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E.M, PS-OP shut-down lectures, 20/02/ Requirements of the LHC on its injectors (2/3) Choice of the nominal LHC parameters
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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
E.M, PS-OP shut-down lectures, 20/02/2001 2
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 fekNNL
1,
,
Brightness = transverse bunch densityBeam current
E.M, PS-OP shut-down lectures, 20/02/2001 3
Requirements of the LHC on its injectors (2/3)Requirements of the LHC on its injectors (2/3)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
E.M, PS-OP shut-down lectures, 20/02/2001 4
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)
Requirements of the LHC on its injectors (3/3)Requirements of the LHC on its injectors (3/3)
Major upgrade needed all along the injector chain
E.M, PS-OP shut-down lectures, 20/02/2001 5
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
E.M, PS-OP shut-down lectures, 20/02/2001 6
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
E.M, PS-OP shut-down lectures, 20/02/2001 7
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
E.M, PS-OP shut-down lectures, 20/02/2001 8
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
E.M, PS-OP shut-down lectures, 20/02/2001 9
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)
E.M, PS-OP shut-down lectures, 20/02/2001 10
SynchronisationNon-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
ns327ns28678t
78t 8h7h
PSPS
C805
PSB (3/5)PSB (3/5)
E.M, PS-OP shut-down lectures, 20/02/2001 11
X & Y shavers
[ms]Time
)10(ringIntensity/ 10
PSB (4/5)PSB (4/5)
E.M, PS-OP shut-down lectures, 20/02/2001 12
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
E.M, PS-OP shut-down lectures, 20/02/2001 13
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
E.M, PS-OP shut-down lectures, 20/02/2001 14
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)
E.M, PS-OP shut-down lectures, 20/02/2001 15
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
E.M, PS-OP shut-down lectures, 20/02/2001 16
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
E.M, PS-OP shut-down lectures, 20/02/2001 17
-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
14000I [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
E.M, PS-OP shut-down lectures, 20/02/2001 18
ns/div300
ns/div30
ns/div1
PS (6/10)PS (6/10)Longitudinal beam structure in the last turn of the PS
E.M, PS-OP shut-down lectures, 20/02/2001 19
0
0.5
1
1.5
2
2.5
3
3.5
0 500 1000 1500 2000 2500Time [m s]
H54H64V75V85
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
E.M, PS-OP shut-down lectures, 20/02/2001 20
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)
E.M, PS-OP shut-down lectures, 20/02/2001 21
Emittance measurements using the Semfils in TT2 with bunch rotation
H - plane
=> Electrons are created ...
PS (9/10)PS (9/10)
E.M, PS-OP shut-down lectures, 20/02/2001 22
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
E.M, PS-OP shut-down lectures, 20/02/2001 23
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
E.M, PS-OP shut-down lectures, 20/02/2001 24
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 issuesCollective 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)
E.M, PS-OP shut-down lectures, 20/02/2001 25
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)
E.M, PS-OP shut-down lectures, 20/02/2001 26
SPS and LHC filling (3/4)SPS and LHC filling (3/4)
Bunch disposition in the LHC, SPS and PS
E.M, PS-OP shut-down lectures, 20/02/2001 27
SPS and LHC filling (4/4)SPS and LHC filling (4/4)
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