CERN Accelerating science

  High power test results on C-band accelerating structures
  by David Alesini (INFN-LNF) & Marica Biagini (INFN-LNF)

  Fig1: C-Band structure installed in                                        Fig2: C-band accelerating structure under test
     SPARC for high power tests.                                                                                  Image credit: INFN-LNF

C-Band structures for the SPARC photo-injector energy upgrade have been designed, built and tested at the INFN-LNF Laboratories in Frascati (Italy).

In the SPARC photo-injector facility at the INFN Frascati National Laboratories (LNF, Italy) an R&D program on C-Band structures was being carried out in order to upgrade the beam energy from 180 to more than 250 MeV in the facility. This work was supported by INFN and TIARA Preparatory Phase EU program within the High Gradient Acceleration (HGA) Work Package.

The two C-Band structures are Traveling Wave (TW) and Constant Impedance (CI), with an integrated axial symmetric input coupler. High power tests have demonstrated the structure capability of withstanding operation accelerating gradients larger than 35 MV/m. A stable and flexible C-band digital low level RF system has been also developed by the Paul Scherrer Institute and integrated in the SPARC control system. The RF conditioning for the first RF structure lasted about 10-15 full equivalent days. As a result, it reached 38 MW input power in the structure (44 MW from the klystron) at a nominal repetition rate and pulse length. The corresponding accelerating field was 36 MV/m peak and 32 MV/m average, the BreakDown Rate, not yet measured, is expected to be lower than 10-5. Finally, the modulator voltage was 340 kV. The RF conditioning of the second RF structure was concluded in February 2014 with similar results.



  News about Tiara
  by Céline Tanguy (CEA)

Fig 1. Initiated within TIARA-PP, the Accelerators for Society website and tri fold-brochure invite you to discover how accelerators benefit Society. Image credit: Accelerators for Society

The TIARA preparatory phase has been extended for one year, until December 31st 2014. The reason for this extension is to pursue the work toward the implementation of a cluster of accelerator R&D infrastructures and related accelerator R&D centres named “Test Infrastructure and Accelerator Research Area (TIARA)”.

The main purpose of TIARA is to play a coordinating role, to exchange expertise and information concerning the “Accelerator Research Area”, and to facilitate collaborative R&D programmes in the field of Accelerator Science and Technology in Europe. The means and structures required to bring about these objectives have been developed through the TIARA Preparatory Phase (TIARA-PP).

The TIARA-PP project has started on January 1st 2011 and includes 11 participant institutes from 8 countries. Co-funded by the European Union 7th Framework Programme, it is divided into 9 Work Packages (WPs). The first 5 WPs are dedicated to organizational issues, while the other 4 WPs deal with technical aspects. Numerous achievements (most of them already highlighted in Accelerating News), can be found via the TIARA-PP website.

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  RF drive system for MICE installed at the ICTF
  by Kevin Ronald, (University of Strathclyde), Andrew Moss (Daresbury Lab), Tim Stanley (Rutherford Appleton Lab) for the MICE Collaboration

Fig. 1: Installation of the triode amplifier, visible are (a) the 3” feedline from the preamplifier on the mezzanine above, (b) the preamplifier test load, (c) the final stage amplifier assembly and (d) the 6” output line from the final stage. Image credit: TIARA/MICE.

Ionisation cooling is required to reduce the emittance of a muon beam rapidly for application in future accelerators for neutrino factories and muon colliders. The first RF power amplifier, developed under TIARA Work Package 7, by Daresbury Laboratory working with the Rutherford Appleton Laboratory (RAL), the University of Strathclyde and Imperial College has been installed and tested at the Ionisation cooling Test Facility (ICTF).

Fig 2: Engineering model illustrating the test installation of the 1st Amplifier system in the RF power station at the ICTF, the preamplifier tetrode (a), SSPA and Source are on the mezzanine with the power supplies (b), the tall triode final stage (c) is installed between the main floor and the mezzanine. Image credit: TIARA/MICE.

