# Presentation: 472180

## IR and Beam-beam 

- Tanaji Sen
- October 6, 2005

## Topics

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

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

##  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

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## IR designs

-  Quadrupoles first – extension of baseline
- Dipoles first – triplet focusing
- Dipoles first – doublet focusing

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## Triplet first optics

**J. Johnstone**

-  **β***** ****= 0.25**

**Nominal ****β***** = 0.5**

- Lattice Vers. 6.2

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## Gradients, beta max – quads first optics

| Quad | B’[T/m]
  Left | B’[T/m]
 Right |  βmax[m]
 Left |  βmax[m]
 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 |

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## Dipole first optics 

|  | Earlier layout
 (PAC 03) | Present layout |
| --- | --- | --- |
| D1 dipole

TAN absorber

 β* 
 βmax | 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 |

- Additional TAS absorber in the present layout – per N. Mokhov

- IP

- D1a

- TAS2

- D1b

- TAN

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## 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 < 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 <   160T/m

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## 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 β*= 0.25m

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## Gradients, beta max – dipoles first, triplets

| Quad | B’[T/m]
  Left | B’[T/m]
 Right | βmax[m]
 Left | βmax[m]
 Right | Coil aperture
2(1.1*9*σ+8.6+4.5+3) 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 |

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## Dipoles first and doublet focusing

- IP

- D1

- D2

- D2

- Q1

- Q2

- 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.

- Focusing symmetric about IP

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## Doublet Optics – Beta functions

- J. Johnstone

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## Gradients, beta max – dipoles first, doublets

| Quad | B’[T/m]
  Left | B’[T/m]
 Right | βmax[m]
 Left | βmax[m]
 Right | Coil aperture
2(1.1*9*σ+8.6+4.5+3) 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 |

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## 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, β*x= 0.462m, β*y = 0.135m, β*eff= 0.25m
- Same separation in units of beam size with a smaller crossing angle ΦE = √(β*R/ β*E) ΦR = 0.74 ΦR
- Luminosity gain compared to round beam

- Including the hourglass factor,

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## Chromaticity comparison

| 
 β* = 0.25m | Complete
     Q’x | Insertion
      Q’y |      Inner
      Q’x | Magnets
     Q’y |
| --- | --- | --- | --- | --- |
| 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

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## 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

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## Long-range beam-beam tune shifts

-  Vertical crossing at IP1 and horizontal
-    crossing at IP5
-                   **Round beams**
-  Cancellation of tune shifts is very good
-     (< 0.001 ξ) for separations beyond 4σ
-                  **Elliptical beams**
-  Doublet optics, beam vertically large at
-    IP1 (σy/σx = 2) with vertical crossing
-    and horizontally large (σy/σx= 0 .5)
-    at IP5 with horizontal crossing
-  Difference in long-range tune shifts
-    between round and elliptical beams
-    < 0.07 ξ for separations > 9σ
-  With 12 parasitics per IR, difference ~ ξ
-  Footprint is larger with the elliptical beams

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## Energy Deposition

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## 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

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## 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 > 4 mW/g,   (P/L)max > 120 W/m, Ptriplet >1.6 kW at L = 1035 cm-2 s-1.
- Radiation lifetime for G11CR < 6 months at hottest spots. More radiation hard material required.

- A. Zlobin et al, EPAC 2002

- N, Mokhov

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## 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

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## Open mid-plane dipole

- Open mid-plane => 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

- R. Gupta et al, PAC 2005

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## 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

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## Beam-beam phenomena

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## RHIC Beam-beam experiment

-  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 ~10σ at
-      opposite parasitic

***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

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## RHIC beam-beam experiment

- 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 7σ
- There is something to compensate
-  Phenomena is tune dependent
-  Remote participation at FNAL

- W. Fischer et al (BNL)

- Orbit data – time stamp corresponds to time of measurement, Not to time of orbit
- change
- Shift orbit data to the right

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## RHIC – Wire compensator

- Possible location of wire

- Parasitic interaction

- Phase advance from parasitic to wire = 6o

- IP6

- 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
-  beams, alignment errors, ...

**New LARP Task for FY06**

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## Strong-strong beam-beam simulations

- 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

**J. Qiang, LBL**

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## RHIC Long-Range Simulation Scan 2 

- RHIC Long-Range Simulation Scan 2
-             (rms emittance vs. turn)

- 4.70 separation

- 5.54

- 7.15

- One million macroparticles for each
-  beam and 128 x128 grid points

- Beam 1 (blue beam)

- Beam 2 (yellow beam)

**J. Qiang**

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## 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

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen

## 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 IR+BB,
-                                                1 postdoc on ED

- IR and Beam-beam - Oct 6, 2005

- Tanaji Sen