cured by controlled longitudinal blow-up

Horizontal orbit correction => PR.GSDHZ15,60-OC

At high energy (26 GeV/c momentum)

Synchronisation H1 => the worst

1st double splitting => 18 × 2 = 36 bunches (H42)

2nd double splitting => 36 × 2 = 72 bunches (H84)

Bunch compression by a step voltage

=> longitudinal mismatch

=> bunch rotation and ejection after 1/4 of synchrotron period

Ejection at 26 GeV/c

fast extraction towards the SPS through the TT2/TT10 transfer line

1 cavity C20

1 cavity C40

eVs35.0lns16b ns4b

1 cavity C40 (H84)2 cavities C80 (H168)

with

Cavities C200 (H420)

Ej 16 at C2395

It will change this year=> new high-energy timings

PS (4/10)PS (4/10)C2120


-100

0

100

200

300

400

500

600

700

800

900

1000

100 600 1100 1600 2100

Time [ms]

0

2000

4000

6000

8000

10000

12000

14000

I [e10]

B [Gauss]

inj1 +10msC180

inj2 -10msC1360

inj2 +5msC1375

ej -6msC2389

[ms]Time

PS (5/10)PS (5/10)

Magnetic field and double-batch injection

No 3.5 GeV/c plateau


ns/div300

ns/div30

ns/div1

PS (6/10)PS (6/10)Longitudinal beam structure in the last turn of the PS


0

0.5

1

1.5

2

2.5

3

3.5

0 500 1000 1500 2000 2500Time [m s]

H54

H64

V75

V85

PSB output(SEM grids in meas.line)

BAD

GOOD

2nd batchinjection

1st batch injection 1.4-25GeVacceleration

PS output(SEM grids inTT2 line)

without bunch rotation!

PS (7/10)PS (7/10)

Normalised transverse emittances at 1


Only 1 measurement is still missing the transverse emittances in TT2 in the presence of bunch rotation

H - plane V - plane

Emittance measurements using the Semfils in TT2 without bunch rotation

PS (8/10)PS (8/10)


Emittance measurements using the Semfils in TT2 with bunch rotation

H - plane

=> Electrons are created ...

PS (9/10)PS (9/10)


Without solenoid

With solenoid~ 50-100 G

Also observed in the PS

Apparently the beam is not affected this is only a measurement

problem for the PS (contrary to the SPS and LHC)

PS (10/10)PS (10/10)Baseline drift on electrostatic pick-ups in TT2


Future workFuture work The nominal beam is within reach, but one item is missing the quantitative

analysis of the non-linear effects due to the stray-field at PS extraction. It could

create an optical mismatch blow-up

4 other subjects need to be investigated in the near future

Consolidation of the nominal beam improvements in pulse-to-pulse injection mis-

steerings, kicker ripples, PSB-PS transverse and energy matching, bunch to bunch

intensity fluctuations, instrumentation…

Multi-gap/multi-spacing beams preparation for SPS MDs (e.g. 50 and

100 ns bunch spacing). In particular, cures for longitudinal instabilities have to be

investigated (feedback systems, HOM damping)

The so-called initial beam should be prepared

good for collective effects

bad for injection mis-steerings => damper at injection certainly useful

The so-called ultimate beam should also be looked at 1/6 of the intensity, 1/4 of the transverse emittance

1.6 the intensity


SPS and LHC filling (1/4)SPS and LHC filling (1/4) The cycle will consist of either 3 or 4 PS injections at 3.6 s intervals

3-batch 2.38 1013 protons in 26% of the SPS circumference

4-batch 3.17 1013 protons in 35% of the SPS circumference

The injection plateau will therefore lasts up to 10.8 s

The acceleration phase is about 8.3 s and brings the beam from 26 GeV/c to 450

GeV/c

A 1 s flat-top is presently assumed. This will be used to prepare the extraction

equipment (bumpers, etc...) and perform any RF re-phasing necessary to put the

beam on the correct location in the LHC

SPS issues

Collective instabilities in both longitudinal and transverse planes

programme for impedance reduction + electron-cloud studies

Fast extraction towards the LHC through TI2 (via the West extraction channel)

or TI8 (via the new East extraction channel)


This cycle is repeated 12 times for each LHC ring. 3 or 4-batch cycles

will be interleaved in the form 334 334 334 333 to fill each ring with a

total of 2808 bunches. The LHC filling time will be 12 21.6 s = 4.3

minutes per ring

SPS and LHC filling (2/4)SPS and LHC filling (2/4)

LHC Proton Injection Cycle (21.6 s)



Bunch disposition in the LHC, SPS and PS



The same Main Timing Generator will be used to pilot the PS complex,

SPS and LHC

Several levels of super-cycles will be introduced

642216

16 SPS levels

2 PS levels for each SPS level

Normal + spare

requirements of the lhc on its injectors what are the nominal & already achieved beams at ps...

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