Frequency Of Microwave Radiation Research Articles

Enhancing the performances of traditional electron cyclotron resonance ion sources with multiple-discrete-frequency microwave radiation

The performances of electron cyclotron resonance (ECR) ion sources, in terms of high-charge-state yields and intensities within a particular charge state, can be enhanced by increasing the physical sizes of the ECR zones in relation to the sizes of their plasma volumes. The creation of a large ECR plasma “volume” permits coupling of more power into the plasma, resulting in the heating of a much larger electron population to higher energies, the effect of which is to produce higher charge-state distributions and higher intensities within a particular charge state than possible in present forms of the ECR source. The ECR plasma “volumes” of traditional B-minimum ECR sources can be increased by injecting broadband microwave radiation (multiple-discrete-frequency, variable frequency, or broad-band-width frequency microwave radiation) derived from standard klystron, gyrotron, or traveling-wave-tube (TWT) technologies (frequency domain). To demonstrate that the frequency domain technique can be used to enhance the performance of a traditional B-minimum ECR ion source, comparative studies were made to assess the relative performances of the Oak Ridge National Laboratory Caprice ECR ion source, in terms of multiply charged ion-beam generation capabilities, when excited with high-power, single-frequency, or multiple-discrete-frequency microwave radiation, derived from standard klystron and/or TWT technologies. These studies demonstrate that the charge-state populations for Ar q+ and Xeq+ move toward higher values when excited with two and three discrete-frequency, microwave power compared to those observed when single-frequency microwave power is used. For example, the most probable charge state for Xe is increased by one charge-state unit while the beam intensities for charge states higher than the most probable are increased by factors of ∼3 compared to those observed for single-frequency plasma excitation. The results of these measurements along with details on the modifications to the injection system required to couple the microwave radiation into the plasma volume of the Caprice source will be presented in this report.

Use of multiple-discrete-frequency microwave radiation to enhance the performances of traditional B-minimum electron cyclotron resonance ion sources

The performances of electron cyclotron resonance (ECR) ion sources, in terms of high-charge-state yields and intensities within a particular charge-state, can be enhanced by increasing the physical sizes of the ECR zones in relation to the sizes of their plasma volumes. The ECR plasma “volumes” of traditional B-minimum ECR sources can be increased by injecting broadband microwave radiation (multiple-discrete frequency, variable frequency, or broad-bandwidth frequency microwave radiation) derived from standard klystron, gyrotron, or traveling-wave-tube (TWT) technologies (frequency domain). In this work, comparisons were made of the charge-state distributions of Arq+ and Xeq+ extracted from the ORNL Caprice ECR ion source, when excited with single frequency and multiple-discrete-frequency microwave radiation, derived from standard klystron and/or TWT technologies. The charge-state populations for Arq+ and Xeq+ move toward higher values when excited with modest power from two and three discrete frequency, microwave radiation compared to those generated with power from single-frequency radiation. For three-frequency plasma excitation, the most probable charge state for Xe is increased by one charge-state unit while the beam intensities for charge-states higher than the most probable are increased by factors of ∼3 over those for the single frequency plasma case. The results of these measurements along with details on the modifications to the injection system required to couple the microwave radiation into the plasma volume of the Caprice source will be presented in this article.

Adhesive Bonding Via Exposure to Variable Frequency Microwave Radiation

AbstractAdhesive bonding through the application of variable frequency microwave (VFM) radiation has been evaluated as an alternative curing method for joining composite materials. The studies showed that the required cure time of a thermosetting epoxy adhesive is substantially reduced by the use of VFM when compared to conventional (thermal) curing methods. Variable frequency microwave processing appeared to yield a slight reduction in the required adhesive cure time when compared to processing by the application of single frequency microwave radiation. In contrast to the single frequency processing, the variable frequency methodology does not readily produce localized overheating (burnt or brown spots) in the adhesive or the composite. This makes handling and location of the sample in the microwave oven less critical for producing high quality bonds and allows for a more homogeneous distribution of the cure energy. Variable frequency microwave processing is a valuable alternative method for rapidly curing thermoset adhesives at low input power levels.

