eeFACT2016 held in Daresbury UK

Jennifer Toes — Tue, 06 Dec 2016 13:41:30 +0000

eeFACT2016 held in Daresbury UK
by Ralph Aβmann (DESY), Peter Ratoff (Cockcroft Institute) and Frank Zimmermann (CERN)

eeFACT2016: Participants of eeFACT2016 on the Daresbury campus (Image: Cockcroft Institute)

From 24 to 27 October 2016, accelerator experts from around the world gathered in Daresbury, UK, to discuss the state of the art, the challenges and the future directions for circular high-luminosity electron-positron factories.

The eeFACT2016 workshop was organized under the umbrella of ICFA and co-sponsored by the EuCARD-2 “Extreme Beams” accelerator network. An international committee co-chaired by Yoshihiro Funakoshi from KEK, Qing Qin from IHEP, and Frank Zimmermann from CERN had assembled a programme reflecting the breadth of the ongoing worldwide efforts.

The Cockcroft Institute, with the hospitality of its Director Peter Ratoff and the outstanding support from Liz Kennedy and Sue Waller, proved a perfect host for this event. Participants hailing from China, Italy, Japan, Russia and the United States appreciated the smooth organization, wonderful venue, plus the chance to visit nearby historical Chester. The timing of the workshop could not have been better, including for the weather: during all four days the sun was shining, in what seemed like a British Indian summer.

Circular colliders have been a frontier technology of particle physics for half a century, with more than a factor 10 luminosity increase every ten years. Several lower-energy factories are in operation, continually improving their performance: BEPC-II at IHEP Beijing, DAΦNE at INFN Frascati, and VEPP-2000 at BINP Novosibirsk.

The Super-B-factory SuperKEKB, presently under commissioning in Japan, will be the next big upward step in luminosity. Among other future projects, a Super-charm-tau factory is being developed in Russia, while two ambitious highest-energy circular Higgs-Z-W (and top) factories are under design: the Circular Electron Positron Collider (CEPC) in China, and the electron-positron version of the Future Circular Collider (FCC-ee) on the Franco-Swiss border.

At eeFACT2016, DESY leading scientist Ralph Assmann recognized the continuing high level of innovation, even after an already 50-year long history of colliders, and a wealth of novel concepts. Over the last couple of years, several game-changing schemes have been introduced, for example colliding beams with a crab waist, large Piwinski angle and extremely low emittance.

The crab-waist concept was presented by its inventor Pantaleo Raimondi, now Director of the Accelerator and Source Division at the ESRF. This crab-waist scheme has already demonstrated its great merits in actual beam operation at DAΦNE. Other novel concepts include the use of a double ring or partial double ring, magnet tapering for the energy sawtooth, top-up injection, cost-effective 2-in-1 magnets, ultra-low beta function, “virtual crab waist” and asymmetric interaction-region optics.

The last two concepts were rather recently developed by Katsunobu Oide, former Director of KEK’s Accelerator Laboratory. Upcoming colliders like SuperKEKB will test the limits of these new schemes and manifest their positive impact. The upgraded VEPP-2000 collider will push the concept of round beams. In parallel much progress is being made in the design and operation of storage-ring light sources. An excellent review by ESRF’s world expert Dieter Einfeld revealed numerous topics of common interest with the collider world. Lastly, not to be forgotten is the built-in synergy of a future large circular high-energy lepton collider, such as CEPC or FCC-ee, with a subsequent hadron collider installed in the same tunnel, called SPPC and FCC-hh, respectively – as was highlighted by Alain Blondel from the University of Geneva.

The projected performance of the future factories is further lifted by a dramatic progress in accelerator technology. An entire session, convened by JLAB’s Bob Rimmer, was devoted to the radiofrequency (RF) system, which, working in continuous wave mode, needs to transmit a large power and support high beam currents at a high efficiency.

