  The quality of the proton beam produced by Target Normal Sheath Acceleration
(TNSA) with high power lasers can be significantly improved with the use of
helical coils. While they showed promising results in terms of focusing, their
performances in terms of the of cutoff energy and bunching stay limited due to
the dispersive nature of helical coils. A new scheme of helical coil with a
tube surrounding the helix is introduced, and the first numerical simulations
and an analytical model show a possibility of a drastic reduction of the
current pulse dispersion for the parameters of high power laser facilities. The
helical coils with tube strongly increase bunching, creating two collimated
narrow-band proton beams from a broad and divergent TNSA distribution. The
analytical model provides scaling of proton parameters as a function of laser
facility features.
