The Two-Screen Measurement Setup to Indirectly Measure Proton Beam Self-Modulation in AWAKE

The goal of the first phase of the AWAKE \cite{AWAKE1,AWAKE2} experiment at CERN is to measure the self-modulation \cite{SMI} of the $\sigma_z = 12\,\rm{cm}$ long SPS proton bunch into microbunches after traversing $10\,\rm{m}$ of plasma with a plasma density of $n_{pe}=7\times10^{14}\,\rm{electrons/cm}^3$. The two screen measurement setup \cite{Turner2016} is a proton beam diagnostic that can indirectly prove the successful development of the self-modulation of the proton beam by imaging protons that got defocused by the transverse plasma wakefields after passing through the plasma, at two locations downstream the end of the plasma. This article describes the design and realization of the two screen measurement setup integrated in the AWAKE experiment. We discuss the performance and background response of the system based on measurements performed with an unmodulated Gaussian SPS proton bunch during the AWAKE beam commissioning in September and October 2016. We show that the system is fully commissioned and adapted to eventually image the full profile of a self-modulated SPS proton bunch in a single shot measurement during the first phase of the AWAKE experiment.Comment: 5 pages 8 figure

Programmability of covariant quantum channels

A programmable quantum processor uses the states of a program register to specify one element of a set of quantum channels which is applied to an input register. It is well-known that such a device is impossible with a finite-dimensional program register for any set that contains infinitely many unitary quantum channels (Nielsen and Chuang's No-Programming Theorem), meaning that a universal programmable quantum processor does not exist. The situation changes if the system has symmetries. Indeed, here we consider group-covariant channels. If the group acts irreducibly on the channel input, these channels can be implemented exactly by a programmable quantum processor with finite program dimension (via teleportation simulation, which uses the Choi-Jamiolkowski state of the channel as a program). Moreover, by leveraging the representation theory of the symmetry group action, we show how to remove redundancy in the program and prove that the resulting program register has minimum Hilbert space dimension. Furthermore, we provide upper and lower bounds on the program register dimension of a processor implementing all group-covariant channels approximately.Comment: 24 pages, 2 figures, published version, added Remark 13, expanded Section 3.1 and Example 23 significantl

Indirect Self-Modulation Instability Measurement Concept for the AWAKE Proton Beam

AWAKE, the Advanced Proton-Driven Plasma Wakefield Acceleration Experiment, is a proof-of-principle R&D experiment at CERN using a 400 GeV/c proton beam from the CERN SPS (longitudinal beam size sigma_z = 12 cm) which will be sent into a 10 m long plasma section with a nominal density of approx. 7x10^14 atoms/cm3 (plasma wavelength lambda_p = 1.2mm). In this paper we show that by measuring the time integrated transverse profile of the proton bunch at two locations downstream of the AWAKE plasma, information about the occurrence of the self-modulation instability (SMI) can be inferred. In particular we show that measuring defocused protons with an angle of 1 mrad corresponds to having electric fields in the order of GV/m and fully developed self-modulation of the proton bunch. Additionally, by measuring the defocused beam edge of the self-modulated bunch, information about the growth rate of the instability can be extracted. If hosing instability occurs, it could be detected by measuring a non-uniform defocused beam shape with changing radius. Using a 1 mm thick Chromox scintillation screen for imaging of the self-modulated proton bunch, an edge resolution of 0.6 mm and hence a SMI saturation point resolution of 1.2 m can be achieved.Comment: 4 pages, 4 figures, EAAC conference proceeding

Expected signal for the TBID and the ionization chambers downstream of the CNGS target station

Downstream of the carbon graphite target of the CNGS (CERN Neutrinos to Gran Sasso) facility at CERN a secondary emission monitor called TBID (Target Beam Instrumentation Downstream) is installed to measure the multiplicities and the left/right as well as up/down asymmetries of secondary particles from the target. Calculations show that the titanium windows used to close off the TBID vacuum tank might not withstand the highest beam intensities with small spot sizes expected at CNGS, in case the proton beam accidentally misses the 4-5 mm diameter target rods. Therefore it has been suggested to place two ionisation chambers as a backup for the TBID, located left and right of the TBID monitor. Monte Carlo simulations with the particle transport code FLUKA were performed firstly to obtain the fluence of charged particles in the region of interest and secondly to estimate the induced radioactivity (background signal) in this area. This allows to assess the actual signal/noise situation and thus to determine the optimal position of the ionisation chambers. This paper presents the results of these calculations

LHC Beam Loss Monitors

At the Large Hadron Collider (LHC) a beam loss system will be installed for a continuous surveillance of particle losses. These beam particles deposit their energy in the super-conducting coils leading to temperature increase, possible magnet quenches and damages. Detailed simulations have shown that a set of six detectors outside the cryostats of the quadrupole magnets in the regular arc cells are needed to completely diagnose the expected beam losses and hence protect the magnets. To characterize the quench levels different loss rates are identified. In order to cover all possible quench scenarios the dynamic range of the beam loss monitors has to be matched to the simulated loss rates. For that purpose different detector systems (PIN-diodes and ionization chambers) are compared

Theoretical investigation of the performance of an Alpha Stirling engine for low temperature applications

