Microwave Ion Source Research Articles

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.

Overview of high intensity ion source development in the past 20 years at IMP.

Ion source development over the last 20 years at the IMP is reviewed. For versatile purposes, several types of ion sources have been involved in the research and development work at the IMP, i.e., the highly charged ECR (Electron Cyclotron Resonance) ion source, intense microwave ion source or the 2.45 GHz intense beam ECR ion source, and laser ion source (LIS). In the development of ECR ion sources, SECRAL (Superconducting ECR ion source with Advanced design in Lanzhou), Lanzhou ECR ion source, and Lanzhou all permanent magnet ECR ion source series have been made, which can cover the operation microwave frequency range of 10-28 GHz. The LIS with an Nd:YAG laser with a maximum output energy of 8 J in 8 ns pulse duration has been developed for very intense short pulse ion beams from solid materials such as C, Ti, Ni, Ag, and so on. Microwave ion sources have been built to produce intense pulsed or direct current beams from several mA to 100 mA for either high intensity accelerators or applications. This paper will give an overview of the high intensity ion source development at the IMP, especially on the recent progress and new results, such as the status of the fourth generation ECR ion source (first fourth generation ECR ion source), the production of recorded highly charged ion beams with SECRAL sources, key technology research studies, and so on.

Status of high intensity proton injector for Facility for Antiproton and Ion Research.

The high intensity proton injector for the international accelerator Facility for Antiproton and Ion Research located at GSI-Darmstadt in Germany consists of a pulsed 2.45 GHz microwave ion source, a Low Energy Beam Transport (LEBT), and an electrostatic chopper matching the proton beam to the radio frequency quadrupole. The ion source is based on electron cyclotron resonance plasma production and it has to provide a proton beam at 95 keV energy and up to 100 mA current. The LEBT system with two short solenoids each including two magnetic steerers will transport the proton beam into the compact proton linac, accelerating it to the energy of 68 MeV and serving as the injector of the upgraded heavy ion synchrotron (SIS18). This paper describes the commissioning of the proton injector including beam characterization measurements that have been done at CEA/Saclay in France and is currently at the final commissioning stage.

Study on beam current extraction and magnetic circuit design of microwave negative ion source for sealed neutron tube

A new structure of microwave ion source was designed to improve the ion beam intensity of sealed neutron tube, and the beam extraction simulation of microwave negative ion source was carried out. In this paper, we studied the magnetic field of microwave ion source and designed a multiple magnetic pole configurations system by magnetic field trap the fast electrons to improve the plasma density in the ion source chamber. Compared with the traditional double magnetic ring, the microwave ion source with multiple pole magnetic structure is stronger in limiting ions, thus generating a higher negative ion current. Simultaneously the multiple magnetic pole configurations design has a certain inhibitory effect on electrons. To improve the quality of the extraction beam, a magnetic filter with an external magnet and a multihole filtration system were set up, which can effectively filter the electrons in the extraction beam. The multihole design improves the uniformity of thermal load of the target. Moreover, multihole extraction system can effectively reduce the interference of the target on the ion source and has good stability. The kind microwave ion source could be applied to make sealed neutron tubes with good properties.

Physical design and evaluation of a high-intensity accelerator-based D-D/D-T fusion neutron source

A high-intensity accelerator-based D-D/D-T fusion neutron source (ZF-400) with a thick adsorption target is designed with an intensity of $ 10^{13}$ n/s. A high-current microwave ion source is used to produce a large current deuteron beam, and neutrons are generated by irradiating the deuteron beam on a deuterium-adsorption target or tritium-adsorption target. According to the particle-in-cell (PIC) code, the length of the whole high-current D+ beam transport line is 500cm, the D+ beam transfer efficiency is up to 96%, and various components can match each other. On the rotating target, the D+ beam spot size is about 20.0 mm with energy of 450 keV. Based on the heat conduction theory, the thick adsorption rotating target with water-cooling can withstand the D+ ions beam with 450 kV/50 mA and ensure that the temperature is less than 200 °C. According to the multi-layer computing model, neutron energy spectra, angular distributions and yields for the thick target can be calculated with remarkable precision. The neutron energy spectra are non-mono-energetic neutrons for the ZF-400 neutron generator, the neutron angular distributions are anisotropic distributions, and they can provide neutrons with an intensity of $ 2.8\times 10^{11}$ n/s (D-D) and $ 1.4\times 10^{13}$ n/s (D-T), respectively, with the deuteron of 450 keV/50 mA.

