= Solution
The accelerating supply transfers $I_eV=50$ kW into the beam, but the <electrons> need not be discarded with that <kinetic energy>. An electrostatic recovery system decelerates the used beam before collection and returns most of its <energy> to the <electric field> or supply. The net required <power> then covers unrecovered beam <energy> and losses, rather than the whole circulating kinetic-energy flux.
For example, $99\%$ recovery leaves $0.01(50\,\mathrm{kW})\simeq500$ W of unrecovered beam <power>, plus auxiliary loads. This explains the stated two-order-of-magnitude scale. It does not imply that gun heating, vacuum equipment, magnets and all electrical losses are automatically included in a $500$ W total plant budget.
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