PSI, Villigen
In March 2010 one of the most exposed collimators of the 590 MeV proton beam line at PSI, was visu-ally inspected after 20 years of operation without failure. It is made out of OFHC copper and cooled by water tubes. At currents of 2.2 mA, the temperature inside the collimator is ~ 350 C. From the total beam charge of 120 Ah, ~15 % are absorbed. The main motivation for the inspection was to investigate the present condition of the collimator after the long exposure in a high intensity proton beam. According to MARS15 the inner parts have seen 35 DPA. For the inspection, the collimator was removed remotely from the beam line by a shielded exchange flask and transferred to the hot cell. In order to enter the collimator opening and examine the inner structure without any contact or damage, a special tool was built, using the principle of a periscope. By moving and rotation the tool with the power manipulator, sharp pictures of the inner surface were taken with a high resolution reflex camera, operated remotely. Because of the high radiation (> 50 Sv/h in 0.2 m) camera and electronics were shielded. After the inspection, the collimator was built in to the beam line again.
GSI, Darmstadt
IAP, Frankfurt am Main
RAS/INR, Moscow
The research into the activation of materials used for accelerator components is held in GSI as a part of studies of FAIR relevant materials. In the frame of these studies the project "Verification of Monte Carlo transport codes: FLUKA, MARS and SHIELD" was started. Series of irradiations were already done. This work presents the results of irradiation of aluminum target with uranium beam. Experimentally achieved depth profiles of residual activity and stopping range of primary ions are compared with Monte Carlo simulations. Correspondences and discrepancies of different codes with experiment are discussed.
IHEP Beijing, Beijing
Momentum collimation in a high intensity RCS is a very important issue. Based on the two-stage collimation principle, a combined momentum collimation method is proposed and studied here. The method makes use of the combination of secondary collimators in both the longitudinal and transverse planes. The primary collimator is placed at a high-dispersion location of an arc, and the transverse and longitudinal secondary collimators are in a dispersion-free long straight section and in an arc, respectively. The particles with a positive momentum deviation will be scattered by a carbon scraper and then cleaned by the transverse collimators, whereas the particles with a negative momentum deviation will be scattered by a Tantalum scraper and cleaned by the longitudinal secondary collimators. This is due that a carbon foil produces relatively more scattering than a Tantalum foil if the energy loss is kept the same. The relevant requirements on the lattice design are also discussed, especially for compact rings. The multi-particle simulations using both TURTLE and ORBIT codes are presented to show the physical images of the collimation method, with the input of the CSNS RCS ring.
CERN, Geneva
GSI, Darmstadt
The Large Hadron Collider and the next future linear accelerators deal with extraordinary high beam energies (in the order of hundreds of mega-Joules for LHC) and with increasingly smaller beam sizes. It is important to understand the damage potential of such high energy beams to accelerator equipment and surroundings. Simulations have shown that the impact of the full LHC beam into copper can penetrate up to 35m as opposed to 140cm that is the typical penetration length for 7TeV protons. It becomes evident that when working with high energy densities, it is no longer possible to neglect the hydro-dynamic. A hybrid approach combining FLUKA and BIG-2 is proposed to treat HED problems. This approach can improve current simulations. It is foreseen to experimentally irradiate different materials with different beam intensities in the SPS-HiRadMat facility at CERN. First, these experiments will validate the simulation results by reproducing the density depletion along the beam path. Finally, the information obtained with these tests will be very useful in the understanding of the consequences of beam-matter interaction. Results could be applied to the LHC Beam Dump system,collimation?
* N.A.Tahir, R.Schmidt et al., Nucl. Instrum. Methods Phys. Res., A 606 (2009)
** N.A.Tahir, R.Schmidt, New J. Phys.10 (2008) 073028
*** N.A.Tahir, R.Schmidt et al., J. Appl. Phys.97 (2005) 083532
CERN, Geneva
JINR, Dubna, Moscow Region
The probability of inelastic nuclear interaction in crystals well aligned to the incoming beam is considerably smaller than for its amorphous orientation. Tests performed with 400 GeV/c protons of the CERN SPS and a short bent silicon crystal confirm this behavior: channeled protons interact with crystal nuclei at a rate more that 20 times smaller than protons with randomly oriented trajectories. On the other hand, the quasi parallel beam halo in a collider has a large probability of being channeled in a bent silicon crystals. Tests performed with 120 GeV stored protons in the SPS show that the inelastic nuclear losses decrease by more than five times when the silicon crystal is well oriented respect to the beam envelope. These observations suggest that bent silicon crystals used as a primary collimator in a hadron collider, such as the LHC, will produce a considerably reduced flux of nuclear losses respect to an amorphous material.
