Technology Archives – Page 30 of 116

A luminous future for the LHC

A prototype Roebel cable to be used to wind a high-temperature superconductor demonstration dipole magnet.
Image credit: CERN-PHOTO-201407-151-3.

To maintain scientific progress and exploit the full capacity of the LHC, the collider will need to operate at higher luminosity. Like shining a brighter light on an object, this will allow more accurate measurements of new particles, the observation of rarer processes, and increase the discovery reach with rare events at the high-energy frontier. The High-Luminosity LHC (HL-LHC) project began in 2011 under the framework of a European Union (EU) grant as a conceptual study, with the aim to increase its luminosity by a factor of 5–10 beyond the original design value and provide 3000 fb^–1 in 10 to 12 years.

The HL-LHC timeline as of 24 September 2014.

Two years later, CERN Council recognized the project as the top priority for CERN and for Europe (CERN Courier July/August 2013 p9), and then confirmed its priority status in CERN’s scientific and financial programme in 2014 by approving the laboratory’s medium-term plan for 2014–2019. Since this approval, new activities have started up to deliver key technologies that are needed for the upgrade. The latest results and recommendations by the various reviews that took place in 2014 were the main topics for discussion at the 4th Joint HiLumi LHC/LARP Annual Meeting, which was hosted by KEK in Tsukuba in November.

The latest updates

The event began with plenary sessions where members of the collaboration management – from CERN, KEK, the US LHC Accelerator Research Program (LARP) and the US Department of Energy – gave invited talks. The first plenary session closed with an update on the status of HL-LHC by the project leader, CERN’s Lucio Rossi, who also officially announced the new HL-LHC timeline. The plenary was followed by expert talks on residual dose-rate studies, layout and integration, optics and operation modes and progress on cooling, quench and assembly (together known as QXF). Akira Yamamoto of KEK presented the important results and recommendations of the recent superconducting cable review.

Collaboration members at the 4th Joint HiLumi LHC-LARP Annual Meeting.
Image credit: KEK.

There were invited talks on the LHC Injectors Upgrade (LIU) by project leader Malika Meddahi from CERN, and on the outcomes of the 2nd ECFA HL-LHC Experiments Workshop held in October – an indication of the close collaboration with the experimentalists. One of the highlights of the plenaries was the status update on the Preliminary Design Report – the main deliverable of the project, which is to be published soon. There were three days of parallel sessions reviewing the progress in design and R&D in the various work packages – named in terms of activities – both with and without EU funding.

Refined optics and layout of the high-luminosity insertions have been provided by the activity on accelerator physics and performance, in collaboration with the other work packages. This new baseline takes into account the updated design of the magnets (in particular those of the matching section), the results of the energy deposition and collimation studies, and the constraints resulting from the integration of the components in the tunnel. The work towards the definition of the specifications for the magnets and their field quality has progressed, with an emphasis on the matching section for which a first iteration based on the requirements resulting from studies of beam dynamics has been completed. The outcomes include an updated impedance model of the LHC and a preliminary estimate of the resulting intensity limits and beam–beam effects. The studies confirmed the need for low-impedance collimators. In addition, an updated set of beam parameters consistent through all of the injectors and the LHC has been defined in collaboration with the LIU team.

Progress with magnets

The 20-m-long electrical transmission line containing two 20 kA MgB₂ cables.
Image credit: CERN.

The main efforts of the activity on magnets for insertion regions (IRs) in the past 18 months focused on the exploration of different options for the layout of the interaction region. The main parameters of the magnet lattice, such as operational field/gradients, apertures, lengths and magnet technology, have been chosen as a result of the worldwide collaboration, including US LARP and KEK. A baseline for the layout of the new interaction region is one of the main results of this work. There is now a coherent layout, agreed with the beam dynamics, energy deposition, cooling and vacuum teams, covering the whole interaction region.

The engineering design of most of the IR magnets has now started and the first hardware tests are expected in 2015. There was also good news from the quench-protection side, which can meet all of the key requirements based on the results from tests performed on the magnets. In addition, there is a solution for cooling the inner triplet (IT) quadrupoles and the separation dipole, D1. It relies on two heat exchangers for the IT quadrupole/orbit correctors assembly, with a separate system for the D1 dipole and the high-order corrector magnets. Besides these results, considerable effort was devoted to selecting the technologies and the design for the other magnets required in the lattice, namely the orbit correctors, the high-order correctors and the recombination dipole, D2.

Crabs and collimators

A crystal target for advanced collimation under test in CERN’s HiRadMat facility.
Image credit: CERN.

The crab-cavities activity delivered designs for three prototype crab cavities, based on four-rod, RF-dipole (RFD) and double quarter-wave (DQW) structures. They were all tested successfully against the design gradient with higher-than-expected surface resistance. Further design improvements to the initial prototypes were made to comply with the strict requirements for higher-order-mode damping, while maintaining the deflecting field performance. There was significant progress on the engineering design of the dressed cavities and the two-cavity cryomodule conceptual design for tests at CERN’s Super Proton Synchrotron (SPS).

