IR and Beam-beam

1
IR and Beam-beam

• Tanaji Sen
• October 6, 2005

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Topics

• IR optics designs
• Energy deposition calculations
• Beam-beam experiment at RHIC
• Strong-strong beam-beam simulations
• Future plans

3
Effort on IR designs

• Main motivation is to provide guidance for magnet
  designers
• Example aperture and gradient are no longer
  determined by beam optics alone. Energy
  deposition in the IR magnets is a key component
  in determining these parameters
• Use as an example for field quality requirements
• Examine alternative scenarios
• Not intended to propose optimized optics designs

4
IR designs

• Quadrupoles first extension of baseline
• Dipoles first triplet focusing
• Dipoles first doublet focusing

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Triplet first optics
Lattice Vers. 6.2
Nominal ß 0.5
ß 0.25
J. Johnstone
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Gradients, beta max quads first optics
Quad BT/m Left BT/m Right ßmaxm Left ßmaxm Right
Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 Q9 Q10 QT11 QT12 QT13 -200 200 -200 82 -67 59 -199 150 -164 184 57 -43 -40 -Q1.L -Q2.L -Q3.L -Q4.L -Q5.L -58 199 -155 166 -193 -56 -55 -QT13.L 4537 9189 9333 9440 3322 1559 984 285 241 291 141 170 176 4545 9205 9350 9424 3327 1561 986 285 261 270 154 179 174
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Dipole first optics
Additional TAS absorber in the present layout
per N. Mokhov
IP
D1a
TAS2
D1b
TAN
Earlier layout (PAC 03) Present layout
D1 dipole TAN absorber ß ßmax 10m long After D1 0.26 m 23 km D1a 1.5m long, D1b 8.5m long TAS2, after D1a TAN after D1b 0.25 m 27 km
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Dipoles First - Matching

• Beams in separate focusing channels
• Matching done from QT13(left) to QT13(right)
• Lattice Version 6.2
• Triplet quads Q1 Q3 at fixed gradient 200
  T/m, exactly anti-symmetric
• Positions and lengths of magnets Q4-QT13 kept the
  same
• Strengths of quads Q4 to Q9 lt 200 T/m
• Q10 on the left has 230 T/m. Could be changed
• if positions and lengths of Q4-Q7 are
  changed.
• Trim quad strengths QT11 to QT13 lt 160T/m

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Dipole first collision optics, triplets

• TAS1 absorber (1.8m) before D1a
• Dipole D1a starts 23 m from IP
• TAS2 absorber (1.5m) after D1a
• 0.5m space between D1a-TAS2
• and TAS2-D1b
• L(D1b) 8.5m
• D1, D2 each 10m long, 14T
• 5m long space after D2 for a
• TAN absorber
• Q1 starts 55.5 m from the IP
• L(Q1) L(Q3) 4.99 m,
• L(Q2a) L(Q2b) 4.61m

Collision optics ß 0.25m
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Gradients, beta max dipoles first, triplets
Quad BT/m Left BT/m Right ßmaxm Left ßmaxm Right Coil aperture 2(1.19s8.64.53) mm
Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 Q9 Q10 QT11 QT12 QT13 -200 200 -200 78 -104 80 -146 107 -92 230 170 161 -158 -Q1.L -Q2.L -Q3.L -112 137 -38 172 -196 31 -120 41 -156 -160 18478 26936 27135 8183 3441 2858 2185 953 1418 210 192 185 176 18619 27143 26926 8253 3845 932 3089 460 164 206 210 167 174 93 106 106 73 60 56 57 46 49
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Dipoles first and doublet focusing

• Features
• Requires beams to be in
• separate focusing channels
• Fewer magnets
• Beams are not round at the IP
• Polarity of Q1 determined by
• crossing plane larger beam
• size in the crossing plane to
• increase overlap
• Opposite polarity focusing at other
• IR to equalize beam-beam tune shifts
• Significant changes to outer triplet
• magnets in matching section.