CERN, Geneva
Modern particle interaction and transport codes such as FLUKA allow one to predict radioactivity and associated residual dose rates caused by high energy beam losses in accelerator components in great detail. Phaenomenological models of high energy hadronic interactions linked to sophisticated generalized cascade, pre-equilibrium and fragmentation models are able to describe the production of individual radioactive nuclides with good accuracy (often within less than 20%), as comprehensive benchmark studies have demonstrated. The calculation of induced radioactivity has thus become an integral part of design studies for high energy beam absorbers. Results provide valuable information on material choices, handling constraints and waste disposal and allow an early optimization of components in order to increase the efficiency of the later operation of the facility while keeping doses to personnel as low as reasonably achievable. The present paper gives examples of both generic studies with FLUKA for different absorber materials as well as studies for collimators and absorbers of the Large Hadron Collider.
Fermilab, Batavia
Recent developments in the MARS15 code are described for the critical modules related to demands of hadron and lepton colliders and Megawatt proton and heavy-ion beam facilities. Details of advanced models for particle production and nuclide distributions in nuclear interactions at medium and high energies, energy loss, atomic displacements and gas production are presented along with benchmarking against data wherever is possible. Examples are given for the most demanding areas. The current experimental activities are described towards reduction of existing uncertainties in simulations.
BNL, Upton, Long Island, New York
Fermilab, Batavia
Proton irradiation effects on materials supporting high power experiments have been studied extensively using the BNL 200 MeV proton beam and the target station of the Linear Isotope Producer (BLIP). The goal has been to (a) observe changes in physio-mechanical properties in widely used materials and in new alloys and composites induced by energetic protons, (b) identify thresholds of flux/fluence, (c) study the role of temperature in damage reversal, and (d) correlate damage effects of different species such as energetic protons and neutrons. Experience data from experiments, i.e. NuMI, on target performance have been integrated with observations and aided by simulation studies to assess the role of energy and irradiation rate. Based on the correlation experimental results, experience data and simulation studies, new irradiation experiments linked to the long baseline neutrino experiment (LBNE) have been designed and performed. Results of irradiation studies in support of the neutrino factory initiative, the LBNE and the LHC will be presented and coupled with confirmatory simulations employed to reconcile experimental observations with anticipated NuMI target performance.
GSI, Darmstadt
STU, Bratislava
Assessment of the radiation hazards from activated accelerator components due to beam-losses is a serious issue for high-energy hadron facilities. Important radiation-safety principle ALARA (As Low As Reasonably Achievable) calls for minimizing exposure to people. That is why the uncontrolled beam-losses must be kept on the reasonable low level. The beam-losses below 1 W/m are considered as a tolerable for “hands-on” maintenance on proton accelerators. The activation of the heavy-ion accelerators is in general lower than the activation of the proton machines. In our previous work, we estimated the "hands-on" maintenance criteria for heavy ions up to uranium in stainless steel and copper by scaling the existing criterion for protons. It was found out that the inventory of the isotopes and their relative activities do not depend on the primary-ion mass but depend on the target material. For this reason in the present work the activation of other important accelerator construction materials carbon and aluminum was studied using the FLUKA code.
ANL, Argonne
Atomic displacements by high energy particles in a crystalline solid induce formation of point defects and defect clusters of vacancies and interstitial atoms. The damaged microstructure results in significant changes in materials physical and mechanical properties. Besides displacement damage, nuclear transmutation reactions occur, producing He and H gas atoms that can have pronounced effect on materials performance even at low concentrations. Radiation effects in materials have been studied using various irradiation sources, and, radiation damage correlation is essential so that radiation effects produced by different irradiation sources can be compared and data can be transferred or extrapolated. The parameter commonly used to correlate displacement damage is the total number of displacements per atom (dpa). Considering that several aspects of radiation exposure can give rise to property changes, the extent of radiation damage cannot be fully characterized by a single parameter. This paper will discuss damage correlation under various irradiation environments, key irradiation parameters and their effects on irradiation-induced property changes.
STFC/RAL, Chilton, Didcot, Oxon
Kyoto University, Kyoto
KEK, Ibaraki
The T2K experiment began operation in April 2009. It utilises what is projected to become the world’s highest pulsed power proton beam at 0.75 MW to generate an intense neutrino beam. T2K uses the conventional technique of interacting the 30 GeV proton beam with a graphite target and using a magnetic horn system to collect pions of one charge and focus them into a decay volume where the neutrino beam is produced. The target is a two interaction length (900 mm long) graphite target supported directly within the bore of the first magnetic horn which generates the required field with a pulsed current of 320 kA. The talk will describe the design and development of the target system, the beam windows and the beam absorber required to meet the demanding requirements of the T2K facility. Challenges include radiation damage, stress waves, design and optimisation of the helium coolant flow, and integration with the pulsed magnetic horn. Conceptual and detailed engineering studies were required to develop a target system that could satisfy these requirements and could also be replaced remotely in the event of failure.
