Design of the electron cyclotron emission diagnostic on EXL-50 spherical torus

The electron cyclotron emission(ECE)diagnostic system has been developed on the ENN spherical torus(EXL-50).The ECE system is designed to detect radiation emitted by energetic electrons,rather than conventional 1D electron temperature profile measurement,in the frequency range of 4-40 GHz.The system is composed of five subsystems,each covering a different frequency band,including the C-band(4-8 GHz),X-band(8-12 GHz),Ku-band(12-18 GHz),K-band(18-26.5 GHz)and Kα-band(26.4-40 GHz).The system uses heterodyne detection to analyze the received signals.The K-band and Kα-band subsystems are located horizontally in the equatorial plane of the EXL-50,while the C-band,X-band and Ku-band subsystems are located under the vacuum vessel of the EXL-50.To direct the microwaves from the plasma to the antennas for the horizontal detection subsystems,a quasi-optical system has been developed.For the vertical detection subsystems,the antennas are directly attached to the port located beneath the torus at R=700 mm,which is also the magnetic axis of the torus.The system integration,bench testing and initial experimental results will be thoroughly discussed,providing a comprehensive understanding of the ECE system s performance and capabilities.

Simulation of ion cyclotron wave heating in the EXL-50U spherical tokamak based on dispersion relations

This study investigates the single-pass absorption(SPA) of ion cyclotron range of frequency(ICRF) heating in hydrogen plasma of the EXL-50U spherical tokamak,which is an upgraded EXL-50 device with a central solenoid and a stronger magnetic field.The reliability of the kinetic dispersion equation is confirmed by the one-dimensional full-wave code,and the applicability of Porkolab's simplified theoretical SPA model is discussed based on the kinetic dispersion equation.Simulations are conducted to investigate the heating effects of the fundamental and second harmonic frequencies.The results indicate that with the design parameters of the EXL-50U device,the SPA for second harmonic heating is 63%,while the SPA for fundamental heating is 13%.Additionally,the optimal injection frequencies are 23 MHz at 0.9 T and 31 MHz at 1.2 T.The wave vector of the antenna parallel to the magnetic field,with a value of k_‖=7.5 m^(-1),falls within the optimal heating region.Simulations reveal that the ICRF heating system can play an important role in the ion heating of the EXL-50U.

Initial testing of ohmic heating through double flux swing during electron cyclotron start-up in the QUEST spherical tokamak

A power-supply system was developed for Ohmic heating(OH)to double×10^(18)the amount of change magnetic flux in the primary central solenoid(CS)on the QUEST spherical tokamak.Two power supplies are connected with stacks of insulated-gate bipolar transistors,and sequentially operated to generate positive and negative CS currents.This bipolar power-supply system is controlled via a field-programmable gate array,which guarantees the safety of the entire system operation.The new OH system,assisted by electron cyclotron heating,enables the stable generation of plasma currents exceeding 100 k A.Moreover,the achieved electron density over the wide range in the major radial direction exceeds the cut-off density for one of the highpower microwave sources in QUEST.This strategy yields target plasmas for future experiments with the electron Bernstein wave.

Design and commissioning of Brav measurement system for SC200 superconducting cyclotron

The SC200 proton therapy superconducting cyclotron was developed by ASIPP (Hefei, China) and JINR (Dubna, Russia). A measurement system was designed to assess the average radial component of the magnetic field (Brav) with 15 search coils in the median plane. The winding differences of the search coils affect the measurement accuracy of the Brav. Based on the electromagnetic induction principle, to measure the Brav accurately, this paper focuses on the design and commissioning of the Brav measurement system. The preliminary results confirm that the system design is reasonable and suitable. After testing the search coil at different speeds, the optimal speed was determined as 2.5 mm/s. The relative error was approximately 0.1% under the maximum radial component of the magnetic field Br of 7 G. The measurement precision was up to 1.0×10^-3, which can provide the required measurement tolerance of 3–7 G for Br in the median plane. The commissioning of the Brav measurement system is an important step for Br measurement. It can check and adjust the asymmetry of the superconducting coils (SCs).

Effect of cyclotron resonance on ‘hot’ dispersion in a staggered double metallic grating sheet beam travelling wave tube

Based on the beam wave synchronous interaction in transverse and longitudinal directions at the same time and starting from Maxwell’s equation and linear Vlasov equation, the beam–wave interaction ‘hot’ dispersion equation considering both cyclotron resonance and Cherenkov resonance in a staggered double metallic grating traveling wave tube is deduced.Through the reasonable selection for geometric and electrical parameters, the numerical calculation and analysis of the ‘hot’ dispersion equation shows that the beam–wave interaction gain and frequency band with the cyclotron resonance enhancement effect are higher than those with only Cherenkov resonance radiation.

