GHz Electron Cyclotron Resonance Research Articles

Development of a 50kV hydrogen-helium mixed ion beam implanter.

Ion implanters have extensively been employed to simulate the irradiation effects of neutrons on relevant nuclear materials. In this study, a 50kV hydrogen-helium mixed ion beam implanter was developed to generate H2+ and He+ ion beams, with a beam current of 20 µA, while keeping the impurity ion content below 2%. The ions are generated by an antenna-type 2.45GHz electron cyclotron resonance ion source, and the hydrogen-to-helium ion beam ratio was controlled using two gas mass flow controllers to ensure long time stability of the beam current. As a result, the H2+/He+ ratio, beam size, and homogeneity of the beam spot can be maintained at a stable level. The beam line consisted of four Wien filters, a movable dual-slit plate, and an accelerator tube. The experimental results demonstrated successful transport of more than 20 µA of H2+ and He+ ion beams onto the target, with a beam axis deviation of less than 0.5mm.

New progress of a 2.45 GHz ECR ion source for carbon positive ion mass spectrometry

Positive ion mass spectrometry (PIMS) is a trace element measurement technique based on positive and negative ion conversion, which is contrary to conventional accelerator mass spectrometry (AMS). To precisely measure 14C, interference of molecular isobars (such as 12CH2 and 13CH) need to be suppressed in the ion source by generating multi-charged carbon ions, such as C2+ or C3+. At present, a high-frequency (> 7 GHz) electron cyclotron resonance (ECR) ion source is commonly used to generate C2+ or C3+ ions through CO2 discharge. At Peking University (PKU), we developed a compact permanent magnet 2.45 GHz ECR ion source attempting to produce C2+ ions. In this work, systematical experiments are performed to further improve the performance of the ion source for the application in PIMS. The results show that it can deliver 1.0 emA C2+ ions with an alumina ceramic liner, and its C consumption is about 10∼20 ng/s. Meanwhile, it is also proved that a certain proportion of He and CO2 mixing can improve the production efficiency of C2+ ions, and the consumption of C can be lower. Furthermore, results confirm that this ECR ion source with alumina liner has a lower memory effect, and the influence of original CO2 discharge can be eliminated by Ar plasma cleaning for several minutes. The experimental results show that the 2.45 GHz ECR ion source has the potential to be used in the PIMS system.

Study of the Characteristics of a 2.45 GHz Electron Cyclotron Resonance Ion Source

Study of the Characteristics of a 2.45 GHz Electron Cyclotron Resonance Ion Source

Short-pulse frequency stabilization of a MW-class ECRH gyrotron at W7-X for CTS diagnostic

At the Wendelstein 7-X stellarator, a 174 GHz Collective Thomson Scattering (CTS) diagnostic will be implemented. One of the 140 GHz Electron Cyclotron Resonance Heating (ECRH) gyrotrons will be operated at around 174 GHz in a higher cavity mode, using it as source for the CTS mm-wave probing beam. To prevent any damage to the CTS receiver, a notch filter cuts out the high-power gyrotron signal at the entrance of the receiver. The bandwidth of the gyrotron signal determines the notch filter bandwidth. First proof-of-principle experiments on frequency stabilization were conducted on W7-X ECRH gyrotrons employing Phase-Locked Loop techniques. The gyrotron output frequency was controlled with the accelerating voltage, which is applied between the anode and cathode of the gyrotron diode-type Magnetron Injection Gun. Frequency stabilization experiments with 10 ms pulses were conducted at the gyrotron nominal frequency of 140 GHz as well as at 174 GHz. It is concluded that the gyrotron frequency could be stabilized for at least 3 ms at 140 GHz and 8 ms at 174 GHz. In the frequency spectrum, a clear main peak of the gyrotron frequency at 140 GHz with a full -15 dB linewidth of below 500 Hz was achieved.