KAERI, Daejon
A beam dump for 20 MeV, 4.8mA proton beam had been manufactured in KAERI. The 20 MeV beam dump was made of graphite to reduce radioactivity by the materials around the beam dump as well as the beam dump itself. The beam dump was designed to by placing two plates of 30 cm by 60 cm at an angle of 12 degree. The IG430 graphite and OFHC copper were brazed with TiCuSil filler metal for cooling. The proton beam was assumed to be expanded for the peak heat flux in the graphite to be less than 200 W/cm2. The beam dump designed for maximum temperatures of graphite, copper and cooling water to be less than 223, 146 and 85 celsius degrees, respectively. The activation analysis of the beam dump was also performed with MCNP code. The sensitivity analyses of graphite tensile stresses to optimize the thicknesses of graphite with copper brazing were performed with ANSYS code. The tensile stress of graphite during the brazing process was the smallest around 1 cm thickness of graphite. A 100 MeV proton beam dump was designed with copper. The optimal angles between two copper plates for the minimum peak heat fluxes are 10~20 degrees. The peak heat flux in the copper plates at 15 degree is 333 W/cm2.
PSI, Villigen
PSI is gradually upgrading the 590 MeV proton beam intensity from the present 2.2 mA towards 3 mA, which poses a significant challenge to the reliable operation of the accelerator facility. Of particular concern is the collimator system which is exposed to the dispersed beam from a muon production target. It shapes an optimal beam profile for low-loss beam transport to the neutron spallation source SINQ. The collimator system absorbs slightly more than 10 % of the proton beam power and the maximum temperature of the collimator system exceeds 350 C at 2.2 mA, which is close to the failure point. In this paper, we present a new collimator system design which could withstand the proton beam intensity of 3 mA, while fulfilling the intended functionalities. Advanced multi-physics simulation technology is used for the geometric and material optimizations, to achieve the lowest possible actual to yield stress ratio at 3 mA. A sensitivity study is performed on the correlation between the beam misalignments and the reliability of the key accelerator components in the proton downstream region. Also reported are the possible proton irradiation effects on the mechanical failure criteria.
IHEP Beijing, Beijing
China Spallation Neutron Source (CSNS) accelerator consists of a 80 MeV linac and a 1.6 GeV Rapid Cycling Synchrotron (RCS), which is designed to produce beam power of 100 kW with a repetition rate of 25 Hz. For such a high intensity RCS, beam loss and control are of primary concern. A two-stage collimation system is designed to localize the beam losses in a restricted area, and keep the uncontrolled losses less than 1 W/m at the other part of RCS. The detailed design of the beam collimation system is presented, including the compare among different schemes. Key issues which affect the collimation efficiency are analyzed, and the collimation efficiency and beam loss distributions are studied by using the code ORBIT.
RIKEN Nishina Center, Wako
BNL, Upton, Long Island, New York
RIKEN Nishina Center for Accelerator-Based Science, Wako, Saitama
Electron stripping process from heavy ion in material is a useful tool in accelerator complex to give higher charge state of the ion, allowing its effective acceleration. This process is competed with electron capture process and reach to the equilibrium charge state. Carbon foils is convenient for charge stripper but have short lifetime due to thermal stress and sputtering. Gas is basically free from lifetime but gives lower charge state due to density effect. Therefore, charge stripper especially for uranium beams at 10-20 MeV/u will be a bottle-neck problem in high power heavy ion facility such as RIBF, FRIB and FAIR. Electron stripping and capture cross section of uranium ion beams in helium gas were measured as a function of their charge state at 11, 14 and 15 MeV/u with expectation that low-Z gas (H2 and He) would provide a better stripping media than nitrogen with a higher charge state. We will show the promising results with discussion about plasma confinement of low-Z gas.
CERN, Geneva
Beam losses are a potential limiting factor in the performance in any high intensity synchrotron. For the new CERN PS2, an overall low loss design has been adopted. However, it is unavoidable that due to different processes a certain fraction of particles leave the beam core populating the so-called beam halo. A collimation system removes in a controlled way all particles outside the prescribed betatron and collimator acceptances. This article presents a two-stage betatron collimation design as an optical device for different long straight sections layouts. Parametric studies for the different main design parameters are presented and their influence in the expected cleaning efficiency of the system is analyzed and compared to the accepted thresholds of admissible losses. Finally, different errors were introduced in the lattice to test the robustness of the design against realistic operation scenarios.
