CERN Accelerating science

Towards 90% power conversion efficiency for klystrons
by Igor Syratchev (CERN)
 
General view of the 6MW, S-band MBK (40 beams) with PPM focusing with expected RF power production efficiency above 75%. Image credit: JSC ‘VDBT’, Moscow, Russia

Computer simulations confirm that RF production efficiency above 90% can be reached in klystrons with a new electrons bunching technique.  

The increase in efficiency of RF power generation for future large accelerators such as CLIC, ILC, ESS, FCC and others is considered a high priority issue. It can contribute to a significant reduction of the investment and operational costs of accelerators. The vast majority of existing commercial high power RF klystrons operate in the electronic efficiency range between 40% and 55%. Only a few klystrons available on the market are capable of operating with 65% efficiency or above.

It is commonly considered the high efficiency klystrons require a low perveance. Limited by technically accessible high voltage levels, this can only be obtained by operating with low currents, thus single beam klystrons are incompatible with the need for high power. The concept of multi-beam klystron (MBK) resolved this inconsistency by introducing many single beams which interact with common RF circuits of the klystron, increasing the power with the multiple beams, whilst preserving low perveance per beam. In the standard klystron optimization procedure the target is to minimize the bunch length prior to it entering the output cavity. Independent studies concluded that in this case the 80% efficiency can be achieved and this value remains as a relatively hard limit.

To reach higher efficiency, the intrinsic limits of the bunching processes and deceleration in the output cavity need to be understood at the level of the electron bunch dynamics.

The new method to increase efficiency is based on the concept of a fully saturated bunch formation using the new bunching technique with bunch core oscillations. The first simulations proved that klystron RF power production efficiency close to 90% can be achieved. The new technology demonstration prototypeis now in fabrication in industry, with expected efficiency above 75% (see image above). The testing of this tube is scheduled for November 2015.

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Applications of Particle Accelerators in Europe
by Angeles Faus-Golfe (UV), Rob Edgecock (HUD/STFC)
 

APAE poster

We are pleased to announce the kick-off meeting of “The Applications of Particle Accelerators in Europe” project that will be held on 18-19 June 2015 at the Royal Academy of Engineering in London.

Organised by the EuCARD‐2 project, this meeting marks the beginning of a process to document the uses and importance of accelerators in Europe. It will study applications which are new or currently under development, and for which technology developed for research can have an impact. The aim will be to demonstrate the potential of particle accelerators and the importance of continuing their development, and deliver a report that can be presented to European policy makers.

This kick‐off meeting brings together people who are willing to contribute to this document and will focus on several topics including Industry and Environment (Ion and Electron beams), Security, Health, Photonics and Energy. If you are working in one of these fields, are interested in this activity and willing to contribute, we invite you to attend, be part of the project and have your say.

For more information on the programme and registration please consult the website

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  First Energy Efficient RF Sources Workshop
  by Erk Jensen (CERN), Charlotte Houghton (STFC)


Attendees of the EnEfficient RF Workshop at the Cockcroft Institute, June 2014.
Image credit: Cockcroft Institute

The first Energy Efficient RF Sources workshop, supported by EuCARD-2, took place in June 2014 at the Cockcroft institute in the UK. Over 40 delegates and 18 speakers were part of the two day workshop which discussed state-of-the-art RF sources.

In the early days of particle accelerators, RF experts concentrated their design work on cavities and amplifiers with large acceleration in mind. Later, when the beam currents in accelerators increased, the focus of their ingenuity shifted towards coping with beam loading, better beam stability and increasing beam power. With demands for ever increasing beam energy and power, the overall energy consumption has now clearly become a major concern; large future particle accelerators must remain economically and ecologically sustainable and acceptable, so the overall power conversion efficiency has taken centre stage. Optimization of this efficiency could reduce both power consumption and wasted energy, both relevant for the society at large. At this Daresbury workshop, these concerns were discussed among international experts, and many novel and interesting solutions to make better RF systems were proposed.

Workshop highlights included, pioneering ideas proposed to substantially increase the power conversion efficiency of high power klystrons. Klystrons are Multi-Megawatt RF power amplifiers at the heart of many particle accelerators. While present-day klystrons are limited to efficiencies below 70%, the proposed improvements may push efficiencies to 90%. Much attention was also devoted to high power solid-state amplifiers. These amplifiers are still limited to much smaller power limits than vacuum electronic devices, but the trend over the last decade is very promising; and it is predicted  they will become important in the future. Inductive output tubes (IOT’s), combine the advantages of grid tubes, this allows them to run without DC current, i.e. at lower power consumption. With the advantages of high frequency klystrons, IOT’s do not yet reach the power levels needed in accelerators, but promise better efficiency. This  has encouraged recent results and plans for further research.