An essential component of this system is superconducting RF (SRF) cavities, whose overall efficiency is revolutionized by novel production schemes such as nitrogen doping and thin-film Nb3Sn coating. Several novel klystron concepts are on track to boost the power conversion efficiency of RF power generators. Thanks to this type of innovation, when compared with previous colliders the next generation can be considered truly green facilities.

The luminosity-energy plane of past, present and proposed future e+e- colliders. Combining successful ingredients of recent colliders and adding further innovative concepts promises extremely high luminosities at energies ranging from the Z pole to the tt threshold as illustrated by the plotting symbols for FCC-ee and CEPC (Image: Marica Biagini and Frank Zimmermann).

Alex Chao, an eminent physicist from SLAC, summarized that with performance being pushed so hard at the future factories, more subtleties that were unimportant in the past now arise. Indeed new effects keep being discovered for the beam-beam effects, such as the requirement of crab waist, residual nonlinearities after the crab waist cancellation, beamstrahlung, 3D flip-flop instability, interplay with lattice nonlinearities, and the possible interplay with collective effects. Alex Chao underlined that the beam-beam issue will become more critical than ever.

The large future collider concepts FCC-ee and CEPC build upon the recent innovations and are planning to exploit their full potential at the precision frontier, measuring the properties, couplings and decays of the Higgs and several other high energy particles with extreme accuracy. New ideas for compact low-energy crab-waist colliders, possibly based at universities, are emerging as well and these might offer attractive alternative paths for research and science.

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eefact2016

EuCARD-2

FCC-ee

CEPC

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electron-positron factories

issue 19

First concept design for FCC-ee magnets

Panagiotis Charitos — Thu, 24 Mar 2016 15:54:37 +0000

First concept design for FCC-ee magnets

by Panos Charitos with Attilio Milanese (CERN)

A first concept for the FCC-ee main dipoles, with an X iron yoke (blue) and two aluminium busbars (red). The dimensions are about 40 cm wide per 12 cm high (Image: CERN).

The FCC-ee (Future Circular Collider lepton-lepton scenario) machine requires about 65 km of such magnets, to steer the counter-rotating electron and positron beams, before they collide at the energy of 350 GeV. As the preparation for the upcoming FCC week (11-15th April) is in full swing, researchers from CERN have presented a first concept for the main bending magnets for FCC-ee.

The proposed design for the FCC-ee main bending magnets features a twin aperture geometry, with a common iron yoke and two busbars, operated at room temperature. The dimensions are about 40 cm wide per 12 cm high. The design shows how compact these dipoles could be – at the moment their cross section fits on an A3 sheet. This concept will be further refined, to match the evolving requirements coming from the other FCC-ee work packages, including those on beam dynamics and vacuum.

The idea presented recently is based on a novel layout, where two classical C shapes are arranged back to back to create an unconventional X geometry. The great advantage of the novel design is that the magnetic field in one of the apertures comes at no extra cost, since it is generated by the return conductor of the other aperture. Compared to a system with separate magnets for the two rings, this solution reduces electrical consumption by 50% and of course the number of units to be manufactured, transported, installed and (eventually) removed, for the installation of FCC-hh.

The low fields needed in this case do not require superconducting technology for the magnets, like those used in the LHC and further developed for HL-LHC and FCC-hh (read more).

“The FCC-ee main dipoles require a different type of R&D,” says Attilio Milanese, the CERN engineer who proposed the concept. He explains “at the moment, the focus is to work on the design while optimising the costs and the environmental impact.”

The yoke can be assembled from sheets of electrical steel, of a similar kind used in electric machines like transformers or generators. The excitation current is provided by two busbars in aluminium, which is lighter and cheaper than copper for the same power consumption. Full recycling the raw materials after dismantling the collider is also an option explored, with the team running simulations to understand how these materials will be activated from the high synchrotron radiation emitted by the beams.

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eeFACT2016 held in Daresbury UK

First concept design for FCC-ee magnets