Full design studies, including thermal and mechanical analysis, were done for all three cavities, culminating in a major international design review where the three designs were assessed by a panel of independent leading superconducting RF experts. As an outcome of this review, the activity will focus the design effort for the SPS beam tests on the RFD and DQW cavities, with development of the 4-rod cavity continuing at a lower priority and not foreseen for the SPS tests. A key milestone – to freeze the cavity designs and interfaces – has also been met. In addition, a detailed road map to follow the fabrication and installation in the SPS has been prepared to meet the deadline of the extended year-end technical stop of 2016–2017.

Nb₃Sn coil for the 11-T dipole-model tests.
Image credit: CERN.

The wrap-up talk on the IR-collimation activity also reviewed the work of related non-EU-funded work packages, namely machine protection (WP7), energy deposition and absorber co-ordination (WP10), and beam transfer and kickers (WP14). The activity has reached several significant milestones, following the recommendations of the collimation-project external review, which took place in spring 2013. Highlights include important progress towards the finalization of the layouts for the IR collimation. A solid baseline solution has been proposed for the two most challenging cleaning requirements: proton losses around the betatron-cleaning insertion and losses from ion collisions. The solution is based on new collimators – the target collimator long dispersion suppressor, or TCLD – to be integrated into the cold dispersion suppressors. Thanks to the use of shorter 11 T dipoles that will replace the existing 15-m-long dipoles, there will be sufficient space for the installation of warm collimators between two cold magnets. This collimation solution is elegant and modular because it can be applied, in principle, at any “old” dipole location. As one of the most challenging and urgent upgrades for the high-luminosity era, solid baselines for the collimation upgrade in the dispersion suppressors around IR7 and IR2 were also defined. In addition, simulations have continued for advanced collimation layouts in the matching sections of IR1 and IR5, improving significantly the cleaning of “debris” from collisions downstream around the high-luminosity experiments.

Cold powering

The cold-powering activity has seen the world-record current of 20 kA at 24 K in an electrical transmission line consisting of two 20-m-long MgB₂ superconducting cables. Another achievement was with the novel design of the part of the cold-powering system that transfers the current from room temperature to the superconducting link. Following further elaboration, this was adopted as the baseline. The idea is that high-temperature superconducting (HTS) current-leads will be modular components that are connected via a flexible HTS cable to a compact cryostat, where the electrical joints between the HTS and MgB₂ parts of the superconducting link are made. Simulation studies were also made to evaluate the electromagnetic and thermal behaviour of the MgB₂ cables contained in the cold mass of the superconducting link, under static and transient conditions.

Computer-generated image of Fermilab’s 1-m-long 11-T dipole model and a pair of CERN coils.
Image credit: Don Mitchell/Fermilab.

The final configuration has tens of high-current cables packed in a compact envelope to transfer a total current of about 150 kA feeding different magnet circuits. Cryogenic-flow schemes were also elaborated for the cold-powering systems at points 7, 1 and 5 on the LHC. An experimental study performed in the 20-m-long superconducting line at CERN was launched to understand quench propagation in the MgB₂ superconducting cables operated in helium gas. In addition, integration studies of the cold-powering systems in the LHC were also done, with priority given to the system at point 7.

The meeting also covered updates on other topics such as machine protection, cryogenics, vacuum and beam instrumentation. Delicate arbitration took place between the needs of crab-cavity tests in the SPS at long straight section 4 and the requirements for the continuing study and tests of electron-cloud mitigation of those working on vacuum aspects (see Old machine to validate new technology below).

Summaries of the EU-funded work packages closed the meeting, showing “excellent technical progress thanks to the hard and smart work of many, including senior and junior”, as project leader Rossi concluded in his wrap-up talk.

Upcoming meetings will be the LARP/HiLumi LHC meeting on 11–13 May at Fermilab and the final FP7 HiLumi LHC/LARP collaboration meeting on 26–30 October at CERN. As a contribution to the UNESCO International Year of Light, special events celebrating this occasion will be organized by HL-LHC throughout the year – see cern.ch/go/light. (See also Viewpoint )

Old machine to validate new technology

Crab cavities have never been tested on hadron beams. So for the recently selected HL-LHC crab cavities (RFD and DQW, see main text), tests in the SPS beam are considered to be crucial. The goals are to validate the cavities with beam in terms of, for example, electric field, ramping, RF controls and impedance, and to study other parameters such as cavity transparency, RF noise, emittance growth and nonlinearities.