The first of the four compact amplifiers for the Muon Ionisation Cooling Experiment (MICE), which recently achieved the required performance of 2MW peak power in 1ms pulses at 1Hz has now been installed in the Ionisation Cooling Test Facility at RAL. This required the establishment of all necessary services in the limited space available for the RF power stations. The amplifier has been tested to the limits of the available RF loads and exhibited the same performance characteristics as achieved in the tests previously conducted at Daresbury. This is a major step in preparing the infrastructure for MICE. Through synergy with a US NSF-MRI programme at Mississippi, the components required for the distribution network developed under the TIARA project have been procured, and some parts used in the recent tests. The support of TIARA, the UK STFC, the US NSF and e2v technologies is gratefully acknowledged.

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Upgrade of the Swiss Light Source for R&D on ultralow vertical emittance
  by Andreas Streun (PSI), Yannis Papaphilippou (CERN), Marica Biagini (INFN)

Fig1: Image of vertical polarized synchrotron light: for an ideal beam of zero emittance, the image would show complete extinction of light in the midplane. Finite midplane intensity allows one to determine the beam size from the "valley to peak" intensity ratio of the image profile. Image credits: TIARA/ Andreas Streun (PSI)

A high resolution beam size monitor has been commissioned at the SLS for verification of vertical emittance values below 1 pm.

The SLS Vertical Emittance Tuning (SVET) Work Package within the TIARA preparatory phase was a collaboration between PSI, CERN, INFN and MAX IV Lab on instruments and methods for establishing an R&D infrastructure on vertical emittance reduction at the SLS storage ring of PSI. The final report was issued at the end of 2013.

Methods have been established to reduce the vertical emittance through re-alignment of the storage ring lattice and through systematic and random optimization of the optics. Values down to 1 pm have been achieved, and values of about 1.5 pm can be set routinely.

A new monitor was built for measurements of very small beam size and has been tested down to a level of 4 μm to date, corresponding to a vertical emittance of about 1.1 pm for the present SLS optics. The measurement is based on an image of vertically polarized synchrotron radiation, see figure beside.

The monitor beam line extends out of the storage ring tunnel in order to provide a large magnification factor and to allow the optical end station to be accessed during operation. A core component of the monitor is a toroidal mirror for wavelength independent focusing, in use since 2014. In 2013 an intermediate configuration composed from a planar mirror and a lens was used.

Monitor fine tuning is in progress, and a new emittance reduction campaign is scheduled. Further studies on intra-beam scattering effects are planned as an application of the ultralow vertical emittance beam.

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  Concluding the TIARA Preparatory Phase
  by Celine Tanguy (CEA)

The final general meeting of the TIARA Preparatory Phase was hosted by STFC at Daresbury Laboratory on November 25-28. Image credit:TIARA.

Almost 3 years since the TIARA Kickoff meeting, the TIARA participants met in Daresbury to review the progress within the Work Packages (WPs) and finalise the last deliverables.

The organisational Work Packages provided details about the Infrastructure Need and Resource Comparison (WP3), the final plan of the collaborative R&D Program (WP4) and the results of the survey of market needs for trained personnel and recommendations for promoting accelerator science and technology (WP5).

From the technical Work Packages, the following achievements were highlighted (among others): ultralow (world record) vertical emittance at the Swiss Light Source (WP6), multi-MegaWatt RF systems for the Ionisation Cooling Test Facility (WP7), new C-band structures at SPARC and overview of C-band technology at other international projects (WP8), design of innovative multi-MegaWatt Irradiation Facility for complex target testing (WP9).

On this occasion, an overview of R&D Infrastructures and Accelerator Programmes in UK was given, as well as Industrial Engagement in UK Accelerator R&D. Status of the on-going work toward 14 TeV operation of LHC and R&D for High Luminosity Upgrade was also showcased.

Governing Council meetings, including the Steering Committee members, were also organised, in particular to pursue discussion toward the TIARA implementation.


