Some Features of ICR Heating by a Solenoidal Antenna

A study is made of some characteristic features of ion cyclotron resonance (ICR) heating in plasma-based isotope separators. The effects associated with ion drift in the RF field of a solenoidal antenna are considered in the single-particle approximation. Estimates are obtained and numerical calculations are carried out for ICR heating in the case of a “narrow” (ρ/r ～ 1, where ρ is the ion gyroradius) plasma flow.     

ICR heating of a plasma with a complex ion composition

Two methods for simultaneously heating ions with different masses and, accordingly, with different gyrofrequencies are considered. The first is heating in a steady uniform magnetic field by a nonmonochromatic RF field, and the second is heating in a nonuniform magnetic field by a monochromatic RF field. In the first method, the cyclotron resonance condition is ensured by the finite width of the RF field spectrum, while in the second one, by a drop in the magnetic field along the system. The study is based on the previously developed analytic model of the excitation of RF fields by current-carrying antennas. Nonlinear effects caused by variations in the longitudinal ion velocities during the ICR interaction are taken into account. It is found that ions with atomic masses in the range 85 < A < 150 (fragments of a spent nuclear fuel) can be efficiently heated in systems with moderate parameters.     

ICR heating in ion separation systems

A systematic procedure for analyzing the physical processes that govern ICR heating in systems for ion separation is developed. The procedure is based on an analytic model of an rf antenna generating rf fields within a plasma column in a magnetic field and includes such issues as the calculation of rf fields, examination of the ICR interaction of ions with these fields, and determination of the distribution function of the ion flow at the exit from the ICR heating system. It is shown that, even in ICR heating systems with easily achievable parameter values, ions with appreciably different masses can be efficiently separated by energy.     

Measurements of the load resistance of a poloidal antenna and the phase velocity of fast magnetosonic waves during ICR plasma heating in the L-2M stellarator

The propagation and damping of waves excited by a poloidal antenna in a hydrogen plasma at the ion cyclotron resonance (ICR) frequency were investigated. The longitudinal wavenumber and damping length of waves excited in the ohmically heated plasma of the L-2M stellarator, the dependence of the damping length of fast magnetosonic waves on the magnetic field strength, and the dependence of the antenna load resistance on the plasma density were measured. It is the first time that such complex measurements were performed in experiments on ICR heating of a hydrogen plasma at the fundamental harmonic of the ion gyrofrequency in toroidal magnetic confinement systems.     

Near field of a loop antenna operating in plasma in the whistler frequency range

The structure of the RF magnetic field in the vicinity of a loop antenna operating in the whistler frequency range has been studied experimentally and theoretically. The experiments were performed over a wide frequency range at different values of the plasma density, electron temperature, and ambient magnetic field strength. It is shown that, when a loop antenna is smaller than the wavelength of a quasi-longitudinal whistler, the structure of the magnetic field of such an antenna is nearly the same as that of the field of a current-carrying loop in vacuum; otherwise, the RF field is localized near the antenna wire. The results of numerical calculations agree with the measured field distributions. The antenna field is calculated by expanding it in the eigenmodes of a magnetized plasma with allowance for not only propagating but also nonpropagating (exponentially decaying) waves, which make the main contribution to the near field. An analytic estimate of the depth to which the RF magnetic field of a loop antenna penetrates into the plasma is obtained.     

Plasma asymmetric dipole antenna excited by a surface wave

A study is made of a quarter-wave asymmetric dipole antenna in which the conducting rod is replaced by a plasma column with an electron density much higher than the critical density. The parameters of such an antenna are determined by the exited surface wave, which affects the electromagnetic field structure in the near-field zone. It is shown analytically, numerically, and experimentally that the resonant length of the plasma dipole antenna is close to one-quarter of the length of the surface wav and that the conversion efficiency of plasma antenna power into radiation can be no worse than that of a metal dipole antenna. It is also shown experimentally that the plasma in a dipole antenna can be self-consistently excited by an RF oscillator and that the excited RF oscillations can be efficiently radiated into the surrounding space.     

