ELECTRON COOLING STATUS

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ELECTRON COOLING STATUS

• Why electron cooling?
• LHC requirements, implications for LEIR, results
  of 1997 cooling stacking experiments.
• Optimum parameters for the LEIR cooler.
• Technical considerations, design specification.
• Cost manpower.
• Schedule.
• Where we are, where we are going.
• Summary.

http//tranquil.home.cern.ch/tranquil/LEIR/
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Why electron cooling?

• LHC requirements for Pb ions
• Luminosity L 1x1027 cm-2 s-1.
• Number of ions per bunch 7x107.
• Normalised emittance of 1.5 mm.
• Implications for LEIR
• 1.2x109 ions accumulated and cooled in 1.6 s at
  4.2 MeV/u.
• Acceleration to 72 MeV/u.
• At extraction 0.9x108 ions to the PS with an of
  emittance lt 0.7 mm.

Only a storage ring with fast electron cooling
can meet these requirements.
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Cooling experiments with Pb ions.

• Cooling and stacking tests made between 1994 and
  1997.
• Short periods in 1994 and 1996.
• Dedicated run in 1997 with a specially prepared
  machine.
• Investigated
• Ion beam lifetime.
• Cooling time as a function of various parameters.
• Stack equilibrium emittance and emittance growth.
• Stacking at Linac III repetition rate of 2.5 Hz.
• Results well documented
• Experimental Investigation of Electron Cooling
  and Stacking of Lead Ions in a Low Energy
  Accumulation Ring, Particle Accelerators, Vol.
  63 pp. 171-210.

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What did we learn from the tests?

• Ion beam lifetime.
• Strong dependence of the lifetime on the charge
  state and electron current.
• Measured rate coefficients cannot be explained by
  radiative recombination.
• DIELECTRONIC RECOMBINATION SEEMS TO BE THE
  DOMINANT EFFECT (STILL A PUZZLE FOR ATOMIC
  PHYSICISTS). THREE-BODY RECOMBINATION? VACUUM
  EFFECTS?
• USE CHARGE STATE 54.
• IMPROVE VACUUM IN THE MACHINE.
• Cooling times.
• Near linear increase of the cooling rate as a
  function of electron current.
• Expected gain due to increased cooler length did
  not show up.
• Strong influence of the lattice parameters on the
  cooling process.
• ELECTRON BEAM SPACE-CHARGE INCREASES THE DRIFT
  VELOCITY.
• ELECTRON BEAM UNSTABLE ABOVE 120 mA.
• ALIGNEMENT TOLERANCES CRITICAL.
• INTERMEDIATE VALUES OF b ARE BETTER FINITE
  VALUE OF D INCREASES THE COOLING RATE.

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What did we learn from the tests?

• Equilibrium emittance fits the LHC requirement
  and emittance growth is not an issue.
• Stacking principle demonstrated and is compatible
  with the filling scheme.

• Factor of 3 missing in the total accumulated
  intensity in 1.6 s.
• COOLING TIME LIMITED BY THE PERORMANCE OF THE
  GUN.
• INTENSITY LIMITED BY LOSSES DUE TO CHARGE
  EXCHANGE AND ELECTRON-ION RECOMBINATION.

3.5x108
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Parameters for the LEIR cooler

• Choice of parameters based on the results from
  the 1994-97 experiments, our experience of
  operating electron cooler devices (LEAR/LEIR, AD)
  for more than 12 years and collaborations with
  other accelerator laboratories (MSL Stockholm,
  MPI Heidelberg).
• Electron energy range from 2 keV to 40 keV.
• High perveance gun (6 mP at 2.3 keV gt Ie 600
  mA).
• Variable electron beam density.
• Cold electron beam, Etlt100 meV, E//lt1 meV.
• Adiabatic expansion.
• Maximum cooling length possible. 3m?
• Homogeneous magnetic guiding field
  (DBt/B//lt10-4).
• Efficient collection of the electron beam
  (DIe/Ielt10-4).
• Electrostatic deflector plates.

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The LEIR electron cooler
High perveance, variable density gun
2.5m cooling section
Adiabatic expansion solenoid
Electron beam collector
90o toroid to bend the electron beam onto the ion
beam
Integrated closed orbit distortion correction
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Vacuum system power supplies

• The vacuum system must follow the stringent
  criteria applied for the LEIR machine.
• 316LN stainless steel, hydroformed bellows.
• NEG coated vacuum chamber, NEG cartridges close
  to the gun and collector where there is a high
  gas load.
• The whole system will be bakeable at 350oC.
• High voltage power supplies.
• gun (40kV/10mA), control (-/ 2kV,5mA), grid
  (6kV,5mA)
• suppressor (6kV,5mA), collector (5kV,5A),
  electrostatic bends (4x 6kV,5mA)
• Common spares with AD electron cooler, use
  existing HT infrastructure.
• Cathode heating power supply(20V,5A).
• Magnetic elements
• 3 power supplies needed for the gun/collector
  solenoids, toroids and cooling solenoids.
• All standard CERN power supplies (1000A,200V
  500A,100V).
• 26 small (10A,70V) power supplies for steering
  coils.

