The status of the research on muon colliders is discussed and plans are outlined for future theoretical and experimental studies. Besides work on the parameters of a 3-4 and 0.5 TeV center-of-mass (COM) energy collider, many studies are now concentrating on a machine near 0.1 TeV (COM) that could be a factory for the s-channel production of Higgs particles. We discuss the research on the various components in such muon colliders, starting from the proton accelerator needed to generate pions from 1098-4402͞99͞2(8)͞081001(73)$15.00 © 1999 The American Physical Society 081001-1 PRST-AB 2 CHARLES M. ANKENBRANDT et al. 081001 (1999) a heavy-Z target and proceeding through the phase rotation and decay (p ! m n m ) channel, muon cooling, acceleration, storage in a collider ring, and the collider detector. We also present theoretical and experimental R&D plans for the next several years that should lead to a better understanding of the design and feasibility issues for all of the components. This report is an update of the progress on the research and development since the feasibility study of muon colliders presented at the Snowmass '96

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PURE covalent solids, e.g. B, Si, C, Sic, and BN, cannot be densified by either sintering or conventional hot-pressing . However, some of these covalent solids can be densified in the presence of liquid-forming additions. For example, appreciable densification has been obtained in S&N, sintered with MgO' and YzO, + SO,?In Sic, liquid sintering has been observed in the presence of a B,C-Sic eutectic3 and in a melt of a composition in the system Al-B-C-Si.4 With liquid-phase sintering, however, only limited densification (= 85 to 90%) was obtained.P m~h a z k a~.~ has reported sintering of Sic to densities near theoretical with the use of additions of several tenths of a percent boron to pure p-Sic powders. It was concluded that densification occurred by solid-state sintering. Boron, introduced as elemental B (amorphous or crystalline), B,C, or LiBH,, induces sintering in fine-grained S i c powders, and densities >95% of theoretical can be consistently obtained. Compacts of the same powders exposed to the same sintering conditions (2100°C in He) without B did not shrink significantly. Further experiments indicated that the presence of free C in the powder compacts is another necessary condition for achieving of high sintered densities. The present note describes sintering experiments in which the effects of both B and C were evaluated quantitatively and separately.Free C was removed from an SIC powder by exposing it to air at 650°C for 50 h; the expected oxidation products were removed from the surface of the S i c crystallites by leaching the powder with 20% HF and washing it with water and alcohol. Spectrographic analysis of the yellowish powder obtained revealed (in ppm) B 20, A1 10, Fe 70, W 300, Ca 50, and other metals (Cr, Mg, Ti, and Mn).Chemical analysis showed 0.17% 0,0.008% N, and 0.00% freeC. The surface area of the sample was 9.2 m2/g, whereas the mean average particle size was 0.13 pm. The S i c phase present was p-Sic.Carbon was reintroduced by mixing the powder with a carbonaceous organic compound in solution (polymethylphenylene in benzene), and B was added by mixing the sample with another powder which was heavily doped with B on preparation but otherwise had identical characteristics and in which B was assumed to be present partly in solid solution but mainly as B4C. Three-gram cylinders were pressed from each composition and sintered in flowing He at 1 atm (0.7 ppm 0,) in a carbon-element resistance furnace at 2100°C (established by preliminary experiments). The shrinkages and final densities measured by liquid displacement are given in Table I. A lower limit to the B and free C concentrations necessary to effect the maximum density of S i c exists. At any level of C, densification of Sic in the absence of B is virtually nil and reaches a maximum at -0.3% B. The optimum B concentration is probably related to the solubility limit of B in Sic, which must be exceeded to initiate densification. The solubility of B in a-Sic at 2100°C is =0.2%.7*8 However, much higher estimates are found in the literat...

Abstract-We report on the progress in our R&D program, targeted to develop the technology for the application of Bi2Sr2CaCu2Ox (Bi-2212) in accelerator magnets. The program uses subscale coils, wound from insulated cables, to study suitable materials, heat treatment homogeneity, stability, and effects of magnetic field and thermal and electro-magnetic loads. We have addressed material and reaction related issues and report on the fabrication, heat treatment, and analysis of subscale Bi-2212 coils. Such coils can carry a current on the order of 5000 A and generate, in various support structures, magnetic fields from 2.6 to 9.9 T. Successful coils are therefore targeted towards a hybrid Nb3Sn-HTS magnet which will demonstrate the feasibility of Bi-2212 for accelerator magnets, and open a new magnetic field realm, beyond what is achievable with Nb3Sn.

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