Weak-field H3O+ ion cyclotron resonance alters water refractive index

Heretofore only observed in living systems, we report that weak-field ion cyclotron resonance (ICR) also occurs in inanimate matter. Weak magnetic field (50 nT) hydronium ICR at the field combination (7.84 Hz, 7.5 µT) markedly changes water structure, as evidenced by finding an altered index of refraction exactly at this combined field. This observation utilizes a novel technique which measures the scattering of a He–Ne laser beam as the sample is exposed to a ramped magnetic field frequency. In addition to the hydronium resonance, we find evidence of ICR coupling to a more massive structure, possibly a tetrahedral combination of three waters and a single hydronium ion. To check our observations, we extended this technique to D₂O, successfully predicting the specific ICR charge-to-mass ratio for D₃O⁺ that alters the index of refraction.     

Plasma method for processing spent nuclear fuel

Plasma methods for processing spent nuclear fuel are analyzed. It is shown that, by ICR heating in a nonuniform magnetic field, the energy of the heated ash ions can be increased substantially, while nuclear fuel ions can be kept cold. Two methods for extracting heated ash ions from a cold plasma flow are considered, specifically, that by increasing the ion gyroradius and that due to ion drift in a curved magnetic field. It is found that the required degree of separation of ash and fuel ions can be achieved in systems with quite moderate parameters.     

低功率2 450 MHz射频磁场对神经元延迟整流钾通道的抑制作用

由于电子设备的广泛使用,人类已经越来越多地暴露在射频磁场的辐射下,但射频磁场的辐射效应却一直不明确．采用全细胞膜片钳技术,记录2 450 MHz射频磁场辐射对小鼠脑皮层神经元延迟整流钾电流IK的影响．利用Ansoft HFSS软件对6 dB全向天线建模仿真,验证距天线2~3 cm处磁场分布均匀,使用Agilent E5070B网络分析仪经该天线发射出2 450 MHz输出功率为39.81 mW电磁场,对细胞进行刺激．实验发现,2 450 MHz低功率射频磁场暴露5、10和15 min对IK均有明显的抑制作用;显著影响IK激活特性,对照组与磁场暴露组半数激活电压分别为（－1.13±2.32）mV和（19.52±1.03）mV(n=10, P <0.05);斜率因子分别为（23.21±3.29）mV和（13.95±1.27）mV(n=10, P <0.05)．结果表明,低功率射频磁场通过减小延迟整流钾通道电流,影响神经元的生理功能,为进一步研究电磁辐射所引发的生物学效应提供了一种新的方法．     

Studies in RF Power Communication,SAR, and Temperature Elevation in Wireless Implantable Neural Interfaces

Implantable neural interfaces are designed to provide a high spatial and temporal precision control signal implementing high degree of freedom real-time prosthetic systems. The development of a Radio Frequency (RF) wireless neural interface has the potential to expand the number of applications as well as extend the robustness and longevity compared to wired neural interfaces. However, it is well known that RF signal is absorbed by the body and can result in tissue heating. In this work, numerical studies with analytical validations are performed to provide an assessment of power, heating and specific absorption rate (SAR) associated with the wireless RF transmitting within the human head. The receiving antenna on the neural interface is designed with different geometries and modeled at a range of implanted depths within the brain in order to estimate the maximum receiving power without violating SAR and tissue temperature elevation safety regulations. Based on the size of the designed antenna, sets of frequencies between 1 GHz to 4 GHz have been investigated. As expected the simulations demonstrate that longer receiving antennas (dipole) and lower working frequencies result in greater power availability prior to violating SAR regulations. For a 15 mm dipole antenna operating at 1.24 GHz on the surface of the brain, 730 uW of power could be harvested at the Federal Communications Commission (FCC) SAR violation limit. At approximately 5 cm inside the head, this same antenna would receive 190 uW of power prior to violating SAR regulations. Finally, the 3-D bio-heat simulation results show that for all evaluated antennas and frequency combinations we reach FCC SAR limits well before 1 °C. It is clear that powering neural interfaces via RF is possible, but ultra-low power circuit designs combined with advanced simulation will be required to develop a functional antenna that meets all system requirements.     

