Influence of a Static Magnetic Field on Laser Induced Tungsten Plasma in Air

In this work,laser induced tungsten plasma has been investigated in the absence and presence of 0.6 T static transverse magnetic field at atmospheric pressure in air.The spectroscopic characterization of laser induced tungsten plasma was experimentally studied using space-resolved emission spectroscopy.The atomic emission lines of tungsten showed a significant enhancement in the presence of a magnetic field,while the ionic emission lines of tungsten presented little change.Temporal variation of the optical emission lines of tungsten indicated that the atomic emission time in the presence of a magnetic field was longer than that in the absence of a magnetic field,while no significant changes occurred for the ionic emission time.The spatial resolution of optical emission lines of tungsten demonstrated that the spatial distribution of atoms and ions were separated.The influence of a magnetic field on the spatial distribution of atoms was remarkable,whereas the spatial distribution of ions was little influenced by the magnetic field.The different behaviors between ions and atoms with and without magnetic field in air were related to the various atomic processes especially the electrons and ions recombination process during the plasma expansion and cooling process.     

Structural biology investigation of EMF effect on insulin in solution

It was reported that the a-helix of protein molecules could be destroyed when they were exposed to the electromagnetic field(EMF) and finally the signal transduction could be affected.To study this effect,one signal molecule,insulin,was exposed to electromagnetic fields at different combinations of the field strength,repetition rate and exposure time.For the first time,structural biology approach was used to detect the EMF effect.The results of a series of measurements on the interaction of electromagnetic fields with insulin in vitro are described.Under our experimental conditions,no effects of electromagnetic field exposure were observed on the molecular conformation.     

Biological effects of implantation and penetration of nitrogen ion beams on wheat seeds

The biological effects of wheat seeds irradiated by 48MeV/u and 20MeV/u ^14N^7 beams are studied,respectively.The results show.both penetration and implantation of heavy ions can significantly inhibit growing pwer(height of plant stem)of wheat seeds.The greater dose is ,the weaker growing power is,and the implantation influence on growing power is stronger than the penetration;a great variety of chromosomal aberrations were observed in root tip cells of irradiated seeds and the aberration frequencies were several hundred times higher than that of the corresponding control;it has been proved by 3H-TdR incorporation test that unscheduled DNA synthesis exists in irradiated wheat seed embryos.It is found by ESR spectroscopy that the variation of free radical concentration with total dose has different features for the pentrated and implanted seeds.     

Investigation of the self-induced magneticfield characteristics in a pulsed plasma thruster with flared electrodes

The self-induced magnetic field in a pulsed plasma thruster(PPT)with flared electrodes is investigated for a better understanding of the working process and the structural design of the thruster.A two-dimensional model of the magnetic field is built and is validated by comparing the simulated results with the experimental results in literature.The magnetic flux density in the discharge channel during the working process is presented and analyzed regarding the electrode structures.The calculated magnetic field flux density decreases from 0.8 T at the upstream to 0.1 T and below at the downstream in the discharge channel(68 J).The peak of the magnetic flux density over time lags behind the current peak,which provides evidence for the existence of a moving plasma sheet in the discharge process.The magnetic field induced by the current in the extra bending part of the anode enhances the Lorentz force,which acts on the charged particles near the propellant.Finally,the geometric study indicates that the electromagnetic impulse bit does not monotonically increase with the flared angle of the electrodes.Instead,it reaches a maximum at a certain flared angle,which could provide significant suggestions for structural optimization.     

Identification of Plasma Boundary and Position for HL-2A Tokamak

Using the virtual-case principle, the plasma boundary, the plasma current center, and the x-point are identified for the HL-2A tokamak. The plasma current is represented by the current center and the virtual multipole moments which produce a magnetic flux in a form of polynomial. Adaptive parameters in the polynomial are determined by the least-square fit of the poloidal magnetic fields. The measurement of the magnetic field is performed using pick-up coils. The virtual-case principle is applied outside the plasma boundary. The virtual-case currents decide the position of the current center and produce a negative confinement magnetic field inside the plasma and the magnetic field generated by the plasma current outside the plasma boundary. The convergence is fast enough to get a picture between the sequent shots. The configuration reconstructed is in good agreement with the TV image taken by camera with a tangential view.     

