Daniel Wollmann

First experimental evidence of hydrodynamic tunneling of ultra–relativistic protons in extended solid copper target at the CERN HiRadMat facility

A novel experiment has been performed at the CERN HiRadMat test facility to study the impact of the 440 GeV proton beam generated by the Super Proton Synchrotron on extended solid copper cylindrical targets. Substantial hydrodynamic tunneling of the protons in the target material has been observed that leads to significant lengthening of the projectile range, which confirms our previous theoretical predictions [N. A. Tahir et al., Phys. Rev. Spec. Top.-Accel. Beams 15, 051003 (2012)]. Simulation results show very good agreement with the experimental measurements. These results have very important implications on the machine protection design for powerful machines like the Large Hadron Collider (LHC), the future High Luminosity LHC, and the proposed huge 80 km circumference Future Circular Collider, which is currently being discussed at CERN. Another very interesting outcome of this work is that one may also study the field of High Energy Density Physics at this test facility

Development of the Next Generation Superconductive Undulators for Synchrotron Light Sources

Superconducting insertion devices are very attractive for synchrotron light sources. For a given gap and period length, higher fields can be reached in respect to permanent magnet insertion devices thus permitting to reach higher photon fluxes. A new R&D program has been recently launched at ANKA aiming for the development of the next generation superconducting insertion devices for light sources. A cold bore superconducting undulator (14 mm period length, 100 full periods long) is installed in the ANKA storage ring since three years. This will be replaced by an improved version which shows a more efficient cooling system and a high precision design aiming for reduced field errors. Two additional devices are scheduled. One will allow to electrically switch the period length between 15 mm and 45 mm corresponding to an undulator and a wiggler mode, respectively. The other will be optimized for third generation light sources. It will be capable of tolerating higher beam heat loads up to 6 W while achieving very small field errors. The field error minimization will be obtained through the use of new shimming concepts which will correct inaccuracies due to manufacturing tolerances. This paper describes the technical concepts of the three projects.

Retraining of the 1232 Main Dipole Magnets in the LHC

The Large Hadron Collider (LHC) contains eight main dipole circuits, each of them with 154 dipole magnets powered in series. These 15-m-long magnets are wound from Nb-Ti superconducting Rutherford cables, and have active quench detection triggering heaters to quickly force the transition of the coil to the normal conducting state in case of a quench, and hence reduce the hot spot temperature. During the reception tests in 2002-2007, all these magnets have been trained up to at least 12 kA, corresponding to a beam energy of 7.1 TeV. After installation in the accelerator, the circuits have been operated at reduced currents of up to 6.8 kA, from 2010 to 2013, corresponding to a beam energy of 4 TeV. After the first long shutdown of 2013-2014, the LHC runs at 6.5 TeV, requiring a dipole magnet current of 11.0 kA. A significant number of training quenches were needed to bring the 1232 magnets up to this current. In this paper, the circuit behavior in case of a quench is presented, as well as the quench training as compared to the initial training during the reception tests of the individual magnets.

High energy density physics issues related to Future Circular Collider

A design study for a post-Large Hadron Collider accelerator named, Future Circular Collider (FCC), is being carried out by the International Scientific Community. A complete design report is expected to be ready by spring 2018. The FCC will accelerate two counter rotating beams of 50 TeV protons in a tunnel having a length (circumference) of 100 km. Each beam will be comprised of 10 600 proton bunches, with each bunch having an intensity of 1011 protons. The bunch length is of 0.5 ns, and two neighboring bunches are separated by 25 ns. Although there is an option for 5 ns bunch separation as well, in the present studies, we consider the former case only. The total energy stored in each FCC beam is about 8.5 GJ, which is equivalent to the kinetic energy of Airbus 380 (560 t) flying at a speed of 850 km/h. Machine protection is a very important issue while operating with such powerful beams. It is important to have an estimate of the damage caused to the equipment and accelerator components due to the accid...