Large scale in vitro experiment system for 2 GHz exposure

A beam formed radiofrequency (RF) exposure-incubator employing a horn antenna, a dielectric lens, and a culture case in an anechoic chamber is developed for large scale in vitro studies. The combination of an open type RF exposure source and a culture case through which RF is transmitted realizes a uniform electric field (+/-1.5 dB) in a 300 x 300 mm area that accommodates 49 35 mm diameter culture dishes. This large culture dish area enables simultaneous RF exposure of a large number of cells or various cell lines. The RF exposure source operates at 2142.5 MHz corresponding to the middle frequency of the downlink band of the International Mobile Telecommunication 2000 (IMT-2000) cellular system. The dielectric lens, which has a gain of 7 dB, focuses RF energy in the direction of the culture case and provides a uniform electric field. The culture case is sealed and connected to the main unit for environmental control, located outside the anechoic chamber, via ducts. The temperature at the center of the tray, which contains the culture dishes in the culture room, is maintained at 37.0 +/- 0.2 degrees C by air circulation. In addition, the appropriate CO2 density and humidity supplied to the culture case realizes stable long-term culture conditions. Specific absorption rate (SAR) dosimetry is performed using an electric field measurement technique and the Finite Difference Time Domain (FDTD) calculation method. The results indicate that the mean SAR of the culture fluid at the bottom of the 49 (7 x 7 array) culture dishes used in the in vitro experiments is 0.175 W/kg for an antenna input power of 1 W and the standard deviation of the SAR distribution is 59%. When only 25 culture dishes (5 x 5 array) are evaluated, the mean SAR is 0.139 W/kg for the same antenna input power and the standard deviation of the SAR distribution is 47%. The proliferation of the H4 cell line in 72 h in a pair of RF exposure-incubators reveals that the culture conditions are equivalent to those of a common CO2 incubator.     

Parent-of-origin-specific binding of nuclear hormone receptor complexes in the H19-Igf2 imprinting control region

Parent-of-origin-specific expression of the mouse insulin-like growth factor 2 gene (Igf2) and the closely linked H19 gene located on distal chromosome 7 is regulated by a 2.4-kb imprinting control region (ICR) located upstream of the H19 gene. In somatic cells, the maternally and paternally derived ICRs are hypo- and hypermethylated, respectively, with the former binding the insulator protein CCCTC-binding factor (CTCF) and acting to block access of enhancers to the Igf2 promoter. Here we report on a detailed in vivo footprinting analysis-using ligation-mediated PCR combined with in vivo dimethyl sulfate, DNase I, or UV treatment-of ICR sequences located outside of the CTCF binding domains. In mouse primary embryo fibroblasts carrying only maternal or paternal copies of distal chromosome 7, we have identified five prominent footprints specific to the maternal ICR. Each of the five footprinted areas contains at least two nuclear hormone receptor hexad binding sites arranged with irregular spacing. When combined with fibroblast nuclear extracts, these sequences interact with complexes containing retinoic X receptor alpha and estrogen receptor beta. More significantly, the footprint sequences bind nuclear hormone receptor complexes in male, but not female, germ cell extracts purified from fetuses at a developmental stage corresponding to the time of establishment of differential ICR methylation. These data are consistent with the possibility that nuclear hormone receptor complexes participate in the establishment of differential ICR methylation imprinting in the germ line.     

Self-consistent modeling of radio-frequency plasma generation in stellarators

A self-consistent model of radio-frequency (RF) plasma generation in stellarators in the ion cyclotron frequency range is described. The model includes equations for the particle and energy balance and boundary conditions for Maxwell’s equations. The equation of charged particle balance takes into account the influx of particles due to ionization and their loss via diffusion and convection. The equation of electron energy balance takes into account the RF heating power source, as well as energy losses due to the excitation and electron-impact ionization of gas atoms, energy exchange via Coulomb collisions, and plasma heat conduction. The deposited RF power is calculated by solving the boundary problem for Maxwell’s equations. When describing the dissipation of the energy of the RF field, collisional absorption and Landau damping are taken into account. At each time step, Maxwell’s equations are solved for the current profiles of the plasma density and plasma temperature. The calculations are performed for a cylindrical plasma. The plasma is assumed to be axisymmetric and homogeneous along the plasma column. The system of balance equations is solved using the Crank-Nicholson scheme. Maxwell’s equations are solved in a one-dimensional approximation by using the Fourier transformation along the azimuthal and longitudinal coordinates. Results of simulations of RF plasma generation in the Uragan-2M stellarator by using a frame antenna operating at frequencies lower than the ion cyclotron frequency are presented. The calculations show that the slow wave generated by the antenna is efficiently absorbed at the periphery of the plasma column, due to which only a small fraction of the input power reaches the confinement region. As a result, the temperature on the axis of the plasma column remains low, whereas at the periphery it is substantially higher. This leads to strong absorption of the RF field at the periphery via the Landau mechanism.     

