Claus Schmitzer

Experimental Test of Quantum Contextuality in Neutron Interferometry

We performed an experimental test of the Kochen-Specker theorem based on an inequality derived from the Peres-Mermin proof, using spin-path (momentum) entanglement in a single neutron system. Following the strategy proposed by Cabello et al. [Phys. Rev. Lett. 100, 130404 (2008)10.1103/PhysRevLett.100.130404], a Bell-like state was generated, and three expectation values were determined. The observed violation 2.291 +/- 0.008 not less, dbl equals1 clearly shows that quantum mechanical predictions cannot be reproduced by noncontextual hidden-variable theories.

High duty factor plasma generator for CERN's Superconducting Proton Linac

CERNs Linac4 is a 160 MeV linear accelerator currently under construction. It will inject negatively charged hydrogen ions into CERNs PS-Booster. Its ion source is a noncesiated rf driven H(-) volume source directly inspired from the one of DESY and is aimed to deliver pulses of 80 mA of H(-) during 0.4 ms at a 2 Hz repetition rate. The Superconducting Proton Linac (SPL) project is part of the luminosity upgrade of the Large Hadron Collider. It consists of an extension of Linac4 up to 5 GeV and is foreseen to deliver protons to a future 50 GeV synchrotron (PS2). For the SPL high power option (HP-SPL), the ion source would deliver pulses of 80 mA of H(-) during 1.2 ms and operate at a 50 Hz repetition rate. This significant upgrade motivates the design of the new water cooled plasma generator presented in this paper. Its engineering is based on the results of a finite element thermal study of the Linac4 H(-) plasma generator that identified critical components and thermal barriers. A cooling system is proposed which achieves the required heat dissipation and maintains the original functionality. Materials with higher thermal conductivity are selected and, wherever possible, thermal barriers resulting from low pressure contacts are removed by brazing metals on insulators. The AlN plasma chamber cooling circuit is inspired from the approach chosen for the cesiated high duty factor rf H(-) source operating at SNS.

A new extraction system for the Linac4 H− ion sourcea)

As part of the CERN accelerator complex upgrade, a new linear accelerator for H(-) (Linac4) is under construction. The ion source design is based on the non-caesiated DESY RF-driven ion source, with the goal of producing an H(-) beam of 80 mA beam current, 45 keV beam energy, 0.4 ms pulse length, and 2 Hz repetition rate. The source has been successfully commissioned for an extraction voltage of 35 kV, corresponding to the one used at DESY. Increasing the extraction voltage to 45 kV has resulted in frequent high voltage breakdowns in the extraction region caused by evaporating material from the electron dump, triggering a new design of the extraction and electron dumping system. Results of the ion source commissioning at 35 kV are presented as well as simulations of a new pulsed extraction system for beam extraction at 45 kV.

Magnetic Cusp Configuration of the SPL Plasma Generator

The Superconducting Proton Linac (SPL) is a novel linear accelerator concept currently studied at CERN. As part of this study, a new Cs‐free, RF‐driven external antenna H− plasma generator has been developed to withstand an average thermal load of 6 kW. The magnetic configuration of the new plasma generator includes a dodecapole cusp field and a filter field separating the plasma heating and H− production regions. Ferrites surrounding the RF antenna serve in enhancing the coupling of the RF to the plasma. Due to the space requirements of the plasma chamber cooling circuit, the cusp magnets are pushed outwards compared to Linac4 and the cusp field strength in the plasma region is reduced by 40% when N‐S magnetized magnets are used. The cusp field strength and plasma confinement can be improved by replacing the N‐S magnets with offset Halbach elements of which each consists of three magnetic sub‐elements with different magnetization direction. A design challenge is the dissipation of RF power induced by edd...

Plasma characterization of the superconducting proton linear accelerator plasma generator using a 2 MHz compensated Langmuir probe

The CERN study for a superconducting proton Linac (SPL) investigates the design of a pulsed 5 GeV Linac operating at 50 Hz. As a first step towards a future SPL H(-) volume ion source, a plasma generator capable of operating at Linac4 or nominal SPL settings has been developed and operated at a dedicated test stand. The hydrogen plasma is heated by an inductively coupled RF discharge e(-) and ions are confined by a magnetic multipole cusp field similar to the currently commissioned Linac4 H(-) ion source. Time-resolved measurements of the plasma potential, temperature, and electron energy distribution function obtained by means of a RF compensated Langmuir probe along the axis of the plasma generator are presented. The influence of the main tuning parameters, such as RF power and frequency and the timing scheme is discussed with the aim to correlate them to optimum H(-) ion beam parameters measured on an ion source test stand. The effects of hydrogen injection settings which allow operation at 50 Hz repetition rate are discussed.

High-efficiency manipulations of triply entangled states in neutron polarimetry

Entanglement occupies a peculiar position in quantum mechanics (QM). It occurs in quantum systems that consist of space-like separated parts or—more generally—in systems whose observables belong to disjoint Hilbert spaces. The latter is the case with single-neutron systems. Here, we report on a neutron polarimetric experiment, where a triply entangled Greenberger-Horne-Zeilinger state is exploited. The entanglement of spin, momentum and total energy degree of freedom is generated utilizing a suitable combination of radio-frequency and static magnetic fields. An average deviation of expectation values from theory—ideal circumstances—of 0.016(1) confirms the predictions of QM with high accuracy, demonstrating the high-efficiency manipulation of the entangled single-neutron system.

