1. Multi-Turn Extraction for PS2 Preliminary considerations
PS2 Meeting
Multi-Turn Extraction for PS2 Preliminary considerations
M. Giovannozzi and Y. Papaphilippou
February 9th, 2007

2. Need for a new PS Multi-Turn Extraction
Present scheme limitations
Losses (about 15% of total intensity) are unavoidable due to the presence of the electrostatic septum used to slice the beam.
Increased radiation levels observed around the complex this year (not only near the septum where shielding seems better) due to scattered particles from the septum (S. Gilardoni, APC, )
Non-optimal phase space matching in the SPS and emittance blow-up.
Slices have different emittances and optical parameters.
Length
Kicker strength
Four turns
Fifth turn
Efield=0
Electrostatic septum blade X X’ 1 3 5 2 4
Efield≠0
Slow bump
Electrostatic septum
(beam shaving)
Extraction septum
Kicker magnets
Extraction line
09/02/2007
M.Giovannozzi and Y.Papaphilippou

3. Beam losses versus septum and beam parameters
Dependence of beam losses vs. emittance, septum angle and thickness shows that losses can be reduced to ideally 6%.
For a technologically challenging electrostatic septum with thickness of 0.1mm (B. Goddard et al AB-note ), losses reduction of 20% with respect to present one of 0.2mm
Almost no dependence on the rise time
M. Giovannozzi (ed.)., CERN
09/02/2007
M.Giovannozzi and Y.Papaphilippou

4. New multi-turn extraction ingredients
Beam is separated in the transverse phase space using
Nonlinear magnetic elements (sextupoles ad octupoles) to create stable islands.
Slow (adiabatic) tune-variation to cross an appropriate resonance.
Benefits
Losses are reduced to ideally 0
The phase space matching is improved
The beamlets have the same emittance and optical parameters.
Other potential applications
Multi-turn injection
Different number of turn extraction for different resonances
Production of hollow beams
M. Giovannozzi, COULOMB 05
09/02/2007
M.Giovannozzi and Y.Papaphilippou

5. Normalised phase space
Island parameters
M. Giovannozzi, P. Scaramuzzi EPAC 04
Analytical estimate of island’s parameters for controlling the island size and position as a function of the strength of the non-linear elements
Normalised phase space
Distance of fixed points from origin of phase space
Distance from resonance
Secondary frequency
Island’s surface
Distance between separatrices
with
and
09/02/2007
M.Giovannozzi and Y.Papaphilippou

6. Principle and Implementation in the actual PS
Beam splitting
Two pairs of two sextupoles and one octupole used, in order to control the phase of the island in the extraction point
Extraction
Extraction point in SS16 (magnetic extraction septum towards the SPS)
Electrostatic septum in SS31 not required
Slow bump to approach the beam toward magnetic septum, using 6 independently powered magnets (aperture constraints)
Fast bump to extract the beamlets over five turns, with three new kickers. Extraction kicker used for the central part of the beam.
Trajectory correction in the TT2 line
Two kickers, capable of generating a deflection changing from turn to turn (already used for CT extraction)
09/02/2007
M.Giovannozzi and Y.Papaphilippou

7. Constraints for MTE on PS2
Non-linear elements
Two pairs of sextupoles/octupoles separated by 2π, acting as a single element but with roughly twice the strength (depending on the beta functions)
Installed in a dispersion-free region to avoid chromatic effects
Minimum βy and maximum βx for optimal strength and minimal non-linear coupling
Additional sextupole/octupoles may be foreseen in different phase advances for cancelling any non-linear effect produced by the MTE elements and the fine tuning of beamlets’ properties
Slow bump
Should be placed outside of the nonlinear elements to avoid feed-down. For the same reason, special care in the multi-pole errors of the elements inside the bump
Four independently powered magnets are enough to create the required bump, but special care to the aperture around this area
Pulsed quadrupoles similar to the QKE elements 2π apart may be needed to enhance the kick provided by the bump/kickers and special tuning of the optics at extraction
Extraction kicker:
Its phase should be chosen such that the central core can be kicked into the island that is used for extracting the previous four turns
09/02/2007
M.Giovannozzi and Y.Papaphilippou

8. Implementation in the future PS2
Non-linear elements
Place them in the RF region in order to have flexibility in the choice of phase advances and avoid interference with extraction bumps
Taking into consideration that in the actual PS the optics functions near their location are (βx,βy)= (22,12)m, an optics with βx>30m and βy < 10m is ideal.
The size of the sextupoles in the actual PS are around 0.2m and the octupole is 0.72m, with diameters of m
Scaling from the actual PS, and assuming the same β functions, the maximum integrated strength 50GeV is around 175 T.m-1 for the sextupoles and 4715 T.m-2 for the octupole (NB: this is achieved for currents of 700 and 460A).
These strengths can be scaled by reducing the diameter, increasing the length, the number of elements, or the horizontal beta function, to achieve a reasonable pole tip field.
Similar scaling should be done for 75GeV
Slow bump and extraction kickers
See B. Goddard et al AB-note for preliminary considerations
An additional kicker may be foreseen for the transfer line to correct the slightly different position of the central beamlet
09/02/2007
M.Giovannozzi and Y.Papaphilippou