The two-day workshop, which is part of the EnEfficient EuCARD-2 work package, addressed the above interesting and promising topics and more. The workshop included a tour of the Versatile Electron Linear Accelerator (VELA), located at the Daresbury Laboratory.

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  Accelerator quality HTS dipole magnet demonstrator design
  by Agnes Szeberenyi (CERN), Glyn Kirby (CERN)


Figure 1: Aligned block development HTS magnets, (bottom right) Feather-M0 quench detection development coil, (top left) Feather-M2 the EuCARD-2 five Tesla standalone approaching accelerator field quality insert magnet. Image credit: CERN

Future high-energy accelerators will need very high magnetic fields in the range of 20 T. The EuCARD-2 Future Magnets activity is a collaborative push to take HTS materials into an accelerator quality demonstrator magnet. A new coil layout concept, named aligned block was developed which can result in 2.3 times less conductor that leads to more cost efficiency than with the conventional Cosine Theta design using the same conductor.

The collaboration between CEA-CERN-KIT-TUT-INFN-LNBL aims to develop a High Temperature Superconductor (HTS) accelerator quality magnet demonstrator, capable of producing a 5 T central magnetic field in standalone configuration. Both REBCO and BSCCO conductors are being considered. The BSCCO design is part of the US-BSCCO programme based on Canted Cosine-Theta (CCT) geometry. The European collaboration is focusing on REBCO coated conductors, based on aligned block and cosine-theta.

At CERN scientists are developing the align block concept, named Feather-M0/2 (FeaTHeR - Five Tesla HTS Research, see Figure 1). Feather-M0 is used to develop coil winding and quench detection, while Feather-M2 will produce 5 Tesla standalone and between 17 and 20 Tesla, when inserted into the 100 mm aperture of Fresca-2 high field out-sert magnet. The main objective with the aligned block design is to maintain a close alignment of the magnetic field with the cable throughout the entire coil assembly. This layout makes optimal use of the anisotropy of the REBCO coated conductor (Figure 2). The design, although in its initial phase, addresses most issues related to the use of Roebel cable for a dipole cable. In a second step it is foreseen to approach a 17 T central field when inserted in a 13T high field magnet. Model coils are under construction, cables and magnet designs are progressing. Models will test dynamic field quality and confirm if it is possible to detect and protect the REBCO high current density present in the aligned Roebel cable design.


Figure 2:In the layouts the magnetic field angle is highest at the edges of the cable causing a large variation of the critical current over its width. Image credit: CERN

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  New approach to characterize RF properties in complex structures
  by Margarita Synanidi (CERN) with Thomas Flisgen, Johann Heller, and Ursula van Rienen (Uni Rostock)


Magnitude of the electric field of  a higher order multi-cavity eigenmode in a chain of eight superconducting 3.9 GHz cavities (zoom at the bottom), which are connected via beam-pipes and bellows (zoom at the top). Image credit: UniRostock

The computation of RF properties  of large and complex accelerating structures is a challenging and important task for the design and operation of particle accelerators. A new method, developed under EuCARD-2 WP12 allows for the characterization of radio frequency properties such as field distributions, quality factors or impedance/scattering parameters of large and complex structures.

Until now direct approaches that determine these properties required expensive supercomputers due to the vast number of degrees of freedom arising from the direct discretization of the complex structure. Moreover, results delivered by direct methods could be unsatisfying due to round-off errors or numerical instabilities arising from ill-conditioned system matrices. The computational demand of the direct computations of the full chain can be avoided by decomposing the structure into single elements. In a next step,  the individual segments are described by means of reduced order state-space models, which are combined to a reduced order model of the entire structure. The approach is referred to as state-space concatenations (SSC) and enables the computation of radio frequencies properties of complex structures by using standard workstation computers, rather than supercomputers.

The novelty of this approach is the description of the individual segments by means of state-space models. The state-space models provide a rigorous description of the radio frequency properties of the segments, in particular, they enable to reconstruct field distributions. Computations or radio frequency properties are not only relevant for cavities, but are also performed in other studies, e.g. in case of modelling bunch compressors. The SSC approach is not restricted to a special topology or particle accelerator applications and can be used to other similar calculations as well to avoid the usage of expensive cluster computers.

