edited by L Cifarelli and L Maritato, World Scientific Science and Culture Series – Physics, ISBN 080243197.
Imagine the ultimate high-energy physics project – 10 times as powerful as CERN’s mighty LHC collider. This ambitious goal, which is aiming for a hadron collider with a collision energy of 200-1000 TeV and with a luminosity as high as 1036, is the theme of Antonino Zichichi’s foreword to this book. The vision of the multihundred TeV “ultimate collider”, the Eloisatron, is supported by the conviction that no energy threshold well beyond the Standard Model seems near.
The book is dedicated to the memory of Tom Ypsilantis and gives a full description of a workshop held in Erice, Sicily, at the end of 1999 on superconducting materials for future high-energy colliders. This marked the return of a full European perspective of the Eloisatron workshops, after a period during which the European community had been busy designing the LHC, while our US colleagues emerged from the trauma of the cancelled SSC and set up a new programme that is now focused on the VLHC.
With the LHC on track to produce physics by 2006, European scientists began to look beyond the present horizon. The workshop provided an excellent forum where materials scientists met with accelerator specialists to exchange information and to focus R&D towards common goals.
Superconductivity is the key accelerator technology, and the communities striving for high field (magnets) and for high gradient (radiofrequency cavities) exploit the absence of electrical resistance at low temperatures. In the reverse direction, high-energy physics has provided the right environment (and resources) to achieve real progress in applied superconductivity, by developing high-critical current density cables with fine filaments and achieving mass-production. A good example is magnetic resonance imaging (MRI), which could not have progressed from a laboratory-scale experiment to a general medical technique without the impetus of high-energy physics cryogenics.
At the Erice workshop, Philippe Lebrun, head of CERN’s LHC division, addressed the problem of technical management of megascience projects and described what we are learning with the LHC, the first global accelerator project, and reviewed the main machine subsytems, including the powerful cryogenics needed to keep some 50,000 tons of superconducting magnets at 1.9 K – the coldest point of the universe and twice as cold as the relic cosmic microwave radiation. Also for the LHC, Tom Taylor covered the vigorous technical effort that is under way to design and build the LHC’s superconducting components to conform to stringent energy and luminosity requirements, and the room for improvements.
Kjell Johnsen, the designer of CERN’s ISR, the first hadron collider, reviewed the tentative feasibility study of the Eloisatron, just 10 years after it was issued, showing that the machine, although very ambitious, is technically feasibly with a 300 km ring where some 16,000 dipoles reaching 10 Tesla can provide 100 TeV proton beams (200 TeV collisions).
On basic superconductivity, C Grimaldi (Lausanne) introduced the present understanding of high-temperature superconductors (HTS), stressing that much work still needs to be done, but the reward would be the cheap and easy cryogenics of liquid nitrogen.
J Halbrittner (Karlsruhe) described the detailed analysis of radiofrequency losses in superconducting cavities, showing the present superiority of bulk niobium cavities over sputtered ones for very high power.
Superconducting cavities for frontier colliders were the topic of an extensive review by H Padamsee (Cornell) on the impressive progress with bulk niobium and niobium-sputtered copper cavities. With proper selection and treatment of the material, the road is open to 40 MV/m and a TeV electron_positron superconducting linear collider. A Cassinese (INFM-Naples) described microwave measurements of superconducting films of niobium and niobium-tin, stressing the need to understand surface resistance.
L Rossi (Milan) turned to the design and characteristics of accelerator magnets, highlighting the demands on superconductor performance to build 5-15 T dipole and quadrupole magnets. He included an overview of worldwide R&D for magnets beyond the LHC-phase1, emphasizing the necessity of a vigorous effort to improve niobium-tin characteristics to reach a critical current of 1000 A/mm2 at 18 T (LHC-phase1 material reaches this level at 8 T and 4.2 K) and showed the novel magnet designs being explored in the US for VLHC studies.
The Japanese effort on doped niobium-tin reinforced with a copper-niobium matrix was covered by K Watanabe (IMR, Tohoku) who showed the potential of this technique to overcome the problems posed by the brittleness of niobium-tin. Japan is also leading the effort on the less brittle niobium-aluminium superconductor, and K Inoue (NRIM, Tsukuba) described the potential of the recently developed, rapid-quenching and transforming process. Although very difficult, this process could achieve interesting current densities.
For HTS, K Salama (Houston) reviewed the fabrication technique for bismuth- and yttrium-based, silver-stabilized superconducting tapes, reporting an improvement in critical current of almost an order of magnitude using suitable heat treatment. His former assistant, L Martini (ENEL-Ricerca, Milan), reported on his unique “accordion-folding method” to produce short (0.1-1 m) Bi-2223 samples with a very low silver content, useful for low-consumption multi-kA current leads (needed in large quantities for the LHC).
J Scudiere (American Superconductor Corporation) reviewed the results obtained by the leading company in HTS development and production. The impressive results on short samples have yet to be reproduced in long samples. However, for fields above 18 T, HTS could become a viable alternative to niobium within a few years. He highlighted the necessity of reasonable homogeneity and reliability of such a delicate (ceramic) material under “industrial” conditions and indicated that a production rate of at least 2000 km/year of tapes is needed to reduce prices to a reasonable level. Considering that such a quantity is approximately equivalent to about 50 LHC dipoles, major projects are needed to drive this promising material to market (as for MRI). Finally, C M Friends (BICC General Superconductors) reported on 13 kA HTS current leads for the LHC and the development of Bi-2223 tapes and of round wires (radial filaments) for low losses in AC conditions.
The book gives the impression that accelerator technology is far from saturation and there is plenty of room yet for exciting developments and significant breakthroughs. On an optimistic note, in the two years since the workshop was held, the increase in conductor performance from LHC values to final goals is already half-achieved. A field of 14.5 T at 4.2 K was attained earlier this year at Berkeley in a short model with a new niobium-tin coil configuration.
