  The guiding and control of ultrahigh flux, femtosecond relativistic electron
pulses through solid density matter is of great importance for many areas of
high energy density science. Efforts so far include the use of magnetic fields
generated by the propagation of the electron pulse itself or the application of
hundreds of Tesla magnitudes, pulsed external magnetic fields driven by either
short pulse lasers or electrical pulses. Here we experimentally demonstrate the
guiding of hundreds of keV mega-ampere electron pulses in a magnetized
neodymium solid that has a very modest, easily available static field of 0.1
tesla. The electron pulses driven by an ultrahigh intensity, 30 femtosecond
laser are shown to propagate beam-like, a distance as large as 5 mm in a high Z
target (neodymium), their collimation improved and flux density enhanced nearly
by a factor of 3. Particle-in-cell simulations in the appropriate parameter
regime match the experimental observations. In addition, the simulations
predict the occurrence of a novel, near-monochromatic feature towards the high
energy end of the electron energy spectrum, which is tunable by the applied
magnetic field strength. These results may prove valuable for fast electron
beam-driven radiation sources, fast ignition of laser fusion, and laboratory
astrophysics.
