# Presentation: 196462

## IR Ratings

- Tanaji Sen and John Johnstone
- FNAL

##  Ratings proposal

- Luminosity reach: multi-parameter space but energy deposition critical
- R&D time: time required to develop the most critical hardware and to integrate it in the LHC
- Operational time: time required o experimentally validate an upgrade scheme and to implement it in routine accelerator operation

- Proposed by F. Ruggiero and W.Scandale

- LARP April 2006: IR Ratings

- T. Sen & J. Johnstone

## Luminosity reach

- Energy deposition
- Beam-beam interactions
- Magnet apertures
- Achievable β* (dependence on L*)
- Chromaticity correction: linear & nonlinear, chromatic beta beat
- Nonlinear correctors; dynamic aperture
- Dispersion correction
- Sensitivity to errors: ground or quad motion, power supply ripple, ...
- Feed-down effects
- Large crossing angles, crab cavities

- LARP April 2006: IR Ratings

- T. Sen & J. Johnstone

## Quads first vs Dipoles first

**Advantages**
- Quads are closest to the IP, hence allow for a larger reduction in β*, minimizes nonlinear and chromatic aberrations.
- Lower accumulation of charged particle debris from the IP than in dipoles
- Operational experience from the first several years of running.
**Disadvantages**
- Larger number of parasitic beam-beam interactions.
- Crossing angle has to increase as 1/√β*, so smaller increase in luminosity
- Correction systems in IR have to act on both beams simultaneously.

**Advantages**
-  Early separation of the beams, fewer parasitic interactions.
-  Correction systems act on single beams  with double bore quads.
-  No feed-down effects in the quads due to the crossing angle.
**Disadvantages**
-  Large energy deposition in the dipoles. Makes dipole design challenging.
-  Quads are further from the IP so beta functions are larger → increases nonlinear and chromatic aberrations.
-  Longer commissioning time after the upgrade due to different geometry.

- Dipoles 1st

- Quads 1st

- LARP April 2006: IR Ratings

- T. Sen & J. Johnstone

## Energy Deposition

- At L = 1035 cm-2 s-1, debris power ~ 9kW
- Quads 1st
-  power deposited in the triplets ~ 1.6 kW
-  new quad designs with mid-plane spacers and higher Z (tungsten-Rhenium) liners
-  MARS simulations by N. Mokhov, I. Rakhno
-  Test for optimum apertures, liner thickness, ...
- Dipoles 1st
-     Power deposited in dipoles ~3.5 kW
-     Energy deposition can be mitigated with an unconventional dipole design (R. Gupta)
-    LARP dipole program postponed.
-    Not clear if Europeans are designing dipoles for the IR upgrade.

- LARP April 2006: IR Ratings

- T. Sen & J. Johnstone

##  Lower L*: Quads 1st vs Dipoles 1st 

- Moving magnets closer to the IP allows smaller β* for the same βmax
- Expect larger benefit with quads first optics
- Example,
-    at L* = 19m,
-    Quads 1st: β* =0.2 m for a 25% increase in Luminosity
-     Dipoles 1st: β* = 0.22 m for a 15% increase in luminosity

- Quads 1st: βmax ~ 9km

- Dipoles 1st: βmax ~ 25km

- LARP April 2006: IR Ratings

- T. Sen & J. Johnstone

## 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
-  |Q’| (dipoles 1st  with triplets) - |Q’| (quads 1st ) > 99,  per plane
-  |Q’| (dipoles 1st  with doublets) - |Q’| (dipoles 1st  with triplets) > 31, per plane
-  Second order chromaticity Q’’ ~ β2, expect larger differences between quads 1st and dipoles 1st.

- LARP April 2006: IR Ratings

- T. Sen & J. Johnstone

## Flux jumps and chromaticity

- Chromaticity change depends on the level of spurious dispersion in the IR.
- If Dx~1cm at IP, then for
-      Δb3 = 1unit,    ΔQ’ ~ 2
-      with dipoles 1st or quads 1st
-     Nonlinear effects may be important

- Q3

- Q2b

- Q2a

- Q1

- Q1

- Q2a

- Q2b

- Q3

- Quads 1st

- Dipoles 1st

**Qx’**

**Qy’**

*Large fluctuations in the normal and skew quadrupole components of HFDA04 dipole magnet are observed.*
*They are not necessarily complying with the magnetic field symmetry (e.g. dipole) and  can produce fluctuations in allowed and unallowed harmonics.*
*                                    **V. Kashikin*

- Flux jumps have been measured
- in the model Nb3Sn dipole magnets

- Changes in the multipole harmonics of the
- IR quads could have a major impact on the
- beam, e.g. changes in b3 (European) change
- the chromaticity

- LARP April 2006: IR Ratings

- T. Sen & J. Johnstone

## Sensitivity to errors

- Offsets at the IP         hit on luminosity
-    e.g. from orbit errors (magnified by triplet), ripple in the triplets, ground motion, liquid helium turbulence, ....
- Crossing angle errors
- Dispersion correction errors
- Nonlinear field correction errors
- Chromaticity correction errors
-          ratings of layouts should include sensitivity to errors

- Offsets > 0.1σ lead to large
- emittance growth.
-                      J. Qiang

- LARP April 2006: IR Ratings

- T. Sen & J. Johnstone

##    Comparison: dipoles 1st vs quads 1st 

- Magnet apertures: max. apertures about the same in both
- Energy deposition:
-     in dipoles: requires new design
-     in quads: studies in progress for both layouts
- Beam-beam interactions
-         Worse with quads 1st. Open question: will wire compensation work? If yes, it could resolve the issue.
- Chromaticity correction: smaller strengths with quads 1st
- Nonlinear correction: smaller strengths with quads 1st
- Flux jumps:
-     changes in chromaticity ~ the same in both
-     changes in nonlinear multipoles – expect larger changes with dipoles 1st
- Lower L*: larger gains with quads 1st.
- Feed-down effects: smaller with dipoles 1st
- R&D time: Design and test of accelerator quality dipoles will take longer
-                                                     ------ the story continues

- LARP April 2006: IR Ratings

- T. Sen & J. Johnstone