Mercury Jet Research Articles

New target solution for a muon collider or a muon-decay neutrino beam facility: The granular waterfall target

A new target solution, the granular waterfall target, is proposed here for a muon collider or a muon-decay neutrino beam facility, especially for the moment which adopts a 15 MW continuous-wave (cw) superconducting linac. Compared to the mercury jet target, the granular waterfall target works by a much simpler mechanism which can operate with a much more powerful beam, which are indicated by the detailed investigations into the heat depositions and the evaluations of the temperature increases for different target concepts. By varying proton beam kinetic energy and the geometrical parameters of the waterfall target, an overall understanding of the figure of merit concerning muon production for this target concept as the target solutions of the long-baseline neutrino factory and the medium-baseline moment is obtained. With 8 GeV beam energy and the optimal geometrical parameters, the influence on muon yield by adopting different beam-target interaction parameters is explored. Studies and discussions of the design details concerning beam dumping are also presented.

Particle production and energy deposition studies for the neutrino factory target station

We present FLUKA and MARS simulation studies of the pion production and energy deposition in the Neutrino Factory baseline target station, which consists of a 4 MW proton beam interacting with a liquid mercury jet target within a 20 T solenoidal magnetic field. We show that a substantial increase in the shielding is needed to protect the superconducting coils from too much energy deposition. Investigations reveal that it is possible to reduce the magnetic field in the solenoid capture system without adversely affecting the pion production efficiency. We show estimates of the amount of concrete shielding that will be required to protect the environment from the high radiation doses generated by the target station facility. We also present yield and energy deposition results for alternative targets: gallium liquid jet, tungsten powder jet and solid tungsten bars.

Ninety Years of Polarography

Ninety Years of Polarography

Optimization of a mercury jet target for a neutrino factory or a muon collider

A study of target parameters for a mercury jet target for a neutrino factory or muon collider is presented. We simulate particle production initiated by incoming protons with kinetic energies between 2 and 100 GeV. For each proton beam kinetic energy, we maximize production by varying the geometric parameters of the target: the mercury jet radius, the incoming proton beam angle, and the crossing angle between the mercury jet and the proton beam. With an 8-GeV proton beam, we study the variation of meson production with the entry direction of the proton beam relative to the jet. We also examine the influence on the meson production by the focusing of the proton beam. The number of muons surviving through the neutrino factory front end channel is determined as a function of the proton beam kinetic energy.

Energy deposition studies for the Neutrino Factory target station

A study of the energy deposition in the Neutrino Factory baseline target stationis presented. FLUKA simulations are used to study howmuch of the 4 MW proton beam power is distributed within thetarget station, and these results are compared with MARSsimulations. About 10% of the beam power is deposited in the mercury jet target,with more than 2 MW absorbed by the tungsten-carbide shielding.Heating in the superconducting coils,that generate most of the magnetic field in the target region, can be substantially reduced by increasing the surrounding shielding.Estimates of radiation damage are also given for different sectionsof the target geometry.

Computational algorithms for multiphase magnetohydrodynamics and applications to accelerator targets

An interface-tracking numerical algorithm for the simulation of magnetohydrodynamic multiphase / free surface flows in the low-magnetic-Reynolds-number approximation of (Samulyak R., Du J., Glimm J., Xu Z., J. Comp. Phys., 2007, 226, 1532) is described. The algorithm has been implemented in multi-physics code FronTier and used for the simulation of MHD processes in liquids and weakly ionized plasmas. In this paper, numerical simulations of a liquid mercury jet entering strong and nonuniform magnetic field and interacting with a powerful proton pulse have been performed and compared with experiments. Such a mercury jet is a prototype of the proposed Muon Collider / Neutrino Factory, a future particle accelerator. Simulations demonstrate the elliptic distortion of the mercury jet as it enters the magnetic solenoid at a small angle to the magnetic axis, jet-surface instabilities (filamentation) induced by the interaction with proton pulses, and the stabilizing effect of the magnetic field.

Optical diagnostics of mercury jet for an intense proton target

An optical diagnostic system is designed and constructed for imaging a free mercury jet interacting with a high intensity proton beam in a pulsed high-field solenoid magnet. The optical imaging system employs a backilluminated, laser shadow photography technique. Object illumination and image capture are transmitted through radiation-hard multimode optical fibers and flexible coherent imaging fibers. A retroreflected illumination design allows the entire passive imaging system to fit inside the bore of the solenoid magnet. A sequence of synchronized short laser light pulses are used to freeze the transient events, and the images are recorded by several high speed charge coupled devices. Quantitative and qualitative data analysis using image processing based on probability approach is described. The characteristics of free mercury jet as a high power target for beam-jet interaction at various levels of the magnetic induction field is reported in this paper.

