  Simple model of electron cloud is developed in the paper to explain e-cloud
instability of bunched proton beam in the Fermilab Recycler. The cloud is
presented as an immobile snake in strong vertical magnetic field. The
instability is treated as an amplification of the bunch injection errors from
the batch head to its tail. Nonlinearity of the e-cloud field is taken into
account. Results of calculations are compared with experimental data
demonstrating good correlation.
