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The Large Hadron Collider has (LHC) 1572 superconducting circuits which are distributed along the eight 3.5 km LHC sectors [1]. Time and resources during the commissioning of the LHC technical systems were mostly consumed by the powering tests of each circuit. The tests consisted in carrying out several powering cycles at different current levels for each superconducting circuit. The Hardware Commissioning Coordination was in charge of planning, following up and piloting the execution of the test program. The first powering test campaign was carried out in summer 2007 for sector 7-8 with an expected duration of 12 weeks. The experience gained during these tests was used by the commissioning team for minimising the duration of the following powering campaigns to comply with the stringent LHC project deadlines. Improvements concerned several areas: strategy, procedures, control tools, automatization, and resource allocation led to an average daily test rate increase from 25 to 200 tests per day. This paper describes these improvements and details their impact on the operation during the last months of LHC Hardware Commissioning.

The incident of 19 September 2008 at the LHC was caused by a faulty inter-magnet splice of about 200 nΩ resistance. Cryogenic and electrical techniques have been developed to detect other abnormal splices, either between or inside the magnets. The existing quench protection system can be used to detect internal splices with R>20 nΩ. Since this system does not cover the bus between magnets, the cryogenic system is used to measure the rate of temperature rise due to ohmic heating. Accuracy of a few mK/h, corresponding to a few Watts, has been achieved, allowing detection of excess resistance, if it is more than 40 nΩ in a cryogenic subsector (two optical cells). Follow-up electrical measurements are made in regions identified by the cryogenic system. These techniques have detected two abnormal internal magnet splices of 100 nΩ and 50 nΩ respectively. In 2009, this ad hoc system will be replaced with a permanent one to monitor all splices at the nΩ level.

The core task of the commissioning of the LHC technical systems was the individual test of the 1572 superconducting circuits of the collider, the powering tests. The two objectives of these tests were the validation of the different sub-systems making each superconducting circuit as well as the validation of the superconducting elements of the circuits in their final configuration in the tunnel. A wide set of software applications were developed by the team in charge of coordinating the powering activities (Hardware Commissioning Coordination) in order to manage the amount of information required for the preparation, execution and traceability of the tests. In all the cases special care was taken in order to keep the tools consistent with the LHC quality assurance policy, avoid redundancies between applications, ensure integrity and coherence of the test results and optimise their usability within an accelerator operation environment. This paper describes the main characteristics of these tools; it details their positive impact on the completion on time of the LHC Hardware Commissioning Project and presents usage being envisaged during the coming years of operation of the LHC.

After the incident occurred on the 19th September all equipment and systems (such as QPS racks, PC, BLM, Cryo instrumentation control etc.) located in the tunnel, especially in the incident affected area, were removed from the tunnel in order to allow an easy damage inspection. After a change or repair, during the re-installation phase, all these equipments will be put back in the tunnel and re-tested once connected to the others. In this paper we point out what are the needs of every system (and infrastructure: ventilation, civil engineering, control network…) and the activities to be done in order to avoid interference, facilitate and optimize the process of re-commissioning of the Sector 34.

We will give an overview of the training of all the LHC superconducting magnets based on the experience acquired diring the hardware commissioning. Using this information and the data relative to the test of individual magnets during manufacturing, we will give a view on the expected requirements for the training at 5 and 7 TeV.

The LHC has 1572 superconducting circuits. Most of the time and resources during the Hardware Commissioning were consumed by tests of each circuit of the collider, the so-called powering tests. The tests consisted in carrying out several powering cycles at different current levels for each superconducting circuit. The number of tests needed for each sector was around 1500, thus more than 12000 for the whole machine. The aim for the 2009 campaign is to minimise the total time needed for re-commissioning these circuits before beam operation at 5 TeV. This will be done by reducing the number of steps needed for those circuits which have been already commissioned in a similar way as it was done for the second commissioning campaign in sector 4-5 and by optimising the test planning and execution applying the huge experience gathered in the last two years of powering tests. The special powering plan designed for sector 3-4 and the commissioning of the new systems such as the QPS upgrade are also presented.