Falsification of Leggett's model using neutron matter waves

According to Bells theorem, no theory based on the joint assumption of realism and locality can reproduce certain predictions of quantum mechanics. Another class of realistic models, proposed by Leggett, that demands realism but abandons reliance on locality, is predicted to be in conflict with quantum mechanics. In this paper, we report on an experimental test of a contextual realistic model analogous to the model of Leggett performed with matter waves, more precisely with neutrons. Correlation measurements of the spin-energy entangled single-particle system show violation of a Leggett-type inequality by more than 7.6 standard deviations. Our experimental data falsify the contextual realistic model and are fully in favor of quantum mechanics.

Status of Proton Beam Commissioning of the MedAustron Particle Therapy Accelerator

MedAustron is a synchrotron-based ion beam therapy centre, designed to deliver clinical beams of protons (60250 MeV) and carbon ions (120-400 MeV/u) to three clinical irradiation rooms (IR) and one research room, which can also host 800 MeV protons. The commissioning activities for the first treatments with proton beams in IR3 have been completed and commissioning of IR1-2 is ongoing. The present paper describes the activities which took place during the last year, which involved all accelerator components from the ion source to the IR. INTRODUCTION The MedAustron accelerator provides beam rigidities of up to 6.4 Tm. Its layout is shown in Fig. 1. The design originates from those of PIMMS [1] and CNAO. The injector produces 7 MeV/n beams of H/C for injection into the synchrotron. After acceleration, the beam is extracted via a third-integer resonant slow extraction, driven by a betatron core. The high energy beam transfer line (HEBT) adapts the transverse and longitudinal beam properties and transports the beam into one of the four IRs: IR1 with a horizontal (H) beamline for non-clinical research, IR2 with H and vertical (V) beamlines for clinical treatment, IR3 with an H beamline for clinical treatment and IR4 with a gantry for proton clinical treatments. Since last year [2], the commissioning of the accelerator for proton clinical treatments in IR3 is completed, first proton beams were sent to IR1/2-H, IR2-V is installed and magnets for IR4 are in tendering process. COMMISSIONING STRATEGY The clinical penetration depths in water (range) of the proton beams are 30-380 mm, with 255 steps of 1 mm up to 190 mm range and 2 mm thereafter, corresponding to kinetic energy steps of 0.5-1.0 MeV. In addition, each beam of a given energy should be delivered in 5 s spills with 4 different intensity levels. The main tolerance specifications for the beam properties for all 1020 combinations for the accelerator commissioning are given in Table 1. In addition, the expected intensity is 1e10 protons per spill, the ‘dead-cycle’ time between spills is 2 s and the peak-over-mean of the extracted beam intensity within the spill (for 5 ms averaging time and 10 kHz sampling) is 5. The commissioning started with the optimization of beam properties for the highest energy and highest intensity. The subsequent fine-tuning was done for 4 main energies equally interspaced in the clinical energy range. The beam parameters at the IR3-isocenter (IC) were checked and fine-tuned in collaboration with the medical physicists. Table 1: Specifications for Accelerator Commissioning Parameter at the IC Tolerance Absolute Range ± 0.3 mm Range variation within spill ± 0.15 mm Absolute Position ± 0.5 mm Position variation within spill ± 0.25 mm Absolute Size 40% of Monte Carlo model and 10 % of 3 order polynomial fit Symmetry Min{10%, 1 mm} Size variation within spill ± 5 % INJECTOR The main recent activities in the injector consisted in the commissioning of a passive absorber system, called degrader. Degrader The degrader consists of 3 moving copper plates with a regular pattern of holes of different diameters. It is used to reduce the injected beam current by nominally 50%, 80% and 90% without affecting transverse and longitudinal beam parameters. SYNCHROTRON The main recent commissioning activities in the synchrotron consisted in fast acceleration ramps [3] and the setup of the resonant extraction for the 4 main energies [3-5].

MedAustron Synchrotron RF Commissioning for Medical Proton Beams

MedAustron is a medical accelerator facility for hadron therapy cancer treatment using protons and carbon ions. The facility features 4 irradiation rooms, 3 of which are dedicated to medical treatment, with one currently being medically commissioned, and 1 irradiation room for nonclinical research (NCR) which will be put into operation this year. A 7MeV/n Injector feeds a 77m circumference synchrotron which provides flexible beams for treatment and research. The Synchrotron is driven by a 0.47-3.26 MHz Finemet® loaded wideband cavity powered by 12x 1kW solid state amplifiers connected to a digital Low Level RF system. It was developed in collaboration with CERN and put to operation at MedAustron in early 2014. The main Synchrotron RF (sRF )commissioning steps for proton beams involved the setup of the adiabatic capture process, the setup of the frequency and voltage ramps and feedback loops for fast acceleration and the RF jump for extraction. The adiabatic capture process was optimized in terms of energy and voltage mismatch by analyzing longitudinal empty bucket scans after beam injection into the synchrotron. The acceleration ramp optimization was based on calculations using a software tool developed inhouse and adapted experimentally to minimize losses at injection and during acceleration. This paper provides an overview of the acceleration system and describes the commissioning process of the sRF system and the related beam commissioning efforts at MedAustron. Typical corrective measures are described as well as typical acceleration cycles and optimization tools.

Tests of alternative quantum theories with neutrons

According to Bell’s theorem, every theory based on local realism is at variance with certain predictions of quantum mechanics. A theory that maintains realism but abandons reliance on locality, which has been proposed by Leggett, is incompatible with experimentally observable quantum correlations. In our experiment correlation measurements of spin-energy entangled single-neutrons violate a Leggett-type inequality by more than 7.6 standard deviations. The experimental data falsify the contextual realistic model and are fully in favor of quantum mechanics.