  E-learning: a new training opportunity for European accelerator science
  by Philip Burrows (JAI, University of Oxford)

An additional recommendation by TIARA WP5 is to set up a www portal for providing a comprehensive source of information on accelerator opportunities, namely job and internship vacancies, bursaries and fellowships, and research group and personnel expertise, as well as news on conferences, workshops and training schools and access to online training materials and resources. Image credit: Max Bradbury (JAI, University of Oxford).

Currently around 500 students each year commence master’s and PhD courses related to accelerator science and technology. TIARA Work Package 5 (WP5) proposes measures to improve training access. For science and engineering undergraduates, and high-school students, we recommend setting up an e-learning course: ‘Introduction to Accelerator Science and Technology’.

Based on the surveys on education and training provision, and the market needs for accelerator scientists and engineers, TIARA WP5 (“Education & Training”) has issued its final report, which includes recommendations for promoting Accelerator Science and Technologies at a European level. Among these TIARA WP5 recommends improved support for students to participate in training programmes, including accelerator schools and lab-based internships. It is believed that a prestigious European fellowship scheme for master’s and PhD students would help to improve the supply of trained personnel, as well as raise the profile of the field. It is also recommended setting up an e-learning course (‘Introduction to Accelerator Science and Technology’) to open up training opportunities to European undergraduate science students, as well as a module suitable for high-school students and teachers. See the report ’Recommendations for promoting accelerator science and technology in Europe for full details.


  A versatile test cryostat for low beta superconducting cavities
  by Sébastien Bousson (CNRS/IN2P3/IPN Orsay), Hervé Saugnac (CNRS/IN2P3/IPN Orsay) and Sébastien Blivet (CNRS/IN2P3/IPN Orsay)

Fig 1: Top-loading of the cryostat with a double spoke cavity. Image credit: TIARA.
Fig 2: Cryostat integrating a quarter-wave resonator. Image credit: TIARA.

In Work-Package 9 (WP9) of the TIARA-PP project, the IPN Orsay team (CNRS/IN2P3) has raised the challenge of designing a versatile test cryostat capable to host almost all type of fully-equipped superconducting (SC) cavities, including the wide range of low beta structures.

In the process of developing a SC accelerating cavity, the integrated test of the fully dressed cavity (i.e. equipped with its RF power coupler and cold tuning system) in the nominal condition of RF power and temperature is a key step towards the validation of the expected performances of the accelerating structure. To perform this experiment, a specific cryostat is required, adapted to the geometry and configuration of the cavity to be tested.

This type of infrastructure already exists for elliptical-type SC cavities, but not for the low beta structures due to difficulty of integrating the large variety of geometries, configurations and frequencies: quarter-wave or half-wave resonators, spoke or CH-type cavities, single-gap or multi-gap, frequencies ranging from 60 to 700 MHz...

As shown in Fig.1 with a spoke cavity or in Fig. 2 with a quarter-wave resonator, the chosen configuration of the cryostat is a top-loading, where the equipped cavity coming from the assembly in the clean room is suspended to the cryostat top-plate. The various openings located laterally or on the bottom closing plate of the cryostat allow to implement the power coupler and cold tuning system and give access to the cavity for the assembly process and to integrate the instruments. With a length of 2.7 m, a width of 1.5 m and a height of 3.4 m, the cryostat dimension is optimized to minimize the footprint in the test stand but sufficient enough to integrate a string of a SC cavity and a SC solenoid for specific tests.


  Demonstration of Rf drive system MICE achieved
  By Kevin Ronald (University of Strathclyde), Andrew Moss (Daresbury Lab), Ken Long (Imperial College) for the MICE Collaboration

Fig 1: The triode amplifier under test. The connections are a) the HT feedline, (b) output 9 inch coaxial line, (c) input 3 inch line. Image credit: TIARA/MICE.
Fig 2: Power meter display showing peak pulsed power. Image credit: TIARA/MICE.

Ionisation cooling is required to reduce the emittance of a muon beam rapidly for application in future accelerators for neutrino factories and muon colliders. Under Work Package 7 of the TIARA-PP project, Daresbury Lab in collaboration with Rutherford Appleton Lab, Strathclyde University and Imperial College has developed the RF drive system and distribution network for the International Muon Ionization Cooling Experiment (MICE).

