At present the most promising detector is a pixel type such as CCD
vertex detectors[7] in order to measure dense positions of
particles. We do not need to measure their energies since momenta
of our interesting particles are analyzed by the 2 tesla solenoidal
magnetic field as described in the previous section.
The densest regions are 
and 
, whose density is
estimated to be 120(particles) x 72(bunches) /4.1cm
(0.32MHz/cm) if the detector can be read out only between RF
pulses at 150Hz for the JLC-I[9]. The occupancy rate is below
1% in the CCD-detector with 25x25
m pixel size.
Assuming that the energy of electrons(positrons) traversing the
detector is 200MeV, the total dose is estimated to be 110Krad for a
year(100days)'s experiment. This estimated dose is very close to
present life time of CCD-detectors. For experiments in
several years, we should need more radiation-hard CCD detectors
resisting up to 1Mrad. Since there are good prospects, megarad
hard CCD detectors are available in the near future[7, 8].
In order to get any useful information inside a bunch-train of
201.6nsec (2.8ns x 72bunches), it is greatly required to have a
fast-gating CCD. Since there is few possibilities to realized such
a CCD in future, it is very difficult to extract informations
for each bunch during collisions.
However, there is a solution to get information inside the
bunch-train when one of two LINACs can be operated with a single
bunch which is called a test beam.
This test beam can probe inside the bunch-train in the other LINAC
by colliding with the specific bunch in it at IP. We can easily
choose any bunch to be probed in the train by adjusting a timing of
the test beam. For this test beam operation, any information
concerning a bunch property can be obtained.
As clearly seen in Tab.1, where measurement errors are
statistical ones corresponding to numbers of bunch collisions listed
in the second column, beam sizes (
) and vertical
displacements can be measured sufficiently even for a single bunch.
For the measurements of transverse rotations a few bunch trains must
be necessary for the statistical accuracy.