Portable neutron generator with microwave ion source for wide applications

The paper presents the issues related to the development of a portable neutron generator with a microwave source of heavy hydrogen ions for a wide range of applications. The paper analyzes the effect of electromagnetic microwave field strength and the magnetic induction value of a constant external magnetic field on the ionization rate of molecular deuterium and determines their optimal ratios. It also describes the configuration of the magnetic system of permanent magnets made of NdFeB material, which provide a homogeneous magnetic field with an induction of 850 Gs necessary for the effective operation of the device using the electron cyclotron resonance (ECR). The dynamics of the primary deuteron flux, as well as secondary particles in the ion-optical system are analyzed. Elements of a conceptual design of a portable neutron generator are described.

Analysis of the Operation of the Microwave Ion Source in the Electron–Cyclotron Resonance Mode for a Portable Neutron Generator

The authors present the results of numerical simulation of the kinetic processes in deuterium microwave-resonator plasmas with electron–cyclotron resonance at a nonuniform distribution of the magnetic and electric fields. For the actual configuration of the resonator module, the authors show the optimal magnetic field distribution in terms of energy efficiency. The solution of the kinetic scheme of the microwave discharge in deuterium plasmas makes it possible to relate the gas-discharge plasma properties with the parameters of the deuterium-ion source: the residual gas pressure, the gas flow into the microwave resonator, the charged particle flows on the wall and into the ion-optical system, the electrical and magnetic field strength and distribution in the resonator, and the power input into it. The results make it possible to reveal and implement generator operation modes with the highest characteristics ever recorded.

Woodpile EBG waveguide as a DC electrical break for microwave ion sources

AbstractThis article presents a dielectric waveguide, operating at 18 GHz that can sustain 40 kV DC voltages and can be used to feed microwave ion sources. The metallic‐to‐woodpile waveguide transition optimization gives a very low maximum insertion loss of 0.3 dB over a 3.75% bandwidth.

Commissioning of the ECR ion source of the high intensity proton injector of the Facility for Antiproton and Ion Research (FAIR).

The CEA at Saclay is in charge of developing and building the ion source and the low energy line of the proton linac of the FAIR (Facility for Antiproton and Ion Research) accelerator complex located at GSI (Darmstadt) in Germany. The FAIR facility will deliver stable and rare isotope beams covering a huge range of intensities and beam energies for experiments in the fields of atomic physics, plasma physics, nuclear physics, hadron physics, nuclear matter physics, material physics, and biophysics. A significant part of the experimental program at FAIR is dedicated to antiproton physics that requires an ultimate number 7 × 1010 cooled pbar/h. The high-intensity proton beam that is necessary for antiproton production will be delivered by a dedicated 75 mA/70 MeV proton linac. A 2.45 GHz microwave ion source will deliver a 100 mA H+ beam pulsed at 4 Hz with an energy of 95 keV. A 2 solenoids low energy beam transport line allows the injection of the proton beam into the radio frequency quadrupole (RFQ) within an acceptance of 0.3π mm mrad (norm. rms). An electrostatic chopper system located between the second solenoid and the RFQ is used to cut the beam macro-pulse from the source to inject 36 μs long beam pulses into the RFQ. At present time, a Ladder-RFQ is under construction at the University of Frankfurt. This article reports the first beam measurements obtained since mid of 2016. Proton beams have been extracted from the ECR ion source and analyzed just after the extraction column on a dedicated diagnostic chamber. Emittance measurements as well as extracted current and species proportion analysis have been performed in different configurations of ion source parameters, such as magnetic field profile, radio frequency power, gas injection, and puller electrode voltage.