Long straight section 4 (LSS4) of the SPS already has a cold section, which was set up for the cold-bore experiment (COLDEX). Originally designed to measure synchrotron-radiation-induced gas release, COLDEX has become a key tool for evaluating electron-cloud effects. It mimics the cold bore and beam screen of the LHC for electron-cloud studies. Installed in the bypass line of the beam pipe, COLDEX is assembled on a moving table so that beam can pass either through the experiment during machine development runs or through the standard SPS beam pipe during normal operation. It has been running again since the SPS started up again last year after the first long shutdown, providing key information on new materials and technology to reduce or suppress severe electron-cloud effects that would otherwise be detrimental to LHC beams with 25 ns bunch spacing – as planned for Run 2.

Naturally, SPS LSS4 would be the right place to put the crab-cavity prototypes for the beam test. The goal was originally to install them during the extended year-end technical stop of 2016–2017, to validate the cavities in 2017, the year in which series construction must be launched. However, installing the cavities together with their powering and cryogenic infrastructure in an access time of 11–12 weeks is a real challenge. So at the meeting in Tsukuba, the idea of bringing forward part of the installation to 2015–2016 was discussed. However, in view of the severe electron-cloud effects that were computed in 2014 for LHC beam at high intensity, and the consequent need for a longer and deeper study to validate various solutions, COLDEX needs to run beyond 2015.

So what other options are there for testing the crab cavities? A preliminary look at possible locations for an additional cold section in the SPS led to LSS5. This would result in having two permanent “super” facilities to test equipment with proton beams. The hope is that these facilities would not only be available for testing crab cavities for the HL-LHC project, but would also provide a world facility for testing superconducting RF-accelerating structures in intense, high-energy proton beams. With the installation of adequate cryogenics and power infrastructure, a facility in LSS5 could further evolve and possibly also allow tests of beam damage and other beam effects for future superconducting magnets, for example for the Future Circular Collider study (CERN Courier April 2014 p16). This new idea raises many questions, but the experts are confident that these can be solved with suitable design and imagination.

The LHC gears up for season 2

Beams came knocking on the LHC’s door in November. These images show the transverse beam profile in the LHC injection lines (TI2 left, TI8 right).
Credit: CERN

With the end of the long shutdown in sight, teams at CERN have continued preparations for the restart of the Large Hadron Collider (LHC) this spring after reaching several important milestones by the end of 2014. Beams came knocking at the LHC’s door for the first time on 22–23 November, when protons from the Super Proton Synchrotron passed into the two LHC injection lines and were stopped by beam dumps just short of entering the accelerator. The LHC operations team used these tests to check the control systems, beam instrumentation and transfer-line alignment. Secondary particles – primarily muons – generated during the dump were in turn used to calibrate the two LHC experiments located close to the transfer lines: ALICE and LHCb.

During the same weekend, the operations team also carried out direct tests of LHC equipment. They looked at the timing synchronization between the beam and the LHC injection and extraction systems by pulsing the injection kicker magnets and triggering the beam-dump system in point 6, despite having no beam.

Tests of each of the eight LHC sectors continued apace. By the end of November, copper-stabilizer continuity measurements were underway in sector 4-5 and were about to start in sector 3-4. Electrical quality assurance tests were being carried out in sectors 2-3 and 7-8, and powering tests were progressing in sectors 8-1, 1-2, 5-6 and 6-7. Cooling and ventilation teams were also busy carrying out maintenance of the systems at points around the LHC ring.

Meanwhile, the operations team were training the magnets in sector 6-7. The first training quench was performed on 31 October, reaching a current of around 10,000 A, which corresponds to a magnetic field of 6.9 T and a proton beam energy of 5.8 TeV (during Run 1, the LHC ran with proton energies of up to 4 TeV). On 9 December, the team successfully commissioned sector 6-7 to the nominal energy for Run 2 – 6.5 TeV, for proton collisions at 13 TeV. The 154 superconducting dipole magnets that make up this sector were powered to around 11,000 A. This increase in nominal energy was possible thanks to the long shutdown, which began in February 2013 and allowed the consolidation of 1700 magnet interconnections, including more than 10,000 superconducting splices. The magnets in all of the other sectors are undergoing similar training prior to 6.5 TeV operation.

In mid-December, the cryogenics team finished filling the arc sections of the LHC with liquid helium. This marked an important step on the road to cooling the entire accelerator to 1.9 K. During the end-of-year break, the cryogenic system was then set to stand-by, with elements such as stand-alone magnets emptied of liquid helium. These elements were to return to cryogenic conditions in January, to allow the operations team to perform more tests on the road to the LHC’s Run 2.

The four large experiments of the LHC – ALICE, ATLAS, CMS and LHCb – are also undergoing major preparatory work for Run 2, after the long shutdown during which important programmes for maintenance and improvements were achieved. They are now entering their final commissioning phase. Here, members of the ATLAS collaboration are cleaning up the inside of the ATLAS detector prior to closing the cavern in preparation for Run 2.