Experiment on low-frequency electromagnetic waves propagating in shock-tube-generated magnetized cylindrical enveloping plasma

We propose a method of applying a static magnetic field to reduce the attenuation of the magnetic field component(S_H) of low-frequency electromagnetic(LF EM) waves in dense plasma. The principle of this method is to apply a static magnetic field to limit electron movement, thereby increasing the equivalent resistance and thus reducing the induced current and S_H. We consider the static magnetic field acting on the plasma of the entire induced current loop rather than on the local plasma, where the induced current is excited by the magnetic field component of LF EM waves. Analytical expressions of S_H suitable for magnetized cylindrical enveloping plasma are derived by adopting an equivalent circuit approach, by which S_His calculated with respect to various plasma parameter settings. The results show that S_H can be reduced under a static magnetic field and the maximum magnetic field strength that mitigates blackout is less than 0.1 T. Experiments in which LF EM waves propagate in a shock-tubegenerated magnetized cylindrical enveloping plasma are also conducted. S_H measured under the magnetic field(the magnetic field strength B0 acting on the magnetic field probe was about0.06 T) reduces at f=10 MHz and f=30 MHz when n_e≈1.9×10~(13) cm~(-3), which is consistent with theoretical results. The verification of the theory thus suggests that applying a static magnetic field with a weak magnetic field has the potential to improve the transmission capacity of LF EM waves in dense plasma.     

Study and Measurement of Glidarc Driven by Magnetic Field

Non-thermal plasma at atmosphere was generated through glidarc discharge driven by magnetic field and observed by using a high speed charge coupled device （CCD） and photo multiplier tube （PMT）. The arc diameter projecting in the direction of arc motion （front-viewed diameter） and the diameter projecting in the perpendicular direction of arc motion （side-viewed diameter） were measured. The effect of both the arc current and the magnetic field was analysed. The front-viewed diameter was compared with the side-viewed one. Simultaneously the electricfield intensity was measured directly and analysed by considering the effect of the external magnetic field and arc current.     

Investigation of cathode spot characteristics in vacuum under transverse magnetic field (TMF) contacts

With the continuous improvement of current levels in power systems,the demands on the breaking capacity requirements of vacuum circuit breakers are getting higher and higher.The breaking capacity of vacuum breakers is determined by cathode spots,which provide electrons and metal vapor to maintain the arc.In this paper,experiments were carried out on two kinds of transverse magnetic field (TMF) contacts in a demountable vacuum chamber,the behavior of the cathode spots was recorded by a high-speed charge-coupled device (CCD) video camera,and the characteristics of the cathode spots were analyzed through the image processing method.The phenomenon of cathode spot groups and the star-shaped pattern of the spots were both discovered in the experiment.The experimental results show that with the condition of TMF contacts the initial expansion speed of cathode spots is influenced by some parameters,such as the tested current,contact gap,the structure of the contact,the contact diameter,the number of slots,etc.In addition,the influence of the magnetic field on the formation of the cathode spot groups,the distribution,and the dynamic characteristics of the cathode spots were analyzed.It is concluded that the characteristics of the cathode spots are due to the effect of the magnetic field on the near-cathode plasma.The study of the characteristics of cathode spots in this paper would be helpful in the exploration of the physical process of vacuum arcs,and would be of guiding significance in optimizing the design of vacuum circuit breakers.     

Surface Treatment of Polypropylene Films Using Dielectric Barrier Discharge with Magnetic Field

Atmospheric pressure non-thermal plasma is of interest for industrial applications.In this study,polypropylene (PP) films are modified by a dielectric barrier discharge (DBD) with a non-uniform magnetic field in air at atmospheric pressure.The surface properties of the PP films before and after a DBD treatment are studied by using contact angle measurement,atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS).The effect of treatment time on the surface modification with and without a magnetic field is investigated.It is found that the hydrophilic improvement depends on the treatment time and magnetic field.It is also found that surface roughness and oxygen-containing groups are introduced onto the PP film surface after the DBD treatment.Surface roughness and oxygen-containing polar functional groups of the PP films increase with the magnetic induction density.The functional groups are identified as C-O,C=O and O-C=O by using XPS analysis.It is concluded that the hydrophilic improvement of PP films treated with a magnetic field is due to a greater surface roughness and more oxygen-containing groups.     

Chiral phase transition of quark matter in the background of parallel electric and magnetic fields

We report on our results about spontaneous chiral symmetry breaking for quark matter in the background of static and homogeneous parallel electric field,E,and magnetic field,B.A Nambu–Jona–Lasinio model is used to compute the dependence of the chiral condensate at finite temperature,E and B.We study the effect of this background on inverse catalysis of chiral symmetry breaking for E and B of the same order of magnitude.We also consider the effect of equilibration of chiral density,n_5,produced by axial anomaly on the critical temperature.The equilibration of n_5 allows for the introduction of the chiral chemical potential,u_5,which is computed selfconsistently as a function of temperature and field strength.We find that even if the chiral medium is produced by the fields the thermodynamics,with particular reference to the inverse catalysis induced by the external fields,it is not very affected by n_5 at least if the average u_5,at equilibrium is not too large.     