Study on the beam properties of the microwave ion source

A test bench of the microwave ion source has been developed at Korea Multipurpose Accelerator Complex (KOMAC). Several modifications were done to improve the performance of the ion source. Beam properties such as an emittance and a profile were measured according to the operating parameters and extraction geometries. In this paper, the characteristics of ion source at test bench are presented in a viewpoint of the beam properties and the improvement of the ion source for 100 MeV linac based on the result is reported.

Compact high current proton cyclotron and associated beam dynamics

A compact proton cyclotron of 1 MeV, 5 mA is being developed at VECC is an R{&}D project to study and settle various problems related with the transport, injection and acceleration of high current beams in a cyclotron. Proton beam from 2.45 GHz microwave ion source (already operating with 8 mA @ 80 keV) will be first bunched using a sinusoidal buncher and then will be injected axially in the central region of the cyclotron where a spiral inflector will place the beam on the proper orbit. In this paper we discuss the design of the magnet of 1 MeV cyclotron, simulation results of beam transmission through the spiral inflector and the results of studies on the behaviour of transverse envelopes of space charge dominated beam along the accelerated orbits. Efforts have been made to obtain the proper matching conditions at the central region by optimizing the input beam parameters of the injected beam. The maximum beam current that can be accelerated through the available aperture of the cyclotron focusing channel has also been estimated.

100 years of the physics of diodes

The Child–Langmuir Law (CL), discovered a century ago, gives the maximum current that can be transported across a planar diode in the steady state. As a quintessential example of the impact of space charge shielding near a charged surface, it is central to the studies of high current diodes, such as high power microwave sources, vacuum microelectronics, electron and ion sources, and high current drivers used in high energy density physics experiments. CL remains a touchstone of fundamental sheath physics, including contemporary studies of nanoscale quantum diodes and nano gap based plasmonic devices. Its solid state analog is the Mott–Gurney law, governing the maximum charge injection in solids, such as organic materials and other dielectrics, which is important to energy devices, such as solar cells and light emitting diodes. This paper reviews the important advances in the physics of diodes since the discovery of CL, including virtual cathode formation and extension of CL to multiple dimensions, to the ...

Study on the microwave ion source of the 100-MeV proton linac

A microwave ion source is used as an ion source of 100-MeV proton accelerator at Korea Multipurpose Accelerator Complex (KOMAC). The specifications of the ion source are 50 keV in energy and 20 mA in peak current. The plasma is operated in CW mode using magnetron and the pulse beam is extracted using semiconductor switch located in the extraction power supply. The beam characteristics were measured based on the pulse voltage and current. A test stand was also installed to study the beam characteristics of the ion source in off-line. In this paper, the pulse beam characteristics of the ion source are presented and the installation of the test stand is reported.

Development and test of 2.45 GHz microwave ion source based intense ion beam experimental facility

An intense low energy ion beam facility has been designed, developed at Inter University Accelerator Centre (IUAC), New Delhi. This facility comprises of a 2.45 GHz microwave ion source, multi-electrode extraction system and an experimental chamber. The facility was designed to perform experiments using intense ion beams having energy in range of a few keV to a few tens of keV. The plasma chamber was designed keeping two additional ports for plasma diagnostics. In order to deliver intense ion beams on the target with low electric field, a four-electrode extraction system has been developed. This facility has been used for 10 keV N+ & O+ ion implantation in silicon at varying doses. The implanted samples have been characterized by using Rutherford Back Scattering (RBS), RBS Channeling (RBS-C) and Nuclear Resonance Analysis (NRA).

Development of a microwave ion source for ion implantations.

A microwave ion source is expected to have a long lifetime, as it has fewer consumables. Thus, we are in the process of developing a microwave ion source for ion implantation applications. In this paper, we report on a newly developed plasma chamber and the extracted P(+) beam currents. The volume of the plasma chamber is optimized by varying the length of a boron nitride block installed within the chamber. The extracted P(+) beam current is more than 30 mA, at a 25 kV acceleration voltage, using PH3 gas.

Studies on space charge neutralization and emittance measurement of beam from microwave ion source.