LHCf detectors are back in the LHC tunnel

The Large Hadron Collider forward (LHCf) experiment measures neutral particles emitted around zero degrees of the hadron interactions at the LHC. Because these “very forward” particles carry a large fraction of the collision energy, they are important for understanding the development of atmospheric air-shower phenomena produced by high-energy cosmic rays. Two independent detectors, Arm1 and Arm2, are installed in the target neutral absorbers (TANs) at 140 m from interaction point 1 (IP1) in the LHC, where the single beam pipe is split into two narrow pipes.

After a successful physics operation in 2009/2010, the LHCf collaboration immediately removed their detectors from the tunnel in July 2010 to avoid severe radiation damage. The Arm2 detector, in the direction of IP2, came back into the tunnel for data-taking with proton–lead collisions in 2013, while Arm1 was being upgraded to be a radiation-hard detector, using Gd₂SiO₅ scintillators. After completion of the upgrade for both Arm1 and Arm2, the performance of the detectors was tested at the Super Proton Synchrotron fixed beam line in Prévessin in October 2014. Both Arm1 and Arm2 were then reinstalled in the LHC tunnel on 17 and 24 November, respectively.

CCnew5_01_15th — LHCf’s Arm1 detectors installed in the LHC tunnel.
Image credit: T Sako.

The installation went smoothly, thanks to the well-equipped remote-handling system for the TAN instrumentation. During the following days, cabling, commissioning and the geometrical survey of the detectors took place without any serious trouble.

LHCf will restart the activity to relaunch the data-acquisition system in early 2015, to be ready for the dedicated operation time in May 2015 when the LHC will provide low luminosity, low pile-up and high β* (20 m) proton–proton collisions. At √s = 13 TeV, these collisions correspond to interactions in the atmosphere of cosmic rays with energy of 0.9 × 10¹⁷ eV. This is the energy at which the origins of the cosmic rays are believed to switch from galactic to extragalactic, and a sudden change of the primary mass is expected. Cosmic-ray physicists expect to confirm this standard scenario of cosmic rays based on the highest-energy LHC data.

Another highlight of the 2015 run will be common data-taking with the ATLAS experiment. LHCf will send trigger signals to ATLAS, and ATLAS will record data after pre-scaling. Based on a preliminary Monte Carlo study using PYTHIA8, which selected events with low central activity in ATLAS, LHCf can select very pure (99%) events produced by diffractive dissociation processes. The identification of the origin of the forward particles will help future developments of hadronic-interaction models.

Two teams take big steps forward in plasma acceleration

CCnew15_01_15th — Beam spectra from 92 shots, sorted by the total energy-transfer efficiency (black line), in the plasma-wakefield experiment at FACET. The red line shows the core energy-transfer efficiency.

The high electric-field gradients that can be set up in plasma have offered the promise of compact particle accelerators since the late 1970s. The basic idea is to use the space-charge separation that arises in the wake of either an intense laser pulse or a pulse of ultra-relativistic charged particles. Towards the end of 2014, groups working on both approaches reached important milestones. One team, working at the Facility for Advanced Accelerator Experimental Tests (FACET) at SLAC, demonstrated plasma-wakefield acceleration with both a high gradient and a high energy-transfer efficiency – a crucial combination not previously achieved. At Lawrence Berkeley National Laboratory, a team working at the Berkeley Lab Laser Accelerator (BELLA) facility boosted electrons to the highest energies ever recorded for the laser-wakefield technique.

CCnew16_01_15th — Energy-spectrum of a 4.2 GeV electron beam accelerated in the laser-wakefield experiment at BELLA.

Several years ago, a team at SLAC successfully accelerated electrons in the tail of a long electron bunch from 42 GeV to 85 GeV in less than 1 m of plasma. In that experiment, the particles leading the bunch created the wakefield to accelerate those in the tail, and the total charge accelerated was small. Since then, FACET has come on line. Using the first 2 km of the SLAC linac to deliver an electron beam of 20 GeV, the facility is designed to produce pairs of high-current bunches with a small enough separation to allow the trailing bunch to be accelerated in the plasma wakefield of the drive bunch.

Using the pairs of bunches at FACET, some of the earlier team members together with new colleagues have carried out an experiment in the so-called “blow-out” regime of plasma-wakefield acceleration, where maximum energy gains at maximum efficiencies are to be found. The team succeeded in accelerating some 74 pC of charge in the core of the trailing bunch of electrons to about 1.6 GeV per particle in a gradient of about 4.4 GeV/m (Litos et al. 2014). The final energy spread for the core particles was as low as 0.7%, and the maxiumum efficiency of energy transfer from the wake to the trailing bunch was in excess of 30%.