Q1
D2
Q2
IP
D1
D2
Focusing symmetric about IP
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Doublet Optics Beta functions
J. Johnstone
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Gradients, beta max dipoles first, doublets
Quad BT/m Left BT/m Right ßmaxm Left ßmaxm Right Coil aperture 2(1.19s8.64.53) mm
Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 Q9 Q10 QT11 QT12 QT13 -200 200 46 -50 0 -155 -31 147 -204 186 -98 -27 92 Q1.L Q2.L Q3.L -Q4.L -Q5.L -Q6.L -Q7.L -147 205 -198 78 -44 -108 24446 24446 4462 3908 1549 1354 443 388 267 199 185 168 176 24446 24446 4462 3909 1547 1367 512 356 257 209 190 170 173 102 102 62 60 50 49 42 41
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Features of this doublet optics

• Symmetric about IP from Q1 to Q3, anti-symmetric
  from Q4 onwards
• Q1, Q2 are identical quads, Q1T is a trim quad
  (125 T/m). L(Q1) L(Q2) 6.6 m
• Q3 to Q6 are at positions different from
  baseline optics
• All gradients under 205 T/m
• Phase advance preserved from injection to
  collision
• At collision, ßx 0.462m, ßy 0.135m, ßeff
  0.25m
• Same separation in units of beam size with a
  smaller crossing angle FE v(ßR/ ßE) FR 0.74
  FR
• Luminosity gain compared to round beam

Including the hourglass factor,
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Chromaticity comparison
ß 0.25m Complete Qx Insertion Qy Inner Qx Magnets Qy
Quads first Dipoles first triplets Dipoles first - doublets -48 -99 -105 -48 -96 -121 -44 -82 -103 -44 -82 -112

• Including IR1 and IR5
• Chromaticity of dipoles first with triplets is 99
  units larger per plane than
• quads first
• Chromaticity of dipoles first with doublets is 31
  units larger per plane than
• dipoles first with triplets

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Chromaticity contributions

• Inner triplet and inner doublet dominate the
  chromaticity
• Anti-symmetric optics upstream and downstream
  quads have opposite
• chromaticities
• Symmetric optics upstream and downstream quads
  have the same sign of
• chromaticities

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Long-range beam-beam tune shifts

• Vertical crossing at IP1 and horizontal
• crossing at IP5
• Round beams
• Cancellation of tune shifts is very good
• (lt 0.001 ?) for separations beyond 4s
• Elliptical beams
• Doublet optics, beam vertically large at
• IP1 (sy/sx 2) with vertical crossing
• and horizontally large (sy/sx 0 .5)
• at IP5 with horizontal crossing
• Difference in long-range tune shifts
• between round and elliptical beams
• lt 0.07 ? for separations gt 9s
• With 12 parasitics per IR, difference ?
• Footprint is larger with the elliptical beams

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Energy Deposition
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Energy Deposition Issues

• Quench stability Peak power density
• Dynamic heat loads Power dissipation and
  cryogenic implications
• Residual dose rates hands on maintenance
• Components lifetime peak radiation dose and
  lifetime limits for various materials

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Energy Deposition in Quads First

• Energy deposition and radiation are major issues
  for new IRs.
• In quad-first IR, Edep increases with L and
  decreases with quad aperture.
• Emax gt 4 mW/g, (P/L)max gt 120 W/m, Ptriplet
  gt1.6 kW at L 1035 cm-2 s-1.
• Radiation lifetime for G11CR lt 6 months at
  hottest spots. More radiation hard material
  required.

N, Mokhov
A. Zlobin et al, EPAC 2002
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Energy deposition in dipoles
Problem is even more severe for dipole-first IR.
Cosine theta dipole On-axis field sprays
particles horizontally power deposition
is concentrated in the mid-plane L 1035 cm-2
s-1 Emax on mid-plane (Cu spacers) 50
mW/g Emax in coils 13 mW/g Quench limit
1.6 mW/g Power deposited 3.5 kW
Power deposition at the non-IP end of D1 N.
Mokhov et al, PAC 2003
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Open mid-plane dipole
R. Gupta et al, PAC 2005
Open mid-plane gt showers originate outside the
coils peak power density in coils is
reasonable. Tungsten rods at LN temperature
absorb significant radiation.

