THE LHC PROTON BEAM
E&G Métral
PS-OP shut-down lectures, 1/02/2002
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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
 PSB
 PS
LHC beam in 2001
Future work
1 february 2002
1
Requirements of the LHC on its injectors
Choice of the nominal LHC parameters
Energy
E [TeV]
Dipole field
B [T]
Luminosity
-2 -1
L [cm s ]
Harmonic number
h
Number of bunches
kb
Protons / bunch
Nb
Bunch spacing
b.s [ns]
emittances
x&y
norm,1
 x, y
[m]
Long. emittance
 l2  [eVs]
1 february 2002
7
8.3
1034
35640
2808
1.11011
25
3.75
0.5  1
2
Requirements of the LHC on its injectors

LHC project leader  L. Evans
 Major upgrade needed
all along the injector chain
1 february 2002
3
What are the nominal & already achieved beams at PS exit?
Achieved
25
Nominal
25
84
84
72
72
1.11011
1.11011
25
25
2.5
3
Long. emittance
 l2  [eVs]
0.35
0.35
Total bunch length
b [ns]
Momentum spread
2 p/p
4
4
2.210-3
2.210-3
Energy
E [GeV]
Harmonic number
h
Number of bunches
kb
Protons / bunch
Nb
Bunch spacing
b.s [ns]
emittances
x&y
norm,1
 x, y
[m]
 The specifications are met in the PS complex
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How is it obtained in the PS complex?
General aspects
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Main challenges
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High brightness & very short bunches
Solutions
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Double-batch filling of the PS  Lowers the space charge effects at PSB

Increase of the PS injection energy  Lowers the space charge effects at PS
injection
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Multi splittings => bunch number, bunch spacing & emittance
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Bunch rotation to produce the desired bunch length
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PSB
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General aspects for PSB
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2 consecutive cycles (LHC, TSTLHC)
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1 bunch per ring (H1)
Different possibility to fill the 6 buckets of the PS
2 PSB rings + 4 PSB rings, 2 times 3 PSB rings, 4 PSB rings + 2 PSB
rings
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Multi-turn injection : 3 turns exactly (for homogeneous longitudinal
distribution)
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Special tune due to large tune shift
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Double harmonics operation (bunch flattening) => decreases the space
charge tune shift at injection
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Available controlled blow-up  C16 (H9)
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No coupling between the transverse planes
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Standard settings of multipoles for resonance compensations
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Transfer PSB PS
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C805
Synchronization
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Non-standard bunch spacing at ejection to fit the PS H7 RF system
t

PS
h 7
TrevPS 2290


 327 ns
7
7
Adjustment with the phase offsets : BAx.PSYNCOFFSET (ring 3 is always
used as the reference)

Remember that the Timing used in that process is in H8

more difficulties to adjust the timing for the synchronization & for the
instrumentation
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Ejection at 1.4 GeV

fast extraction towards the PS through the BT/BTP transfer line
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PSB
Beam parameters at PSB extraction
Protons / bunch
1 february 2002
Achieved
Nominal
1.4  10 12
1.32  10 12
Hor. emittance
 xnorm,1 [m]
2 .2
2 .5
Ver. Emittance
 ynorm,1 [m]
1 .8
2 .5
Long. emittance
 l2  [eVs]
1.4
1 .5
Tot. bunch length
 b [ns]
195
Momentum spread
2 p / p
-3
(10 )
2.2
195
2.45
8
PS
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General aspects
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Double-batch injection : separated by 1.2 s  6 bunches out of 7 buckets

Longitudinal beam slicing  complicated RF gymnastics
PSB exit
PS exit
~ 300 ns

High brightness conservation  careful control of collective effects,
injection
oscillations, working
point,
chromaticity,
non-linearity
extraction…
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at
PS 1.4 GeV kinetic energy
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At low energy
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Inj42 at C170
1st injection => 2 or 3 bunches (H7)
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Transverse matching between PSB and PS, orbit correction...
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RF phase adjustment (PA.PDISC-H7)
adjusted from the CB if the PSB extraction phase is correct
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Working point during the long flat-bottom  Qh ~ 6.21 and Qv ~ 6.23
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RMS current on low energy power supply
Inj42 at C1370
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2nd injection => 3 or 4 bunches
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(after the first batch )
Momentum adaptation PSB-PS => PSB synchro. made with PS beam
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Same frequency sent to the PSB for the same MRP as the first
injection one & same PS magnetic field
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RF phase adjustment (PA.PDISC-H7)
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PS 1.4 GeV kinetic energy
Head-Tail resistive-wall instability
Intensity (1010 )
Beam-Position Monitor
(20 revolutions superimposed)
R signal
I skew  0.33 A
Time [ms]
Time (20 ns/div)
m 6
1 february 2002
I skew   0.4 A
11
PS
Remember that the
Timing of the second injection
can also be adjusted by
the Timing_f_t program
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12
PS 1.4 GeV kinetic energy
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1.4 Gev after second injection
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Triple splitting
6 × 3 = 18 bunches
H7 to H21
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C1563
PS Acceleration
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At transition : -jump + change of the chromaticity sign
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Longitudinal coupled-bunch instabilities between 6 and 20 GeV/c cured by
controlled longitudinal blow-up
Cavities 200MHz
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From 20 to 26 GeV/c, horizontal orbit correction => PR.GSDHZ15,60-OC
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At high energy (26 GeV/c momentum)
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Synchronization H1 => the worst
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1st double splitting => 18 × 2 = 36 bunches (H42)
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2nd double splitting => 36 × 2 = 72 bunches (H84)
1cavity 20MHz
1 cavity 40MHz
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PS ejection
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Orbit correction during the Bump
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Bump compensation in the RF phase loop system
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New ABS interface with virtual GFAs
Without, the phase loop is not strong enough
1 cavity 40 MHz (H84)
2 cavities 80 MHz
Bunch compression by a step voltage
=> longitudinal mismatch
=> bunch rotation and ejection after 1/4 of synchrotron period
Ej 16 at C2395
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Ejection at 26 GeV/c
 fast extraction towards the SPS through the TT2/TT10 transfer line
 b  16 ns
1 february 2002