The next step incorporates the generation of detailed computer models of chains of four and eight third harmonic cavities, which are accommodated in FLASH or the XFEL. Previous studies have shown that the consideration of the entire chain is required rather than restricting to individual cavities. It is planned to generate a modal compendium (list of eigenmodes and their properties) for these structures based on the detailed computer models.

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  Universities and Laboratories for a common goal
  by Giuliano Franchetti (GSI) and Frank Zimmermann (CERN)


Some of the ULA2014 participants in front of the Institute of Applied Physics, Goethe-University Frankfurt am Main. Image credit: Fips Schneider, IAP, U. Frankfurt

Universities meet Laboratories” (ULA2014) workshop was a pioneering attempt to bring together representatives of the academic world and of laboratories to resolve differences and discuss synergies for working toward a common goal. Amongst many, this included topics like research evaluation and how to make accelerator science an attractive career choice. The event was attended by over 40 key players from all over Europe.

The workshop revealed a unanimous consensus among the participants from universities across Europe that the field of accelerator physics and technology appears to be often disadvantaged by an inadequate standing in the academic environment.

A very critical observation and issue is that students across European universities do not choose accelerator physics as a study topic and most importantly, many of them are not even aware of accelerator physics as a possible career path. For that reason greater efforts should be made for attracting students in the first stage of their studies. Another issue that was raised is that joint PhD supervision has become a difficult process because the needs of the laboratories do not always match the university research interest.

In terms of research assessments the workshop has evidenced a distinct difference of the research evaluation at universities and laboratories. This difference does not only prevent some laboratory staff from competing for job posts at universities, but it also renders collaboration with laboratories less attractive for the university staff. One reason is that laboratories traditionally disseminate their work in conference proceedings (if at all), while the universities consider only the publications in peer-reviewed journals. Moreover, given the strict metric evaluation the universities apply like the h-factor that disregards other relevant scientific outputs, it occurs that accelerator physics journals are suffering from a low impact factor, which is becoming a discriminating element in the research evaluation.

The workshop has also highlighted the positive impact of three major European and  American accelerator schools – CERN Accelerator School (CAS), Joint Universities Accelerator School (JUAS), and US Particle Accelerator School (USPAS) – as well as accelerator training at universities, with Germany leading the way. In Japan the combination of the Graduate University for Advanced Studies (SOKENDAI) and the Inter-University Research Institute Corporation has proven effective. A report on the TIARA survey results showed that many ongoing activities require more training in accelerators. In most of the European countries the elevation of the discipline to the same as level as other more established branches of physics is being pursued by self-organization of the community (e.g. KfB in Germany, CONECTA in Spain), and with the support of the EPS-AG. In general a deeper discussion of these subjects is required. Although, good experience with joint research, and including green field academic accelerator studies, has been reported from the UK.

Many ways to attract more students to the accelerator science were discussed. In particular, Philip Bambade, Accelerator Department Head at LAL Orsay, proposed and highlighted several promising approaches.

A key to attractiveness can be the multi/inter-disciplinary character of accelerator science. Another factor can be that compared to fields like HEP or even nuclear physics, accelerator scientists can be both theorists and experimentalists at the same time.

With the evolution towards smaller, very sophisticated, accelerators, another possible path is a closer connection between the accelerator scientists and the users, through approaches integrating these two communities.

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  Beam Dynamics meets Magnets supported by EuCARD-2
   by Giuliano Franchetti (GSI)

                                         
                                         Group photo from the recent workshop at the Darmstadtium.
                                                                                  Image credit: Paul Goergen 

An unforeseen collaboration was formed as a result of a workshop last December, which brought together two independent working groups, the beam dynamics and magnets experts.

“EuCARD-2XBEAM-XRING activity makes it possible to think out of the box and to bring experts together to exchange their ideas who would otherwise not collaborate“, says Franchetti, the father of this initiative.
The “Beam Dynamics meets Magnets” workshop has attracted over 80 members of the Particle Accelerator Beam Dynamics and of the Accelerator Magnet communities.. Topics covered ranged from energy frontier to intensity frontier. The meeting has been an unprecedented forum for traditionally independent entities to share experiences accumulated in different laboratories characterized by different traditions, different projects, and different people.

The discussions at the meeting have primarily been center on FAIR project issues. Discussion on inside aspects of LHC, J-PARC, and ATF2, along with ISIS put the FAIR effort into a new and more positive prospective. The open discussions, and information from the workshop contributed to tune the FAIR roadmap for dipoles and quadrupoles procurement, and the strategies of magnet measurements as well as the interplay with beam dynamics to a new and more efficient level. Remarkably, at the end of the workshop, the participants have acknowledged the need to keep the “meeting” going and sharing information.