Helium-Free Field Measurement System for Superconducting Undulator Coils

Superconducting undulators generate, for a given period length and a given gap, higher fields than permanent magnet undulators. Since in an undulator the photons add up coherently over the whole undulator length, even small magnetic field errors can disturb the superposition of photons and reduce the intensity of the generated photon beam. Therefore, as in any other undulator, the magnetic field has to be measured with high accuracy.

Beam Loss Measurements for Recurring Fast Loss Events During 2017 LHC Operation Possibly Caused by Macroparticles

The availability of the LHC machine was adversely affected in 2017 by tens of beam aborts provoked by frequent loss events in one standard arc cell (16L2). In most of the cases, the dumps were triggered by concurrently developing fast beam instabilities leading to particle losses in the betatron cleaning insertion. Many of the events started with a distinct sub-millisecond loss peak comparable to regular dust particle events, which have been observed along all the LHC since the start-up. In contrast to regular dust events, persistent losses developed in cell 16L2 after the initial peaks which can possibly be explained by a phase transition of macroparticles to the gas phase. In this paper, we summarize the observed loss characteristics such as spatial loss pattern and time profiles measured by Beam Loss Monitors (ionization chambers). Based on the measurements, we estimate the energy deposition in macroparticles and reconstruct proton loss rates as well as the gas densities after the phase transition. Differences between regular dust events and events in 16L2 are highlighted and the ability to induce magnet quenches is discussed.

A Statistical Analysis of Electrical Faults in the LHC Superconducting Magnets and Circuits

The large hadron collider (LHC) at CERN has been operating and generating physics experimental data since September 2008, and following its first long shut down, it has entered a second, 4-year-long physics run. It is to date the largest superconducting installation ever built, counting over 9000 magnets along its 27-km long circumference. A significant operational experience has been accumulated, including the occurrence and consequences of electrical faults at the level of the superconducting magnets, as well as their protection and instrumentation circuits. The purpose of this paper is to provide a first overview of the most common electrical faults and their frequency of occurrence in the first years of operation, and to perform a statistical analysis that can provide reference values for future productions of similar dimensions and nature.

JACoW : Requirements for Crab Cavity System Availability in HL-LHC

Crab Cavities will be installed in the High Luminosity LHC in order to increase the effective peak luminosity through a partial compensation of the geometric factor. This will allow extending the levelling time resulting in an increased production of integrated luminosity. Based on the availability of the LHC during 2016 operation, the expected yearly-integrated luminosity of the future HLLHC was estimated using a Monte Carlo model. Crab cavity faults were added to the observed failure distributions and their impact on integrated luminosity production as a function of fault time and fault frequency was studied. This allows identifying a breakeven point in luminosity production and defining minimum system availability requirements for the crab cavities to reach the design goal of 250 fb of integrated luminosity per year. CRAB CAVITIES AND INCREASED LUMINOSITY In the High-Luminosity upgrade program of the Large Hadron Collider (HL-LHC), it is planned to use smaller beam sizes at the interaction points and higher bunch intensities in order to achieve higher instantaneous luminosities. The relevant parameters of the HL-LHC are recalled in Table 1 [1]. Table 1: HL-LHC Luminosity Parameters Name Nominal value Unit Levelled luminosity 5×10 cm.s

Operational results with fast automatic beam-based LHC collimator alignment

Abstract. The CERN Large Hadron Collider (LHC) is the largest and highest-energy particle accelerator ever built. It is designed to collide particles at a centre-of-mass energy of 14 TeV to explore the fundamental forces and constituents of matter. Due to the potentially destructive high-energy particle beams, with a total design energy of 362 MJ, the collider is equipped with a series of machine protection systems. The beam cleaning or collimation system is designed to passively intercept and absorb particles at large amplitudes. The cleaning efficiency depends heavily on the accurate positioning of the jaws with respect to the beam trajectory. Beam-based collimator alignment is currently the only feasible technique that can be used to determine the beam centre and beam size at the collimator locations. If the alignment is performed without any automation, it can require up to 30 hours to complete for all collimators. This reduces the beam time available for physics experiments. This article provides a brief recap of the algorithms and software developed to automate and speed up the alignment procedure, and presents the operational results achieved with fast automatic beam-based alignment in the 20112013 LHC runs.