1. Requirements for the ELENA Electron Cooler

2. A Bit of History
August 2011 : Initial contacts with Kyoto University (Akira Noda) and MPI Heidelberg (Manfred Grieser) for a possible collaboration to build the cooler.
Sep – Dec 2012 : Exchange of information with Kyoto Uni. (Akira Noda & Toshiyuki Shirai).
May 2012 : Official letter to Toshiba.
June 2012 : Drawing samples received from Toshiba.
Dec : Addendum No. 1 to the MoU of June 2012 (Contribution by the University of Tokyo to ELENA). 2 MCHF for experimental line beam instrumentation, electron cooler and prototype electrostatic device.
May 2013 : Visit to Kyoto University (Toshiyuki Shirai) and talks with Toshiba.
End 2013 : Decision to build the cooler «in-house» (vacuum design at CERN, magnets in industry)
Nov : Contract awarded to TESLA Engineering for the magnet system and supporting frame.

3. General Requirements
Operate at very low electron energies (down to 55 eV).
Operate at very low magnetic field to minimize disturbance to circulating low energy antiprotons – we have chosen 100 Gauss in the cooler.
Have extremely good vacuum.
Adiabatic expansion of electron beam to reduce transverse temperatures.
Very good field quality – especially in the cooler solenoid (Bt/Bǁ < 5 × 10-4 ).
Compact design to fit in section 4.
Orbit correctors and solenoid compensators.

5. Magnetic System Components
Main cooler solenoid
Gun solenoid
Collector solenoid
Expansion solenoid
Squeeze coil at collector
2 x Toroid section consisting of
9 racetrack coils each
Various corrector coils to
ensure good field quality
Orbit correctors
Solenoid compensators
The whole system will be shielded to obtain a better field quality and to exclude stray fields - ~ 1 Gauss in the area of the AD hall where it will be installed.

6. Why?
Electron cooling can be treated as Coulomb interactions between and ion and the electrons.
The cooling force is dependent on the relative velocity between ions and electrons.
The intrinsic velocity spread of the electron beam that enters in the distribution function 𝑓 𝑣𝑒 is described by the longitudinal and transverse temperatures:
F 𝑣𝑖 = 4𝜋𝑞2𝑒4𝑛𝑒 4𝜋𝜖𝑜 2𝑚𝑒 𝐿𝑐 𝐮 𝑓 𝑣𝑒 𝐮 𝑢3 𝑑3𝑣𝑒 , 𝐮=𝑣𝑖 −𝑣𝑒
𝐾𝑇∥ =𝑚𝑒 Δ𝑣𝑒∥ , 𝐾𝑇⊥= 1 2 𝑚𝑒 Δ𝑣𝑒⊥

7. Small electron temperatures result in an increase of the cooling force.
For efficient cooling all systematic deviations of the ion and electron beam trajectories have to be minimized.
The most important parameters for fast and efficient cooling are the straightness of the magnetic guiding field and the alignment between the ion and electron beams in the cooling section.

8. Fine Tuning the Field
Saddle coils
24 fine tune coils.