The LHC as a proton-nucleus collider: Status and plans John Jowett Special thanks to: R. Alemany-Fernandez, P. Baudrenghien, C. Carli, E. Carlo-Giraldo, S. Hancock, R. Jones, D. Manglunki, J. Wenninger, and many others in ABP, BI, OP, RF groups. 1 J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011 p Pb
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The LHC as a proton-nucleus collider: Status and plans John Jowett
Pb. p. The LHC as a proton-nucleus collider: Status and plans John Jowett. Special thanks to: R. Alemany -Fernandez, P. Baudrenghien , C. Carli, E. Carlo- Giraldo , S. Hancock, R. Jones, D. Manglunki, J. Wenninger , and many others in ABP, BI, OP, RF groups. Plan of talk. - PowerPoint PPT Presentation
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The LHC as a proton-nucleus collider:
Status and plansJohn Jowett
Special thanks to:R. Alemany-Fernandez, P. Baudrenghien,
C. Carli, E. Carlo-Giraldo, S. Hancock, R. Jones,D. Manglunki, J. Wenninger,
and many others in ABP, BI, OP, RF groups.
1J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011
pPb
Plan of talk Brief history The revolution frequency problem– Moving long-range beam-beam effects
Status of preparation of LHC systems Feasibility test in 2011– Goals– Possible bonus: some physics
Possible p-Pb run in 2012
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011 2
3
Before Jan 2011: Vox clamantis in deserto Not part of “LHC Baseline” … no resources. CERN Workshop in 2005 (link)
– Physics case, experiments’ performance, …– Reviewed RHIC experience with d-Au in 2002-3 (T. Satogata)– Schemes for LHC injector operation (C. Carli)– LHC operation, beam dynamics concern identified (JMJ)– Executive summary of accelerator part (in 2011 report)
LHC Project Report 928 (= paper at EPAC 2006) Key systems groups kept aware meanwhile
– Eyes open for any showstoppers Requested by ALICE for 2012
– First Pb-Pb run successful. If not 2012 then would otherwise be much later because of shutdown schedule, energy increase.
– Discussion at Chamonix workshop, Jan 2011. – ATLAS and CMS heavy-ion groups– Some resources now available:
OP, RF, BI, … collaborating on implementation and operation Fellow to work on beam dynamics in ABP arrived … today
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011 4
Relation between Beam Momenta LHC accelerates protons through the momentum
range
– Use this as reference, measure of magnetic field in main bending magnets
The two-in-one magnet design of the LHC (unlike RHIC) fixes the relation between momenta of beams in the two rings
0.45 TeV (injection from SPS) 7 TeV (collision)pp
Pbp
where 82, 208 for fully strippe
d Pb in LHCQ Z
p p
AZ
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011
5
Critical difference between RHIC and LHC
RHIC: Independent bending field for the two beams
LHC: Identical bending field in both apertures of two-in-one dipole
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011
6
RF Frequency for p and Pb
RFRF
p
RF RF
RF frequency , ,
where the harmonic number , 35640 in LHC
hfT p m Q
h h
RF frequencies needed to keep p or Pb on stable central orbit of constant length C are different at low energy.
No problem in terms of hardware as LHC has independent RF systems in each ring.
fRF(Pb)
fRF(p)
Which is Beam 1 and which is Beam 2 ? Initial preference for ALICE spectrometer
asymmetry:
Beam 1=p, Beam 2=Pb
Assume this for definiteness in rest of this talk.
But switching of the beams between the two rings is important and requested– Clearly equally feasible, just some setup time
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011 7
Distorting the Closed Orbit
2
pp
p
p
2p
2 2
, , 1
( )where is a fractional momentum deviation and
the phase-slip factor , 1 , 55.8 for LHC optics.
Moves beam on
1 1
to off-momentum orb
(
it,
1 )
l
TT
C mcT p m Qc Qp
p QpQp
Qpmc
onger for 0. Horizontal offset given by dispersion: .xx D s
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011 8
Additional degree of freedom: adjust length of closed orbits to compensate different speeds of species.– Done by adjusting RF frequency
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011
9
Momentum offset required through ramp
22 22Pb
p Pb p2 2p
Minimise aperture needed by .4T mc m
p Z
Limit in normal operation (1 mm in arc QD)
Limit with pilot beams
Revolution frequencies must be equal for collisions at top energy.Lower limit on energy of p-Pb collisions, E=2.7 Z TeV. RF frequencies must be unequal for injection, ramp!Moving long-range beam-beam encounters may be a problem (cf RHIC).
