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Progress in the interaction region magnets of HL-LHC

Panagiotis Charitos — Mon, 06 Mar 2017 14:06:40 +0000

Progress in the interaction region magnets of HL-LHC
by Ezio Todesco (CERN)

During the past months, significant advancements have been done in the development of the interaction region magnets for HL-LHC.

In KEK, Japan, the short model of the separation dipole D1, that showed insufficient quench performance after the first test, has been disassembled. Significant movements of the coils (up to few mm) were observed in the heads, and a clear evidence of a lack of prestress in the straight part was found. The new assembly took place during winter, and a prestress increase in the straight part of about 35 MPa has been achieved. The magnet was tested in February, reaching nominal current after 2 quenches and ultimate after 5 quenches (see Figure 1). “The magnet performance is now in line with the project requirements – says T. Nakamoto, in charge of the D1 project – we will have a warm-up and cool-down to prove the magnet memory in the next weeks”. The short model design is being updated in some features of the iron yoke, and to account for an unexpected contribution to field quality from the coil heads in the strong regime of saturation. A second model will be built in the second part of 2017, and tested in 2018.

Figure 1: Training of MBXFS1 in KEK: quenches (markers), nominal and ultimate current (solid lines) and short sample limit (dotted line). (Credit: HL-LHC WP3 collaboration)

In the US, the first 4-m-long coil has been tested in a mirror configuration, reaching 85% of short sample limit (see Figure 2). “This is the new world record for coil length in Nb₃Sn accelerator magnets – says G. Ambrosio, in charge of the US contribution for the triplet - and paves the way to the assembly and test of the first 4-m-long quadrupole, to be done in the second part of the year”. At the same time at CERN the first 7.15-m-long dummy coils are being produced to validate the assembly procedures (see Figure 3).

Figure 2: Training of mirror 4-m-long coil in BNL: quenches (markers), 70% and 80% of short sample (solid lines) and short sample limit (dotted line). (Credit: HL-LHC WP3 collaboration)

Figure 3: Winding of the first 7.15-m-long dummy coil of the triplet quadrupole at building 180 (CERN)

Furthermore, in CIEMAT, Madrid, the prototype for the nested orbit correctors is entering the construction phase. The concept of double collaring has been validated on a mechanical model with the final design of the collars and a dummy coil made of aluminum (see Figure 4). This is an important step of the validation of the mechanical concept of this magnet, where a mechanical lock between the horizontal and vertical dipoles is required to control the large torque. In particular, the second collaring of the outer dipole on the inner one is critical. “Both collaring operations were in line with our expectations, and we managed to insert pins without any criticality – said F. Toral from CIEMAT, in charge of the Spanish contribution for the orbit correctors – we saw some asymmetries that need more investigations, but given the complexity of the design, this is a very encouraging first step towards construction”.

Figure 4: Double collaring of the nested corrector in CIEMAT

Finally, in LASA, Milano the activity on the high order corrector prototypes is at full speed. After the successful test of the sextupole, the first decapole coil in a single coil configuration has been tested successfully. The coil reached twice the ultimate current with negligible training, thus proving the assembly procedures and tooling concepts. LASA is working in parallel on two magnets: besides the first decapole coil, eigth octupole coils have been completed and will be assembled in the first prototype, and tested in April.

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issue 20

First test of the HL LHC separation dipole short model in KEK

Panagiotis Charitos — Mon, 27 Jun 2016 12:00:24 +0000

First test of the HL LHC separation dipole short model in KEK

By T. Nakamoto (KEK) & E. Todesco (CERN)

Figure 1: Collaring test of the final cross-section of the D1 in KEK. Yoking press is in the background

A key element of the High Luminosity LHC interaction region is the superconducting separation dipole D1, which will replace the resistive dipole presently installed in the LHC. Thanks to the superconductive technology of Nb-Ti, this magnet will increase the field from the present 1.28 T to 5.6 T, thus reducing the overall length from 25 m to 7 m (A first layout for the High Luminosity Upgrade) and providing at the same time a 30% stronger kick. This large saving in terms of space along the beam line is crucial to allow the installation of longer triplet and of the crab cavities, which are among the main pillars of the luminosity upgrade.

The D1 upgrade was one of the first HL LHC magnets to be studied in collaboration with KEK. Activities started in 2011, led by T. Nakamoto, with the contribution of a young scientist (Q. Xu, now in IHEP, Bejing) focusing on the conceptual design. After the selection of the triplet aperture of 150 mm, KEK has developed an engineering design in 2013-2014: the construction of a short model has been carried out during 2015. The magnet is not trivial due to its large aperture, the relatively high field for Nb-Ti technology, the tight requirements on field quality, and the constraints imposed on the mechanical structure. Since one needs to maximize the iron dimension to limit saturation and fringe fields outside the magnet, the KEK team opted for a concept where the collars are thin spacers and forces are kept by the massive iron: this is the same mechanical structure that was used for the triplet magnet MQXA presently installed in the LHC. Since forces are kept by the iron, the assembly of laminations around the coils and the control of the compression given under the press (see Fig. 1) is critical and entailed in the iteration in the design.