A newly constructed Linear Experimental Advanced Device LEAD

The Linear Experimental Advanced Device (LEAD) has been constructed for comprehensive studies on plasma turbulence, plasma-material interaction and new techniques for tokamaks at Southwestern Institute of Physics (SWIP). The vacuum vessel of this linear device is 3055 mm long. It consists of three parts, i.e. the source chamber, the linear magnetized confinement chamber and the plasma-material interaction (PMI) chamber. Kinds of plasma sources, including radio-frequency (RF) sources and a hot cathode source, have been developed to produce steady-state plasma. Wave-mode helicon plasmas can be excited by a large-size four-ring-antenna RF source when the input power is higher than 180 W. The typical electron density is higher than 1019/m3. Transfer from distinct narrowband drift waves to broadband turbulence is observed by means of adjusting the axial magnetic field, which makes LEAD a suitable device to investigate plasma turbulence. Auxiliary heating systems, including a 2.45 GHz Electron Cyclotron Resonance and an ion heating source, and a 1.5 MV ion accelerator are to be installed on LEAD. It promises a particle flow of over 1023/m2s and a heat load of several MW/m2, which makes LEAD a suitable platform for not only fundamental plasma physics but also PMI research.

Microstructural Characteristics of ECR Plasma Etched and Heat Treated Commercial Copper Foil

AbstractThe structural quality of the catalytic transition metal substrate plays a critical role in pristine graphene synthesis by chemical vapor deposition. In this work, the microstructural parameters of commercial copper foils are investigated in lieu of conventional laboratory grade crystalline copper foils. Initially, the commercial copper foils are simultaneously plasma etched and heat treated for a period of 30, 45 min, and 1 h respectively at two elevated temperature levels of 823 and 923 K under the exposure of hydrogen plasma. The experiments are carried out in a 2.45 GHz Electron Cyclotron Resonance (ECR) Plasma Enhanced Chemical Vapor Deposition (PE‐CVD) reactor, at an operating pressure of 5 × 10−2 mbar. X‐ray diffraction (XRD) results are plotted and analyzed by Williamson–Hall (W–H) method to determine microstructural parameters, e.g., micro‐strain, stress, average domain size, and energy density associated to the processed copper foils.

Plasma simulation of hot-surface-microwave hybrid ion sources

To generate high-current hard-to-ionize elements such as B+, a hybrid ion source that combines electron cyclotron resonance and thermal surface ionization, which is called a high-temperature surface microwave source (HSMS), is under development. A high-temperature hot surface (2000°) and microwave heating are the essential components of an HSMS to produce high-energy electrons for B+ generation. A helical tungsten filament is used in the HSMS source to obtain a high temperature and provide an axial configuration with a magnetic field of approximately 87.5 mT for the 2.45 GHz electron cyclotron resonance (ECR). The effects of high-temperature surface ionization and ECR ionization were separately evaluated. The magnetic field configuration, microwave power, and air pressure have been studied through this plasma model. A 30% B+ improvement was achieved.

A few ECRIS developments at LBNL

In addition to the ongoing investigation of bremsstrahlung radiation produced by energetic electrons in the superconducting Electron Cyclotron Resonance (ECR) ion source VENUS, the LBNL ion source group has pursued several other research topics since 2015 to explore potential advancements of ECR ion sources. Three of these activities are investigations into the benefits of non-cylindrical plasma chambers, the development of new high-temperature ovens that will efficiently produce the intense, metallic ion beams necessary for super heavy element production at the 88-Inch Cyclotron facility, and the finalization of the conceptual and engineering design of the superconducting NbTi magnet structure for the 4th generation, 45 GHz ECR ion source MARS-D. This article summarizes and briefly discusses the highlights of these ECRIS developments.

Influence of axial mirror ratios on the kinetic instability threshold in electron cyclotron resonance ion source plasma

Electron Cyclotron Resonance (ECR) ion source plasmas are prone to kinetic instabilities. The onset of the instabilities manifests as emission of microwaves, bursts of electrons expelled from the plasma volume, and the collapse of the extracted highly charged ion (HCI) currents. Consequently, the instabilities limit the HCI performance of ECR ion sources by limiting the parameter space available for ion source optimization. Previous studies have shown that the transition from stable to unstable plasma regime is strongly influenced by the magnetic field structure, especially the minimum field value inside the magnetic trap (Bmin). This work focuses to study the role of the magnetic confinement on the onset of the kinetic instabilities by probing the influence of the injection and extraction mirror field variation on the instability threshold. The experiments have been performed with a room-temperature 14.5 GHz ECR ion source with an axially movable middle coil that provides flexible control over the axial field profile and especially the Bmin, which was used to quantify the variation in the instability threshold. The experimental results show that variation of the extraction field Bext, which defines the weakest magnetic mirror, correlates systematically with the variation of the instability threshold; decreasing the Bext allows higher threshold Bmin. The result demonstrates the importance of electron confinement and losses on the plasma stability. The connection between the weakest mirror field and the onset of instabilities is discussed taking into account the variation of magnetic field gradient and resonance plasma volume.

