  In the FRAGM experiment at heavy ion accelerator complex TWAC-ITEP, the
proton yields at an angle 3.5$^\circ$ have been measured at fragmentation of
carbon ions at $T_0 = $ 0.6, 0.95 and 2.0 GeV/nucleon on beryllium target. The
data are presented as invariant proton yields on cumulative variable $x$ in the
range 0.9 < $x$ < 2.4. Proton spectra cover six orders of invariant cross
section magnitude. They have been analyzed in the framework of quark cluster
fragmentation model. Fragmentation functions of quark-gluon string model are
used. The probabilities of the existence of multi-quark clusters in carbon
nuclei are estimated to be 8--12% for six-quark clusters and 0.2--0.6% for
nine-quark clusters.
