Florian Burkart

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

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...

MEASUREMENTS OF THE EFFECT OF COLLISIONS ON TRANSVERSE BEAM HALO DIFFUSION IN THE TEVATRON AND IN THE LHC

Beam-beam forces and collision optics can strongly affect beam lifetime, dynamic aperture, and halo formation in particle colliders. Extensive analytical and numerical si mulations are carried out in the design and operational stage o f a machine to quantify these effects, but experimental data is scarce. The technique of small-step collimator scans was applied to the Fermilab Tevatron collider and to the CERN Large Hadron Collider to study the effect of collisions on transverse beam halo dynamics. We describe the technique and present a summary of the first results on the dependence of the halo diffusion coefficient on betatron amplitude in the Tevatron and in the LHC.

Sources of Emittance Growth at the CERN PS Booster to PS Transfer

The CERN PS Booster (PSB) has four vertically stacked rings. After extraction from each ring, the bunches are recombined in two stages, comprising septum and kicker systems, such that the accumulated bunch train is injected through a single line into the PS. Bunches from the four rings go through a different number of vertical bends, which leads to differences in the betatron and dispersion functions due to edge focussing. The fast pulsed systems at PSB extraction, recombination and PS injection lead to systematic errors of delivery precision at the injection point. These error sources are quantified in terms of emittance growth and particle loss. Mitigations to reduce the overall emittance growth at the PSB to PS transfer within the LHC injectors upgrade are presented. ERROR SOURCES AND STABILITY CALCULATION For this study the error sources at the PSB to PS transfer have been divided into correctable and uncorrectable or dynamic errors. Correctable errors comprise magnet misalignments, magnet systematic errors such as different laminations or steel, and magnet random errors, e.g. different transfer function within a production series. Also long term drifts of the trajectory due to temperature and humidity are considered correctable. Uncorrectable errors can be random, such as shot-to-shot stability, in particular in view of the pulse-to-pulse modulated energy levels (1.4 and 2.0 GeV) of the transfer, and systematic like power converter ripple and fast pulsed kicker waveforms. Initially, only correctable errors were assigned in the transfer line model and its correction feasibility verified. During this transfer, four lines are combined into one line within a relatively short distance compared to the vertical offset. Due to the important deflection angles there are strong error sources which have to be compensated by few instrumentation and correction elements. The study showed that failure of beam position monitors are detrimental to the correction capability, and it is required to include the extraction septum as correction knob into the automatic trajectory algorithm used in the control room. Figure 1: Layout of the PSB recombination [1]. After this verification the machine was assumed to be free of correctable errors and dynamic errors were assigned separately to identify the main contributors to delivery imprecision. The effect of these errors was evaluated firstly, by their impact on the beam envelope of the line and consequently losses and activation of material, secondly, by comparison of trajectory variations and beta beating with the forseen margins in the envelope calculation and thirdly, by calculation of emittance growth due to offsets in position and angle at PS injection. Due to the different number of deflections seen by each bunch in the vertical recombination, Fig. 1, edge focussing from the vertical dipoles causes the optics to be different for each line [2]. This leads to an unavoidable emittance growth from betatron and dispersion mismatch at PS injection. The optics of the four lines can be perfectly matched to the PS injection optics for one of the four lines, but it is deliberately mismatched for all lines with the aim to minimize the overall emittance growth for all four lines. The optics for the transfer line coming from ring 4 is shown in Fig. 2. Figure 2: Present (thin) and new (thick) optics for the PSB to PS transfer in the top part. Horizontal betatron and dispersion functions are denoted in black and green, vertical betatron and dispersion functions in red and blue, respectively. In the bottom part the 3 σ horizontal LHC beam envelope is shown.

Experimental Studies and Theoretical Interpretation of Hydrodynamic Tunneling of SPS Protons in Solid Targets

The phenomenon of hydrodynamic tunneling has been experimentally studied at the CERN HiRadMat facility using the SPS beam [1]. The beam parameters include, proton energy = 440 GeV, bunch intensity = 1.5x10 , bunch length = 0.5 ns, bunch separation = 50 ns and σ of the transverse intensity distribution = 0.2 mm. In two experiments, 108 and 144 proton bunches, respectively, were used and the protons were delivered in sets of 36 bunches each while a separation of 250 ns was considered between the bunch packets.

Numerical Simulations of Hydrodynamic Tunneling Experiments Performed at HiRadMat Facility Using SPS Proton Beam

Extensive simulations carried out over the past 10 years to study the full impact of the LHC beam on solid targets has revealed substantial hydrodynamic tunneling of protons and their shower [1-3]. This effect has very important implications on the LHC machine protection design. In order to confirm the validity of these simulations, experiments have been carried out at the HiRadMat facility using 440 GeV protons impacting on solid targets. Detailed numerical simulations have been done to interpret the experiments. The experimental results together with a comparison with the simulations has been reported elsewhere [4,5]. In the present contribution we present the details about the simulations.