1 st september 2005lhc-lumi 05 - g.arduini – cern/ab optical requirements for the magnetic lattice...

1st September 2005 LHC-LUMI 05 - G.Arduini – CERN/AB

Optical requirements for the Optical requirements for the magnetic lattice of the high energy magnetic lattice of the high energy injectorsinjectors (SSPS in the SPS tunnel) (SSPS in the SPS tunnel)

G. Arduini – CERN-AB/ABP


OutlineOutline

Constraints from SPS tunnelExpected functionalitiesArc apertureSPS to SSPS transferSlow extraction in the SSPSFast extractionOther issues


AssumptionsAssumptions

SSPS:– Injection momentum=100 GeV/c– Extraction momentum=1 TeV/c– Beam characteristics:• LHC beam (*=7 m, p/p=± 2×10-3)• FT beam (*=12(H)/7(V) m, p/p=± 2×10-3 )


Constraints for SSPS in the SPS tunnelConstraints for SSPS in the SPS tunnel

The SPS tunnel geometry: – Circumference: 2 x 1100 m = 6911.5 m– 6-fold symmetry 6 Long Straight Sections (LSS) ~ 130

m long Additional constraints if SSPS cohabitation with

SPS:– Need installation at ~ 2 m from the tunnel floor– Need different radial position: ~ 1 m inside of the

straight sections to be compatible with present SPS HW (e.g. RF waveguides and loads in LSS3)

– SPS extraction, SSPS injection and SPS to SSPS transfer in the same LSS.



RF

BI – TAIL CLEANING

INJ. – BEAM DUMP


Required functionalitiesRequired functionalities

1. Injection2. Acceleration 3. Fast extraction 1 to LHC (LSS4 if we want to use the TI8

tunnel)4. Fast extraction 2 to LHC (LSS6 if we want to use the TI2

tunnel)5. Slow resonant extraction (LSS2 if we want to use the TT20

tunnel to North area)6. Beam dump7. Betatron collimation8. Momentum collimationNeed to combine 2 functions in at least 2 LSSs


Present SPS latticePresent SPS lattice

FODO structure – 6-fold symmetry ~900 phase advance per cell – 18 cell/sextant 4 dipoles/half-cell (each 6.26 m long – 8.45 mrad –

6.6 mm sagitta ~ 1.1mm×dipole length) Approximate dispersion suppression in the long

straight sections by missing magnet scheme gives dispersion beating in the arcs

Very simple lattice – 1 QF power supply, 1 QD power supply

tr ~ 23


Present SPS latticePresent SPS lattice


Arc apertureArc aperture

Required half-aperture in the arcs for a lattice a la SPS

51 / 86 (H) × 27 (V) mm (value for slow extraction)

dipoles in the sagitta beam-halfmm 3.3sag

tolerancealignmentandmechanical2mmt

4mmΔ

beatingβ1.1k

errorsradialincludingoffsetmomentummax.103δ

m4.5/0D

mm 47 ExtractionSlowforseparatixtheofamplitudemax.A

106.6βγ

m104β

halosecondaryformargin1.2~m

scollimatorprimarybydelimited6n

sagtΔkδDA,βγ

βεnMax mA

r

VCOpeakH,

β

3p

VmaxH,

maxsep.

VmaxH,

halo

rVCOpeakH,βpVmaxH,maxsep.VmaxH,

*VH,

haloVH,


Arc apertureArc aperture The estimated maximum amplitude of the separatrix in the arcs

Asepmax is based on the assumption that the spiral step size at the electrostatic septum (ES) is approximately 16 mm to keep losses at % level.

gain in increasing locally H at ZS need special insertion for the slow extraction

e.g. H at ES = 400 m required half-aperture ~ 57 mm (instead of 86 mm) – now comparable with aperture at injection

ZSH

arcmax Hmaxsep. β

βA


Arc apertureArc aperture A reduction of

the required horizontal aperture can be achieved by a proper matching of the dispersion with independently powered quads in the insertion need to probably extend in 1 arc cell to get symmetric solution



Peak dispersion 4.5 to 3 m Required half-aperture in the arcs: 46 / 82 (H) × 27 (V) mm (10 % gain in the aperture at injection)

Useful if together with increased H at ES proper insertions with independent

powering of the quadrupoles in the dispersion suppressor, in the straight section and possibly in 1 arc cell might be required.



