  We consider several ILC energy upgrade paths beyond 1 TeV depending on the
needs of high energy physics. Parameters for four scenarios will be pre-sented
and challenges discussed. 1. From 1 TeV to 2 TeV based on: A. Gradient advances
of Nb cavities to 55 MV/m antici-pated from on-going SRF R&D on Nb structures.
B. Radically new travelling wave (TW) superconducting structures optimized for
effective gradients of 70+ MV/m, along with 100% increase in R/Q (discussed in
more detail in paper WEOCAV04 at this confer-ence. The large gain in R/Q has a
major beneficial impact on the refrigerator heat load, the RF power, and the AC
operating power. OR 2. From 1 TeV to 3 TeV based on: A. Radically new
travelling wave (TW) superconducting structures optimized for effective
gradients of 70+ MV/m, along with 100% increase in R/Q. The large gain in R/Q
has a major beneficial impact on heat load, RF power, and the AC operating
power. B. 80 MV/m gradient potential for Nb3Sn with Q of 1x1010, based on
extrapolations from high power pulsed measurements on single cell Nb3Sn
cavities. Further, the operating temperature is 4.2 K instead of 2K due to the
high Tc of Nb3Sn.