Upstream proton cyclotron waves: occurrence and amplitude dependence on IMF cone angle at Mars——from MAVEN observations

Proton cyclotron waves(PCWs)can be generated by ion pickup of Martian exospheric particles in the solar wind.The solar wind ion pickup process is highly dependent on the“IMF cone angle”—the angle between the solar wind velocity and the interplanetary magnetic field(IMF),which also plays an important role in the generation of PCWs.Using data from 2.15 Martian years of magnetic field measurements collected by the Mars Atmosphere and Volatile Evolution(MAVEN)mission,we have identified 3307 upstream PCW events.Their event number distribution decreases exponentially with their duration.A statistical investigation of the effects of IMF cone angle on the amplitudes and occurrence rates of PCWs reveals a slight tendency of PCWs’amplitudes to decrease with increasing IMF cone angle.The relationship between the amplitude and IMF cone angle is weak,with a correlation coefficient r=–0.3.We also investigated the influence of IMF cone angle on the occurrence rate of PCWs and found that their occurrence rate is particularly high for intermediate IMF cone angles(~18°–42°)even though highly oblique IMF orientation occurs most frequently in the upstream region of the Martian bow shock.We also conclude that these variabilities are not artefacts of temporal coverage biases in MAVEN sampling.Our results demonstrate that whereas IMF cone angle strongly influences the occurrence of PCWs,IMF cone angle may also weakly modulate their amplitudes in the upstream region of Mars.

Cyclotron Resonance of Free Magnetopolaron in Quantum Well Wires

The cyclotron resonance of magnetopolaron in quantum well wires (QWWs) have been studied withthe use of variational solutions to the effective mass equation. The results show that both the abso-lute value of the electron-phonon interaction energy and the cyclotron resonance frequency de-crease with the increase of the sizes of QWWs, and also that the cyclotron resonance frequency in-creases with the external magnetic field.

Design and testing of an internal hot-cathode-type PIG ion source for superconducting cyclotron

The superconducting cyclotron SC200 is intended to generate a 200 MeV, 400 nA proton beam for future particle therapy. The internal hot-cathode-type Penning ionization gauge (PIG) ion source for the SC200 is designed for the generation of hydrogen ions. A brief description of the design of ion source and test bench, which are used in SC200, is given in this paper. The ion source has been verified on the test bench, and the results indicated that the designed ion source meets the expected requirements. The lifetime of the filament exceeded 100 h in the test. In addition, the extraction voltage and the gas flow that influence the extracted ion current intensity have been tested in the experiment.

Correlation ofⅢ/Ⅴsemiconductor etch results with physical parameters of high-density reactive plasmas excited by electron cyclotron resonance

Reactive ion etching is the interaction of reactive plasmas with surfaces. To obtain a detailed understanding of this process, significant properties of reactive composite low-pressure plasmas driven by electron cyclotron resonance(ECR) were investigated and compared with the radial uniformity of the etch rate. The determination of the electronic properties of chlorine-and hydrogen-containing plasmas enabled the understanding of the pressure-dependent behavior of the plasma density and provided better insights into the electronic parameters of reactive etch gases. From the electrical evaluation of I(V) characteristics obtained using a Langmuir probe,plasmas of different compositions were investigated. The standard method of Druyvesteyn to derive the electron energy distribution functions by the second derivative of the I(V)characteristics was replaced by a mathematical model which has been evolved to be more robust against noise, mainly, because the first derivative of the I(V) characteristics is used. Special attention was given to the power of the energy dependence in the exponent. In particular, for plasmas that are generated by ECR with EM modes, the existence of Maxwellian distribution functions is not to be taken as a self-evident fact, but the bi-Maxwellian distribution was proven for Ar-and Kr-stabilized plasmas. In addition to the electron temperature, the global uniform discharge model has been shown to be useful for calculating the neutral gas temperature. To what extent the invasive method of using a Langmuir probe could be replaced with the noninvasive optical method of emission spectroscopy, particularly actinometry, was investigated,and the resulting data exhibited the same relative behavior as the Langmuir data. The correlation with etchrate data reveals the large chemical part of the removal process—most striking when the data is compared with etching in pure argon. Although the relative amount of the radial variation of plasma density and etch rate is approximately ?5%, the etch rate shows a slightly concave shape in contrast to the plasma density.

