A Fast Magnet Current Change Monitor for Machine Protection in HERA and the LHC

ABSTRACT Fast Magnet Current Change Monitors (FMCM) have been designed to provide a reliable trigger signal for dumping the beam(s) in case of powering failures of magnets with fast effects on the particles. Rather than relying on current measurements that can be imprecise and affected by noise, the voltage drop over the circuit is measured and the magnetic field in the magnets is derived in real time, based on an impedance model of the electrical circuit. Developed at DESY for the HERA storage ring to protect the superconducting magnets in case of sudden power supply failures, the system has been recently validated for its use in critical circuits of the LHC and its transfer lines. The benefits of the system and the experience at DESY and CERN are discussed and presented along with results of the tests performed. The system will be integrated into the CERN accelerator controls structure and provide additional protection for operation with high intensity beams in the LHC and its injector from 2006 onwards. HISTORY AND MOTIVATION AT DESY AND CERN For DESY, it turned out that, in case of failures of power converters for some critical quadrupole magnets, the beam was not dumped in time to avoid a possible damage of detector components. The beam loss monitors were too slow, and the internal power converter monitoring did not cover all failure cases, especially not the failures in the current control loop. Driven by beam incidents in 2003, the internal alarm reaction time of the power converters was improved and FMCMs were developed and installed for 14 critical magnet circuits in 2004. For CERN, during several session of the Chamonix XIV conference [1] and the Machine Protection Review [2] "Fast Current Change Monitors" were proposed for additional protection, based on the system already operational at DESY. A beam incident in the TT40 extraction line of the SPS (destroying several vacuum chambers and a quadrupole magnet) showed the necessity of an additional protective device POWER CONVERTER FAILURE SCENARIOS After a power converter failure feeding a quadrupole magnet in a circular machine with current, the following happens: up to a certain magnet current deviation, the beam orbit will only slightly deviate, depending on the distance of the beam orbit from the quadrupole centre. After reaching a certain limit, the beam will suddenly blow up within only a few turns. With very fast beam loss monitors such failures can be captured for most cases, but in any case only after the beginning of the beam loss. For a dipole magnet in a circular machine, the beam will change its orbit proportional to the current deviation and after some time hit the vacuum chamber. Again, fast beam loss monitors could capture such failures only once beam losses occur. For a dipole magnet in a transfer line, there is no circulating beam which could trigger a beam loss monitor. For a wrong magnet current, the full beam will be lost in the chamber without warning. Magnet current or field monitoring before and during an extraction is the only way to prevent damage. OPERATING MODES The FMCM can be used for two operating modes: circulating beam mode (for HERA and LHC) and pulsed beam mode (for transfer lines used for extraction from the SPS towards LHC and CNGS). Circulating beam mode is used to protect a machine with circulating beam. Magnets are in general ramped very slowly (typically within several minutes). A triggering of the FMCM will dump the beam(s). False triggers are very annoying because machine operation will be interrupted for several hours in case of the LHC. The frequency of false triggers must not be higher than once per severa

Improvement of Neuroenergetics by Hypertonic Lactate Therapy in Patients with Traumatic Brain Injury Is Dependent on Baseline Cerebral Lactate/Pyruvate Ratio.

Energy dysfunction is associated with worse prognosis after traumatic brain injury (TBI). Recent data suggest that hypertonic sodium lactate infusion (HL) improves energy metabolism after TBI. Here, we specifically examined whether the efficacy of HL (3h infusion, 30-40 μmol/kg/min) in improving brain energetics (using cerebral microdialysis [CMD] glucose as a main therapeutic end-point) was dependent on baseline cerebral metabolic state (assessed by CMD lactate/pyruvate ratio [LPR]) and cerebral blood flow (CBF, measured with perfusion computed tomography [PCT]). Using a prospective cohort of 24 severe TBI patients, we found CMD glucose increase during HL was significant only in the subgroup of patients with elevated CMD LPR >25 (n = 13; +0.13 [95% confidence interval (CI) 0.08-0.19] mmol/L, p < 0.001; vs. +0.04 [-0.05-0.13] in those with normal LPR, p = 0.33, mixed-effects model). In contrast, CMD glucose increase was independent from baseline CBF (coefficient +0.13 [0.04-0.21] mmol/L when global CBF was <32.5 mL/100 g/min vs. +0.09 [0.04-0.14] mmol/L at normal CBF, both p < 0.005) and systemic glucose. Our data suggest that improvement of brain energetics upon HL seems predominantly dependent on baseline cerebral metabolic state and support the concept that CMD LPR - rather than CBF - could be used as a diagnostic indication for systemic lactate supplementation following TBI

The LHC Post Mortem Analysis Framework

The LHC with its unprecedented complexity and criticality of beam operation will need thorough analysis of data taken from systems such as power converters, interlocks and beam instrumentation during events like magnet quenches and beam loss. The causes of beam aborts or in the worst case equipment damage have to be revealed to improve operational procedures and protection systems. The correct functioning of the protection systems with their required redundancy has to be verified after each such event. Post mortem analysis software for the control room has been prepared with automated analysis packages in view of the large number of systems and data volume. This paper recalls the requirements for the LHC Beam Post Mortem System (PM) and the necessity for highly reliable data collection. It describes in detail the redundant architecture for data collection as well as the chosen implementation of a multi-level analysis framework, allowing for automated analysis and qualification of a beam dump event based on expert provided analysis modules. It concludes with an example of the data taken during first beam tests in September 2008 with a first version of the system

Testing Beam-Induced Quench Levels of LHC Superconducting Magnets

In the years 2009-2013 the Large Hadron Collider (LHC) has been operated with the top beam energies of 3.5 TeV and 4 TeV per proton (from 2012) instead of the nominal 7 TeV. The currents in the superconducting magnets were reduced accordingly. To date only seventeen beam-induced quenches have occurred; eight of them during specially designed quench tests, the others during injection. There has not been a single beam- induced quench during normal collider operation with stored beam. The conditions, however, are expected to become much more challenging after the long LHC shutdown. The magnets will be operating at near nominal currents, and in the presence of high energy and high intensity beams with a stored energy of up to 362 MJ per beam. In this paper we summarize our efforts to understand the quench levels of LHC superconducting magnets. We describe beam-loss events and dedicated experiments with beam, as well as the simulation methods used to reproduce the observable signals. The simulated energy deposition in the coils is compared to the quench levels predicted by electro-thermal models, thus allowing to validate and improve the models which are used to set beam-dump thresholds on beam-loss monitors for Run 2.Comment: 19 page

Information Management within the LHC Hardware Commissioning Project

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