Given the positive results of the meeting, the next one has already been scheduled for 1-4 December 2014. It will be coordinated by the EuCARD2 XBEAM-XRING Network and hosted by PSI.

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  EuCARD-2 Highlights from Hamburg
  by Thomas Hind (CERN)

 
 Group photo from the recent meeting in Hamburg. Image credit: EuCARD-2

Over 140 accelerator specialists from all over the world came together recently at the DESY laboratory in Hamburg for the 1st annual meeting for EuCARD-2 and the 1st Workshop on Accelerator Magnets in High Temperature Superconductors (HTS), which took place on 19-23 May.

The meeting saw presentations from speakers from each work package, including reports from the networks, which organised over 15 workshops on the topics of catalysing innovation, energy efficiency, accelerator applications, extreme beams, low emittance rings and novel accelerators. There were also updates from the technical work packages, including reports that a Surface Analysis/Preparation Installation (SAPI) has been constructed and commissioned for carrying out research on metal photocathode materials, on completed irradiation tests on ions and protons at GSI and RCC-KI and on the demonstration and characterisation of spatial and temporal synchronisation of laser and electron beams.

The 1st Workshop on Accelerator Magnets in HTS was an invite-only event organised as part of WP10 and included researchers from elsewhere in the world. It was the first in a series of planned workshops dedicated to High Temperature Superconductors, focusing on the construction and design of an HTS-dipole capable of boosting the field of an accelerator dipole from 15T to about 20T.

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  Workshop on Accelerators for ADS
  by Alessandra Lombardi (CERN)


MYHRRA Layout: injector building to the left, the long straight for acceleration and the reactor building to the right. Image credit: MYHRRA - SCK CEN

A workshop on accelerators for Accelerator Driven Systems took place on 20-21 March 2014.

The workshop counted 42 registered participants and 30 contributions. The main European projects were represented with representatives from MYRRHA, Linac4/SPL, ESS, Saraf and SPIRAL2/IPHI.

An accelerator for ADS should provide a beam of protons with energies above 800 MeV and a beam power between a few and 10-15 MW. Beam losses should be controlled to minimize the irradiation of the accelerator and of the environment, but the most important quality of an ADS accelerator is its reliability. The number of beam trips should be minimised and the limitation comes mainly from thermal stress in the fuel structure. As a guideline, MYRRHA requirement are not more than 100 trips per day lasting between 0.1 sec and 3 seconds and no more than 10 trips per trimester lasting more than 3 seconds. The energy efficiency, the size of the accelerator and its cost are also important parameters. In the end, the solution chosen among LINAC, Cyclotron or Fixed Field Alternating Gradient Accelerator (FFAG) will be the one best fulfilling all these requirements.

During the workshop several synergies were identified between Max and Eucard2 AccApplic, amongst which are reliability issues, the dynamics in the low energy beam transport and neutralisation effects and the concept of a virtual Accelerator.

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  Explore accelerator applications with EuCARD-2
   by Rob Edgecock (HUD)

           
Spot scanning gantry (Gantry 2), which was designed specifically to enable treatment of moving tumours with scanned beams. Image credit: PSI.

Work Package 4 (AccApplic) of the EuCARD2 project is a Network investigating existing and possible new applications of particle accelerators. The aim is to find applications that could benefit from accelerators and techniques developed for research activities, particularly in Particle Physics.

More than 30,000 accelerators are in use around the World for applications in the areas of healthcare, the environment, industry, energy and security. Together, these are responsible for nearly $0.5T/year of economic activity. Although the accelerators used for many of these applications are very well suited to the task, there are cases in which improvements in performance are possible or work is required to reduce the size or cost of the accelerator or there are particular problems to be solved. The AccApplic Network will be studying these cases.

As a Network, the main method of doing this will be to bring together experts to discuss the problems and possible solutions in workshops. The purpose is to initiate collaborations to further address the problems. The first such workshop, on Modern Hadron Therapy Gantry Developments, has already taken place and the summarizing report is now available. The next two are upcoming, on Accelerators for Accelerator Driven Systems and Neutron Production and BNCT. Further workshops on muon production for energy, materials and security applications and accelerators for flue gas, water and food treatment are also planned.

If you would like to participate in the Network or have suggestions for other workshops, please contact the coordinator, Rob Edgecock.

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