STUDY OF GYROMONOTRON WITH A COMBINING PERIODIC MAGNETIC FIELD AND A COAXIAL CYCLOTRON ELECTRON BEAM

On the basis of a work of Wu Jianqiang et al.(1987),by making use of the linear kinetictheory,the gyromonotron with a combining periodic magnetic field and a coaxial cyclotron electron beam hasbeen analysed in detail.And the formulas of the electron beam to wave interaction power,frequency shift andstarting current,etc.have been derived.

CHARACTERISTICS OF CYCLOTRON AUTORESONANCE MASER WITH A LARGE-ORBIT ELECTRON RING IN A PARTIALLY DIELECTRIC-LOADED WAVEGUIDE

The cyclotron autoresonace masers with a large-orbit electron ring in a dielectric-loaded waveguide have been analyzed.The stability properties are investigated self-consistentlyon the basis of the linearized Vlasov-Maxwell equations.The numerical results show that thedielectric liner can greatly reduce the energy of the electron beam,and a novel effective radiationdevice with low electron beam energy in the millimeter and submillimeter wave region have beenproposed.

COMPARISON BETWEEN FEL AND CYCLOTRON RADIATION

In general,in free electron lasers there are two kinds of stimulated radiations:FELradiation and cyclotron radiation.This paper chows theoretically that if the initial transversevelocity of electron beam is large and the selected parameters for FEL are not suitable,thecyclotron radiation will be dominant,especially when the energy of electron beam is low.But thecyclotron radiation does not have double Doppler frequency upshift effect,its frequency is limitedby axial megnetic field,and when the energy of electron beam is high,the cyclotron radiationfrequency will be much lower than FEL radiation frequency.Therefore,in FEL experimentshow to distinguish these two kinds of radiations and to suppress the cyclotron radiation are veryimportant.

Evaluation of electron cyclotron current drive performance for CFETR

A number of simulations of electron cyclotron current drive (ECCD) have been carried out for the China Fusion Engineering Test Reactor (CFETR) using the C3PO/LUKE code to investigate the performance and optimize schemes of power injection for the design of the launcher.The operation ranges of the toroidal field,cutoff density,and resonance layer location are given at different source frequencies in CFETR phases Ⅰ and Ⅱ.A comparison of ECCD performance between the horizontal and top port launch is presented.ECCD efficiency (γEC) estimated for CFETR phase Ⅰ is γEC =0.21 for top port launch and γEC =0.20 for horizontal port launch.The ECCD efficiency and second-harmonic absorption is calculated at different wave frequencies (from 170 to 230 GHz) in CFETR phase Ⅱ.It is found that the highest driven efficiency is obtained at 210 GHz with the toroidal field of 6.5 T,and the second-harmonic absorption increases rapidly with the increase of frequency.

Train probe for beam diagnostics of the SC200 superconducting cyclotron

The SC200 proton therapy system commissioned by the Hefei CAS Ion Medical and Technical Devices Co.,Ltd.(HFCIM;Hefei,China)and the Joint Institute for Nuclear Research(JINR;Dubna,Russia)has made significant progress.A main radial beam diagnostic system(MRBDS)equipped with a new type of train probe was developed to satisfy the requirements of beam diagnosis.In this paper,the detailed design of the mechanical structure and electronics system of the MRBDS is presented.The electronics system,which includes hardware and software components,was tested and calibrated.The results show that measurement errors can be significantly reduced by the designed calibration procedures.The repeatability of the mechanical structure was also verified,and the experimental results indicate that the unidirectional repeatability of the positioning is better than 0.3 mm.Finally,the MRBDS was used to measure the phase lag of the particles in the beam,and the results showed a high degree of agreement with theoretical calculations,which proved the applicability and high efficiency of the MRBDS.

Forward-wave enhanced radiation in the terahertz electron cyclotron maser

Based on the principle of electron cyclotron maser(ECM),gyrotrons are among the most promising devices to generate powerful coherent terahertz(THz)radiation and play a vital role in numerous advanced THz applications.Unfortunately,THz ECM systems using a conventional high-Q cavity were theoretically and experimentally demonstrated to suffer from strong ohmic losses,and,accordingly,the wave output efficiency was significantly reduced.A scheme to alleviate such a challenging problem is systematically investigated in this paper.The traveling-wave operation concept is employed in a 1-THz third harmonic gyrotron oscillator,which strengthens electron-wave interaction efficiency and reduces the ohmic dissipation,simultaneously.A lossy belt is added in the interaction circuit to stably constitute the traveling-wave interaction,and a down-tapered magnetic field is employed to further amplify the forward-wave(FW)component.The results demonstrate that the proportion of ohmic losses is nearly halved,and output efficiency is nearly doubled,which is promising for further advancement of high-power continuous-wave operation of the ECM-based devices.