A 2.45 GHz microwave ion source together with a beam transport system has been developed at VECC to study the problems related with the injection of high current beam into a compact cyclotron. This paper presents the results of beam profile measurement of high current proton beam at different degrees of space charge neutralisation with the introduction of neon gas in the beam line using a fine leak valve. The beam profiles have been measured at different pressures in the beam line by capturing the residual gas fluorescence using a CCD camera. It has been found that with space charge compensation at the present current level (∼5 mA at 75 keV), it is possible to reduce the beam spot size by ∼34%. We have measured the variation of beam profile as a function of the current in the solenoid magnet under the neutralised condition and used these data to estimate the rms emittance of the beam. Simulations performed using equivalent Kapchinsky-Vladimirsky beam envelope equations with space charge neutralization factor are also presented to interpret the experimental results.

Design Study for Pulsed Proton Beam Generation

Fast neutrons with a broad energy spectrum, with which it is possible to evaluate nuclear data for various research fields such as medical applications and the development of fusion reactors, can be generated by irradiating proton beams on target materials such as beryllium. To generate short-pulse proton beam, we adopted a deflector and slit system. In a simple deflector with slit system, most of the proton beam is blocked by the slit, especially when the beam pulse width is short. Therefore, the available beam current is very low, which results in low neutron flux. In this study, we proposed beam modulation using a buncher cavity to increase the available beam current. The ideal field pattern for the buncher cavity is sawtooth. To make the field pattern similar to a sawtooth waveform, a multiharmonic buncher was adopted. The design process for the multiharmonic buncher includes a beam dynamics calculation and three-dimensional electromagnetic simulation. In addition to the system design for pulsed proton generation, a test bench with a microwave ion source is under preparation to test the performance of the system. The design study results concerning the pulsed proton beam generation and the test bench preparation with some preliminary test results are presented in this paper.

Breakdown transient study of plasma distributions in a 2.45 GHz hydrogen discharge

Plasma distribution transients associated with the breakdown of a 2.45GHz hydrogen discharge similar to high current microwave ion sources are studied by means of an ultra-fast frame image acquisition system in visible light range. Eight different plasma distributions have been studied by photographing the 2D projections of the discharge through a transparent plasma electrode. The temporal evolution of images in Balmer-alpha and Fulcher band wavelengths have been recorded associated to atomic and molecular excitation and ionization processes. Some unexpected plasma distributions transient behaviors during breakdown are reported.

Studies on the coupling transformer to improve the performance of microwave ion source.

A 2.45 GHz microwave ion source has been developed and installed at the Variable Energy Cyclotron Centre to produce high intensity proton beam. It is operational and has already produced more than 12 mA of proton beam with just 350 W of microwave power. In order to optimize the coupling of microwave power to the plasma, a maximally flat matching transformer has been used. In this paper, we first describe an analytical method to design the matching transformer and then present the results of rigorous simulation performed using ANSYS HFSS code to understand the effect of different parameters on the transformed impedance and reflection and transmission coefficients. Based on the simulation results, we have chosen two different coupling transformers which are double ridged waveguides with ridge widths of 24 mm and 48 mm. We have fabricated these transformers and performed experiments to study the influence of these transformers on the coupling of microwave to plasma and extracted beam current from the ion source.

Frequency scaling with miniature COmpact MIcrowave and Coaxial ion sources

We will present recent basic developments about possible extension of the COMIC (for COmpact MIcrowave and Coaxial) devices up to 5.8 GHz in place of the present 2.45 GHz operation [P. Sortais, T. Lamy, J. Médard, J. Angot, L. Latrasse, and T. Thuillier, Rev. Sci. Instrum. 81, 02B314 (2010)]. New applications associating multiple COMIC devices for thin film deposition will be described and we will explain why an increase of the current density delivered by each individual ion source could lead to the increase of the deposition rate. For this purpose, we will present results of about two devices working at 5.8 GHz. The first one is a tiny ion source, the world smallest microwave ion source, exactly similar to COMIC but operating at 5.8 GHz with a quarter wave cavity structure and a few watts microwave power consumption. We will show that the frequency scaling effect is effective inside such small machines. The second one is a more ambitious ion source designed around a three quarter wave structure that works with a few tens of watts at 5.8 GHz.