2% - would move beam by 35 mm in QF!!
Wolfram Fischer
10
Example – beam lifetimes with (Br)d = (Br)Au 2003
beam-beam effect during injection, d and Au with same rigidity, frf = 44 kHz, vertical separation=10mmAside: RHIC is the 1st bunched beam hadron collider exhibiting strong-strong effects [W. Fischer, et al., “Observation of Coherent Beam-Beam Modes in RHIC”, BNL C-A/AP/75 (2002)]
Beam envelopes around ALICE at injection
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011
11
Crossing angle from spectrometer and external bump separates beams vertically everywhere except at IP (also in physics). Parallel separation also separates beams horizontally at the IP during injection, ramp, squeeze.Other experiments vary ..
ALICE – Separation at injection - CMS
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011
12
ATLAS - Separation at injection - LHCb
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011
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Long-range beam-beam effects
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011
14
,
2 20 0
02 2
For separations , , the (angular) beam-beam kick on a particle of charge , due to an opposing
, where / (4 )
and gives rise to
2 ( , )
beam of total charge
pertu
(
,
i
)
sx y
x yZNr x y r e mc
x yZ
p p
e
x y
e N
ò
2 2, 0
, , , 2 2 2
rbative betatron tune-shi
( , )(
fts
)4 ( )
2x y x y
x y x y x y
x yZNrQ px y
LHC separation configurations were chosen to minimise the tune effects in physics (“footprint”).
Example: beam-beam for Pb around ALICE
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011
15
Dashed lines are “normal” position of encounters which will move 15 cm along IR on next turn …
Overlap knock-out resonances ?
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011
16
,
Bunch harmon
p Pb
1,2,transve
icrse mode
,
s
Encounter points move at speed 1734 m/s 0.15 m/turn2Hamiltonian is no longer periodic in .
Excites modulational resonances
x y
x x y y
m
v vV
s
m Q m Q p k
6
p Pb
3. 10 at injection,decreases in ram
891 or at most 3564
p
; , , ,
Known as "overlap knock-out resonances" at the ISR.
However with LHC tunes, 64.3, 59.3, only ext
2
remely
x y
x x
m m p kv
Q
v
Q
c
high-order resonance conditions can be satisfied. (similar in RHIC, W. Fischer).
We are nevertheless looking at calculations of driving termVery unlikely
s, compensatio
to
n b
be a problem
etween
IRs, etc.
Diffusion models Naively regarding the kicks as purely random
– Works fairly well for RHIC data (W. Fischer)
Better calculate combination of beam-beam kicks on a particle on a given turn as the encounters move– Add them up with proper betatron phases
Partial compensations– Take out static component (closed-orbit) from long-term
averaging and look at fluctuations around it– RMS fluctuation gives emittance growth rate ?– Other resonant effects?
Work ongoing
Assuming pseudo-random Spectral analysis can confirm Implement detailed collision schedule
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011 17
2, 2
0 , ,1 1 ( ) ( )2
where [..] denotes mean-square deviationgives an emittance doubling time around 40 min
x ynx y x y
df s p s
dt
Build of beam-beam kicks around ring
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011
18
Horizontal and vertical, kicks represented in normalised betatron phase space.On a turn where encounters occur at the usual IpsOn later turns the resultant is different.
Variation over ~100 turns
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011
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J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011 20
Transverse Feedback 4 independent systems, 1 per plane and per ring High bandwidth to act on individual bunches Located in IP4, so no concerns about timing of p-
Pb bunch passages. Potentially very important for p-Pb: – Damping any coherent oscillations driven by
the coherent dipole kicks from moving beam-beam encounters at injection and during ramp
Inject p beam in Ring 1, fRF for p– Orbit, ramp established in advance
Inject Pb beam in Ring 2, fRF for Pb– Orbit, ramp established in advance
Ramp both beams on central orbits – Orbit feedback decouples RFs
Rephase RF and bring fRF together to lock Squeeze, collide, (almost) as usual Pb-Pb
– Preliminary off-momentum set-up for 3.5 Z TeV?
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011 21
Review of LHC systems RF (P. Baudrenghien, A. Butterworth)
– Independent for two rings, OK– Decouple radial control
Transverse Damper (ADT) (D. Valuch, W. Hofle)– Independent for two rings, OK– Possible variable Q reference should be OK
Beam instrumentation (R. Jones, E. Giraldo, …)– Common BPMs identified as main concern at LMC50 –
later slide– All other BI independent for two beams
Orbit and tune feedback – very important– Looks OK (J. Wenninger, R. Steinhagen)
Q/Q' systems are independent for both beams Orbit feedback does not use common BPMs Need to decouple radial control Check possibility of variable Q reference ?