Rapid and sensitive analysis of trace b-blockers by magnetic solidphase extraction coupled with Fourier transform ion cyclotron resonance mass spectrometry

A rapid and sensitive method for analyzing trace b-blockers in complex biological samples,which involved magnetic solid-phase extraction(MSPE)coupled with Fourier transform ion cyclotron resonance mass spectrometry(FTICR-MS),was developed.Novel nanosilver-functionalized magnetic nanoparticles with an interlayer of poly(3,4-dihydroxyphenylalanine)(polyDOPA@Ag-MNPs)were synthesized and used as MSPE adsorbents to extract trace b-blockers from biological samples.After extraction,the analytes loaded on the polyDOPA@Ag-MNPs were desorbed using an organic solvent and analyzed by FTICR-MS.The method was rapid and sensitive,with a total detection procedure of less than 10 min as well as limits of detection and quantification in the ranges of 3.5-6.8 pg/mL and 11.7-22.8 pg/mL,respectively.The accuracy of the method was also desirable,with recoveries ranging from 80.9%to 91.0%following the detection of analytes in human blood samples.All the experimental results demonstrated that the developed MSPE-FTICR-MS method was suitable for the rapid and sensitive analysis of trace b-blockers in complex biological samples.

Neoclassical tearing mode stabilization by electron cyclotron current drive for HL-2M tokamak

Investigation of neoclassical tearing mode and its suppression by electron cyclotron current drive(ECCD)has been carried out in HL-2 M tokamak.The current driving capability of the electron cyclotron wave is evaluated.It is found that the deposition location can be effectively controlled by changing the poloidal angle.The validation of electron cyclotron wave heating and current driving has been demonstrated for the upper launcher port.We show that 3.0 MW and2.5 MW modulated ECCD can completely stabilize(2,1)and(3,2)NTMs,respectively.The non-modulated ECCD,radial misalignment as well as current profile broadening have deleterious effect on the NTM stabilization.The time required for suppression of(3,2)mode is shorter than that required for the suppression of(2,1)mode.Moreover,the time needed for complete stabilization at different initial island width has been quantitatively presented and analyzed.

Study of the fast electron behavior in electron cyclotron current driven plasma on J-TEXT

In J-TEXT tokamak,fast electron bremsstrahlung diagnostic with 9 chords equipped with multichannel analyzer enables detailed studies of the generation and transport of fast electrons.The spatial profiles and energy spectrum of the fast electrons have been measured in two ECCD cases with either on-axis or off-axis injection,and the profiles processed by Abel-inversion are consistent with the calculated power deposition locations.Moreover,it is observed that the energy of fast electrons increases rapidly after turning off the ECCD,which may be attributed to the acceleration by the recovered loop voltage at low electron density.

Relativistic effect on synergy of electron cyclotron and lower hybrid waves on EAST

In recent experiments on EAST,the electron temperature at the center can be raised to 9.7 ke V by injecting electron cyclotron(EC)and lower hybrid(LH)waves simultaneously.With such strong core electron heating,the relativistic effect could play an important role in the interactions between the plasma and waves.In order to explore the relativistic effect on synergy between the EC and LH waves on EAST,ray-tracing/Fokker-Planck simulations are conducted to investigate electron heating for a typical discharge with a center electron temperature of 9.7 ke V.It is found that the relativistic effect can cause the EC wave to deposit its power deeper in the plasma core,where the synergy between the EC and LH waves occurs and enhances the absorption of the LH waves.As a result,a high center electron temperature can be achieved.

On the heating mechanism of electron cyclotron resonance thruster immerged in a non-uniform magnetic field

To study the heating mechanism of electron cyclotron resonance thruster(ECRT)immersed in a non-uniform magnetic field,experiments and simulations are performed based on an electron cyclotron resonance plasma source at ASIPP.It is found that the first harmonic of electron cyclotron resonance is essential for plasma ignition at high magnetic field(0.0875 T),while the plasma can sustain without the first and second harmonics of electron cyclotron resonance at low magnetic field(till 0.0170 T).Evidence of radial hollow density profile indicates that upper hybrid resonance,which has strong edge heating effect,is the heating mechanism of low-field ECRT.The heating mode transition from electron cyclotron resonance to upper hybrid resonance is also revealed.Interestingly,the evolutions of electron temperature and electron density with input power experience a‘delayed’jump,which may be correlated with the different power levels required for cyclotron and ionization.Moreover,when the field strength decreased,the variation of electron density behaves in an opposite trend with that of electron temperature,implying a possible competition of power deposition between them.The present work is of great interest for understanding the plasma discharge in ECRT especially immersed in a non-uniform magnetic field,and designing efficient ECRT using low magnetic field for economic space applications.