CERN, Geneva
A single-sided mobile diluter (TCDQ) and a horizontal secondary collimator(TCSG) are installed in the extraction region of the LHC to protect the downstream elements from damage in case of asynchronous beam dump. These collimators have to be precisely setup to shield the arc aperture at 450 GeV, the triplet apertures and the tungsten tertiary collimators (TCT) at the low-beta collision points. During the LHC beam commissioning, several machine protection tests were carried out to validate collimator setup and hierarchy at different beam energies and intensities. The outcomes of these measurements are presented in this paper together with the results of particle tracking simulations for asynchronous beam dump. These studies allowed to quantify the leakage expected from dump protection collimators to the downstream elements, and to validate the system performance towards higher beam intensity.
CERN, Geneva
The LHC transfer lines, injection and beam dump systems are equipped with a series of active and passive protection systems. These are designed to prevent as many failures as possible, for example through surveillance and interlocking, or to absorb any beam which is mis-kicked or mis-steered on passive absorbers. The commissioning, validation tests and performance of the different systems are described, and the implications for the protection of the LHC against different failures during beam transfer are discussed.
Fermilab, Batavia
FZJ, Jülich
The long term performance of Tevatron Electron Lenses (TEL1 and TEL2) are summarized. Both of them are operated reliably. Besides their main function as DC beam cleaner, TEL2 is also a test bed for beam-beam compensation, space charge compensator and soft collimator. And its operation as collimator will be tested after the installation of the new electron gun with hollow cathode in planed summer shutdown peroid.
CERN, Geneva
The very demanding LHC beam parameters put very strict requirements on the beam quality along the SPS-to-LHC transfer. In particular, the budget for the emittance increase is very tight. During the LHC commissioning, the emittances have been measured in the SPS, the two SPS-to-LHC transfer lines and in the LHC. Preliminary results show the importance of a very well controlled beam steering in the transfer lines together with the need of a robust trajectory correction strategy in order to guarantee long-term reproducibility. Another source of emittance comes from the tilt mis¬match be¬tween the LHC and its trans¬fer lines which generates cou¬pling at in¬jec-tion into the LHC and in turn will contribute to emittance increase. Preliminary results are also discussed.
CERN, Geneva
As one of the pre-injectors for the Large Hadron Collider, the CERN Proton Synchrotron must reliably deliver a wide range of beam parameters. The large variety of bunch spacings from 25 to 150 ns at extraction requires the acceleration of small, high-density bunches as well as highly intense ones. Above a threshold bunch density, longitudinal coupled-bunch instabilities are observed after transition crossing and the main accelerating cavities have been identified as part of the impedance driving them. Transient beam loading causes asymmetries of the various bunch splittings used to establish the required bunch spacing, compromising beam quality at the head of the bunch train delivered. Recent measurements and longitudinal limitations of beams for the LHC are presented, together with possible cures and options for future hardware improvements.
CERN, Geneva
To prevent from beam-induced quenches of the superconducting magnets a system of about 4000 beam loss detectors is installed on the magnets cryostats. These detectors, being ionization chambers, measure the particle shower starting inside the magnet. Examples of simulations linking the heat deposited in the superconducting coils with signals in the ionization chambers are presented. A comparison of the simulations to the data is done. Limits of the present system are discussed.
CERN, Geneva
EPFL, Lausanne
The energy ramp and the betatron squeeze at the CERN Large Hadron Collider (LHC) are particularly critical operational phases that involve the manipulation of beams well above the safe limit for damage of accelerator components. In particular, the squeeze is carried out at top energy with reduced quench limit of superconducting magnets and reduced aperture in the triplet quadrupoles. In 2010, the commissioning of the ramp from 450 GeV to 3.5 TeV and the squeeze to 2 m in all the LHC experiments has been achieved and smoothly became operational. In this paper, the operational challenges associated to these phases are discussed, the commissioning experience with single- and multi-bunch operation is reviewed and the performance during standard operation is presented.
CERN, Geneva
After more than a year of repairing and preparing the Large Hadron Collider after a major technical problem, beams were injected again in November 2009. The commissioning plan for the 2009 to 2011 run was ambitious, aiming for centre-of-mass collision energies of 7 TeV and an integrated luminosity of 1 fb-1. To date the LHC has not disappointed its user group or its designers. The first energy ramp to 1.2 TeV took place only 1 1/2 weeks after the start-up. A short technical break at the beginning of 2010 was followed by a series of commissioning highlights, including beams at 3.5 TeV, first collisions at 3.5 TeV, collisions with squeezed beams and injection of nominal bunch intensity. The major challenge for 2010 is to prepare the machine for higher and higher intensities to reach the target integrated luminosity by the end of 2011. This talk will give a short introduction to the LHC and its challenges and then focus mainly on the commissioning strategy, the preparation, the commissioning highlights, the status of the LHC and the plans for the coming months.