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Cost manpower
Item Cost (kSFr) Responsible
Design 160 BINP
Gun, collector
Magnets
Support frame 1200 BINP
Vacuum chambers
Vacuum system (incl. Bake out, pumps etc.) 550 CERN
Power supplies (HT,DC) 530 CERN
Electrical installation 100
Cooling installation 50
Controls 50 CERN
Related instrumentation 120 CERN
Industrial support 240
TOTAL 3000

• Infrastructure and a lot of material from the
  LEAR installation will be reused.

• Manpower needs (FTE)
• 2003
• 1.6 cat 2, 1 cat 3, 0.5 IS
• 2004
• 1.6 cat 2, 1.3 cat 3, 1.5 IS.
• 2005
• 1.6 cat 2, 1.3 cat 3, 1 IS.
• TOTAL
• 4.8 cat 2, 3.6 cat 3 3 IS over 3 years

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Schedule, where we are

• Technical specifications made in 2001/2002.
• LEIR electron cooler conceptual study, PS/BD/Note
  2001-17.
• Specifications for the LEIR electron cooler
  magnetic components, PS/BD/Note 2002-18.
• General mechanical parameters for the LEIR
  electron cooler, PS/BD/Note 2002-23.
• Design/feasibility study completed by BINP in
  April 2003.
• Modifications requested at the September meeting.
• Vacuum specifications made by AT/VAC group,
  waiting for final drawings of vacuum components.
• Addendum to the CERN-Russian Federation Agreement
  (Skrinsky II) approved in June 2003.
• Construction of the solenoids (pancakes)
  started at BINP.
• Vacuum material ordered.
• Power supplies ordered (PO group).
• ECEB (bld 233) refurbished.

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Schedule, where we are going

• 1st half of 2004
• Delivery of material to BINP, production of
  solenoids, vacuum elements, electron gun and
  collector.
• Magnet measurements and adjustments.
• July, August 2004
• Tests in Novosibirsk.
• Vacuum leak tests. Ultra-high vacuum not needed
  at this stage.
• Generation of electron beam with characteristics
  needed for Pb54 ions (2.3 keV, 600mA variable
  density x10 less in the centreelectron beam,
  electron beam collection inefficiency lt10-4).
• Test at higher energy (40 keV, 3A).
• September 2004
• Delivery to CERN.
• October 2004 March 2005
• Vacuum elements cleaned and prepared, remounting,
  magnet measurements, bakeout of complete system
  to reach ultimate vacuum, commissioning with
  beam, ready for cooling.

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Summary

• The design of the new cooler is technically
  sound.
• The different ideas/techniques that we will use
  have been demonstrated on existing coolers.
• However the LEIR cooler will be the first to
  incorporate them all on one device.
• More variables to deal with. Commissioning a
  little more complicated.
• Cooling with a variable density electron beam has
  yet to be demonstrated.
• Keep a close eye on the results from IMP Lanzhou,
  China (2004).
• Backup solution? Use the gun as a classical
  high perveance gun i.e. no variable density.
• Schedule is tight and leaves little room for
  important delays.

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Some photos of the IMP cooler
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The electron gun

• Convex thermionic cathode at high voltage.
  Cathode radius 14mm.

• Control electrode shapes the electron beam
  density.
• Equivalent perveance of 6 mP on the border and a
  factor of 10 less in the centre.

• Grid electrode determines the intensity.

• The gun is immersed in a strong longitudinal
  field (2.35 kG).

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Variable density profiles
Electron beam profiles with control electrode
potentials Uc 0V, 100V, 200V, 350V, 400V,
600V, grid potential Ug500V and cathode
potential Ucath 1000V.
Vc -100 V
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Adiabatic expansion

• Needed for
• Adapting the electron beam size to the injected
  beam size for optimum cooling.

Bo0.235T, B0.075T, ro14mm gt r24.8mm

• Reducing the magnetic field in the toroids, thus
  reducing the closed orbit distortion.

• Reducing the transverse thermal temperature of
  the electron beam.

Bo0.235T, B0.075T, Eo100meV gt E32meV
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The electron beam collector

• Suppressor electrode slows down the primary
  electrons at the collector entrance.

• Magnetic field is reduced to spread out the
  electrons on the collector surface.

• Surface on which the electrons are collected is
  water cooled.

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The electrostatic bend

• Electrons experience a centrifugal force in the
  toroid.
• This drift can be compensated by an additional
  magnetic field in the opposite direction.
• Reflected and secondary electrons however are
  excited by this field and can oscillate between
  the gun and collector before being lost.
• Complete compensation is obtained by
  superimposing an electric field on the magnetic
  field

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Closed orbit perturbation correction

• The vertical magnetic field component of the
  toroids induce a horizontal perturbation on the
  closed orbit.

• Correction dipole placed in the toroid.