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Electron cooling

G.I. Budker is discussing electron cooling

The electron cooling process was invented by G.I.Budker at 1965 as method for preparing of the beams for hadron collider. The electron beam moving with the same average velocity as proton beam absorbs the kinetic energy of heavy particles (protons or ions). The first experiments carried out in Novisibirsk in 1974 demonstrated the high efficiency of this method and triggered all the development of heavy particle cooling methods. First electron cooler had cooling length of 1 m.

First electron cooler

In the course of the experiments carried out at the NAP-M facility it was discovered that the time required for cooling, expected to be several seconds, in fact turned out to be 0.1 s. Such an enormous increase in cooling efficiency was the result of the electron beam magnetization.

For a detailed study of the kinetics of cooling under the conditions of strong magnetization, an installation called MOSOL, with a field of 4 kG and a very good field straightens <10-5 was built.

MOSOL facility for measuring of single pass cooling force

The effect of cooling was measured by detection of energy shift of 1 MeV H- or H+ beams. The results of these experiments are shown on the next figure.

The electron beam with the same velocity does not affect energy of ions, but increasing of the electron energy by 0.5 eV produces friction force which accelerates ions (H-) on distance 3 m (electron beam length at MOSOL ) by 45 eV. The proton is 1836 time more heavy then electron and to come at equilibrium it needs to gain energy shift of 0.5*1836=900 eV. Hence, the distance for this should be near 3 m*900/45=60 m, and cooling time for H beam with energy 1 MeV should be 4 ms. At storage rings the electron beam occupied small fraction of orbit (0.01-0.03) and it is possible to have cooling time for magnetized cooling near 1 ms (small amplitude).

The next electron cooler designed and built at BINP was the cooler for heavy synchrotron SIS at GSI (Germany).

Sufficiently more intensive ion beam was obtained at SIS by accumulation due to repeated multi-turn injection, when each injection procedure was made after cooling previously injected ions by electron cooler.

Good results of using an electron coolers at many laboratories in the world stimulated IMP (Lanzow) to start new project CSR for development of heavy ion physics at China. Collaboration agreement with IMP for development of new generation of electron coolers was signed. Two coolers named EC35 for 35 keV and EC300 for 300 keV of electron energies were built already.

Several unique features were used at these coolers:

  1. A new electron gun was developed to produce hollow electron beam. The advantages of hollow electron beam are:

  2. Electrostatic deflector

  3. A new structure of solenoid coils at the cooling section and a new method of the transversal magnetic field components correction at the cooling section were applied.

Perspectives of high energy electron cooling:

The development of high luminosity ion-ion and ion-electron colliders requires to develop the electron cooling systems for continues electron cooling. BNL (RHIC, 50 MeV cooling), FNAL (pbar recycler 5 MeV), GSI (future plan) started RND programs at this subject. BINP takes part in these programs for scientific study of using electron cooling.

Some references for study of electron cooling:

  1. Workshop on the Medium Energy Electron Cooling, Novosibirsk, February 26-28, 1997.

  2. V.V.Parkhomchuk, Review of cooling

  3. V.V.Parkhomchuk, A.N. Skrinsky, Electron cooling: 35 years of development, UFN Volume 43 (2000),Number 5,Pages 433-452

  4. V.V.Parkhomchuk, High Intensity and high brightness hadron beams, AIP conference proceeding v. 642, p. 325-331, 2002

  5. Electron gun with variable profile, EPAC02

  6. http://lepta.jinr.ru/