GSI, Darmstadt
Scintillation screens are widely used for qualitative beam profile monitoring, but precise profile measurements yields ambivalent results for high beam currents. Moreover, these screens are an essential part of a pepper-pot emittance system requiring a quantitative profile evaluation. Therefore, we investigated the optical properties of 14 scintillating materials with different beams in the energy range 5.5 to 11.4 MeV/u as delivered by the heavy ion linac at GSI. Beside sensitive scintillators like YAG we focus on ceramic materials with lower light yield, like BN, ZrO2, Al2O3 and Al2O3+Cr. Their properties (light yield, beam width, high statistical moments etc.) are compared to different quartz glasses. The image of each macro-pulse is recorded by a digital CCD camera and individually evaluated by a high performance data acquisition system. For some materials, a decay of the light yield and an increase of the imaged beam width were observed. Moreover, the light yield depends on the screen temperature, which is significantly increased by the beam impact. A quantitative comparison under different beam conditions is presented.
GSI, Darmstadt
LBNL, Berkeley, California
TU Darmstadt, Darmstadt
Non-intercepting Beam Induced Fluorescence (BIF) monitors determine transversal beam profiles by observation of fluorescence light originating from excited residual gas molecules. Thus they are an alternative to conventional intercepting devices. Single photon counting is performed using an image intensified digital CCD camera. We investigated the BIF process in the energy range of 7.7 keV/u to 750 MeV/u in residual nitrogen. Experiments at low beam energies were performed at a Marx-accelerator (NDCX) at Berkeley Lab whereas mid and high energy experiments were carried out at GSI accelerators. Especially in the vicinity of targets the neutron-generated radiation level limits the monitor's signal to background ratio. Therefore the radiation background was investigated for different ion species and particle energies. Background simulations using a Monte Carlo transport code are compared to experimental data measured with scintillators, thermo luminescence detectors and the BIF monitor. Alternative image intensifier techniques are presented as well as shielding concepts. Furthermore the dynamics of ionized nitrogen molecules in the electric field of intense ion beams is discussed.
Bira, Albuquerque, New Mexico
National Instruments, Austin
LANL, Los Alamos, New Mexico
The design and test of a new beam-profile-wire-scanner actuator for the LANSCE* 800-MeV proton linear accelerator is described. Previous actuator implementations use open-loop stepper-motor control for position indexing. A fixed-frequency, fixed-duration pulse train is sent to the stepper motor driving the linear actuator. This has lead to significant uncertainties in position, mechanical resonances and electrical noise. A real-time, closed loop control system has been developed at tested for more repeatable and accurate positioning of beam sense wires. The use of real-time controller allows one to generate a velocity profile for precise, resonance-free wire position indexing. High radiation levels in the beam tunnel, dictate the use of an electro-magnetic resolver, typically, used in servo applications, as the position feedback element. Since the resolver is an inherently analog device sophisticated digital signal processing is required to generate and interpret the wave forms that the feedback mechanism needs for positioning. All of the electronic and computational duties are handled in one National Instruments compact RIO real-time chassis with FPGA.**
*Los Alamos Neutron Science Center
**Field Programmable Gate Array
CEA, Gif-sur-Yvette
In the IFMIF-EVEDA framework, a high deuteron beam intensity (125 mA - 9 MeV) accelerator will be built and tested at Rokkasho (Japan). The development of this accelerator is shared between France, Italy and Spain. France (CEA-Saclay) and Spain (Ciemat-Madrid) are responsible of the beam instrumentation from the RFQ to the beam dump. One of the most challenging detectors is the Beam Transverse Profile Monitor (BTPM), and the Saclay group decided to investigate such a monitor based on residual gas ionisation. In order to study the feasibility, we plan in a first step to built a prototype. This monitor use a high electric field to drive the products (electrons and ions) of ionisation to resistive micro-strips. At first sight, no amplification is necessary! This prototype will be tested in the IPHI high intensity (100 mA) proton beam at Saclay to answer this question in particular, and to check the feasibility in general.
CERN, Geneva
Wire scanners are instruments to measure the transverse beam profile. The measurement is performed by moving a thin wire across the path of the particle beam while monitoring the secondary particles. One of the limiting factor in application of wire scanners for high-intensity beams is the wire resistance to high temperature. In this work a heat flow equation for a carbon wire passing through a particle beam is solved. The equation contains modeling of wire heating induced by electromagnetic field of the beam and by electronic energy loss of the protons passing through the wire. The cooling processes considered are conduction, radiation, thermionic emission and sublimation enthalpy. Due to the equation nonlinearity a numerical approach based on discretization of the wire movement is used. An estimation of the wire sublimation rate is made. The model is tested on SPS and LEP data. An other limitation of a wire scanner application is a superconducting environment. The energy deposition in the magnet coils of downstream superconducting LHC magnets is estimated using Geant4 simulation package. In conclusions the limits of Wire Scanner operation on LHC beams are drawn.
Fermilab, Batavia
This paper presents a condensed, simplified, and practical discussion of the principles, procedures, and operating parameters of particle accelerator vacuum systems as practiced at Fermilab. It is intended to provide a basis for designers, builders, and operators of accelerator systems to communicate with each other about the needs and impact of the vacuum system. Rigorous analytical development of the equations and concepts are not given. It is assumed that the reader has some limited understanding of the subject. Practical examples of real world experiences are used to illustrate the concepts outlined.