further reduce and D in the arcs by reducing the cell length, keeping the same phase advance per cell, and the same radius of curvature in the dipoles and therefore increasing the tune

2Q

R~D

Q

R~β



Reduction of the length by a factor 2

Tune~51 tr ~ 45

Required aperture: 31 / 56 (H) × 21 (V) mm (value for slow extraction)

Useful if together with increased H at ES



Pros:– Smaller aperture– Smaller sagitta (if we keep constant the number of

magnets)

Cons:– Larger number of magnets (if we do not increase the

dipole length)– Stronger quads– Poorer “filling factor”– Reduction of the cell length and of the available space

for auxiliary elements (instrumentation, correctors, kickers)


SPS to SSPS transferSPS to SSPS transfer

Cohabitation with the SPS in the SPS tunnel will imply hosting the SPS fast extraction to the SSPS and the injection in the SSPS in the same straight section

In order to gain space might need to install the SPS fast extraction kickers in the missing dipole section providing an H kick towards a Lambertson magnet in the following dispersion free section bending the beam vertically

The Injection in the SSPS could be “symmetric” to the SPS extraction. This solution might be incompatible with a reduction of the cell length.


SPS to SSPS transferSPS to SSPS transfer Probably feasible taking into account the aperture of the

existing SPS kickers for the fast extraction to LHC and CNGS and the favorable energy scaling laws assuming similar functions.

The expected length of the transfer line from SPS to SSPS would be 50-60 m need to fit matching section to allow transfer without blow-up between the 2 machines (, , D, D’) in both planes.

p

1~

p

1~


SPS to SSPS transferSPS to SSPS transfer

Additional issues:– Protection elements (like injection

stoppers) need to find place in a crowded area more difficult given the higher energy


Slow extractionSlow extraction

Reliable operation of the electrostatic septa used to cut the separatrix limits the electric field they can provide (in the SPS 110 kV/cm)

The increased extraction energy reduces the separation of the extracted and circulating beam at the downstream magnetic septa because of the limited length of the straight section increased losses


Slow extractionSlow extraction Brute force method =

increase the number of septa in the FODO structure of the LSS (not very efficient use of the HW)

Clearance: ~13 (17) mm at MST and ~39 (41) mm at MSE – present operational clearances

Requirements for extraction bumpers and protection devices not considered

-50

0

50

100

150

200

0 20 40 60 80 100 120 140

POSITION ALONG THE STRAIGHT SECTION [m]

x [m

m]

ES septa Thin MS-4 mm Thick MS-17 mm


Slow extractionSlow extraction Need dedicated insertion providing:

– Dispersion free region for the septa– Larger horizontal beta at the ES– Increased strength for the defocussing quad after the ES to

enhance the kick provided by the ES– Optimization of the length of the drift spaces to maximize the

lever-arm between the ES and the MS maximizing the kick enhancement provided by the defocussing quad after the ZS.

Additional issues:– Trajectory of the beam leaving the magnetic septa at large

radial offset through the magnets of the dispersion suppressor

– Cohabitation of the Slow Extraction with the SC environment and collimation


Fast extractionFast extraction Brute force solution =

increase the number of kickers and septa (MST)

Clearance: ~19 mm at MST

Interference of the extracted beam with the downstream magnetic elements?

Pulsed magnetic septa could provide larger deflection angles for comparable gaps (development work for the SPS FE)

Protection elements for higher energy

-50

0

50

100

150

200

250

0 50 100 150 200 250 300

POSITION [m]

x [m

m]


To be addressed To be addressed

Beam dump insertion– Can we afford an internal dump as for the

SPS?– If not can it be based on the design of the LHC

beam dump insertion (IR6)?– Tracking issues because of the faster ramp?

Collimation insertion(s) How to integrate 8 distinct functionalities

in 6 straight sections cohabitation issues


Tentative summaryTentative summary

Only a few issues have been sketched Constraint on the length of the straight sections

and increased energy impose to design dedicated insertions (no simple FODO lattice)

Slow-extraction and dispersion drive and/or contribute significantly to the aperture in the arcs proper matching and insertion design

Cohabitation of different functionalities in the same straight section is necessary and implications need to be studied

1 st september 2005lhc-lumi 05 - g.arduini – cern/ab optical requirements for the magnetic lattice...

Documents