Each of the 8 MICE cavities demand 1 MW of power at 201.25 MHz in 1ms pulses for a gradient of 8 MV/m. Strong magnetic fields mean the space for the RF drive system is constrained requiring a complex routing to the cavities. Four compact amplifier chains are used to meet these requirements. A signal generator drives a Solid State Power Amplifier (4 kW) feeding a Photonis 4616 tetrode valve amplifier (250 kW) and a Thales 116 triode valve amplifier (2 MW). A complex power supply has been developed to supply and protect the valve amplifiers. Due to the complex and delicate nature of the system, it has been progressively brought to full bias voltage (36 kV on the triode). At these settings the prototype system recently demonstrated the required output parameters. Outstanding support from e2v technologies thyratron section is gratefully acknowledged.


  Irradiation facility for target testing
  by Karel Samec (CERN), Yoann Fusco (CERN), Yacine Kadi (CERN)

Fig 1 left: Compact irradiation device developed at CERN within TIARA WP9. Image credits: TIARA/CERN.
Fig 2 right: Sample holder (one half) with sample loading mechanism. Image credits: TIARA/CERN.

In TIARA Work Package 9, the team led by scientists and engineers from CERN are developing a compact irradiation device. This installation is a key infrastructure for the accomplishment of the R&D programme that is required to enable the construction of EURISOL, the next generation facility for the production of very intense radioactive ion beams (RIB), and also for other projects such as the European Spallation Source (ESS) or the development of Accelerator Driven Systems with the MYRRHA project.

The compact irradiation device is shown in Fig. 1. The target shown in the detail can absorb a 100 kW proton beam and, through spallation of a dense liquid metal flowing inside, releases a high-density hard neutron flux in a volume which can accommodate various experimental devices. One such device is shown in Fig. 2 and illustrates how tensile specimens may be remotely stress-tested using a robust mechanical system, whilst being bombarded by the proton beam and the neutrons released by the spallation of dense liquid metal flowing around the samples.

Evidently the setup can be used to test medical applications, nuclear instrumentation or any other type of device for which a high density neutron field is required. The entire apparatus is housed within a cube 1.5m on a side, for easy transport. Disassembly and treatment of the waste is facilitated by the development of a compact heat exchanger which mechanically separates the primary from the secondary loop.

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  Uppsala University and TIARA highlighting RF power generation for accelerators
  by Tord Ekelof (Uppsala University) and Celine Tanguy (CEA)

Fig 1 left: Poster of the TIARA workshop on RF power generation for accelerators. Image credit: Uppsala University.
Fig 2 right: Inauguration of the FREIA hall in Angstrom laboratory with Eva Akesson, vice chancellor of Uppsala University, Tord Ekelof, director of FREIA department, Mats Lindroos, head of the ESS Accelerator Division, and Roy Aleksan, TIARA-PP coordinator. Image credit: Uppsala University.

The 2nd industry workshop sponsored by TIARA took place on 17-19 June at the Angstrom laboratory in Uppsala University. The event, dedicated to novel concepts for RF power generation for accelerators, was also the occasion to inaugurate the hall of FREIA (Facility for Research Instrumentation and Accelerator Development) Laboratory.

For the 3-day workshop, about 90 experienced researchers and leading companies in the field of RF power generation and related technologies gathered to explore the technical challenges emerging from the design of new accelerators and to match them with state-of-the-art industrial solutions for RF power generation.

An overview of the main types of accelerator projects and their different RF power generation schemes was first presented, followed by sessions focussed on electron tube devices, solid-state amplifiers and phase-stability and timing

On 18 June the conference participants attended the inauguration of the new FREIA laboratory in Uppsala, intended for research and development of RF power generation, distribution and control for superconducting and normal conducting accelerating cavities for future accelerators. It is the key infrastructure required for developing the superconducting accelerating technology needed for future very high intensity proton accelerators, new free electron lasers and other emerging accelerator projects