  We have obtained the first large sample of accurate temperatures for clusters
at z>0.14 from ASCA. We compare the luminosity temperature (L-T) distribution
for these clusters with the low redshift sample of David et al (1993) and find
that there is no evidence for evolution. We also find that the intrinsic
variance in this relation is roughly constant with redshift. Additionally,
there is no detectable change in the relationship of optical velocity
dispersion to X-ray temperature with redshift. Most cosmological simulations
driven primarily by gravity predict substantial changes in the L-T relation due
to the recent rapid growth of clusters. Our results are consistent either with
models in which the cluster core entropy is dominated by pre-heating, or with
low Omega models in which cluster structure does not evolve strongly with time.
The intrinsic variance in the L-T relation at a fixed redshift can be due a
variety of possibilites e.g. a change in the baryonic fraction from cluster to
cluster, variation in the fraction of the total energy in the system arising
from shocks or supernova heating or variations in the emission measure
distributions in multiphase gas.