Swirl Motion of a Mercury Jet Appearing in a Cylindrical Vessel in Transient Period

Swirl Motion of a Mercury Jet Appearing in a Cylindrical Vessel in Transient Period

Cavitation bubble behavior inside a liquid jet

The growth and collapse of laser-induced vapor cavities inside axisymmetric free-falling liquid water jets have been studied. Bubbles of different size are generated at various distances from the jet axis and the effects on the jet interface are recorded by means of ultrafast cinematography. The configuration is characterized by two dimensionless parameters: the bubble to jet diameter ratio δ and the eccentricity coefficient ε defined as the radius of bubble generation divided by the jet radius. For high δ and ε, microjets and droplets are ejected from the liquid jet at speeds exceeding 100m∕s. The observed jet fragmentation shows similarities with experiments conducted on a liquid mercury jet hit by a pulsed proton beam, a candidate configuration for future accelerator based facilities.

Induced radioactivity in a mercury target and solenoid for a 24 GeV proton target test

In the framework of the feasibility study for a future neutrino-production facility, an experiment has been proposed at CERN as a proof-of-principle demonstration of a target system based on a free mercury jet suitable for use in a 4-MW pulsed proton beam. This paper estimates the expected amount of induced radioactivity in the various components of the target-solenoid assembly of the experiment to be carried out at the 24 GeV CERN proton synchrotron. The total activity expected in the mercury target and the specific activities in the components of the solenoid are assessed by Monte Carlo simulations with the FLUKA code. The residual dose rates for various decay times after the end of the irradiation are calculated. The environmental impact of the release of the activated nitrogen used to cool the solenoid is evaluated.

A free-jet Hg target operating in a high magnetic field intersecting a high-power proton beam

A proof-of-principal experiment to investigate the interaction of a proton beam, high magnetic field, and high- Z target is planned to take place at CERN in early 2007. This experiment is part of the Muon Collider Collaboration, with participants from Brookhaven National Laboratory, Princeton University, Massachusetts Institute Of Technology, European Organization for Nuclear Research-CERN, Rutherford Appleton Laboratory, and Oak Ridge National Laboratory. An unconstrained mercury jet target system that interacts with a high power (1 MW) proton beam in a high magnetic field (15 T) is being designed. The Hg jet diameter is 1-cm with a velocity up to 20 m/s. A laser optical diagnostic system will be incorporated into the target design to permit observation of the dispersal of the jet resulting from interaction with a 24 GeV proton beam with up to 20×10 12 ppp. The target system includes instruments for sensing mercury vapor, temperature, flow rate, and sump tank level, and the means to position the jet relative to the magnetic axis of a solenoid and the proton beam. The design considerations for the system include all issues dealing with safely handling approximately 23 l of Hg, transporting the target system and the mercury to CERN, decommissioning the experiment, and returning the mildly activated equipment and Hg to the US.

Radiation protection aspects of a 4 MW target

The CERN Superconducting Proton Linac (SPL) is expected to provide a 2.2 GeV, 4 MW proton beam to feed facilities such as, for example, a neutrino factory or a neutrino superbeam. Material activation in such facilities is an important aspect that has to be taken into account at an early stage in designing it. In particular, the choice of the target has consequences on the induced radioactivity and dose rates in the target station and its surroundings. In the present work, the radiological aspects of a stationary target made up of tantalum pellets are compared with those of a free-surface jet of mercury. An estimation of the hadronic inelastic interactions and the production of residual nuclei in the target, the two concentric magnetic horns, the decay tunnel, the surrounding rock and a downstream dump were performed for both targets using the Monte Carlo code FLUKA. The aim was to assess the dose-equivalent rate that is to be expected during maintenance work and to evaluate the amount of residual radioactivity, which will have to be disposed of after the facility has ceased operation. The problem of after-heat in the tantalum target and the consequences of raising the proton beam energy from 2.2 to 4 GeV were also investigated.

R&D works on high-power targetry for neutrino factories

High power targetry is one of the major technical challenges to realize neutrino factories based on muon storage rings. Various R&D works have been carried out in the framework of international collaboration. Recent progress in a free mercury jet, material studies, and capture/focusing devices are discussed. Future prospects for R&D are briefly described.

Radiological considerations on multi-MW targets. Part I: Induced radioactivity

CERN is designing a Superconducting Proton Linac (SPL) to provide a 2.2 GeV, 4 MW proton beam to feed facilities like, for example, a future Neutrino Factory or a Neutrino SuperBeam. The material activation in such facilities is an important aspect that has to be taken into account at an early design stage. In particular, the choice of the target has consequences on the induced radioactivity and dose rates in the target itself and in its surroundings. In the present work, the radiological aspects of a stationary target made up of small tantalum pellets are compared to those of a free-surface jet of mercury. An estimation of the hadronic inelastic interactions and the production of residual nuclei in the target, the magnetic horn, the decay tunnel, the surrounding rock and a downstream dump were performed for both targets by the Monte Carlo hadronic cascade code FLUKA. The aim was to assess the dose equivalent rate to be expected during maintenance work and to evaluate the amount of residual radioactivity, which will have to be disposed of after the facility has ceased operation.