The first model has been completed in March 2016, and test has been done in April and June. The test started at 4.5 K (see Fig. 2) since the test station underwent an upgrade and some additional cross-checks were required. At 1.9 K, the magnet had a first quench at 9.5 kA, i.e. ~60% of the short sample, and approached the 12 kA nominal current (75% of short sample) after ~10 quenches. After a thermal cycle, the magnet showed good memory (i.e. it started from the same values reached before the warm-up).

Figure 2: Training of the first D1 short model in KEK (Image credit: M. Sugano)

The magnet eventually reached 500 A more than nominal current in the second run, but exhibited an erratic behaviour around these current values. At the same time, the strain gauges gave a clear indication of a lack of support in the coil already at around 8 kA (see Fig. 3). This suggested not to push the training towards the goal of ultimate current, take all the information about field quality and quench protection, and possibly have a second assembly with an increase of prestress (a similar step is being done for the first short model triplet). “We will soon have a review in KEK to present the test result and define the next steps”, says A. Musso, who follows the collaboration from the CERN side. “A second model is foreseen in the HL LHC planning for the year 2016-2017, and the construction of the long prototype will take place from 2018.”

Figure 3. Stress variation during the energization of the magnet, with flattening at 8 kA indicating coil unloading (Image credit: M. Sugano)

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issue 17

Recent progress of the HiLumi project

Margarita Synanidi — Mon, 01 Dec 2014 14:37:51 +0000

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.

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A first layout for the High Luminosity Upgrade

Sabrina El Yacoubi — Thu, 27 Nov 2014 14:26:50 +0000

A first layout for the High Luminosity Upgrade
by Ezio Todesco, Stephane Fartoukh (CERN)

The tentative layout for the insertion: sequence of magnets versus distance to the interaction point in ATLAS or CMS (0 m is the centre of the experiment). The flags indicate a possible origin of the in-kind contribution.
Image credit: HiLumi LHC

A first baseline for the layout of the High Luminosity inner triplet and associated magnets has recently been defined. This is the second major milestone, after the choice of a 150 mm aperture for the quadrupoles in July 2012.

A layout is the selection of the sequence of magnets, their strength, their length, and the associated technology: therefore, it requires inputs both from the optics and from the magnet teams. Its definition is a delicate equilibrium between the search for maximum performance and the need of minimizing complexity and associated risks. Nb3Sn technology had been already selected for the triplet quadrupoles – these magnets are planned to be built with a CERN-US collaboration, heavily relying on the work carried out by LARP in the past 10 years.

After the triplet, a separation dipole of 5.5 T, in Nb-Ti, is being studied by the Japanese team in KEK. The layout is complemented by the challenging orbit correctors, also based on Nb-Ti technology, with nested coils both providing horizontal and vertical field of up to 2 T. A package of higher order correctors relying on superferric technology is also available, in order to correct for the inevitable field imperfections of the inner triplet at the 10-4 level. The triplet corrector package is based on the design developed in Spain by CIEMAT.

As a result, the energy deposition team can start simulations to have a precise estimate of the radiation damage and heat loads coming from the collision debris. It is a heavy shower and magnets will need thick shielding to avoid falling in pieces before reaching the project ambitious goal of 3000 fb-1. The layout has been presented at CERN and will be extensively discussed at theHiLumi/LARP collaboration meeting, 8-10 April 2013, Napa Valley.

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R&D on C-band accelerators

Margarita Synanidi — Wed, 26 Nov 2014 10:35:40 +0000

R&D on C-band accelerators
by David Alesini (INFN-LNF) and Marica Biagini (INFN-LNF)

Fig1: Breakdown rates as measured at different field values before and after conditioning of the SPARC C-Band prototype. After processing, about 50 MV/m accelerating field has been reached, with a breakdown rate (BDR) per meter of the order of 10-6, which is a very good result in such structures. Image credits: INFN-LNF
Fig2: SPARC C-Band structure in the oven before brazing. Image credits: INFN-LNF

The use of Radio-Frequency C-Band accelerating structures for electron acceleration and production of high quality beams has been recently proposed and adopted in several linac projects all over the world.

Two important FEL projects have adopted such type of structures: the Japanese FEL project at SPring-8 and the Swiss-FEL project at the Paul Scherrer Institute (PSI). Even if this technology is less known with respect to the more consolidated S-Band one, beam dynamics calculations and experimental measurements demonstrated the possibility to reach high beam quality and higher gradients, making the C-Band technology very appealing from this point of view. Possibilities to use C-Band structures for hadron therapy are also under study from several years and seem to be very promising.

In the SPARC photo-injector facility at the INFN Frascati National Laboratories (LNF, Italy) an R&D programme on C-Band structures is being carried out in order to upgrade the beam energy from 150 to more than 250 MeV in the facility. Involving both LNF and PSI, this programme is performed within the High Gradient Acceleration (HGA) Work Package of the TIARA Preparatory Phase.

The choice of the C-Band for the energy upgrade was dictated by the opportunity to achieve a higher accelerating gradient, enabled by the higher frequency, and to explore C-Band acceleration combined with a S-Band injector that, from beam dynamics simulations, looks very promising. The energy upgrade of SPARC will be done by replacing one low gradient S-Band accelerating structure with two C-Band structures.

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