CERN, Geneva
The energy stored in the nominal LHC beams surpasses previous accelerators by roughly two orders of magnitude. The LHC relies on a complex machine protection system to prevent damage to accelerator components induced by uncontrolled beam loss. Around 20'000 signals feed directly or in-directly into the machine protection system. Major hardware sub-systems involved in machine protection include beam and powering interlock systems, beam loss and beam excursion monitors, collimators and the beam dumping system. Since the LHC startup in December 2009 the machine protection system components have been progressively commissioned with beam. Besides the usual individual component tests, global machine protection tests have been performed by triggering failures with low intensity beams to validate the protection systems. This presentation will outline the major commissioning steps and present the operational experience with beam of the LHC machine protection system.
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
The J-PARC consists of linac, 3-GeV RCS (Rapid Cycling Synchrotron), 50-GeV MR (Main Ring synchrotron) and three experimental facilities, the MLF (Material and Life science experimental Facility), the hadron experimental facility and the neutrino beam line. The RCS has performed 120 kW beam operation to the MLF since November 2009 and recently the MR has started 50 kW beam delivery to the neutrino beam line. In this paper the recent progress and experience in the course of our beam power ramp-up scenario such as beam loss control and machine activation will be presented.
PSI, Villigen
At the PSI a high intensity proton accelerator complex is routinely operated with a final energy of 590 MeV and with a beam current of 2.2 mA. In the future the beam current will be increased to 3 mA, then carrying a beam power of 1.8 MW. Operating a facility at such a high beam power needs not only a performing and fast protection mechanism against failures but also protection against activation of the facility. This presents a challenge for the beam diagnostics since a high dynamic range of currents is handled. Furthermore several tools, control loops and procedures which are of utmost importance for minimizing the ever present losses in the facility will be presented together with the machine protection system. A new challenge for our facility is the new ultra cold neutron (UCN) facility, coming into operation this year and requiring the switch over from one beam line to another for a duration of 8 sec with the full beam power. Using a short pilot pulse of a few ms the beam position is measured and the beam centered in preparation of the long pulse. We will show the diagnostics that are involved and how we overcome the constraints given by the machine protection system.
ORNL, Oak Ridge, Tennessee
The Spallation Neutron Source (SNS) has been operating at the MW level for about one year. Experience in beam loss control and machine activation at this power level will be presented. Also experience with machine protection systems will be reviewed, which are critical at this power level. One of the most challenging aspect of high power operation has been attaining high availability, and these issues will also be discussed.
STFC/RAL/ISIS, Chilton, Didcot, Oxon
At present ISIS is the world's most productive spallation neutron source. For the last two years (i.e. since 2008) ISIS has been running a second target station (TS-2) optimised for cold neutron production while continuing to run the first target station (TS-1) which began operating in 1984. The ISIS 800 MeV proton synchrotron cycling at 50 Hz produces a total beam power of 0.2 MW which is split between the first target station (TS-1) and TS-2, 40 Hz to TS-1 and 10 Hz to TS-2. The first two years of the new two-target-station operational regime are described.
LANL, Los Alamos, New Mexico
The Los Alamos Neutron Science Center (LANSCE) consists of a pulsed 800-MeV room-temperature linear accelerator and an 800-MeV accumulator ring. It simultaneously provides H+ and H- beams to several user facilities that have their own distinctive requirements, e.g. intensity, chopping pattern, duty factor, etc.. This multi-beam operation presents challenges both from the standpoint of meeting the individual requirements but also achieving good overall performance for the integrated operation. This presentation will touch on various aspects of more recent operations including the some of these challenges.
Fermilab, Batavia
In order to control beam loss for high intensity operation of the Fermilab Main Injector, electronics has been implemented to provide detailed loss measurements using gas-filled ionization monitors. Software to enhance routine operation and studies has been developed and losses are logged for each acceleration cycle. A systematic study of residual radiation at selected locations in the accelerator tunnel have been carried out by logging residual radiation at each of 142 bar-coded locations. We report on fits of the residual radiation measurements to half-life weighted sums of the beam loss data using a few characteristic lifetimes. The data are now available over a multi-year period including residual radiation measurements repeated multiple times during two extended facility shutdown periods. Measurement intervals of a few weeks combined with variable delays between beam off time and the residual measurement permits sensitivity to lifetimes from hours to years. The results allow planning for work in radiation areas to be based on calibrated analytic models.
CERN, Geneva
The collimation system of the CERN Large Hadron Collider (LHC) was built to handled 360 MJ stored in the LHC beams and is one of the most advanced cleaning system built for accelerators. It consist of 88 ring collimators of various designs and materials, for a total of 352 degrees of freedom (4 motors per collimators), that provide a multi-stage cleaning of beam halo as well as a crucial role for the LHC machine protection. Collimator can be moved with functions of time to guarantee the optimum settings during energy ramp and betatron squeeze. The system has been commissioned with beam for the 3.5 TeV LHC run and has ensured a safe operation, providing a close to nominal cleaning performance in the initial LHC operational phases. In this paper, the setup procedure and the setting validation techniques are presented, the operational aspects and challenges are reviewed and the system performance is discussed.
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
The accelerator facilities in J-PARC have been commissioned since January 2007. According to the progress of beam commissioning and construction of accelerators and experimental facilities, operational beam power becomes larger. The RCS produces 120kW beam to MLF and the MR provides 50kW beam to Neutrino target. In such high intensity operation, Linac ACS section, RCS injection and arc section, and MR collimator section become slightly higher residual dose area. We try to improve these losses before it is too late.