Meanwhile, a team at Berkeley has been successfully pursuing laser-wakefield acceleration for more than a decade. This research was boosted when the specially conceived BELLA facility recently came on line with its petawatt laser. In work published in December, the team at BELLA used laser pulses at 0.3 PW peak power to create a plasma channel in a 9-cm-long capillary discharge waveguide and accelerate electrons to the record energy of 4.2 GeV (Leemans et al. 2014). Importantly, the 16 J of laser energy used was significantly lower than in previous experiments – a result of using the preformed plasma waveguide set up by pulsing an electrical discharge through hydrogen in a capillary. The combination of increased electron-beam energy and lower laser energy bodes well for the group’s aim to reach the target of 10 GeV.

ARIEL begins a new future in rare isotopes

**Fig. 1.** TRIUMF’s new ARIEL building houses the target hall, remote-handling facilities, mass-separation and radioactive beam front end, and electrical and mechanical services. Funding for the civil construction was provided by the Province of British Columbia.

TRIUMF is Canada’s national laboratory for particle and nuclear physics, located in Vancouver. Founded in 1968, the laboratory’s particle-accelerator-driven research has grown from nuclear and particle physics to include vibrant programmes in materials science, nuclear medicine and accelerator science, while maintaining strong particle-physics activities elsewhere, for example at CERN and the Japan Proton Accelerator Research Complex. Currently, the laboratory’s flagship on-site programme uses rare-isotope beams (RIBs) for both discovery and application in the physical and health sciences.

Rare isotopes are not found in nature, yet they have properties that have shaped the evolution of the universe in fundamental ways, from powering the burning of stars to generating the chemical elements that make up life on Earth. These isotopes are foundational for modern medical-imaging techniques, such as positron-emission tomography and single-photon emission computed tomography, and are useful for therapeutic purposes, including the treatment of cancer tumours. They are also powerful tools for scientific discovery, for example in determining the structure and dynamics of atomic nuclei, understanding the processes by which heavy elements in the universe were created, enabling precision tests of fundamental symmetries that could challenge the Standard Model of particle physics, and serving as probes of the interfaces between materials.

TRIUMF’s Isotope Separator and Accelerator – ISAC – is one of the world’s premier RIB facilities. ISAC’s high proton-beam power (up to 50 kW) that produces the rare isotopes, its chain of accelerators that propels them up to energies of 6–18 MeV per nucleon for heavy and light-mass beams, respectively, and its experimental equipment that measures their properties are unmatched in the world.

**Fig. 2.** The newly commissioned first stage of the SRF electron linac for ARIEL, showing the electron gun (cylinder far right), injector cryomodule (bottom centre) and accelerator cryomodule (ACM far left). A second ACM will ultimately bring the accelerator to the 50 MeV and 500 kW design specifications. Funding was provided by the Canadian government and the CFI.
All image credits: TRIUMF.

The Advanced Rare IsotopE Laboratory (ARIEL) was conceived to expand these capabilities in important new directions, and to establish TRIUMF as a world-leading laboratory in accelerator technology and in rare-isotope research for science, medicine and business. To expand the number and scope of RIBs feeding TRIUMF’s experimental facilities, ARIEL will add two high-power driver beams – one electron and one proton – and two new isotope production-target and transport systems.

Together with the existing ISAC station, the two additional target stations will triple the current isotope-production capacity, enable full utilization of the existing experimental facilities, and satisfy researcher demand for isotopes used in nuclear astrophysics, fundamental nuclear studies and searches for new particle physics, as well as in characterizing materials and in medical-isotope research. In addition, ARIEL will deliver important social and economic impacts, in the production of medical isotopes for targeted cancer therapy, in the characterization of novel materials, and in the continued advancement of accelerator technology in Canada, both at the laboratory and in partnership with industry.

The e-linac

ARIEL-I, the first stage of ARIEL, was funded in 2010 by the Canada Foundation for Innovation (CFI), the British Columbia Knowledge Development Fund, and the Canadian government. It comprises the ARIEL building (figure 1), completed in 2013, and a 25 MeV, 100 kW superconducting radio-frequency (SRF) electron linear accelerator (e-linac), which is the first stage of a new electron driver designed ultimately to achieve 50 MeV and 500 kW for the production of radioactive beams via photo-fission.

The ARIEL-I e-linac accelerated its first beam to 23 MeV in September 2014

The ARIEL-I e-linac, which accelerated its first beam to 23 MeV in September 2014, is a state-of-the-art accelerator featuring a number of technological breakthroughs (figure 2). The 10 mA continuous wave (cw) electron beam is generated in a 300 kV DC thermionic gridded-cathode assembly modulated at 650 MHz, bunched by a room-temperature 1.3 GHz RF structure, and accelerated using up to five 1.3 GHz superconducting cavities, housed in one 10 MeV injector cryomodule (ICM) and two accelerator cryomodules, each providing 20 MeV energy gain.