 b  4 ns
with
 l  0.35 eVs
15
Inj at C169.8
PS
Inj2 at C1369.8
Ej at C2395
1000
15000
1011Gauss at C160
B up at C1450
Transition at C1563
12576Gauss at C2120
900
13000
800
11000
600
9000
500
7000
400
Gauss
protons nbr (e10)
700
5000
300
200
Blow up2
C1725=>C1825
3000
100
1000
0
Triple split.
C1375 =>C1400
-100
100
Blow up1
C1400=>C1440
-1000
600
1100 Time [ms]
1600
2100
I [e10]
B [Gauss]
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PS
Lock of a
frequency source
on the BEAM
PAX.SSYNCH1INT
C2141
Start sync SPS
Synchro H1
PAX.SD1SYNCSPS
C2155
Start PL H84
C2363
Start fine sync
Synchro H21
PAX.SD2SYNCSPS
C2365
Start PL H42
C2318
350
13000
300
Ej at C2395
250
100
B(Gauss)
V gp4
200 V gp5
V C20
150 V C40
V C80
b
50
0
2000
2050
2100
Start first
Double split.
Start cavity 20MHz
C2258
1 february 2002
2150
2200
2250
2300
End cavity 10Mhz
Start cavity 40mhz
C2338
2350
10000
2400
End cavity 20Mhz
Start GFA cavity 80mhz
C2388
17
PS
Start of the
bunch rotation process
Synchro with
The extraction
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18
PS
Ej at C2395
Start of the bump16
Start of PA.GSCOMP-BSW16
Ej –7.5ms = C2387.5
350
External restart For
PA.GSV40 & PA.GSV80
By PAX.SBRH84
Ej –5.3ms = C2389.7
300
250
200
V C20
150 V C40
V C80
100
50
0
2380
2382
2384
End cavity 20Mhz
Start GFA cavity 80mhz
C2388
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2386
2388
2390
2392
2394
2396
Start cavity 80mhz
~ ej –100us
19
PS RF signals during extraction process
Phase discri H21
Phase discri H42
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1 february 2002
Other important signals on NAOS
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PA.PDISC-H84
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PA.SYNCDISC-H21
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PA.GSCOMP-BSW16
20
PS
Longitudinal beam structure in the last turn of the PS
300 ns/div
30 ns/div
1 ns/div
1 february 2002
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PS
Only 1 measurement is still missing  the transverse emittances in
TT2 in the presence of bunch rotation
Emittance measurements using the Semfils in TT2
without bunch rotation
H - plane
1 february 2002
V - plane
22
PS
Baseline drift on electrostatic pick-ups in TT2
Also
observed
in the PS
Without
solenoid
With
solenoid
~ 50-100 G
Apparently the beam is not affected  this is only a measurement
problem for the PS (contrary to the SPS and LHC)
1 february 2002
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SPS and LHC filling
LHC Proton Injection Cycle (21.6 s)
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
1 february 2002
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SPS and LHC filling
Bunch disposition in the LHC, SPS and PS
1 february 2002
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LHC Beam in 2001

Blow up on the PSB machine
 Better low energy process in the PS machine
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New synchronization at extraction implemented
 Bunch stability better than 0.5ns at ejection (only measurable in CB)
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Better splitting at 26GeV/c (phase loop)
 Bunch to bunch intensity fluctuations <10% as required
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Coupling measurements at different energies
 H/V coupling at transition (tune crossing)
 H/V coupling at 26GeV/c
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50 ns bunch spacing done
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Ultimate beam done
1 february 2002
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LHC Beam in 2002
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New B train (at the start up)
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Magnetic cycle to be reviewed
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LHC beam must be the first operation
Working point at low energy

Suppress the ripple on the PFW GFAs
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TTSM (type EPTTSM) to monitor the phase stability at extraction
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Test of a fast LHC cycle in the PS
1 february 2002
27
Fast LHC cycle
2.4 s - 26 GeV/c cycle for double-batch injection in the PS
14000
B new
B Actuel
26 GeV/c flat-top
240ms (-15ms)
12000
Magnetic field [Gauss]
1st inj
C160
2nd inj
C840
eject
C1710
end of cycle
C2370
10000
8000
1st inj
C170
2nd inj
C1370
eject
C2395
end of cycle
C2350
6000
4000
2000
0
0
1200
2400
3600
time [ms]
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To find documentation
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This file
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N:\Psop\Doc\PS\Presentation\LHCBeam2002.ppt
 All the MD measurements
 N:\Psop\Archives\data\PS\&MDs\Lhc

Beam reference on the WEB

http://srv1ps/psop/cps/BeamRef/lhc/
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