Energy or Luminosity 1 ． Luminosity and energy can be complementary in precise measurement experiments up to some point but in some very important cases the energy is more efficient. Example—branching ratio of Higgs decays Here the higher energy above 1.3 TEV is very powerful because the W or the Z exchange starts to contribute to the Higgs production substantially at this energy,

2.It is very important that we will be able to say something about the supersymmetry in the LC project. Some superparticle ｓ maybe within the range of possible upgraded energy of LC. 3.I do not think it is proper to stay strictly below 1 TEV and make a distinction between the two technologies based on minute differences between the two technologies which so far we have not found in a significant way. There is no physics basis in choosing the 1 Tev as the strict target energy. It is quite ad hoc. We can and should interpret the 1TEV set by ICFA to be somewhere around 1 TEV, allowing us to discuss the energy reach in a meaningful way.

Risk Factor 1.Cold machine Positron sources may disrupt the operation at least it could interfere with the commissioning. Damping ring is no way a risk free item. Space charge is not well understood. The method to overcome this by x-y coupling is interesting idea but can it work? Low energy large circumference machine such as TESLA damping ring could have all kinds of instabilities including the one in the fundamental mode. Dark current is not well understood at least for the 35 GEV/m electro-polished cavities. 2.Warm machine Damage due to high field is not well understood. It could be serious above 65Mev/m. Only a limited number of structures passed the design goal. Whether they work in the entire LC structure is a different matter. Only a few champion data pass the criteria of the design goal In klystron and in beam delivery system. Unless some sort of prototype system be constructed in the near future, the risk factor could be large.

Recommendation With due respect to all who are involved in TESLA R/D especially to late B.Wiik who initiated the project, I must recommend X-band technology as the technology of the LC project. Reason Although the superconducting structure has been well developed above the expectation of most experts, under the leadership of Wiik and then of Wagner, there still remain many components which have not even been touched upon or not well understood, including positron sources and the damping ring which is essential in reaching the high luminosity. Even though we restrict ourselves to an extendable energy of approximately 1 Tev,the judgment based on the physics performance tells us that the energy reach is very important for the LC and simply because the warm machine has so far achieved 60MEV/m(beam non-loaded), and it would be very difficult for the cold machine to reach this value, the warm machine is more suitable as the technology of the LC.