Grain Growth Behavior During Microwave Annealing of Silicon Nitride

AbstractA comparative study of grain growth behavior in silicon nitride under conventional and microwave annealing is presented. Microwave annealed specimens showed a faster growth rate as indicated by the quantitative microstructural analysis. The phenomenon was used in combination with seeding techniques to develop a silicon nitride exhibiting a bi-modal microstructure. Microwave annealing was carried out using a microwave radiation frequency of 28 GHz.

Photon-assisted tunneling through a quantum dot at high microwave frequencies

We investigate the influence of high frequency microwave radiation on single electron tunneling through a quantum dot. Effective coupling of the radiation to the quantum dot is achieved by an on-chip integrated broadband antenna. Simulations of the current distribution on the antenna are shown. We find that radiation with a frequency of ν=155 GHz, which corresponds to half of the bare charging energy Ec/2 results in an additional conductance peak within the Coulomb blockade regime. This additional resonance is attributed to photon-assisted tunneling.

Optical detection of cyclotron resonance for characterization of recombination processes in semiconductors

Abstract Novel applications of the technique of optically detected cyclotron resonance (ODCR) are discussed. This method is an extension of the conventional cyclotron resonance investigations and shows important advantages when applied to characterization of semiconductor materials. These advantages are due to a higher sensitivity and a longer momentum relaxation time caused by photoneutralization of ionized impurities. This in turn enables experiments at lower magnetic fields and lower microwave radiation frequency. Photoexcitation used in ODCR often results in a simultaneous observation of electron and hole cyclotron resonances in the same sample, which is a rare case in a conventional CR study. High magnetic field far infrared ODCR experiments utilize all these advantages of the method. For the most common X-band (10 GHz) microwave setups, the ODCR resolution often is too low to allow accurate CR determination of the band structure parameters of the material studied. In that case, ODCR may be used for ...

High Temperature Dielectric Measurements on Ceramics

ABSTRACTThe use of microwave frequency radiation as an alternative energy source for processing materials is currently receiving considerable worldwide attention. The ability of a material to extract energy from the microwave field depends upon its dielectric properties, however these change as the material heats. There is, therefore, a need for obtaining measurements of the microwave dielectric properties at elevated temperatures. This paper outlines some of the current work on high temperature dielectric measurements which is in progress at the University of Nottingham as part of the Materials and Microwave Processing Group initiative and some results on engineering ceramics are presented.

Microwave induced stimulation of32Pi incorporation into phosphoinositides of rat brain synaptosomes

Exposure of synaptosomes to microwave radiation at a power density of 10 mW/sq cm or more produced stimulation of the 32Pi-incorporation into phosphoinositides. The extent of 32Pi incorporation was found to be much more pronounced in phosphatidylinositol-4-phosphate (PIP), and phosphatidylinositol-4,5-bisphosphate (PIP2) as compared to phosphatidylinositol (PI) and phosphatidic acid (PA). Other lipids were also found to incorporate 32Pi but no significant changes in their labeling were seen after exposure to microwave radiation. Inclusion of 10 mM lithium in the medium reduced the basal labeling of PIP2, PIP and PI and increased PA labeling. Li+ also inhibited the microwave stimulated PIP2, PIP and PI labeling but had no effect on PA labeling. Calcium ionophore, A23187, inhibited the basal and microwave stimulated 32Pi labeling of PIP and PIP2, stimulated basal labeling of PA and PI and had no effect on microwave stimulated PA and PI labeling. Calcium chelator, EGTA, on the other hand, had no effect on basal labeling of PA and PI, stimulated basal PIP and PIP2 labeling but did not alter microwave stimulated labeling of these lipids. Exposure of synaptosomes to microwave radiation did not alter the chemical concentration of phosphoinositides indicating that the turnover of these lipids was altered. These results suggest that low frequency microwave radiation alter the metabolism of inositol phospholipids by enhancing their turnover and thus may affect the transmembrane signalling in the nerve endings.