The design and layout of the e-linac are compatible with a future recirculation arc that can be tuned either for energy-recovery or energy-doubling operation. The electron source, designed and constructed at TRIUMF, exhibits reduced field-emission and a novel modulation scheme: the RF power is transmitted via a ceramic waveguide between the grounded vessel and the gun, so the amplifier is at ground potential. The source has been successfully tested to the full current specification of 10 mA cw. Specially designed short quadrupoles (figure 3) present minimum electron-beam aberrations by shaping the poles to be locally spherical, with radius 4π times the aperture radius (Baartman 2012).

**Fig.3.** Close-up of the “short” quadrupoles used in the electron-beam transport line. These TRIUMF-designed magnets employ a novel pole design that presents minimal aberrations to the electron beam.

The injector and accelerator cryomodules house the SRF cavities (figure 4), which are cooled to 2K and each driven by a 300 kW klystron. To take advantage of prior developments – and to contribute to future projects – TRIUMF chose the 1.3 GHz technology, the same as other global accelerator projects including the XFEL in Hamburg, the LCLS-II at SLAC, and the proposed International Linear Collider.

Through technology transfer from TRIUMF, the Canadian company PAVAC Industries Inc. fabricated the niobium cavities and TRIUMF constructed the cryomodules, based on the ISAC top-loading design (figure 2). The TRIUMF/PAVAC collaboration, which goes back to 2005, was born from the vision of “made in Canada” superconducting accelerators. Now, 10 years later, the relationship is a glowing example of a positive partnership between industry and a research institute.

International partnerships have been essential in facilitating technical developments for the e-linac. In 2008, TRIUMF went into partnership with the Variable Energy Cyclotron Centre (VECC) in Kolkata, for joint development of the ICM and the construction of two of them: one for ARIEL and one for ANURIB, India’s next-generation RIB facility, which is being constructed in Kolkata. In 2013, the collaboration was extended to include the development of components for ARIEL’s next phase, ARIEL-II. In addition, collaborations with Fermilab, the Helmholtz Zentrum Berlin and DESY were indispensable for the project.

**Fig. 4.** Close-up of the 1.3 GHz SRF cavity employed in the ARIEL e-linac. The technology chosen is the same as other current and proposed global accelerator projects. TRIUMF transferred the technical expertise to the Canadian company PAVAC Industries Inc. in a successful research–industry partnership.

ARIEL’s development is continuing with ARIEL-II, which will complete the e-linac and add the new proton driver, production targets and transport systems in preparation for first science in 2017. Funding for ARIEL-II has been requested from the CFI on behalf of 19 universities, led by the University of Victoria, and matching funds are being sought from five Canadian provinces.

ARIEL will bring unprecedented capabilities:

•The multi-user RIB capability will not only triple the RIB hours delivered to users, but also increase the richness of the science by enabling long-running experiments for fundamental symmetries that are not practical currently.

•Photo-fission will allow the production of very neutron-rich isotopes at unprecedented intensities for precision studies of r-process nuclei.

•The multi-user capability will establish depth-resolved β-detected NMR as a user facility, unique in the world.

•High production rates of novel alpha-emitting heavy nuclei will accelerate development of targeted alpha tumour therapy.

The new facility will also provide important societal benefits. In addition to the economic benefits from the commercialization of accelerator technologies (e.g. PAVAC), ARIEL will expand TRIUMF’s outstanding record in student development through participation in international collaborations and training in advanced instrumentation and accelerator technologies. The e-linac has provided the impetus to form Canada’s first graduate programme in accelerator physics. One of only a few worldwide, the programme is in high demand globally and has already produced award-winning graduates.

ARIEL is not only the future of TRIUMF, it also embodies the mission of TRIUMF at large: scientific excellence, societal impact, and economic benefit. And it is off to a great start.

CUORE has the coldest heart in the known universe

CCnew2_10_14 — The CUORE experiment is based on crystals of tellurium dioxide cooled to a few millikelvin.
Image credit: INFN.

The CUORE collaboration at the INFN Gran Sasso National Laboratory has set a world record by cooling a copper vessel with the volume of a cubic metre to a temperature of 6 mK. It is the first experiment to cool a mass and a volume of this size to a temperature this close to absolute zero. The cooled copper mass, weighing approximately 400 kg, was the coldest cubic metre in the universe for more than 15 days. No experiment on Earth has ever cooled a similar mass or volume to temperatures this low. Similar conditions are also not expected to arise in nature.

CUORE – which stands for Cryogenic Underground Observatory for Rare Events, but is also Italian for heart – is an experiment being built by an international collaboration at Gran Sasso to study the properties of neutrinos and search for rare processes, in particular the hypothesized neutrinoless double-beta decay. The experiment is designed to work in ultra-cold conditions at temperatures of around 10 mK. It consists of tellurium-dioxide crystals serving as bolometers, which measure energy by recording tiny fluctuations in the crystal’s temperature. When complete, CUORE will contain some 1000 instrumented crystals and will be covered by shielding made of ancient Roman lead, which has a particularly low level of intrinsic radioactivity. The mass of material to be held near absolute zero will be almost two tonnes.

The cryostat was implemented and funded by INFN, and the University of Milano Bicocca co-ordinated the research team in charge of the design of the cryogenic system. The successful solution to the technological challenge of cooling the entire experimental mass of almost two tonnes to the temperature of a few millikelvin was made possible through collaboration with high-profile industrial partners such as Leiden Cryogenics BV, who designed and built the unique refrigeration system, and Simic SpA, who built the cryostat vessels.

NA62 gets going at the SPS

CCnew3_10_14 — The final straw-tracker module is lowered into position in NA62.
Image credit: CERN-PHOTO-201409-176 – 4.

With the end in sight for CERN’s Long Shutdown (LS1), the accelerator chain has been gradually restarting. Since early October, the Super Proton Synchrotron (SPS) has been delivering beams of protons to experiments, including NA62, which has now begun a three-year data-taking run.

NA62’s main aim is to study rare kaon decays, following on from its predecessors NA31 and NA48, which made important contributions to the study of CP violations in the kaon system. To make beams rich in kaons, protons from the SPS strike a beryllium target. The collisions create a beam that transmits almost one billion particles per second, about 6% of which are kaons.

After almost eight years of design and construction, NA62 was ready for the beam by start-up in October. In early September, the last of the four straw-tracker chambers had been lowered into position in the experiment. The straw tracker is the first of its scale to be placed directly into the vacuum tank of an experiment, allowing NA62 to measure the direction and momentum of charged particles with high precision. From the first design to the final plug-in and testing, teams at CERN worked in close collaboration with the Joint Institute for Nuclear Research in Dubna, who helped to develop the straw-tracker technology and who will participate in the running of the detector now that construction and installation has been completed.

Each straw-tracker chamber weighs close to 5000 kg and is made up of 16 layers of state-of-the-art, highly fragile straw tubes. Although heavy, the four chambers had to be delicately transported to the SPS North Area at CERN’s Prévessin site, lowered into the experiment cavern and installed to a precision of 0.3 mm. The chambers were then equipped with the necessary gas connections, pipes, cables and dedicated read-out boards, before beam commissioning began in early October to tune the tracker prior to integrating it with the other sub-detectors for data taking.

This unique tracker, placed directly inside the experiment’s vacuum tank, sits alongside a silicon-pixel detector and a detector called CEDAR that determines the types of particles from their Cherenkov radiation. A magnetic spectrometer measures charged tracks from kaon decays, and a ring-imaging Cherenkov detector indicates the identity of each decay particle. A large system of photon and muon detectors rejects unwanted decays. In total, the experiment extends across a length of 270 m, of which 85 m are in a vacuum.

• For more about the installation and construction of NA62, see the CERN Bulletin http://cds.cern.ch/record/1951890.

The giant slowly awakes

CCnew4_10_14 — Image credit: CERN-AC-0910152-02.

The giant slowly awakes, as the process to cool down the LHC continues in the final stage of the first long shutdown, LS1. By mid-October, the last remaining sector, 3-4 (seen here in 2009), had begun to cool down, and two of the eight sectors of the machine were already at their final cryogenic operating conditions. By the end of October, cooling and ventilation teams were maintaining systems at point 6. Down in the tunnel, sector 8-1 had completed electrical quality-assurance testing, and preparations were under way for powering tests. Measurements of the continuity of the copper stabilizer were completed in sector 5-6, and ongoing in sectors 7-8 and 2-3. Finally, on 31 October, the first magnet training for the LHC began in sector 6-7, successfully reaching a magnetic field of 5.8 T.

How bright is the LHC?

The LHCb Collaboration has published the results of a luminosity calibration with a precision of 1.12%. This is the most precise luminosity measurement achieved so far at a bunched-beam hadron collider.

CCnew6_10_14 — Results of a global pluridimensional shape fit of the individual LHC beams (left and centre) and of the luminous region (right), based on the distributions of beam–gas and beam–beam interaction vertices. The results are shown here for a selected colliding bunch pair and a central slice on the longitudinal axis.

The absolute luminosity at a particle collider is not only an important figure of merit for the machine, it is also a necessity for determining the absolute cross-sections for reaction processes. Specifically, the number of interactions, N, measured in an experiment depends on the value of cross-section σ and luminosity L, N = σL, so the precision obtained in measuring a given cross-section depends critically on the precision with which the luminosity is known. The luminosity itself depends on the number of particles in each collider beam and on the size of overlap of both beams at the collision point. At the LHC, dedicated instruments measure the beam currents, and hence the number of particles in each colliding beam, while the experiments measure the size of overlap of the beams at the collision point.

A standard method to determine the overlap of the beams is the van der Meer scan, invented in 1968 by Simon van der Meer to measure luminosity in CERN’s Intersecting Storage Rings, the world’s first hadron collider. This technique, which involves scanning the beams across each other and monitoring the interaction rate, has been used by all of the four large LHC experiments. However, LHCb physicists proposed an alternative method in 2005 – the beam-gas imaging (BGI) method – which they successfully applied for the first time in 2009. This takes advantage of the excellent precision of LHCb’s Vertex Locator, a detector that is placed around the proton–proton collision point. The BGI method is based on reconstructing the vertices of “beam-gas” interactions, i.e. interactions between beam particles and residual gas nuclei in the beam pipe to measure the angles, positions and shapes of the individual beams without displacing them.

To date, LHCb is the only experiment capable of using the BGI method. The technique involves calibrating the luminosity during special measurement periods at the LHC, and then tracking relative changes through changes in the counting rate in different sub-detectors. However, the vacuum pressure in the LHC is so low that for the technique to work with high precision, the beam–gas collision rate was increased by injecting neon gas into the LHC beam pipe during the luminosity calibration periods. This allowed the LHCb physicists to obtain precise images of the shapes of the individual beams, as illustrated in the left and middle graphs of the figure, which unravelled subtle but important features of the distributions of beam particles. By combining the beam–gas data with the measured distribution of beam–beam interactions, which provides the shape of the luminous region (the right graph in the figure), an accurate calibration of the luminosity was achieved.

The beam–gas data also revealed that a small fraction of the beam’s charge is spread outside of the expected (i.e. “nominal”) bunch locations. Because only collisions of protons located in the nominal bunches are included in physics measurements, it was important to measure which fraction of the total beam current measured with the LHC’s current monitors participated in the collisions, i.e. contributed to the luminosity. Only LHCb could measure this fraction with sufficient precision, so the results of LHCb’s measurements of the fraction of charge outside the nominal bunch locations – the so-called “ghost” charge – were also used by the ALICE, ATLAS and CMS experiments.

For proton–proton interactions at 8 TeV, a relative precision of the luminosity calibration of 1.47% was obtained using van der Meer scans and 1.43% using beam–gas imaging, resulting in a combined precision of 1.12%. The BGI method has proved to be so successful that it will now be used to measure beam sizes as part of monitoring and studying the LHC beams. Dedicated equipment will be installed in a modified region of the LHC ring near Point 4. This system, dubbed the Beam-Gas Vertexing system (BGV), is being developed by a collaboration from CERN, EPFL and RTWH Aachen. It includes a gas-injection system and a scintillating-fibre tracker telescope, which are expected to be commissioned with beam in 2015.

ILC-type cryomodule makes the grade

CCnew14_10_14 — CM2 in its home at Fermilab’s NML building, as part of the future Advanced Superconducting Test Accelerator.
Image credit: Fermilab.

For the first time, the gradient specification of the International Linear Collider (ILC) design study of 31.5 MV/m has been achieved on average across an entire ILC-type cryomodule made of ILC-grade cavities. A team at Fermilab reached the milestone in early October. The cryomodule, called CM2, was developed to advance superconducting radio-frequency technology and infrastructure at laboratories in the Americas region, and was assembled and installed at Fermilab after initial vertical testing of the cavities at Jefferson Lab. The milestone – an achievement for scientists at Fermilab, Jefferson Lab, and their domestic and international partners in superconducting radio-frequency (SRF) technologies – has been nearly a decade in the making, from when US scientists started participating in ILC research and development in 2006.

Between 2008 and 2010, all of the eight cavities in CM2, after being electropolished, had been individually pushed to gradients above 35 MV/m at Jefferson Lab in vertical tests. They were subjected to additional horizontal tests at Fermilab. They were among 60 cavities being evaluated globally for the prospect of reaching the ILC gradient. This evaluation was known as the S0 Global Design Effort, and was a build-up to the S1-Global Experiment, which put to the test the possibility of reaching 31.5 MV/m across an entire cryomodule. The final assembly of the S1 cryomodule set-up took place at KEK in Japan between 2010 and 2011. In S1, seven nine-cell 1.3 GHz niobium cavities strung together inside a cryomodule achieved an average gradient of 26 MV/m. An ILC-type cryomodule consists of eight such cavities.

Over the years, teams in the Americas region have acquired significant expertise in SRF technology, including increasing cavity gradients. Cavities manufactured by companies in the US, for example, have improved in quality: three of the eight cavities that make up CM2 were fabricated locally.

The CM2 group at Fermilab will push the gradients higher to determine the limits of the technology and to continue to understand and advance it. They expect to send an actual electron beam through CM2 in 2015, to understand better how the beam and cryomodule respond together. The aim is to use CM2 in the Advanced Superconducting Test Accelerator currently being commissioned at Fermilab. The SRF technology developed for FLASH at DESY, the European XFEL and now CM2 also has applications for the proposed PIP-II at Fermilab and at light sources such as LCLS-II at SLAC.

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