The purpose of this paper is to explore the applicability and peculiarities of Alpha engines at low heat source temperature levels of 100 to 200°C. A parameter study of an Alpha engine has been carried out using the commercial Stirling software Sage. The obtained results revealed some interesting insights into the peculiarities of low-temperature Alpha-SEs. A method for optimising the system design-parameters for a SE is described in this paper. The compact design of a double-acting Alpha engine helps to reduce not only engine size and complexity but also costs. At low temperature differences single-cylinder displacer-type (gamma) engines are well documented, while little is known about the performance of Alpha multi-cylinder engines. In order to achieve the highest possible power output not only the thermodynamic side but also the mechanical side of the engine has to be optimised. This is especially important at low temperature differentials, where the conversion efficiencies are inherently small and the driving force for heat absorption and rejection by the working gas is low. It is mandatory not only to convert as much heat as possible to indicated work but also to transfer as much of this hard gained work to usable power output by minimising internal friction, when trying to keep the engine size as small as possible. The indicated power output of an engine of a specific swept volume is dependent on the temperature and pressure levels, the frequency, the phase angle between the two pistons, the working fluid, and the design of the heat exchangers and the regenerator. A simple model of an Alpha engine was created using the commercial SE simulation tool Sage. In order to explore the relations between those parameters a model was developed, where the design parameters (temperature, mean pressure, frequency, and phase angle) were varied, and the heat exchangers and the regenerator were then optimised for each of the parameter combinations to reach the maximum power output. Temperature and mean pressure are shown to have the expected positive influence on the power output. For the frequency and the phase angle, optimum values can be found that differ significantly from those found for high temperature engines. Helium is used as the benchmark working gas. It can be shown that the use of Nitrogen instead cuts the power output in half, whereas Hydrogen doubles the achievable power output. The mechanical efficiency of a kinematic SE is largely dependent on the load that is transferred from the pistons to the crankshaft during expansion and vice versa during compression, as it increases frictional losses. In double-acting engines an identical pressure oscillation acts on the opposing faces of a piston, although it is out of phase. The resulting forces can balance each other to some extent depending on the phase, and thus the net force applied to the crankshaft can be reduced. For a four cylinder engine it is shown that the Siemens arrangement balances internal forces on the pistons to a larger extent than the Franchot arrangement, so that the mechanical losses are inherently smaller and thus the brake power is larger even though the indicated work is identical for both engine types. The contribution of this work is the provision of a modelling methodology, and the identification of a number of insights for system-design considerations for low-temperature applications

Design and Performance of the CNGS Secondary Beam Line

An intense muon-neutrino beam (1017nm /day) is generated at CERN and directed towards the Gran Sasso National Laboratory, LNGS, in Italy, 732 km away from CERN. In the presently approved physics programme, it is foreseen to run the CNGS facility with 4.5.1019 protons per year for five years. During a nominal CNGS cycle, i.e. every 6s, two nominal SPS extractions of 2.4.1013 protons each at 400GeV/c are sent down the proton beam line to the target. The CNGS secondary beam line, starting with the target, has to cope with this situation, which pushes the beam line equipment and instrumentation to the limits of radiation hardness and mechanical stresses during the CNGS operation. An overview of the CNGS secondary beam line is given. Emphasis is on the target, the magnetic focusing lenses (horn and reflector) and the muon monitors. The performance of the secondary beam line during beam commissioning and physics operation is discussed and measurements are compared with simulations

THE CNGS FACILITY: PERFORMANCE AND OPERATIONAL EXPERIENCE

The CNGS facility (CERN Neutrinos to Gran Sasso) aims at directly detecting muon to tau neutrino oscillations. An intense muon-neutrino beam (1E17 muon neutrinos/day) is generated at CERN and directed over 732 km towards the Gran Sasso National Laboratory, LNGS, in Italy, where two large and complex detectors, OPERA and ICARUS, are located. CNGS is the first long-baseline neutrino facility in which the measurement of the oscillation parameters is performed by observation of tau-neutrino appearance. In this paper, an overview of the CNGS facility is presented. The experience gained in operating this 500 kW neutrino beam facility is described. Major events since the commissioning of the facility in 2006 are summarized. Highlights on CNGS beam performance since the start of physics run in 2008 are given

Electron trapping and acceleration by the plasma wakefield of a self-modulating proton beam

It is shown that co-linear injection of electrons or positrons into the wakefield of the self-modulating particle beam is possible and ensures high energy gain. The witness beam must co-propagate with the tail part of the driver, since the plasma wave phase velocity there can exceed the light velocity, which is necessary for efficient acceleration. If the witness beam is many wakefield periods long, then the trapped charge is limited by beam loading effects. The initial trapping is better for positrons, but at the acceleration stage a considerable fraction of positrons is lost from the wave. For efficient trapping of electrons, the plasma boundary must be sharp, with the density transition region shorter than several centimeters. Positrons are not susceptible to the initial plasma density gradient.Comment: 9 pages, 9 figures, 1 table, 44 reference

First Year Physics at CNGS, presented at PAC09, Vancouver, Canada, 4-8 May 2009

The CNGS facility (CERN Neutrinos to Gran Sasso) aims at directly detecting νμ→ντ neutrino oscillations [1]. An intense νμ beam (1017 νμ per day) is generated at CERN and directed over 732 km towards the Gran Sasso National Laboratory, LNGS, in Italy, where two large and complex detectors, OPERA and ICARUS, are located. Having resolved successfully some initial issues that occurred since its commissioning in 2006, that will be briefly summarized here, the facility had its first complete year of physics with 1.78×10^19 protons extracted towards CNGS. The experiences gained in operating this 500 kW neutrino beam facility along with highlights of the beamperformance in 2008 are discussed