Empirical and theoretical dosimetry in support of whole body radio frequency (RF) exposure in seated human volunteers at 220 MHz

This study reports the dosimetry performed to support an experiment that measured physiological responses of seated volunteer human subjects exposed to 220 MHz fields. Exposures were performed in an anechoic chamber which was designed to provide uniform fields for frequencies of 100 MHz or greater. A vertical half-wave dipole with a 90 degrees reflector was used to optimize the field at the subject's location. The vertically polarized E field was incident on the dorsal side of the phantoms and human volunteers. The dosimetry plan required measurement of stationary probe drift, field strengths as a function of distance, electric and magnetic field maps at 200, 225, and 250 cm from the dipole antenna, and specific absorption rate (SAR) measurements using a human phantom, as well as theoretical predictions of SAR with the finite difference time domain (FDTD) method. A NBS (National Bureau of Standards, now NIST, National Institute of Standards and Technology, Boulder, CO) 10 cm loop antenna was positioned 150 cm to the right, 100 cm above and 60 cm behind the subject (toward the transmitting antenna) and was read prior to each subject's exposure and at 5 min intervals during all RF exposures. Transmitter stability was determined by measuring plate voltage, plate current, screen voltage and grid voltage for the driver and final amplifiers before and at 5 min intervals throughout the RF exposures. These dosimetry measurements assured accurate and consistent exposures. FDTD calculations were used to determine SAR distribution in a seated human subject. This study reports the necessary dosimetry to precisely control exposure levels for studies of the physiological consequences of human volunteer exposures to 220 MHz.     

Summary of measured radiofrequency electric and magnetic fields (10 kHz to 30 GHz) in the general and work environment

We have plotted data from a number of studies on the range of radiofrequency (RF) field levels associated with a variety of environmental and occupational sources. Field intensity is shown in units of volts/meter (V/m) for electric field strength and amps/meter (A/m) for magnetic field strength. Duty factors, modulation frequencies, and modulation indices are also reported for some sources. This paper is organized into seven sections, each cataloging sources into appropriate RF frequency bands from very-low frequency (VLF) to super-high frequency (SHF), and covers frequencies from 10 kHz to 30 GHz. Sources included in this summary are the following: Coast Guard navigational transmitters, a Navy VLF transmitter, computer visual display terminals (VDTs), induction stoves or range tops, industrial induction and dielectric heaters, radio and television broadcast transmitters, amateur and citizens band (CB) transmitters, medical diathermy and electrosurgical units, mobile and handheld transmitters, cordless and cellular telephones, microwave ovens, microwave terrestrial relay and satellite uplinks, and police, air traffic, and aircraft onboard radars. For the sources included in this summary, the strongest fields are found near industrial induction and dielectric heaters, and close to the radiating elements or transmitter leads of high power antenna systems. Handheld transmitters can produce near fields of about 500 V/m at the antenna. Fields in the general urban environment are principally associated with radio and TV broadcast services and measure about 0.1 V/m root-mean-square (rms). Peak fields from air traffic radars sampled in one urban environment were about 10 V/m, 300 times greater than the rms value of 0.03 V/m when the duty factor associated with antenna rotation and pulsing are factored in. Bioelectromagnetics 18: 563–577, 1997. Published 1997 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Characteristic properties of the frame-antenna-produced RF discharge evolution in the Uragan-3M torsatron

In the ? = 3 Uragan-3M torsatron, hydrogen plasma is produced and heated by RF fields in the Alfvén range of frequencies (ω ? ω _ci ). To this end, a frame antenna with a broad spectrum of generated parallel wavenumbers is used. The RF discharge evolution is studied experimentally at different values of the RF power fed to the antenna (the anode voltage of the oscillator and the antenna current) and the initial pressure of the fueling gas. It is shown that, depending on the antenna current and hydrogen pressure, the discharge can operate in two regimes differing in the plasma density, temperature, and particle loss. The change in the discharge regime with increasing anode voltage is steplike in character. The particular values of the anode voltage and pressure at which the change occurs are affected by RF preionization or breakdown stabilization by a microwave discharge. The obtained results will be used in future experiments to choose the optimal regimes of the frame-antenna-produced RF discharge as a target for the production and heating of a denser plasma by another, shorter wavelength three-half-turn antenna.     

Properties of morphologically variant haploid frog cells formed by combined treatment with Mengo virus and the polyene antibiotic mediocidin.