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011 22
Collimation – Settings according to beam, mostly separate
– IR2 vertical tertiary collimators (TCTVs) require special consideration ALICE zero-degree calorimeter (ZDC) shadowing with
present location, we have to minimise real crossing angle
IR2 modification (see LMC 79) to move (new) TCTVs behind ZDC should be done for 2012 p-Pb run, otherwise may have to request open TCTs L2 (for incoming proton beam, as for Pb beam in 2010-11) – machine protection ?
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011 23
BPMs (from Eva Calvo Giraldo, Rhodri Jones) BPM sensitivities for B1 and B2 are completely
independent (no limit of p intensity from this) Strip-line monitors can have two types of issues: – Both beams cross exactly at the same time
Located so cannot happen with 100 ns once the frequencies are cogged.
While frequencies separate, both beams will sometimes cross BPM at same time. – Then orbit can have errors 5.5 mm (10% bunch
intensity ratio, unlikely), or ~1 mm (50% bunch intensity ratio, more likely).
– False triggers: see next slide …
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011 24
BPMs (continued)– False triggers: – possible for bunch intensities close to the high end of
each sensitivity mode range (B2 port of monitor sees B1-induced signals), can trigger acquisitions in the wrong channel, degrading orbit precision.
– Nevertheless with bunch intensities of 1e10 p/bunch and ~6e9 charge/bunch, there will be no false triggers.
Common BPMs: disabled on the orbit feedback system most of the time. – Only used in squeeze.
Ghost bunches: – Simulations showed that they could lead to an
error of up to ~120 μm. (More detail in notes from E. Giraldo)
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011 25
Machine Protection (preliminary!) Most protection issues dealt with independently in
the two rings, either for p or Pb Eg, either beam becomes unstable, losses
Injection: must avoid trying to inject wrong beam in wrong ring– Since SPS is phase-locked, impossible to pass
momentum acceptance of transfer lines– Protect SPS and transfer lines with software
interlocks – detailed scheme being implemented
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011 26
Injection Nominal Pb beam has 592 bunches, 100 ns
minimum bunch spacing p-Pb collisions in LHC will be done with a special
proton filling scheme, designed to match the Pb beam – Other p-p schemes are different– Schemes worked out in 2005 by K. Schindl and
C. Carli– This beam is now ready in the injectors (S.
Hancock et al in PS) Useful flexibility in bunch intensity available
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011 27
System Status Date for test Possible issuesBPM - BPM sensitivities for B1 and
B2 are completely independent.- Two independent RF systems used to trigger BPMs
1 . Both beams cross exactly at the same time in these monitors Issue only until cogging is doneSolution: disable common BPMs until cogging is done 2. False triggers: NO with bunch intensities of 1e10 p/bunch (p+)and ~6e9p/bunch (Pb)
RF RF settings completely independent for each ring
RF Rephasing 28.08.2011 (MD3) Last test in Oct 2010 showed high beam losses during rephasing
Feedback Fully decoupled radial loop - p+p+: 05.09.2011 (Start up after TS)- p+Pb: MD4 Nov
Interlocks for MP Protect TL&LHC from wrong particle injection
- 28.08.2011 (MD3)- SIS interlock by Jorg in place- Injection line TT10 settings consistent after TS
Timing: Particle type & Accelerator Mode
-Two telegram words to define the circulating particle type: Proton, Pb82, Ar18, D, Xe54 - Accelerator Mode: PROTON ION PHYSICS
- In place after the September TS
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011 28
From R. Alemany
Proton-lead feasibility study in 2011 Remarks:– This is a new way to operate LHC, very little
previous experience in other hadron colliders– We do not know if it will work!
Could be strongly limited in intensity/luminosity No resources for study (will change on 15/10/2011) Discussed at CERN Machine Advisory Committee
p-Pb filling Beam 1: 100 ns proton beam, ~1010 p/bunch– Should be something close to Nominal Pb
scheme Beam 2: start with a few (probably 2) Pb bunches
for MP reasons– If we succeed in ramping and manually re-
phasing the RF, this could give 1 (or 0) collision/turn in each experiment
– More than this is unlikely but not impossible– Need to clarify conditions for declaring Stable
Beams
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011 30
Potential luminosity In 2011 feasibility test
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011 31
20 0 Pb
2Pb
26 -2 -1 8 10
44 *10 cm s (1 colliding bunch, ~10 Pb/bunch, ~10 p/bunch
nominal emittance 1.5 m)but some emittance blow-up, intensity loss likely,
c Pb p b b
n
k N N f k N fL
5
combined factor 3 ?1.8 barn
10 events/h ?