Microwave radiation energy: A probe for the neurobiologist

Microwave energy radiation is widely used as a method for rapidly sacrificing small laboratory animals so that measurements of endogenous levels of labile neurochemical substances can be assessed after various drug treatments or pharmacological maneuvers. Several factors are important to insure that microwave energy is efficiently coupled to the rodent brain, including: the frequency of microwave radiation, the size of the waveguide for the propagation of the energy, the tuning of the waveguide system, the placement of the animal at the point of maximum power within the waveguide, the amount of power which is delivered, the time during which the power is delivered, and whether the animal is restrained during the microwave protocol.

Infrared-microwave two-photon spectroscopy: Theν2band of NH3

A spectroscopic method is developed in which the frequency of microwave radiation is added to or subtracted from that of infrared radiation by using two-photon processes in molecules. By utilizing many lines of the C${\mathrm{O}}_{2}$ and ${\mathrm{N}}_{2}$O lasers, this method enables us to perform systematic high-resolution spectroscopy in the 10-\ensuremath{\mu}m region. Both straightforward two-photon absorption spectroscopy and two-photon Lamb-dip spectroscopy can be used. We describe the theory of this method and its application to the observation of the ${\ensuremath{\nu}}_{2}$ band of $^{14}\mathrm{N}$${\mathrm{H}}_{3}$ and $^{15}\mathrm{N}$${\mathrm{H}}_{3}$.

Microwave Optical Magnetic Resonance Induced by Electrons (MOMRIE) in H2 G(3d 1Σg+)

The G(3d 1Σg+) state of H2 has been investigated using a new form of molecular double resonance spectroscopy, Microwave—Optical Magnetic Resonance Induced by Electrons (MOMRIE). This state is excited by electron bombardment of ground state H2 molecules residing in a microwave cavity in a magnetic field. Because of L-uncoupling effects, the magnetic moment is of the order of one Bohr magneton so its Zeeman levels can be tuned to resonance with X-band microwave frequency radiation by kilogauss magnetic fields. Such resonances are observed via changes in the polarization of the emitted visible radiation when the state decays. In attempting to interpret the MOMRIE spectrum, we have reviewed previous work on the optical energy levels of the 3d complex and have found the Zeeman effect calculated therefrom to be inadequate to match our present experimental precision; this is probably because of perturbations or inaccuracies in the previously reported optical spectrum. From an approximate Zeeman theory we have obtained values for the lifetime, g value, and nonlinear Zeeman effect in the N=1 level of the G(3d 1Σg+) state.

Observation of Infrared-Microwave Two-Photon Transitions in NH3

An infrared-microwave two-photon absorption is observed in 15NH3. A tunable frequency of microwave radiation is ``added'' to a fixed frequency of laser radiation utilizing the nonlinearity of the molecular absorption. This method will be useful for high-resolution infrared spectroscopy and for experiments which use laser radiation for pumping molecular energy levels.

Fine Structure and Diamagnetic Zeeman Effect in He (4P3)

The $4^{3}P$ state of helium has been excited and aligned by electron impact in a strong magnetic field. Transitions between Zeeman levels of the fine-structure states are induced by microwave frequency radiation and are detected through the resulting change in polarization of 3188-\AA{} fluorescence. The derived values of the fine-structure intervals are $4^{3}P_{0}\ensuremath{-}4^{3}P_{1}=3306.6\ifmmode\pm\else\textpm\fi{}1.0$ MHz and $4^{3}P_{1}\ensuremath{-}4^{3}P_{2}=270.7\ifmmode\pm\else\textpm\fi{}0.8$ MHz. The diamagnetic Zeeman interaction produces an observable effect, and the magnitude of its anisotropic part has been measured. The atomic radius and quadrupole moment are derived from this measurement and agree within experimental error with the values for a hydrogenic $4p$ orbital.