• Magnet design challenges addressed
• Good field quality
• Minimizing peak field in coils
• Dealing with large Lorentz forces w/o a
• structure between coils
• Minimizing heat deposition
• Designing a support structure

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Energy deposition in open mid-plane dipole
TAS
TAS2
TAN

• Optimized dipole with TAS2
• IP end of D1 is well protected by TAS.
• Non-IP end of D1 needs protection.
• Magnetized TAS is not useful.
• Estimated field 20 T-m
• Instead split D1 into D1A and D1B.
• Spray from D1A is absorbed by
• additional absorber TAS2
• Results (N. Mokhov)
• Peak power density in SC coils
• 0.4mW/g, well below the quench limit
• Dynamic heat load to D1 is drastically
• reduced.
• Estimated lifetime based on
• displacements per atom is 10 years

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Beam-beam phenomena
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RHIC Beam-beam experiment
Question Do parasitic interactions in RHIC have
an impact on the beam ? Experiment April 2005
Change the vertical separation between the beams
at 1 parasitic interaction Observe beam losses,
lifetimes, tunes vs separation

• Beam Conditions
• 1 bunch of protons in each ring
• Injection Energy 24,3 GeV
• Bunch intensities 2 x 1011
• 1 parasitic interaction per bunch
• Bunches separated by 10s at
• opposite parasitic

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RHIC beam-beam experiment
W. Fischer et al (BNL)

• Observations
• !st set of studies tunes of blue and yellow
  beam were asymmetric about diagonal
• Blue beam losses increased as separation
  decreased. No influence on yellow beam.
• Next set of studies tunes symmetric about
  diagonal
• Onset of significant losses in both beams for
  separations below 7s
• There is something to compensate
• Phenomena is tune dependent
• Remote participation at FNAL

Orbit data time stamp corresponds to time of
measurement, Not to time of orbit change Shift
orbit data to the right
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RHIC Wire compensator
New LARP Task for FY06

• RHIC provides unique environment
• to study experimentally long-range
• beam-beam effects akin to LHC
• Proposal Install wire compensator
• In summer of 2006, downstream of
• Q3 in IR6
• Proposed Task
• Design and construct a wire
• compensator
• Install wire compensator on
• movable stand in a ring
• First study with 1 proton bunch in
• each ring with 1 parasitic at flat top.
• Compensate losses for each
• separation with wire
• Test robustness of compensation
• w.r.t current ripple, non-round

Possible location of wire
IP6
Parasitic interaction
Phase advance from parasitic to wire 6o
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Strong-strong beam-beam simulations
J. Qiang, LBL

• Strong-strong simulations done with PIC style
  code Beambeam3D (LBNL)
• Emphasis on emittance growth due to head-on
  interactions under different situations
• Beam offset at IP
• Mismatched emittances and intensities
• Numerical noise is an issue growth rate depends
  on number of macro-particles M. Continuing
  studies to extract asymptotic (in M) growth
  rates.
• Latest additions to code crossing angles,
  long-range interactions
• Simulation shows strong nonlinear long-range
  effects at LHC

Nominal case
Beams offset by 0.15 sigma
Emittance growth 50 larger
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RHIC Long-Range Simulation Scan 2
(rms emittance vs. turn)
J. Qiang
4.70s separation
5.54s
7.15s
Beam 1 (blue beam)
One million macroparticles for each beam and 128
x128 grid points
Beam 2 (yellow beam)
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IR and Beam-beam tasks FY06-07

• IR design
• Quad first lowest feasible ? consistent
  with gradients and apertures, field quality
• Dipoles first Triplet ?, apertures,
  gradients, field quality
• Dipoles first Doublet explore feasibility
• Extend scaling laws (JPK) gains with lower
  L, chromatic limits
• Impact of D0 orbit corrector on downstream
  optics (with JPK)
• Issues left over from IR Workshop
• Beam-beam compensation
• Phase 2 Build wire compensator, machine
  studies in RHIC and weak-strong simulations with
  BBSIM
• Strong-strong beam-beam simulations emittance
  growth with swept beams (luminosity monitor),
  wire compensation, and halo formation
  (Beambeam3D)
• Energy Deposition
• IR designs (quadrupole and dipole first),
  tertiary collimators, and the forward detector
  regions (CMS, TOTEM, FP420 and ZDC).
• Issues left over from IR Workshop

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Level of effort - FY06

• IR design Beam-beam Energy deposition Wire
  compensation
• Requested funding
• BNL FNAL LBL
• 180 500K 200K
• Received funding
• BNL FNAL LBL
• 130 230K 80K
• People supported TS, JJ, NM (FNAL), JQ (LBL)
• Wire construction (BNL)
• Requested new hires FNAL 1 postdoc on IRBB,
• 1
  postdoc on ED