The Large Hadron Collider is now entering in its final phase before receiving beam, and the activities at CERN between 2007 and 2008 have shifted from installation work to the commissioning of the technical systems ("hardware commissioning"). Due to the unprecedented complexity of this machine, all the systems are or will be tested as far as possible before the cool-down starts. Systems are firstly tested individually before being globally tested together. The architecture of LHC, which is partitioned into eight cryogenically and electrically independent sectors, allows the commissioning on a sector by sector basis. When a sector reaches nominal cryogenic conditions, commissioning of the magnet powering system to nominal current for all magnets can be performed. This paper briefly describes the different activities to be performed during the powering tests of the superconducting magnet system and presents the scheduling issues raised by co-activities as well as the management of resources.

The Large Hadron Collider operation relies on 1232 superconducting dipoles with a field of 8.33T and 400 superconducting quadrupoles with a strength of 220 T/m powered at 12kA, operating in superfluid He at 1.9K. For dipoles and quadrupoles as well as for many other magnets more than 1700 power converters are necessary to feed the superconducting circuits. A sophisticated magnet protection system is crucial to detect a quench and safely extract the energy stored in the circuits (about 1GJ only in one of the dipole circuits) after a resistive transition. Besides, in such complex architecture, many technical services (e.g. cooling and ventilation, technical network, electrical distribution, GSM network, controls system, etc.) have to be reliably available during commissioning. Consequently, the commissioning of the technical systems and the associated infrastructures has been carefully studied. Procedures, automatic control and analysis tools, repositories for test data, management structures for carrying out and following up the tests have been put in place. This paper briefly describes the management structure and tool created to ensure safe, smooth and rapid commissioning.

For the two counter rotating beams in the Large Hadron Collider (LHC) about 8000 magnets (main dipole and quadrupole magnets, corrector magnets, separation dipoles, matching section quadrupoles etc.) are powered in about 1500 superconducting electrical circuits. The magnets are powered by power converters that have been designed for the LHC with a current between 60 and 13000A. Between October 2005 and September 2007 the so-called Short Circuit Tests were carried-out in 15 underground zones where the power converters of the superconducting circuits are placed. The tests aimed to qualify the normal conducting equipments of the circuits such as power converters and normal conducting high current cables. The correct operation of interlock and energy extraction systems was validated. The infrastructure systems including AC distribution, water and air cooling and the control systems was also commissioned. In this paper the results of the two year test campaign are summarized with particular attention to problems encountered and how they were solved.

The magnetic field in a superconducting magnet is mainly determined by the position of the conductors. Hence, the main contribution to the random field errors comes from random displacement of the coil with respect to its nominal position. Using a Monte-Carlo method, we analyze the measured random field errors of the main dipoles of the LHC, Tevatron, RHIC and HERA projects in order to estimate the precision of the conductor positioning reached during the production. The method can be used to obtain more refined estimates of the random components for future projects.

In this report the method for the localization of the electric shorts circuits in the main LHC dipoles using the magnetic measurements at room temperature is presented. The steps of the method are discussed, and two cases are studied in detail. A complete statistics of the 12 cases analyzed up to now is given.

More than two thirds of the dipoles of the Large Hadron Collider have been manufactured and their magnetic field has been measured at room temperature. In this paper we make a review of the trends that have been observed during the production. In some cases, the trends were traced back to displacements of conductors with respect to the nominal lay-out. The analysis allows detecting the most critical zones in the superconducting coil as far as field quality is concerned. The second part of the paper makes the point of the observed differences in field quality between the three manufacturers. The analysis allows evaluating which multipoles are more affected, what magnitudes of displacements are necessary to explain these differences (the manufacturers all producing the same baseline), and what could be the origin of such differences.

In the Large Hadron Collider, the direction of the guide field versus the magnet mid-plane is tightly toleranced. The correction capability of the orbit correctors is indeed quite limited. It is in practice not possible to measure on the same bench the field direction and the magnet mid-place. This section describes the test that allowed us to estimate the maximum error associated to the procedure. An estimation of Cold Mass torsional stiffness is also presented.