Possibly higher if we have time to try some bunch trains.
Potential luminosity (2) In possible 2012 physics run at 3.5 Z TeV
But we should really wait until after the feasibility test to say anything meaningful.– (With extreme optimism, using full proton
intensity we can dream of factors ~15 more …).
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011 32
20 0 Pb
2Pb
28 -2 -1 8 10
44 *3 10 cm s (~300 colliding bunch, ~10 Pb/bunch, ~10 p/bunch
nominal emittance 1.5 m)but reduction factors almost certainly apply
c Pb p b b
n
k N N f k N fL
Accessible energies and CM rapidities
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011
33
p-p Pb-Pb p-Pb / TeVE 0.45-7 287-574 (2.7-7,287-574)
/ TeVNE 0.45-7 1.38-2.76 (2.7-7, 1.38-2.76)
/ TeVs 7-14 73.8-1148 48.9-126.8
NN / TeVs 7-14 0.355-5.52 3.39-8.79
CMy 0 0 -2.20
NNy 0 0 +0.46
p p
p P b
P b P b
0 1 2 3 4 5 6 70
2
4
6
8
1 0
1 2
1 4
p p T eVc s N
NTeV1 2
1 2
1 2
1 2
1 2
Charges , in rings with magnetic field set for protons of momentum
2 ,
1log2
p
NN p
NN
Z Zp
Z Zs c pA A
Z AyAZ
Possible range of collision energiesMinimum p-Pb energy for equal revolution frequency.Relations between these numbers are a simple consequence of the two-in-one magnet design
Commissioning and run schedule Different from 2010, now available and will be
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011
35
Set up p beam, Pb injection, test injection of Pb on p (2 shifts designated MD)
Time to think … review p-Pb
Set up ALICE squeeze with protons, aperture measurement
Test ramp of p-Pb, while p still available from injectors, possible collisions
Use of physics time for MD will of course be minimised, but this is a very tight schedule.
Pb beam, ramp, squeeze, crossing angles, collimation in two instalments
Conclusions (1) Operational cycle for physics taking shape Matching p beam ready in injectors– Flexibility on intensity available
Check-out of all LHC systems complete– No showstoppers for p-Pb
Machine protection, ~OK Main uncertainty remains beam dynamics– Overlap knock-out resonances very unlikely to
be a problem– Possible diffusive emittance growth ?
Studies advancing …
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011 36
Conclusions (2) Feasibility test this year is crucial– Plan carefully, interleaved with Pb-Pb
commissioning– New, more complicated mode of LHC operation– Risks of being cut short by limited time …
We must be very cautious about projections for 2012– Today’s discussion could usefully define
minimum performance acceptable for physics Go-ahead from Chamonix workshop ?– 6-10 February 2012
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011 37
A second opinion: CERN Machine Advisory Committee, August 2011
J.M. Jowett, Workshop on Prospects of p-Pb collisions during the 2012 LHC HI run, CERN 17/10/2011
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Possible Proton Lead running in 2012 Findings:Asymmetric proton-lead operation is considered for 2012 pending a successful test at the end of 2011. In the test it is planned to demonstrate injection and acceleration of the proton and lead beams with unequal revolution frequencies, a condition necessitated by the equal magnetic fields in both rings due to the 2-in-1-magnet design. The checkout of all system (rf, instrumentation, collimation, machine protection) is almost complete, and no showstoppers were found. Perhaps most importantly the test will also allow evaluating the beam dynamics issues stemming from unequal revolution frequencies, which have been found detrimental in RHIC when operating under such conditions.Comments:The dominating beam dynamics effect from unequal revolution frequencies is likely emittance growth due to the modulated long-range beam-beam interactions. Estimates for RHIC for d-Au operation with unequal revolution frequencies give a time to double the emittance of order minutes. Applying the same analysis to the LHC case one would expect an emittance growth effect that is an order of magnitude smaller with the proposed bunch intensities.With the detailed LHC calculations to estimate the emittance growth completed, comparison with the measured emittance growth in the planned test will be possible. Since an order of magnitude more protons are available than requested for the physics program, the detrimental effects on the lead beam can be enhanced and evaluated over a wide intensity range.