Innovative Analytical Method for X-ray Imaging and Space-Resolved Spectroscopy of ECR Plasmas

At the Italian National Institute for Nuclear Physics-Southern National Laboratory (INFN-LNS), and in collaboration with the ATOMKI laboratories, an innovative multi-diagnostic system with advanced analytical methods has been designed and implemented. This is based on several detectors and techniques (Optical Emission Spectroscopy, RF systems, interfero-polarimetry, X-ray detectors), and here we focus on high-resolution, spatially resolved X-ray spectroscopy, performed by means of a X-ray pin-hole camera setup operating in the 0.5–20 keV energy domain. The diagnostic system was installed at a 14 GHz Electron Cyclotron Resonance (ECR) ion source (ATOMKI, Debrecen), enabling high-precision, X-ray, spectrally resolved imaging of ECR plasmas heated by hundreds of Watts. The achieved spatial and energy resolutions were 0.5 mm and 300 eV at 8 keV, respectively. Here, we present the innovative analysis algorithm that we properly developed to obtain Single Photon-Counted (SPhC) images providing the local plasma-emitted spectrum in a High-Dynamic-Range (HDR) mode, by distinguishing fluorescence lines of the materials of the plasma chamber (Ti, Ta) from plasma (Ar). This method allows for a quantitative characterization of warm electrons population in the plasma (and its 2D distribution), which are the most important for ionization, and to estimate local plasma density and spectral temperatures. The developed post-processing analysis is also able to remove the readout noise that is often observable at very low exposure times (msec). The setup is now being updated, including fast shutters and trigger systems to allow simultaneous space and time-resolved plasma spectroscopy during transients, stable and turbulent regimes.

Microwave preionization and electron cyclotron resonance plasma current startup in the EXL-50 spherical tokamak

Preionization has been widely employed to create initial plasma and help the toroidal plasma current formation. This research focuses on implementing a simple, economical and practical electron cyclotron resonance (ECR) preionization technique on the newly constructed EXL-50 spherical tokamak, and evaluating the effectiveness on improving the plasma current startup. Two types ECR microwave preionization experiments for the plasma initialization without the central solenoid are reported: (1) 2.45 GHz microwave preionization and current startup with 2.45 GHz ECR source; (2) 2.45 GHz microwave preionization and current startup with 28 GHz ECR source. Application of the 2.45 GHz ECR microwave preionization to the experiments has contributed to (1) getting rid of the plasma breakdown delay; (2) the significant improvement of the discharge quality: the discharge is much longer and more stable while the driven plasma current is larger, compared to the discharge without preionization.

Designing and commissioning pre-analysis system for intense D-D/D-T neutron generator

An intense accelerator-based D-D/D-T neutron generator, with neutron yields of 6 × 1010 n/s due to the D-D reaction and 6 × 1012 n/s due to the D-T reaction, is being developed at Lanzhou University in China. The 2.45 GHz electron cyclotron resonance (ECR) ion source and the pre-analysis system, as the front injector for the accelerator tube of the neutron generator, are designed to provide a 35 mA deuterium beam for neutron production and a 50 mA proton beam for commissioning. The pre-analysis system consists of a solenoid, a steering magnet, a vacuum chamber, a dipole magnet, three quadrupole magnets, a beam dump, and a Faraday cup. The ion source and pre-analysis system were completed a trial operation, and the intensity of the proton beam measured at the end of the pre-analysis system was higher than 50 mA when the hydrogen ion beam current extracted from the ECR ion source was greater than 70 mA.