^188 Re labeled MPEG-modified superparamagnetic nanogels：preparation and preliminary application in mice

Superparamagnetic poly（acrylamide） magnetic nanogels produced via photochemical method have been developed. After Hoffmann degradation of carbonyl, the nanogels with amino groups, or poly（acrylamide-vinyl amine） magnetic nanogels, were also obtained. And the magnetic nanogels were further modified by methoxy poly（ethylene glycol） （MPEG） for higher dispersibility and stability. The MPEG-modified magnetic nanogels were characterized by X-ray diffraction （XRD）, photo correlation spectroscopy （PCS） and scanning electron microscopy （SEM）, respectively. The MPEG-modified magnetic nanogels were labeled by ^188 Re radiopharmaceuticals and intravenously injected into tails of mice in the presence and absence of a 0.5 T external magnetic field targeted on the bellies. The radioactivity distribution was monitored in vivo. In the absence of magnetic field, the radioactivity was mainly distributed in liver, spleen, kidney, stomach and lung. In the presence of the magnetic field, the radioactivity was mainly accumulated on the targeted point, verifying the magnetically targeted character.     

IRRADIATION EFFECT OF 0.56GeV C^6＋ on Y1.6Ca1.4V0.45Sn0.5Fe4.05O12

Y1.6Ca1.4V0.45Sn0.5Fe4.05O12 is irradiated by 0.56GeV carbon ion.The irradiation effect is investigated by Moessbauer spctroscopy.The irradiation results in an isotropic distribution of the hyperfine magnetic field.The hyperfine magnetic fields decrease after the irradiation due to the change of supertransferred field.After the irradiation,the chain Fe(a)-oxygen-Fe(d) become longer and it leads to decrease of the supertransferred field.     

The Influence of the Magnetic Field on the Electrical Breakdown Phenomena

A simple phenomenological model and detailed simulation studies of the breakdown phenomena in argon and nitrogen under the simultaneous action of electric and magnetic fields are presented in this paper. Expressions for the breakdown voltage have been derived taking into account variations of both the ionization coefficient and the secondary electron yield in a magnetic field. Calculations were performed by using XOOPIC code, an Object Oriented Particle in Cell code, with both the original and the improved secondary emission model with inclusion of the influence of the magnetic field on the secondary electron production. The simulation results presented here clearly show that the inclusion of the dependence of the secondary electron yield on the magnetic field leads to better agreement with existing experimental results.     

Experimental Investigation on Airfoil Shock Control by Plasma Aerodynamic Actuation

An experimental investigation on airfoil （NACA64-215） shock control is performed by plasma aerodynamic actuation in a supersonic tunnel （Ma -= 2）. The results of schlieren and pressure measurement show that when plasma aerodynamic actuation is applied, the position moves forward and the intensity of shock at the head of the airfoil weakens. With the increase in actuating voltage, the total pressure measured at the head of the airfoil increases, which means that the shock intensity decreases and the control effect increases. The best actuation effect is caused by upwind-direction actuation with a magnetic field, and then downwind-direction actuation with a magnetic field, while the control effect of aerodynamic actuation without a magnetic field is the most inconspicuous. The mean intensity of the normal shock at the head of the airfoil is relatively decreased by 16.33%, and the normal shock intensity is relatively reduced by 27.5% when 1000 V actuating voltage and upwind-direction actuation are applied with a magnetic field. This paper theoretically analyzes the Joule heating effect generated by DC discharge and the Lorentz force effect caused by the magnetic field. The discharge characteristics are compared for all kinds of actuation conditions to reveal the mechanism of shock control by plasma aerodynamic actuation.     

Design and field measurement of a dipole magnet for a newly developed superconducting proton cyclotron beamline

The design, field quality optimization, multipole field analysis, and field measurement of a dipole for a newly developed superconducting proton cyclotron(SC200) beamline are presented in this paper. The maximum magnetic field of the dipole is 1.35 T; the bending radius is 1.6 m with a proton beam energy in the range of70–200 Me V. The magnetic field was calculated with 2 D and 3 D simulations, and measured with a Hall mapping system. The pole shim and end chamfer were optimized to improve the field quality. Based on the simulated results,the multipole field components in the good-field region were studied to evaluate the field quality. The results showed that the field quality is better than ± 5 × 10~(-4) at1.35 T with shimming and chamfering. For the transverse field homogeneity, the third-order(B3) and fifth-order(B5)components should be controlled with symmetrical shims.The second-order(B2) component was the main disturbance for the integral field homogeneity; it could be improved with an end chamfer. The magnet manufacturing and field measurement were performed in this project. The measurement results demonstrated that the magnetic design and field quality optimization of the 45° dipole magnet can achieve the desired high field quality and satisfy the physical requirements.     

