  Powerful radio sources and quasars emit relativistic jets of plasma and
magnetic fields that travel hundreds of kilo-parsecs, ultimately depositing
energy into the intra- or inter-cluster medium. In the rest frame of the jet,
the energy density of the cosmic microwave background is enhanced by the bulk
Lorentz factor squared, and when this exceeds the magnetic energy density the
primary loss mechanism of the relativistic electrons is via inverse Compton
scattering. The microwave energy density is also enhanced by a factor (1+z)^4,
which becomes important at large redshifts. We are using Chandra to survey a
z>3 sub-sample of radio sources selected with 21 cm wavelength flux density >
70 mJy, and with a spectroscopic redshift. Out of the first 12 objects
observed, there are two clear cases of the X-rays extending beyond the
detectable radio jet.
