Electron beam transport for FNAL electron cooler

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Electron beam transport for FNAL electron cooler

E-cooling is referred as “non-magnetized”

OVERVIEW Material is taken from FNAL’s presentations.

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FNAL cooler:

More strict requirements for Low-E RHIC

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not possible for RHIC

Over focusing for RHIC

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For RHICthere should besecond cooling section here

Not good enoughfor RHIC

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FNAL

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FNAL

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Some electron beam transport issues

FNAL Pelletron e-cooler:

1. Works at fixed energy of 4.3MeV.

2. Control of beam envelopes and angles only though single cooling section.

Low-E RHIC e-cooler:

1. Need to work at several energies, especially at low energies all the way down to 0.9MeV!!! Perhaps, even up to 5MeV.

2. Preservation of electron beam quality after first cooling section since the same electron beam will be used for cooling of ions in second RHIC ring. Special/very careful design of U-turn between two cooling section!!!

3. It looks like we will not be able to operate with electron beam size larger than ion beam in the cooling section due to limitation from magnetization & aperture at low energy. Perhaps, we can operate at least with the same magnetization as presently used at FNAL when we go to low energy. We are planning experiment at Pelletron at 1MV this summer.

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Aperture limitations and magnetized beam

• In beam line: 3” pipe

• BPM’s in dipoles: 2” pipe (rectangular)

• Around SPA/D06 (still inside the tank): about 4” – the beam size in this location is large to make small beam size in bends.

The strongest limitation is probably inside the Pelletron with diaphragms there with only 2.54cm diameter. Beam diameter there at 4MeV can be 1.6cm. Without increase of focusing at lowest energy beam diameter would be 4cm, even for the same magnetization.

Therefore, there is a need for an experiment at Pelletron to check whether one can have successful recirculation at lowest energy of 1MeV, and to understand what magnetization is acceptable.

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2, 2mc

eRB ccNeffective

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• FNAL: Electron beam position is adjusted to provide stronger cooling as needed– Adjustments to the cooling rate are obtained by bringing the pbar bunch in an area of

the beam where the angles are low and electron beam current density the highest

5 mm offset 2 mm offset

pbars

electrons

Area of good cooling

e

e

Au

paintingideal for coolingdue to limit by magnetization & aperture

RHIC:at lowest energy

eAu

cs

cs R

B

BR

e

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E-beam transport and simulations

FNAL used:

SAM (UltraSAM/BEAM) code – to design and simulate beam through the gun

OptiM code – to simulate beam optics (accurate treatment of coupling, analytic KV approximation for space charge)

- We do not need to redesign the gun. But at some point we probably still need to do simulations with SAM or Trak codes.

- We can start beam dynamics simulation with known e-beam distribution at some point in Pelletron.

- First task is to set-up lattice similar to FNAL’s and check whether we can use PARMELA for this or we should use OptiM.

- Ultimate goal is to simulate beam dynamics at lowest energies of interest and design an appropriate beam transport.