Magnetic fields in the Planck theory of sonoluminescence

Sonoluminescence(SL) observed in the cavitation of water may be explained by the Planck theory of SL that treats the bubbles as collapsing miniature masers having optical waves standing in resonance with the dimensions of bubble cavity,Microwaves are created from the Planck energy of the standing waves provided the bubble wall may be treated as a perfect blackbody surface.In the ultraviolet,liquid H2O is srongly absorbent and the bubble approaches a Planck blackbody enclosure.The micrwaves are created at frequencies proportional to the bubble collapse velocity and are absorbed by the dipoles of the H2O and other bubble wall molecules.Intense electric fields develop as the liquid H2O bubble wall undergoes dielectric polarization.By this theory,free electrons are created in SL as the electric fields breakdown;the presence of free electrons is required if any magnetic field effect is to be observed in SL.Both local and global magnetic effects on SL are described.The local effect is based on the magnetic pressure due to the electrons moving as currents inside the bubble.The global effect is an accumulatio of local effects at the voids throughout the liquid H2O causing a reduction in the bulk modulus.Numerical solutions of the Rayleigh-Plesset(R-P) equation are presented that show the effect of applied magnetic field on SL to be the global effect causing a reduction in the bulk modulus.Consistent with the Planck theory of SL,the R-P simulations show the suppression of Sl intensity with magentic field to be parabolic and the SL intensity to be linear with collapse velocity.     

3D MHD Jet in a Non-Uniform Magnetic Field

The purpose of this paper is to present a two-phase 3D magnetohydrodynamics （MHD） flow model that combines the volume of fluid （VOF） method with the technique derived from induced-magnetic-field equations for liquid metal free surface MHD-jet-flow. Analogy between the induced-magnetic-filed equation and the conventional computational fluid dynamics （CFD） equation is made, so that the equation can be conveniently accounted for by CFD. A penalty factor numerical method is introduced in order to force the local divergence-free condition of the magnetic fields and an extension of the void insulating calculation domain is applied to ensure that the induced-magnetic field at its boundaries is null. These simulation results for lithium liquid metal jets under magnetic field configurations of Magnetic Torus （Mtor） and National Spherical Torus Experiment （NSTX） outboard divertor have shown that three dimensional jet can not be annihilated by magnetic braking and its cross-section will deform in such a way that the momentum flux of the jet is conserved. 3D MHD effects from a magnetic field gradient cause return currents to interact with applied magnetic fields and produce unfavorable Lorentz forces. Under 3D applied non-uniform magnetic fields of the divertor, unfavorable Lorentz forces lead to a substantial change in flow pattern and a reduction in flow velocity, with the jet cross-section moving to one side of the jet space. These critical phenomena can not be revealed by 2D models.     

Effects of Fast-Ion Injection on a Magnetized Sheath near a Floating Wall

A fully kinetic particle-in-cell/Monte Carlo model is employed to self-consistently study the effects of fast-ion injection on sheath potential and electric field profile in collisional magnetized plasma with a floating absorbing wall. The influences of the fast-ion injection velocity and density, the magnetic field and angle θ0 formed by the magnetic field and the x-axis on the sheath potential and electric field are discussed in detail. Numerical results show that increasing fast-ion injection density or decreasing injection velocity can enhance the potential drop and electric field in the sheath. Also, increasing the magnetic field strength can weaken the loss of charged particles to the wall and thus decrease the potential and electric field in the sheath. The time evolution of ion flux and velocity distribution on the wall is found to be significantly affected by the magnetic field.     

Spin polarization and production rate studies of surface muons in a novel solenoid capture system based on CSNS

A novel surface muon capture system with a large acceptance was proposed based on the China spallation neutron source(CSNS).This system was designed using a superconducting solenoid where a long graphite target was put inside it.Firstly,the spin polarization evolution was studied in a constant uniform magnetic field.As the magnetic field can interact with the spin of the surface muon,both the spin polarization and production rate of the surface muons collected by the new capture system were calculated by the G4beamline.Simulation results showed that the surface muons could still keep a high spin polarization([90%)with different magnetic fields(0–10 T),and the larger magnetic field is,the more surface muons can be captured.Finally,the proton phase space,Courant–Snyder parameters,and intensities of surface muons of different beam fractions were given with magnetic fields of 0 and 5T.The solenoid capture system can focus proton and surface muon beams and collect p?and l?particles.It can also provide an intense energetic positron source.     

Development of Test-stand for Magnetic Field Measurement Apparatus in 230 MeV Proton Cyclotron

<正>The isochronism and focusing of magnetic fields are the key performance indicators for cyclotron,the judge of which should be done by the magnetic field measurement.In order to verity the relevant technologies in advance,and hence minimize the risk of the project,a magnetic field measuring test-stand is needed to support the apparatus.The support platform is mainly