Richtmyer–Meshkov instability in liquid metal flows: influence of cavitation and magnetic fields

The influence of magnetic fields and cavitation on the Richtmyer-Meshkov (RM) instability in liquid mercury has been studied numerically in 2D geometry. Numerical results shed light on the evolution of the Muon Collider target proposed as a pulsed jet of mercury interacting with high intensity proton beams in a strong magnetic field. We have shown that a uniform longitudinal magnetic field significantly reduces amplitudes and velocities of surface instabilities and is able to stabilize the jet during period of time typical for the jet breakup at zero magnetic field. We have developed a simple homogeneous two-phase equation of state for modeling of liquids with cavitation bubbles and applied it to the study of the evolution of mercury due to the interaction with proton pulses.

Thermal shocks and magnetohydrodynamics in high power mercury jet targets

The response of mercury samples submitted to a pulsed proton beam and the magnetohydrodynamic (MHD) effects of a mercury jet injected into a 20 T magnetic field are reported. The experimental conditions differ from those of proposed neutrino factories and the purpose of these measurements is to provide benchmarks for simulation tools of a realistic free mercury jet target. These measurements were completed in June 2002. Analysis is ongoing and the presented results are preliminary.

An R&D program for targetry and capture at a neutrino factory and muon collider source

The need for intense muon beams for muon colliders and for neutrino factories based on muon storage rings leads to a concept of 1–4 MW proton beams incident on a moving target that is inside a 20-T solenoid magnet, with a mercury jet as a preferred example. Novel technical issues for such a system include disruption of the mercury jet by the proton beam and distortion of the jet on entering the solenoid, as well as more conventional issues of materials lifetime and handling of activated materials in an intense radiation environment. As part of the R&D program of the Neutrino Factory and Muon Collider Collaboration, an R&D effort related to targetry is being performed within the context of experiment E951 at Brookhaven National Laboratory, first results of which are reported here.

Experimental observation of proton-induced shocks and magneto-fluid-dynamics in liquid metal

A liquid metal target is one of the options for the pion production target of a ν-factory. The interaction between a liquid metal and a proton beam were observed with static mercury as well as with a free mercury jet and up to 4×10 12 protons/bunch. The experimental method for investigating the magneto-fluid-dynamic effects of a high-velocity liquid metal in a high magnetic field magnet has been validated by recording the behaviour of a 15 m/s mercury burst entering the gradient of a 13 T solenoid at GHMFL Grenoble. The paper includes the description of the optical read-out system as well as numerical results of the mercury drop velocities.

Advanced target concepts for production of radioactive ions and neutrino beams

The 1–20 MW of proton beam power which modern accelerator technology put at our disposal for production of intense secondary beams presents a major technically challenge to the production targets. A conceptual design is presented for a high power pion production target and collection system, which was originally suggested to be used as the source for the proposed CERN muon-neutrino factory. It will be shown that the major parts of this target could also serve as an efficient spallation neutron source for production of 6He and fission products in the two-step converter target concept. The heart of the system consists of a free surface mercury jet with a high axial velocity, which allows the heat to be carried away efficiently from the production region. For the neutrino factory the secondary pions are collected and injected into the pion decay channel by means of a magnetic horn. For the radioactive ion-beam facility the Hg-jet is surrounded by the high-temperature isotope separator on-line (ISOL) production target. The suggested mechanical layout and technical parameters of the Hg-jet, ISOL target, horn and cooling system are discussed. The critical issues are identified and a description of the R&D program designed to provide experimental proof of the principle as well as providing engineering parameters is given.

Conceptual design of pion-capture magnets of up to 15 cm bore and 20 T peak field

For the Neutrino Factory and Muon Collider Collaboration, BNL has considered solenoidal magnet systems of several types to capture pions generated by bombarding a mercury jet with multi-GeV protons. The magnet systems generate up to 20 T, uniform to 5% throughout a cylindrical volume 0.15 m in diameter and 0.6 m long. Axially downstream the Held ramps gradually downward by a factor of sixteen, while the bore increases fourfold. The steady-state system needed for an accelerator has many superconducting coils and a radiation-resistant insert of mineral-insulated hollow conductor. Less costly, pulsed systems suffice to study pion capture and the effect of a magnetic field on a jet hit by a proton beam. BNL has explored three types of magnets, each with its principal coils precooled by liquid nitrogen. One type employs two sets of coils energized sequentially. Charged in 23 s by a power supply of 5 MVA, the 14-ton outer set generates 10 T and stores 28 NU, from which, in 1/3 s, to charge a half-ton inner coil that adds 12 1/2 T to the 7 1/2 T remaining from the outer set. An alternative design uses 25 MVA to energize, in 1.4 s, a single 3-ton set of coils. The third type bows to budgetary constraints and is more modest in size and performance. A magnet of 2-3 tons generates 10-11 T with only 2 MVA, in a bore big enough (11 cm) to accommodate the jet. It foregoes the field ramp that improves pion retention.