CERNMay/June 2020 cerncourier.com COURIERReporting on international high-energy physics WLCOMEE CERN Courier – digital edition Welcome to the digital edition of the May/June 2020 issue of CERN Courier.

This month’s issue looks at the latest progress in niobium-tin (Nb3Sn) accelerator SUPER magnets for high-energy exploration. Discovered to be a superconductor more than half a century ago, and already in widespread commercial use in MRI CONDUCTOR scanners and employed on a giant scale in the under-construction ITER fusion THE RISE OF experiment, it is only recently that high-performance accelerator magnets made NIOBIUM-TIN from Nb3Sn have been mastered. The first use of Nb3Sn conductor in accelerator magnets will be the High-Luminosity LHC (HL-LHC), for which the first

Nb3Sn dipole and quadrupole magnets have recently been tested successfully at CERN and in the US. As our cover feature describes, the demonstration of

Nb3Sn in the HL-LHC also serves as a springboard to future hadron colliders, enabling physicists to reach significantly higher energies than are possible with present-generation niobium-titanium accelerator magnets. To this end, CERN and the US labs are achieving impressive results in driving up the performance of

Nb3Sn conductor in various demonstrator magnets.

Sticking with accelerators, this issue also lays out the possible paths towards a high-energy collider – long considered a dream machine for precision and discovery, but devilishly difficult in its details. We also describe the rapid progress being made at X-ray sources, arguably the most significant application of accelerator science in recent decades, towards understanding the molecular structure of the SARS-CoV-2 virus. The importance of accelerators for neutron science is a theme of the Viewpoint article, and, in addition to the Courier’s regular coverage of the news, conferences and reviews, this issue includes reports on how high-energy physicists are responding to the COVID-19 pandemic.

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EDITOR: MATTHEW CHALMERS, CERN DIGITAL EDITION CREATED BY IOP PUBLISHING The path to a muon collider  Fine structure in antihydrogen  Reacting to COVID-19

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A lvin TollesTrup 1924–2020 Remembering a visionary physicist

Alvin Tollestrup, who passed away on them, Alvin left Caltech for Fermilab, where he 9 February at the age of 95, was a visionary. I would create the first large-scale application of Fermilab joined his group at Caltech in 1960. Alvin had superconductivity. Physics at Fermilab at that helped build Caltech’s electron synchrotron, the time was limited by the energy (200 GeV) of the highest energy photon-producing accelerator at 6.3 km-circumference Main Ring. Alvin made the time. But he thought more exciting physics essential contributions to the design, testing and could be performed elsewhere, and managed to commissioning of superconducting magnets to get approval to run an experiment at Berkeley replace the Main Ring’s copper ones – doubling Lab’s Bevatron to measure a rare decay mode the energy. The new machine, to be known as of the K+ meson. the , was completed in 1983. Alvin went Alvin asked me to help design, build and test on to convert it to a – collider a new type of particle detector called a spark in 1987, which led, within a decade, to the dis- chamber. In retrospect it was remarkable that he covery of the top quark. Alvin was the primary was willing to risk the success of his experiment spokesperson for the CDF collaboration from on the creation of new technology. He also asked 1980 to 1992, and his critical contributions to me to design a transport system of magnetic the Tevatron were recognised in 1989 with a US lenses that would capture as many K mesons as National Medal of Technology and Innovation. possible. I did my calculations on an IBM 709 at UCLA – Alvin checked them by tracing rays at Virtuosity with modesty his drafting table. When the beam design was The virtuosity required to create new acceler- completed and the chain of magnets was in place ators sometimes exceeds what is necessary to o n t h e a c c e l e r a t or flo or, A l v i n t h r e a d e d a s i ngle Alvin Tollestrup led the design of the run the resulting Nobel prize-winning exper- wire through them from the thin window of the superconducting magnets for the Tevatron. iments. Alvin once told me that the Bevatron’s accelerator to our hut. director, Ed Lofgren, never got the recognition The virtuosity he deserved. The Bevatron was designed and Zen master built to find the antiproton, and sure enough I had no idea what he was doing, or why. Around required to create Segrè and Chamberlain found it as soon as Alvin the Zen master, I didn’t say much or ask the machine was turned on, earning them a many questions. After turning the magnets new accelerators Nobel prize. Alvin also didn’t get the recogni- on and running current through the wire, the tion he deserved. His modesty only exacerbated wire snapped to attention, tracing the path a sometimes exceeds the problem. K would follow from where it left the accel- what is necessary There were some things I could never learn erator to where its decays would be observed. from Alvin. His intuition for electronics was Calculations – how much current was required to run the resulting beyond my grasp, a gift from the gods. In the in the wire – followed by testing, were Alvin’s 1950s, when the giants of the day were trying modus operandi. Nobel prize-winning to understand the origin of violation, When run-time arrived a couple of months his knowledge of photomultipliers led him to later, the proton beam was steered into a tung- experiments discover a flaw in an experiment which, once sten target behind the thin window through fixed, validated the V–A theory of the weak which the Ks would pass. We waited for the interactions. scintillation counters to start clicking wildly, but sufficient reason, and persistent. A l v i n d i d n o t s u ffe r fo ol s g l a d l y, b ut o ut s i d eof nothing happened. Eventually, having calmly Alvin was my first thesis advisor. When he work he created a community of collaborators, persuaded the operators to shut the machine taught me how to think about my measurements, an extended family. He fed and entertained us. down, Alvin took a pair of long tongs and pressed he also taught me how to analyse and judge the His pitchers of martinis and platters of whole a s m a l l s q u a r e o f d e nt a l fi l m a g a i n s t t h e r a d ioac- measurements of others. This was essential in hams were memorable. Legendary tightrope tive target. When developed, it showed a faintly understanding which of the many “discover- performer Karl Wallenda is quoted as saying, illuminated edge at the top of the target: the ies” of hadrons in the early 1960s were believ- “Life is on the wire. The rest is waiting.” Alvin Bevatron surveyors had placed the target one able. Without his influence, I never would have showed us how to have fun while waiting, and inch below its proper position, a big mistake. discovered quarks (aces), whose existence was shared a long and phenomenal life with us, both But there was no panic or finger pointing, just later definitively confirmed in deep-inelastic off – and especially on – t he high w ire. measurement and appropriate action. That was scattering experiments. Alvin’s style, always diplomatic with manage- More than a dozen years later, true to his George Zweig Research Laboratory of ment, never asking for something without belief that users of accelerators should improve Electronics MIT.

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