The conceptional design of the proposed linear electron-positron collider TESLA is based on 9-cell 1.3 GHz superconducting niobium cavities with an accelerating gradient of E acc $ 25 MV͞m at a quality factor Q 0 $ 5 3 10 9 . The design goal for the cavities of the TESLA Test Facility (TTF) linac was set to the more moderate value of E acc $ 15 MV͞m. In a first series of 27 industrially produced TTF cavities the average gradient at Q 0 5 3 10 9 was measured to be 20.1 6 6.2 MV͞m, excluding a few cavities suffering from serious fabrication or material defects. In the second production of 24 TTF cavities, additional quality control measures were introduced, in particular, an eddy-current scan to eliminate niobium sheets with foreign material inclusions and stringent prescriptions for carrying out the electronbeam welds. The average gradient of these cavities at Q 0 5 3 10 9 amounts to 25.0 6 3.2 MV͞m with the exception of one cavity suffering from a weld defect. Hence only a moderate improvement in production and preparation techniques will be needed to meet the ambitious TESLA goal with an adequate safety margin. In this paper we present a detailed description of the design, fabrication, and preparation of the TESLA Test Facility cavities and their associated components and report on cavity performance in test cryostats and with electron beam in the TTF linac. The ongoing research and development towards higher gradients is briefly addressed.

For decades, the rubber industry, and the tire industry in particular, have been using mainly carbon blacks as reinforcing fillers. Since their structure and specific surface area can be varied over a wide range, carbon blacks are capable of meeting a wide range of different requirements. Even today, we are unable to exert a specific influence on the third component of reinforcement, the “surface activity” (surface energy) of carbon blacks. This problem and new, more stringent tire performance requirements lend new significance to the need for further carbon black research and development. Silicas, which were developed during the nineteen forties and fifties, were mainly used in shoe soling materials. Specific surface area and structure of the silicas were constantly adjusted to meet new requirements in this area. As our knowledge of the reinforcing mechanism of silicas in rubber increased, the benefits and drawbacks of silicas in rubber, in comparison to carbon blacks, became more and more apparent. The challenge to improve their reinforcing effect was then taken up. Since the beginning of the nineteen seventies, the chemical industry has concentrated on developing silanes for the rubber industry. The significance of the formation of covalent rubber-to-filler bonds for rubber reinforcement was recognized, and ways and means for the optimum and most efficient use of silicas and silanes were found, in a long and difficult process. During the past ten years, research and development efforts were dominated by the demand for increasing abrasion resistance, improving wet traction, and achieving the lowest possible rolling resistance. The combined use of silicas and silanes opened up new possibilities for meeting the requirements of the tire industry. After first adapting silanes to the silicas available, research and development efforts have recently been focused on adjusting the silicas to the silanes in order to achieve optimum effectiveness of this reinforcing system. All in all, a process seems to have been initiated in the tire industry which aims at using the silica/organosilane system to much greater advantage.

Carbon black N110 and a precipitated silica, which have comparable surface area and structure, were selected as model fillers to study the effect of filler surface energies on rubber reinforcement. In comparison with carbon black, the surface energies of silica are characterized by a lower dispersive component, γsd, and higher specific component, γssp. It was found that the high γssp of silica leads to strong interaggregate interaction, resulting in higher viscosity of the compounds, higher αƒ, and higher moduli of the vulcanizates at small strain. The higher γsd of carbon black, in contrast, causes strong filler—polymer interaction, which is reflected in a higher bound-rubber content of the compounds and higher moduli of the vulcanizates at high elongation.

SBR compounds were filled with 17 carbon blacks covering the whole range of rubber grades and tested for bound-rubber content. It was found that the bound-rubber content of a polymer at high loadings is higher for large surface-area carbon blacks. On the other hand, the bound-rubber content per unit of interfacial area in the compound (specific bound-rubber content) decreases with increasing specific surface area and filler loading. This observation was interpreted in terms of interaggregate multiple molecular adsorption, filler agglomeration, and change of molecular weight of rubber during mixing. When the comparison was carried out at critical loading of a coherent mass, the specific bound-rubber content was found to be higher for the high-surface-area products which are characterized by high surface energies. The critical loading of coherent mass of bound rubber also shows a strong surface-area dependence, indicating that large particle carbon blacks give high critical loadings. The measurements of bound rubber at high temperatures for carbon-black-filled compounds and in an ammonia atmosphere for silica-filled compounds suggest that bound rubber is caused essentially by physical adsorption.

PrefaceIt is the purpose of this book to collect the experience gained with the design, construction and operation of the superconducting magnets for large hadron accelerators, and to outline the physical principles of superconductivity and its application in highfield dipole and quadrupole magnets. Most of the material stems from the extensive research and development work at the large high energy physics laboratories and of course also from the authors' own work at the proton-electron colliding beam facility HERA in Hamburg. After the success of the magnets for the Tevatron proton accelerator at the Fermi National Accelerator Laboratory near Chicago, a number of new projects have been initiated and the community of physicists and engineers working in this field has considerably expanded. Many of those people, the authors included, have profited a great deal from the excellent book Superconducting Magnets by Martin N. Wilson. Also the book Superconducting Magnet Systems by H. Brechna is an extremely useful reference. It is by no means our intention to replace these monographs, on the contrary we try to be complementary and focus our attention on the aspects that are specific to accelerator magnets. There is of course some unavoidable overlap, for instance in field computation, the treatment of persistent magnetization currents or quench propagation but also here we concentrate on recent experimental results and their interpretation.Field quality is one of the key issues for the magnets of a hadron collider. The impact of mechanical tolerances, persistent currents and eddy currents on field quality is discussed at length and numerous experimental data are presented. Another key issue is the quench performance of the magnets. Unlike in many other applications of superconducting magnets, for example in magnetic resonance imaging, quenches in accelerator magnets cannot be avoided, because beam losses happen from time to time. The quench detection and magnet protection system is hence of vital importance and needs considerable attention.Within the scope of the book it is impossible to fully cover the enormous amount of research and development work done at the Lawrence Berkeley Laboratory (LBL), Brookhaven National Laboratory (BNL), Commissariat a PEnergie Atomique (CEA) in Saclay, the European Laboratory for Particle Physics (CERN), Deutsches Elektronen-Synchrotron (DESY), Fermi National Accelerator Laboratory (FNAL or Fermilab) VI PREFACE and other measurements are presented to illustrate the properties and performance of practical superconducting dipoles and quadrupoles as well as the implication of superconductor-related properties for the particle beams. Again a selection had to be made, we hope it was fair. When the HERA project was started we received generous help and advice from scientists and engineers at Fermilab, Brookhaven, CERN and Saclay: