CERN Accelerating science

Successful tests of 11T dipole at CERN
By Panos Charitos with Lucio Rossi (CERN)

The 5.5m long prototype being assembled at CERN (Image: CERN)

As part of the LHC upgrade, the HL-LHC will need a more efficient collimation system to be able to handle the two-fold increase in beam intensity compared to the original LHC design value.

Powerful dipoles will be installed at point 7 of the LHC ring (dispersion suppression region, DS). They are foreseen to increase the 8T field of the current machine up to 11T.  

The idea is to replace the present 8T, 15 meter-long LHC dipole magnet with a new 11T, 11 meter-long one (built in two segments of 5.5-m each). The installation of the new dipole will free 4 meters of space in the tunnel, which can be used to insert a cold-to-warm-to-cold bypass module.

This module will allow collimator (at room temperature) to be hosted to catch off momentum particles that otherwise could quench the superconducting magnets. The successful test of the first models magnets of this kind –with an approximate length of two meters- have been reported in a previous issue of Accelerating News.

In January 2016, a complete assembly of an 11T dipole (comprising two full apertures) was tested at the Superconducting Magnet Test Facility of CERN (SM18). Apart from its shorter length (2m vs 5.5 m) the cold mass is identical to the final magnet that will be used in the HL-LHC. Each single aperture magnet was already tested and reached ultimate field of 12 T.

“Not surprisingly, the double aperture dipole also behaved very well. Perhaps more surprising was the exceptional good memory of the magnets” said Frederic Savary, leader of the 11T team at CERN. The magnet reached the nominal 11.2 T field without quench allowing to achieve the ultimate field of 12 T with only two quenches.

Lucio Rossi, leader of the HL-LHC project, elaborated further: “It would have qualified as a “bonus magnet” during the LHC construction, when the ultimate field was 9 T and not 12 T.”

Figure 1: Graph showing the quench current of the dipole (Image: CERN)

Subsequently, the magnet passed 12.5 T (see Figure 1) for the training curve, a record for a double aperture accelerator quality magnets that could go in the tunnel to steer the HL-LHC beams. Within five years of its start “this project is one of the most successful ones in the history of high field magnets”, says Rossi.

The challenge now is to show reproducibility of these results and then to test the 5.5 m-long prototype, which is currently under construction (as can be seen in the picture above). Meanwhile the 11T team deserves the congratulations of the Management of the HL-LHC project and CERN: a further step forwards in the quest of increasing the frontier of high field magnets.

HiLumi HL-LHC Sextupole corrector magnet tested at LASA-INFN
By Antonella Del Rosso (CERN)

Assembly the first sextupole corrector of the HL-LHC at the LASA Laboratory (Image: INFN-Milan)

A sextupole superferric magnet for the High Luminosity upgrade of the LHC was successfully tested earlier in March, and demonstrated it can meet the requirements of the project.

The prototype of the corrector magnet was designed and built at LASA laboratory of the Milan section of INFN. This is the first of a number of magnets developed within a CERN-INFN Collaboration Agreement for the HL-LHC project signed in 2013. The LASA laboratory will further develop high-order magnets from quadrupoles up to dodecapoles.

A superferric magnet is an iron-dominated window frame magnet. The iron shapes the overall field while the coils are made of superconducting material that is kept at cryogenic temperatures to reduce power losses to a minimum.

Though they are low-field magnets and can’t reach the high magnetic fields of the main dipole magnets, the corrector magnets are important as the high-intensity beams will have to complete hundreds of millions of turns in stable conditions before being safely dumped by the operators. The design of these magnets took into account considerations for higher reliability that is critical for the High Luminosity upgrade of the LHC.

The results achieved so far look promising and the magnets will be further tested at CERN. CERN together with INFN will continue working on the design and testing of higher-order corrector magnets before moving to the industrialization phase.

For further information on this corrector magnet you can read more here.

 HiLumi-LHC moves on to construction phase
by Agnes Szeberenyi and Alessia Barachetti (CERN)

October 2015 was a turning point for the High Luminosity LHC (HL-LHC) project, marking the end of the European-funded HiLumi LHC Design Study activities, and the transition to the main hardware prototyping and industrialization phase, which is also reflected in the redesigned logo that was recently presented. The green light was given between 26 and 30 October 2015, when more than 230 experts from all over the world gathered at CERN to attend the 5th Joint HiLumi/LARP Annual Meeting.

During five days of intense plenary meetings and working sessions, a first version of the Technical Design Report was approved and released. The document, following the Preliminary Design Report issued in 2014, describes in detail how the LHC upgrade programme will be carried out. During the meeting, the seventeen Work Packages that over these four years worked to address the technological and technical challenges related to the upgrade also presented the main outcomes of their work.

5th Joint HiLumi LHC-LARP Annual Meeting. Image credits: CERN

The accelerator physics and performance team reported on the parameter sets and machine optics that would allow HiLumi LHC to reach the very ambitious performance target of an integrated luminosity of 250 fb-1 per year. The study of the beam-beam effects confirmed the feasibility of the nominal scenario based on the baseline b* levelling mechanism, providing sufficient operational margin for operation with the new ATS (Achromatic Telescopic Scheme) at the nominal levelling luminosity of 5×1034 cm-2s-1, with possibility to reach up to 50% more. The magnet design activity launched the hardware fabrication of short models of the Nb3Sn quadrupoles’ triplet (QXF), separation dipole, two-in-one large aperture quadrupole and 11 T dipole for Dispersion Suppressor collimators. Single short coils in the mirror configuration have already been successfully tested for the triplet. The first model of the QXF triplet containing two CERN and two LARP coils was assembled in the US in summer 2015 and is being tested this fall, while a short model of the 11 T dipole fabricated at CERN reached 12T. To protect the magnets from the higher beam currents, the collimation team was focusing on the design and verification of the new generation of collimators. The team presented a complete technical solution for the collimation in and around the insertions in HL-LHC, providing improved flexibility against optics changes. The crab cavities activity finalized and launched the manufacturing of the crab cavity interfaces, including the helium vessels and the cryo-module assembly. All cavity parts stamped in the US will be assembled and surface processed in the US in addition to electron-beam welding and testing. Last but not least, as part of their efforts to develop a superconducting transmission line, the cold powering activity hit a world record current of 20kA at 24K in a 40m long MgB2 electrical transmission line. The team has finalised the development and launched the procurement of the first MgB2 PIT round wires. This is an important achievement that will enable the start of a large cabling activity in industry, as required for the production of prototype Cold Powering System for the HL-LHC.

In the recently released open access HiLumi LHC book “The High Luminosity Large Hadron Collider. The New Machine for Illuminating the Mysteries of the Universe”, you can find out more about the High Luminosity LHC project, its technology and design as well as the challenges ahead.



Successful completion of the HQ program, a testbed for the LHC IR quadrupoles
 By Giorgio Ambrosio (FNAL), Guram Chlachidze (FNAL), P. Ferracin (CERN) and GianLuca Sabbi (LBNL)

LARP High Field quadrupole (HQ) magnet cross section.

The US LHC Accelerator Research Program (LARP) scientists, in collaboration with CERN, have completed tests on the latest series of the 120 mm aperture Nb3Sn High-field Quadrupoles (HQ03). The HQ03 serves as a testbed for the development of the new HL-LHC IR quadrupoles (MQXF), for which a short model is currently undergoing tests.  

Two test cycles were carried out on LARP’s latest series of the 120 mm aperture Nb3Sn High-field Quadrupoles (HQ03) that serve as a basis for the MQXF. This third series applies optimized design solutions and improves the coil-to-coil uniformity. Quench training was performed entirely at 1.9 K with a room-temperature cycle between two test cycles. The magnet demonstrated excellent performance: in both test cycles, it surpassed the nominal operating gradient, corresponding to 80% of the conductor (short sample) limit, without quenches. The highest current reached at 1.9 K was 16.1 kA, achieving 90% of the short sample limit (SSL). At 4.5 K the model achieved 98% SSL. Magnetic shims placed inside the iron yoke have also proved effective to correct magnetic field errors.

As we reported in our June 2015 issue, a first 150 mm aperture MQXF coil manufactured in the US was tested at FNAL in a mirror configuration. The coil reached 90% of the short sample limit after 20 quenches. This was the first successful test proving the design of the MQXF coil. Following the mirror test, the first MQXF short model has been assembled in LBNL and is undergoing testing at Fermilab.  

Assembly of MQXFSM1 Mirror magnet. Credits: Reidar Hahn (FNAL)



 First hardware for HL-LHC interaction region magnets
by Ezio Todesco (CERN)

The coil of the sextupole corrector
Courtesy of G. Volpini and LASA laboratories

The mirror QXF entering the FNAL test station 
Courtesy of G. Chlachidze and US-LARP

The Interaction Region (IR) of the HL-LHC project will be made of nine different types of new magnet, relying on three different technologies (Nb3Sn and Nb-Ti with Rutherford cable, and superferric magnets with Nb-Ti coils).

These magnets are in the design and prototype phase, developed by five international collaborations: US-LARP, CIEMAT (Spain), CEA Saclay (France), INFN-Milano LASA laboratories and INFN-Genova (Italy), and KEK (Japan). The HL-LHC design study is now approaching completion: the conceptual design is nearly finished, engineering is in progress and the first hardware that will be used in the prototypes is being manufactured and tested. This is a very exciting phase as the project shifts from paper to hardware.

In April 2015, the winding and impregnation of the first coil of the superferric sextupole corrector (see image above-left) was completed. As a stand-alone coil it was successfully tested in INFN-LASA laboratories. This collaboration has won the race towards the first test of a component of the HL-LHC interaction region magnets. The coil had a first quench at 80% of short sample limit, and reached 91% after 3 quenches, at 2.5 K. In these correctors, the operational current is set at 60% of short sample limit.

In May 2015, the first short coil of the Nb3Sn quadrupoles, manufactured by the LARP collaboration, was tested in a mirror configuration at FNAL, US. The coil had a first quench at 70% of short sample limit, a second one at 76%, and reached 90% after 20 quenches. The triplet will operate at 75% - this value has been recently reduced from the original 80% value to add some margin, following the advice of the review committee held in December 2014 and chaired by Dr. A. Yamamoto (KEK).

Since the beginning of the year, coil winding tests are going on both in KEK, for the 5.6 T Nb-Ti separation dipole (D1), and in Saclay, for the 115 T/m gradient Nb-Ti quadrupole. In KEK, an iteration of the design of the iron yoke has been performed to guarantee a better alignment of the dipole field during assembly. In CEA, first tests have confirmed the correct geometry of the end spacers and of the coil components.

The next step is the test of the Nb3Sn quadrupole short model in autumn 2015, made up of two CERN coils (just shipped to the US) and two LARP coils. At the end of the year a test of the first corrector sextupole is foreseen in LASA, and a test of the first short model of the separation dipole will be carried out in KEK, Japan.



 Hollow electron lenses for enhanced LHC beam collimation
by Stefano Redaelli (CERN) with Emma Cooper (STFC)

Design of the LHC hollow e-lens. Courtesy of D. Perini for the EN/MME team at CERN

Loss spikes have already affected the operation of the LHC, and control of beam losses is recognised as a critical concern for performance at higher beam energies and intensities.

Hollow electron lenses are the most promising of a number of methods being considered to improve the beam collimation system, and are expected to boost the performance of the LHC and of its High-Luminosity (HL) upgrade through active control of halo particles’ diffusion speed and tail population. This is achieved with a low-energy, intensity-modulated hollow electron beam that runs co-axially to the circulating hadron beam, over a few meters, and acts on the halo particles at large transverse amplitudes without perturbing the beam core. Particles outside the core that see the electromagnetic field of the electron beam are driven unstable and disposed of by the present collimation system at controlled loss rates, rather than at larger loss rates and at unpredictable moments.

Following a successful experience at the Tevatron, where a hollow e-lens was used for collimation beam tests for the LHC, a conceptual design of a hollow e-lens optimized for the LHC was produced. At CERN, this is an effort across all departments of the Accelerator and Technology Sector. The conceptual design is rapidly evolving into a technical design for implementation into the LHC. While a detailed timeline for deployment will be established after accumulating some operational experience at 6.5 TeV, the aim is to prepare a technical design by the end of 2015 in order to be ready for LHC needs beyond Long Shutdown 2.

The present baseline design of the LHC hollow e-lens was worked out in collaboration with the Tevatron team. The electron beam parameters achieved in a test stand for LHC collimation studies at Fermilab indicate that a 5 A electron beam current can be achieved with a 2.5 mm radius gun at 10 kV. In order to stabilize the hollow beam and squeeze its inner radius to the required dimensions around the ~300 micron rms size hadron beams, a precise superconducting solenoid of up to 6 tesla is required. An ‘S’ shape design, with injection and extraction of the electron beam on opposite sides of the proton beam, is proposed to compensate edge effects that might otherwise perturb the beam core particles that ‘see’ asymmetric e-beam distributions at the injection and extraction locations. 

Scheme illustrating the conceptual integration of a hollow elens in the present collimation system hierarchy. This device controlled the loss rates while the standard collimation remains in place to dispose of the halo particles. Credit: CERN



 Accelerators celebrating the International Year of Light
by Agnes Szeberenyi (CERN)

Luminous collisions at CERN to promote the year of light
Image credit: CERN

The year 2015, a century after the publication of Einstein’s Theory of General Relativity in 1915, has been proclaimed the International Year of Light and light-based technologies by the UN General Assembly. 

‘Light as luminosity’ is the theme of the CERN celebrations on the occasion of the International Year of Light and Light-based Technologies (IYL 2015). CERN is organizing a series of public events that are broadcasted online, and archived. Follow the webcasts for upcoming and past events here.

Read the viewpoint of prof. Lucio Rossi, the Leader of the High Luminosity LHC on the “luminous” celebrations.

Also visit the International Year of Light blog for more inspirational stories, not only on accelerators. 



  Key highlights towards the High Luminosity LHC era
  by  Agnes Szeberenyi (CERN)

LHC/ HL-LHC Plan (last update 24.09.2014)
Image credit: HiLumi

More than 110 experts from all over the world gathered in Tsukuba, Japan for the 4th  Joint HiLumi LHC/ LARP Annual Meeting between 17 and 21 November 2014, hosted by the High Energy Accelerator Research Organization (KEK).

The event started off with the plenary sessions where management of the collaboration (Dr. Frederick Bordry for CERN, Prof. Yasuhiro Okada for KEK, Dr. Steve Gourlay for USA) gave invited talks. The first plenary session closed with the High Luminosity LHC status updated by Prof Lucio Rossi, HL-LHC Project Leader. Prof Rossi also officially announced the new HL LHC timeline to the collaborators.

One of the highlights of the plenaries was the status update on the Preliminary Design Report, by Dr. Isabel Bejar, as the main deliverable of the project, which will be published soon as a CERN Yellow Report. 3 days focused on the work package parallel sessions, reviewing the progress in design and R&D not only for the EU funded but also non-EU funded work packages.

Key highlights from the Accelerator Physics and Performance activity (WP2) included a refined optics and layout of the high luminosity insertions, an updated impedance model of the LHC and Hl-LHC, and the need of low impedance collimators was confirmed. One of the main results of the IR Magnets activity (WP3) in the past 18 months was a baseline for the layout of the new interaction region. Engineering design and prototyping of most of the magnets has been started, and first tests of near-to-final equipment are expected next year. The Crab Cavities activity (WP4) in this period delivered and tested all 3 prototype crab cavities (4-rod, RFD and DQW) out of which the international design review carried out in in May in  BNL made the downselection to proceed with design of the RFD and DQW. A key milestone, to freeze the cavity designs and interfaces, was also met. Highlights from the wrap up talk of the IR Collimation activity (WP5) include the first lay-out for the IR collimation as well as a solid baselines for the collimation upgrade in the dispersion suppressors of around IR7 and IR2. In addition, simulations have continued for advanced collimation layouts in the matching sections of IR1 and IR5, improving significantly the cleaning of physics debris products downstream around the high-luminosity experiments. The Cold Powering activity (WP6) highlights included the world record current of 20kA at 24K in an electrical transmission line consisting of two 20-metre long MgB2 superconducting cables. Other achievements were a conceptual study and preliminary design of a novel concept of cold powering system (cryostat and current leads) connected to the Superconducting Link, definition of cryogenic requirements and flow schemes. The meeting covered also many progress in the other (non-FP7) WPs, especially for machine  protection, cryogenics, vacuum, beam instrumentation, etc. A delicate arbitration among the needs of CC test in SPS-LSS4 (Coldex experiment) and  the needs of continuing study and tests for e-cloud mitigation by  vacuum people was carried out.

The final FP7 HiLumi LHC / LARP Collaboration Meeting will be held between 26-30 October 2015 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. Stay tuned for the latest updates in the CERN Bulletin and CERN website.



 One step closer to the 11 Tesla dipole magnet supported by

                   by Mikko Karppinen (CERN)

First CERN 11 T –single-aperture model magnet MBHSP101 right after the cold mass assembly in B-180.
Image credit: F. Lackner @CERN

The 11-Tesla dipole project aims to replace some 8-Tesla dipole magnets in the LHC tunnel with shorter, stronger 11-Tesla magnets to create enough space to install additional collimators for the HL-LHC upgrade. The project is progressing well on both sides of the Atlantic as teams from Fermilab and CERN collaborate to reach the ambitious target.  

After their success with the 1-metre-long single-aperture dipole model, Fermilab is just completing the first 1-m-long 2-in-1 model magnet, which is the very first magnet of its kind based on Nb3Sn technology.

At CERN, a 2-metre-long model magnet using the first practise coils -one of which was made from Nb3SN and connected in single coil configuration - has been constructed and shown excellent test results.  The main purpose of this model was to validate the entire assembly process and the tooling before building the first “real” single aperture model magnet. The results of the training performance tests of the practice model magnet exceeded initial expectations reaching a peak field of 12.9T and 12.5T in the coil.  Moreover after a thermal cycle the magnet showed very little re-training, which is also very encouraging.

The first CERN model magnet is at the final stages of assembly and the cold test is planned for early October. “We are keeping our fingers crossed for the magnetic performance to be at the same level as the practice model” says Mikko Karppinen, who for three years has led the design and R&D effort for the 11 T. “This would be encouraging news for the building the full-scale 5.5 m prototype” he adds.



  Second test of HQ02: even better
    by Gian Luca Sabbi (LBNL), Ezio Todesco (CERN)

Fig1: First training of HQ02 (red diamonds), slow training at 2.2 K (blue squares), and second test with fast training towards 17 kA (black circles)
Image credit: CERN and US LARP

HQ is a 120 mm aperture Nb3Sn quadrupole developed by the US LHC Accelerator Research Program (US LARP). It presents all features and technological choices that will be used in the 150 mm quadrupole triplet (QXF in the CERN jargon) for the HL-LHC era.

During the first test, the magnet proved to be able to operate at the nominal current of 15 kA. It has then been pushed towards larger currents (in the LHC we require the magnet to reach 110% of nominal current), showing a pretty long training in the region 15-16 kA [see Fig1]. The analysts suggested to have a second assembly increasing the compression of the coil to guarantee a faster training. In the second test at CERN, the magnet reached nominal current without any quench, and trained to 110% of nominal current in a few quenches. This confirmed once more the validity of mechanical structure, allowing fine tuning of the stress in the coil. HQ outperformed the Nb-Ti twin of the same aperture, which showed a slower training.

The magnet was also used as a test bed for studying quench protection. HL LHC magnets will have a ratio between the stored energy and the coil volume (which absorbs that energy) which is twice of what we have today in the LHC. During the HQ test, special test were done to understand when coil degradation takes place, resulting in broader limits than expected. Moreover, a novel technique (CLIQ) (CLIQ) based on the discharge of a capacitor in the magnet provoking fast quench of the coils, has also been also successfully tested. Results have been presented at the ASC conference in August, where the CLIQ paper got a special award.