CERN, Geneva
HiRadMat is a new facility under construction at CERN that will provide the users with the possibility to investigate the behavior of materials when irradiated with pulsed high energy and high intensity beams extracted from the CERN SPS. The need for such a facility was raised by the LHC collimation project to bridge the gap in knowledge about the resistance of materials under impact with high energy protons. This talk will review the material parameters for which a deeper knowledge would be needed for extensive use in high energy accelerators, and the kind of test that can be conducted in HiRadMat to improve this knowledge. In particular we will discuss destructive testing, meaning test of materials beyond the limit of rupture or at phase change, and damage testing that should reveal changes in materials properties due to long term irradiation below the rupture limit. The facility could be used as well for calibration of radiation detectors like BLMs. The main difficulty connected with the test is how to observe material changes. Some preliminary ideas on on-line and post-irradiation tests will be outlined.
GSI, Darmstadt
CERN, Geneva
Universidad de Castilla-La Mancha, Ciudad Real
IPCP, Chernogolovka, Moscow region
Cylindrical targets made of solid Cu and solid C that are facially irradiated with the LHC beam, have been considered. First, the energy loss of the protons as well as the production and the transport of the secondary particles is calculated using the FLUKA code. This data is then used as input to a 2D hydrodynamic computer code, BIG2, to simulate the thermodynamic and the hydrodynamic response of the target. Our simulations show that the 7 TeV/c LHC protons penetrate up to 35 m in solid Cu and 10 m in solid C during the 89 μs beam duration and the targets are severely damaged in both cases. It is interesting to note that a substantial part of the targets is converted into High Energy Density (HED) state which suggests an additional application of the LHC. To study the effects of accidents involving the SPS beam, we have also simulated the interaction of the full impact of the SPS beam with solid Cu and solid W targets. These simulations have shown that the targets are severely damaged and the beam heated region, in this case, is also converted into HED matter. These simulations could also be very useful to design the experiments for the future HiRadMat facility at CERN.
NSCL, East Lansing, Michigan
High energy heavy ion beams having high power that that are planned for FRIB will deliver very high power densities and will produce significant radiation damage in materials with which they interact. Reliable predictions of component life times for FRIB are needed yet the tools used to make the necessary predictions, e.g. heavy ion radiation transport codes, provide damage estimates whose levels vary significantly. Additionally there are very few appropriate data sets to validate the codes. We will present examples of components, i.e. the target and beam dump systems for FRIB, with attending predicted levels of damage obtained by transport codes and life time ramifictions. We will summarize results from an experiment to produce and to quantify damage in a controlled way. Finally, we will show examples of targets used in experiments at NSCL where damage has been observed, and will present results from transport codes to quantify the damage.
Technical University Darmstadt, Darmstadt
GSI, Darmstadt
ITEP, Moscow
CERN, Geneva
The planned International Facility for Antiproton and Ion Research (FAIR) will consist of a superconducting double-ring synchrotron offering ion beams of intensity increased by a factor of 100-1000 compared to the existing GSI accelerators. Assuming typical beam losses of a few percent, materials close to the beam tube will be exposed to secondary radiation of neutrons, protons, and heavier particles, limiting the lifetime and reliable function of various device components. The present study investigates the radiation hardness of insulating components with focus on polyimide as electrical insulation and “G11”-type glass fiber reinforced plastics (GFRP) as support structure in the superconducting SIS magnets. Dedicated irradiation experiments were performed with different projectiles such as 21 and 800 MeV protons (ITEP, Russia) and various heavy ions of MeV-GeV energy (GSI, Germany). Degradation tests of irradiated materials include structural changes performed by IR spectroscopy, breakdown voltage and thermal conductivity measurements. Special attention is given to effects induced by heavy ions (e.g., Ta, Au) because they are known to create extensive damage at rather low doses.
Fermilab, Batavia
STFC/RAL, Chilton, Didcot, Oxon
BNL, Upton, Long Island, New York
The Long Baseline Neutrino Experiment (LBNE) Neutrino Beam Facility at Fermilab will use a high energy proton beam on a solid target to produce a neutrino beam aimed at underground detectors at the DUSEL site in South Dakota. Initial proton beam power is planned to be 700 kW with upgrade capability to greater than 2 MW. Solid target survivability at such incident beam power is of great interest and an R&D program has been started to study the relevant issues. Areas of study include irradiation testing of candidate target materials at the BLIP facility at BNL, multi-physics simulations of solid target/beam interactions at RAL, autopsies of used NuMI targets, high strain rate effects in beryllium, and alternative methods of target cooling. Status and results of these studies are presented as well as a summary of planned future high power target R&D efforts.