Comparisons have been made of cell surface glycoproteins, concanavalin A agglutinability, and cloning efficiencies in liquid media of ICR 2A (haploid frog cells), ICR 2A M (three cloned populations of haploid frog cells resistant to 5 microgram per ml of the polyene antibiotic mediocidin), and ICR 2A M/MV cells (five cloned populations of morphologically variant haploid frog cells produced by exposure of the parental cells to the combined effects of mediocidin and an RNA mammalian virus, Mengo virus). Independently isolated ICR 2A M/MV clones exhibited altered cell surface glycoproteins, increased concanavalin A agglutinability, and enhanced cloning efficiency in liquid media when compared with ICR 2A parental cells. In contrast, ICR 2A M cells had properties similar to ICR 2A cells, with the exception of the former's increased resistance to mediocidin. The differences in properties between ICR 2A M/MV and ICR 2A cells suggest that alterations resembling transformation have occurred in ICR 2A M/MV cells as a consequence of combined treatment with mediocidin and Mengo virus.     

Properties of morphologically variant haploid prog cells formed by combined treatment with mengo virus and the polyene antibiotic mediocidin

Summary Comparison have been made of cell surface glycoproteins, concanavalin A agglutinability, and cloning efficiencies in liquid media of ICR 2A (haploid frog cells), ICR 2A M (three cloned populations of haploid frog cells resistant to 5 μg per ml of the polyene antibiotic mediocidin), and ICR 2A M/MV cells (five cloned populations of morphologically variant haploid frog cells produced by exposure of the parental cells to the combined effects of mediocidin and an RNA mammalian virus, Mengo virus). Independently isolated ICR 2A M/MV clones exhibited altered cell surface glycoproteins, increased concanavalin A agglutinability, and enhanced cloning efficiency in liquid media when compared with ICR 2A parental cells. In contrast, ICR 2A M cells had properties similar to ICR 2A cells, with the exception of the former's increased resistance to mediocidin. The differences in properties between ICR 2 M/MV and ICR 2 cells suggest that alterations resembling transformation have occurred in ICR 2A M/MV cells as a consequence of combined treatment with mediocidin and Mengo virus. This investigation was supported in part by Contract NIH 69-2161, NIH Grant AI-2095, and NIH Training Grant No. GM 507 from the National Institute of General Medical Sciences.     

Plasma processing of spent nuclear fuel by two-frequency ion cyclotron resonance heating

A previously developed method for analyzing the plasma processing of spent nuclear fuel is generalized to a plasma containing multicharged fuel ions. In such a plasma, ion cyclotron resonance heating of nuclear ash ions should be carried out in two monochromatic RF fields of different frequencies, provided that the fraction of ξ multicharged ions is small, ξ ≤ 0.1, a condition that substantially restricts the productivity of systems for processing spent nuclear fuel. Ways of overcoming this difficulty are discussed.     

Low-power inductive RF plasma sources for technological applications

The objective of the present paper is to develop an analytic theory of cylindrical low-power RF plasma sources operating at an industrial frequency (f=13.56 MHz, ω=8.52×10⁷ s^?1). Inductive surface exciters of electromagnetic fields (exciting antennas) are considered that are positioned either at the side surface of the cylinder or at one of its end surfaces. In the latter case, the plasma flows out of the source through the opposite end surface of the cylinder. A study is made of elongated systems in which the length L of the cylinder exceeds its diameter 2R and of planar disk-shaped systems with L<2R. Simple analytic expressions are derived for electromagnetic fields excited by the antenna in the source plasma. The equivalent plasma resistance and the equivalent RF power deposited in the plasma are calculated for systems with prescribed parameters, i.e., in a non-self-consistent model. Up to now, such sources have been investigated mainly through the numerical solution of the complicated general electrodynamic equations. In the Introduction, the problem is formulated in general terms and the geometry of the sources, as well as the characteristic parameters of the source plasma, is discussed. In Section 2, plasma sources operating without an external magnetic field are investigated. In Section 3, helicon plasma sources in a sufficiently strong external magnetic field are considered. Analytic predictions are compared with the results from solving the problem numerically without using the helicon approximation. Section 4 gives a brief discussion of an electron cyclotron resonance-based RF plasma source. In the Conclusion, the main results of the paper are summarized and the technological efficiency of the sources under consideration is estimated at a qualitative level.