The influence of the geometry of the collars in the main LHC dipole on the magnetic field harmonics is analyzed. The study aims at finding if the collar geometry is the driving mechanism of field quality for some harmonics and if the two different collar suppliers give a special signature on the magnetic field. Data of more than 700 magnets of the LHC series dipoles are analyzed and discussed. The main result of the analysis is that the collar shape is the driving mechanism of the magnetic field harmonics only for b2 and a3 in one of the three Cold Mass Assemblers (Firm3), where only collars of the supplier S2 are used. Two independent observations support this fact: firstly, strong correlations between apertures of the same magnet as expected from the assembly procedure have been found. Secondly, the expected values based on the measured dimensions of the collars and on a magneto-static model agree with magnetic measurements both for the average and for the standard deviation.

The production of more than 60% of superconducting cables for the main dipoles of the Large Hadron Collider has been completed. The results of the measurements of cable magnetization and the dependence on the manufacturer are presented. The strand magnetization produces field errors that have been measured in a large number of dipoles, all tested in cold conditions. We examine here the correlation between the available magnetic measurements and the large database of cable magnetization. The analysis is based on models documented in the literature. Finally, a forecast of the persistent current effects to be expected in the LHC main dipoles is presented, and the more critical parameters for beam dynamics are singled out.

The quality of the magnetic field in the LHC main dipoles is given by the correct location and dimensions of the superconducting cables. In this paper the measurements of the dimensions of the LHC cables are presented; then the impact on field quality due to the tolerances on cable dimension is analyzed showing that biggest effect is found on even skew field harmonics. A Monte Carlo study is performed: the effect on random components of the field harmonics is studied and the impact on field quality of the coupling of two different cable producers in the same aperture is evaluated. We finally present a study of the correlation, based on the ninety pre-series collared coils, between cable geometry and field measurements.

In order to obtain the required magnetic field quality in the LHC main dipole, the superconductive cables blocks are separated by copper wedges. These components must respect geometrical tolerances of ±30 micrometers. Non-nominal copper wedge dimensions change the position of cables blocks and therefore affect field quality. In this paper we present the measurements of the copper wedges used in the main LHC dipoles. We then evaluate the influence of copper wedge dimensions on field quality, comparing it to the warm magnetic measurements of the collared coils. Finally, in order to foresee the impact of the copper wedge production on the random and on the systematic parts of the field harmonics we implement a Monte-Carlo method. Comparison with targets imposed by beam dynamics is used to judge how critical the tolerances on copper wedges are.

During hardware commissioning of the Large Hadron Collider (LHC), 8 main dipole circuits are tested at 1.9 K and up to their nominal current. Each dipole circuit contains 154 magnets of 15 m length, and has a total stored energy of up to 1.3 GJ. All magnets are wound from Nb-Ti superconducting Rutherford cables, and contain heaters to quickly force the transition to the normal conducting state in case of a quench, and hence reduce the hot spot temperature. In this paper the performance of the first three of these circuits is presented, focussing on quench detection, heater performance, operation of the cold bypass diodes, and magnet-to-magnet quench propagation. The results as measured on the entire circuits will be compared to the test results obtained during the reception tests of the individual magnets.

Superconducting high field magnets are tightly constrained in terms of field quality, since such magnets are usually designed to perform quite demanding tasks, such as focusing particle beams in accelerators, plasma confinement and shaping in fusion devices, and polarizing actions in magnetic resonance. In all these cases, small discrepancies of field map from the design values may strongly impact on device performance. As a consequence, quality insurance procedures are needed to verify if each single coil meets such criteria, e.g., using laser tracking, and possibly warm magnetic measurements. As a matter of fact, external magnetic measurements can be used to estimate the possible deformations of conductors inside the magnet, but this implies inverse problem approaches. The field probes accuracy is therefore critical, and the measurement system must be carefully designed, taking into account the probe characteristics, but also the characteristics of the windings and of the surrounding environment. In this paper, different measurement techniques are compared in terms of sensitivity and accuracy, with reference to various types of sensors and of measurement schemes.