On abnormal behaviors of ion beam extracted from electron cyclotron resonance ion thruster driven by rod antenna in cross magnetic field

In a 2.45 GHz electron cyclotron resonance (ECR) ion thruster powered with rod antenna under a cross magnetic field, abnormal behaviours such as sudden drop of ion beam current (I b) and larger increasing-rate of I b in the high microwave power (P w) discharges at high gas flow rates were observed. A differential method was proposed to reveal the changes in the radial profiles of gray values extracted from the end-view discharge images. The increasing-rate of I b with respect to P w was used to evaluate efficiencies of ion production and transport. Analyses indicate that discharges are dominantly sustained by ordinary wave via electron heating in the electron plasma resonance layer that can shift along the rod-antenna, and extraordinary wave can only ignite a discharge in the ECR layer in the low gas flow rate regime. In terms of the confinement region defined by the magnetic field lines intercepting with the screen grid, the confinement region of the optimized 2.45 GHz cross magnetic field takes the shape of hourglass, enabling the high increasing-rate of I b with respect to P w in high power discharges at high gas flow rates. Correlated with the accompanied bright boundary layer appearing in the differentiated image, the sudden drop of I b in the low gas flow rate regime is attributed to the discharge ignited by the enhanced extraordinary wave in the ECR layer neighbouring the narrowest confinement region, where the produced ions can promptly enter the loss region.

Characteristics of microwave ECR ion thruster powered with plate antenna in cross-magnetic field: Standing wave, skin effect, and mode transition

In a 2.45 GHz electron cyclotron resonance xenon ion source powered with circular plate-antenna, a rapid evolution of radial plasma-profile with discharge power in a region below 35 W and the abrupt jump of ion beam current accompanied by sudden radial-expansion of discharge glow were observed. Based on analyses about quantified glow images captured from the end-view of the discharge chamber and the ion beam current against the discharge power, the fast evolution of the radial plasma-profile is attributed to the counteraction of standing wave and the skin effect, the coincidence of enhanced microwave absorption in the electron plasma resonance layer, and the transverse magnetic confinement of electrons. The jump of ion beam current and the sudden radial-expansion of discharge glow are confirmed to be originated from the extraordinary-wave discharge at the electron cyclotron resonance layer beyond the plate antenna when the skin effect is dominant.

A global model of 2.45 GHz ECR ion sources for high intensity H+, H2+ and H3+ beams

The 2.45 GHz electron cyclotron resonance ion source (ECRIS) is recognized as one of the most efficient devices for the production of high intensity H+, H2+ and H3+ beams. To elucidate the mechanism of electron cyclotron heated (ECH) hydrogen plasma, a global model based on the energy and particle balance equations is developed at Peking University (PKU). This model is applied to a permanent magnet ECRIS named PMECR II at PKU to study the dependences of the H+, H2+, and H3+ ion fractions of the extracted beam on the gas pressure, microwave power, wall material and chamber diameter. The calculated results obtained with the global model are in good agreement with the experimental results. Moreover, a more compact 2.45 GHz ECR ion source is designed and operated under the guidance of the model for the generation of H+, H2+ and H3+ ion dominated beams. Beams with H+, H2+ and H3+ ion fractions greater than 80% were produced under optimized gas pressure and microwave power with this new ECR source.

Proton beam intensity and proton fraction measurement of the 2.45 GHz ECR ion source

In this paper we report results of experimental studies of the dependence of the proton beam intensity and proton fraction of the 2.45 GHz electron cyclotron resonance (ECR) ion source on the operational parameters such as extraction voltage, microwave window, impedance matching, gas flow, microwave power, pipeline gas pressure, plasma chamber size, and magnetic field. The DC hydrogen ion beams are measured and analyzed on the bench of ion source and pre-analysis system of the Lanzhou university high intensity neutron generator ZF400. Our results show that a higher proton beam intensity and fraction can be obtained with a microwave window made up of 2 mm AlN. The proton beam intensity and fraction strongly depend on the three-stub tuner that controls the impedance matching between microwave and plasma. We also observe notable beam loss under the lower vacuum pressure condition.

Conceptual Design of the High Voltage Platform by Using the Aluminum Profile for Considering Dielectric Breakdown for the RAON ECRIS

We designed and manufactured a 28-GHz electron cyclotron resonance ion source (ECRIS) to obtain a steady heavy-ion beam. The ECRIS consists of various equipment for beam extraction and transmission, such as superconducting magnet, electro static quadrupole (ESQ), pair solenoid magnet, dipole magnet and etc. For the support frame of ECRIS, it is necessary to use a material with high strength must be used for stable support, and it should be easy to assemble for installation. In addition, dielectric breakdown should not occur at a high voltage applied when the beam is extracted. The manufactured frame is currently made of steel pipe, which has excellent in strength and dielectric characteristic. However assembly and installation is not convenient due to weight, corrosion, welding, etc. In order to overcome this problem, we redesigned a new frame using an aluminum profile. the advantages of the aluminum profile are easy acquisition, low cost, high strength, and easy assembly and installation. However, dielectric breakdown may occur at the edge of the aluminum profile. Therefore, a high-voltage electricfield analysis is required to design the support frame of the ECRIS. This paper, reports on the design of a high voltage support frame through an electricfield analysis using a finite element method (FEM) and a breakdown experiment.

A miniaturized ECR plasma flood gun for wafer charge neutralization.

In modern ion implanters, a plasma flood gun (PFG) is used to neutralize wafer charge during the doping process, preventing the breakdown of floating wafers caused by the space charge accumulation. Typically, there are two kinds of PFGs, namely, dc arc discharge with filament and RF discharge. As a PFG, the filament one has limited lifetime and cannot avoid metallic contamination because of the thermal emitting filament. RF discharge PFG has been developed to solve these problems, including prolonging the source lifetime and avoiding metal pollution. Recently, a 2.45 GHz electron cyclotron resonance (ECR) ion source is also regarded as a potential choice for PFG. However, the dimension of the 2.45 GHz ECR source system including the size of the source itself and its meter's length RF subsidiary limits its application within an ion implanter. At Peking University, a miniaturized 2.45 GHz permanent magnet electron cyclotron resonance plasma flood gun with a coaxial RF transmission line has been built and tested. The dimensions of the ECR source body are Φ60 mm × Φ88 mm with a Φ30 mm × Φ40 mm plasma chamber. Its RF transmission line consists of a 200 W microwave generator, a 30 cm coaxial line, a 7 cm coaxial-to-waveguide transducer, and a microwave window that also serves as a vacuum seal. In continuous wave experiments, the electron extraction currents can be as high as 8.8 mA at an input RF power of 22 W with argon gas. The gas flow is less than 1.0 SCCM for this test.

An electromagnetic separation system for the enrichment of 39Ar.

An isotope enrichment system for 39Ar has been developed at the Institute of Modern Physics, which is designed to increase the abundance of 39Ar in the incident sample gas. With intense Ar+ beams produced by a 2.45 GHz electron cyclotron resonance ion source and a high mass resolution spectrometer system, Ar isotopes are evidently separated on the target plane and selectively collected by an Al target. The separated Ar isotopes have been identified on the target plane, which is consistent with the simulations. According to the recent cross-checked results with atom trap trace analysis, a high enrichment factor of 39Ar has been successfully achieved. This paper will present the design and test results of this system.

A 2.45 GHz microwave ion source for carbon positive-ion mass spectrometry

Carbon positive-ion mass spectrometry (C-PIMS) is a two stage mass spectrometer by producing high charge state carbon ions (C2+/C3+) directly in the ion source to eliminate molecular interferences and by converting the beam (C2+/C3+) to C− ions in a charge exchange cell to eliminate 14N interference. It has been proven that C-PIMS is an effective method for the detection of radiocarbon at low levels. This article will focus on the multiply charged carbon ion generation. Based on the fact that a C-PIMS system is usually equipped with high frequency electron cyclotron resonance (ECR) ion sources. It is significant to investigate if the simple and low-cost 2.45 GHz ECR ion source is an optional choice for the C-PIMS. At Peking University (PKU), a 2.45 GHz microwave ion source with minimum-B magnetic field configuration is designed for the production of intense C2+ beam. Preliminary experiments have proved that the 2.45 GHz microwave ion source can produce up to 40 μA@40 keV C2+ beam. In addition, it was found that argon could increase the decomposition efficiency of CO2, which can eliminate CO2+ ions of the extracted beam.