Electrode Extraction System Research Articles

Development of a low energy ion irradiation system for erosion test of first mirror in fusion devices

A low energy ion irradiation system based on the deuterium arc ion source with a high perveance of 1 μP for a single extraction aperture has been successfully developed for the investigation of ion irradiation on plasma-facing components including the first mirror of plasma optical diagnostics system. Under the optimum operating condition for mirror testing, the ion source has a beam energy of 200 eV and a current density of 3.7 mA/cm2. The ion source comprises a magnetic cusp-type plasma source, an extraction system, a target system with a Faraday cup, and a power supply control system to ensure stable long time operation. Operation parameters of plasma source such as pressure, filament current, and arc power with D2 discharge gas were optimized for beam extraction by measuring plasma parameters with a Langmuir probe. The diode electrode extraction system was designed by IGUN simulation to optimize for 1 μP perveance. It was successfully demonstrated that the ion beam current of ∼4 mA can be extracted through the 10 mm aperture from the developed ion source. The target system with the Faraday cup is also developed to measure the beam current. With the assistance of the power control system, ion beams are extracted while maintaining a consistent arc power for more than 10 min of continuous operation.

Design upgrade of the ISOLDE target unit for HIE-ISOLDE

The High Intensity and Energy HIE-ISOLDE project is a major upgrade of the existing ISOLDE and REX-ISOLDE facilities with the objective of increasing the energy and the intensity of the delivered radioactive ion beams (RIB) [1]. In order to accommodate the future increase of primary beam intensity delivered by the new LINAC4 H− driver to the Proton Synchrotron Booster (PSB) [2] and from this to ISOLDE, a major study is being carried out to upgrade the existing designs of the ISOLDE target and its supporting infrastructure. In particular, the extraction optics plays an important role in the initial beam transport and the quality of the beam supplied to the mass separators. Important factors include the emittance of the beam and the beam profile to avoid beam losses.A new double electrode extraction system has been developed for simplifying and improving the interface between the target unit and the frontend (target coupling table). Numerical and experimental studies have been performed in order to define the new extraction geometry, and the coupling table has been adapted to keep the compatibility. An alternative heating system is under study. An electron bombardment heating system is being developed as an option for avoiding the employment of big cross section cables. The results of these studies and the mechanical models developed are presented and discussed.

Analytical and simulation studies for diode and triode ion beam extraction systems

This work is concerned with ion beam dynamics and compares the emittance to aberration ratios of two-and three-electrode extraction systems. The study is conducted with the aid of Version 7 of SIMION 3D ray-tracing software. The beam dependence on various parameters of the extraction systems is studied and the numerical results lead to qualitative conclusions.Ion beam characteristics using diode and triode extraction systems are investigated with the aid of the computer code SIMION 3 D, Version 7.0. The diode (two electrode extraction system) and triode (three-electrode extraction, acceleration-deceleration system) extraction systems are designed and optimized with different geometric parameters of the electrode system, voltage applied to the extraction electrode, and plasma parameters inside the ion source chamber, as well as by the ion beam space charge. This work attempts to describe the importance of the acceleration-deceleration extraction system. It shows that besides an increase of the beam energy, the ion beam has lower emittance than the two-electrode extraction system. Ion beams of the highest quality are extracted whenever the half-angular divergence is minimum for which the perveance current intensity and the extraction gap have optimum value. Knowing the electron temperature of the plasma is necessary to determine plasma potential and the exact beam energy.

Low energy micron size beam from inductively coupled plasma ion source

A high brightness inductively coupled plasma ion source based focused ion beam system is being developed. This system is intended to produce a low energy high current micron size beam of the heavier gaseous elements for high speed, micro milling applications. The basic aim of this development is to cater the needs of those applications which cannot be addressed by the conventional liquid metal ion source based FIB. A novel idea has been implemented in the design of the ion source where, a double plasma chamber is designed to initiate the plasma at low RF power. The plasma is first initiated by the capacitive coupling at low RF power in one chamber. This in turn triggers a strong, high density inductive discharge in another chamber, which is Faraday shielded by a thin slotted copper foil. The ion beam is extracted through 1 mm diameter aperture in the plasma electrode using a simple two electrode extraction system. The ion source has produced argon ion beam of 57 mA/cm2 with an angular current density of ∼10 mA/Sr at 160 W of RF power and 7kV of extraction voltage. In addition, the measurements show that the ion source has brightness of >8000 A/m2 Sr−1 V−1. The ion source is integrated with a two lens focusing column and beam currents from 2 nA to 2.5 μA were focused at a working distance of 5 mm. Measurements show that the currents in the range of 500 nA to 1 μA can be focused to spots having diameters in the range of 8–10 μm resulting in a current density of 450 mA/cm2 at the focused spot. In order to evaluate the milling rate of steel, experiments were carried out using 7 keV, 800 nA of argon ion beam. Preliminary results indicate that the milling rate of steel is >100 μm3/s.

Design of a multi-cusp ion source for proton therapy

The permanent magnets of the discharge chamber in a multi-cusp proton source are studied and designed. The three electrode extraction system is adopted and simulated. A method to extract different amounts of current while keeping the beam emittance unchanged is proposed.

Design and construction of a compact microwave proton source for a proton linac

A 100 MeV, 20 mA proton linear accelerator is being developed by the Proton Engineering Frontier Project at the Korea Atomic Energy Research Institute. 20 MeV acceleration system using radio frequency quadrupole and drift tube linac was already developed and has been tested. To operate this acceleration system with a long time, more reliable proton source is needed. A compact microwave proton source was proposed and has been designed and constructed as a prototype ion source for the 100 MeV proton linear accelerator. The design of microwave power injection system is based on the microwave proton injector at LANL and CEA. The wave power from a 2.45 GHz, 2 kW magnetron source is introduced into a compact plasma chamber with 7 cm diameter and 5 cm length through a standard tapered, double-ridged waveguide (WRD250) and a quartz window. The microwave power supply is installed on high voltage platform. Axial magnetic fields up to 1 kG can be provided with a water-cooled solenoid coil. A single-hole three electrode extraction system is designed for an extraction current up to 30 mA at a 50 kV extraction voltage. The design and initial operations of the proton source are presented.

General design of the International Fusion Materials Irradiation Facility deuteron injector: Source and beam line

In the framework of the International Fusion Materials Irradiation Facility-Engineering Validation and Engineering Design Activities (IFMIF-EVEDA) project, CEA/IRFU is in charge of the design and realization of the 140 mA cw deuteron Injector. The electron cyclotron resonance ion source operates at 2.45 GHz and a 4 electrode extraction system has been chosen. A 2 solenoid beam line, together with a high space charge compensation have been optimized for a proper beam injection in the 175 MHz radio frequency quadrupole. The injector will be tested with proton and deuteron beam production either in pulsed mode or in cw mode on the CEA-Saclay site before to be shipped to Japan. Special attention was paid to neutron emission due to (d,D) reaction. In this paper, the general IFMIF Injector design is reported, pointing out beam dynamics, radioprotection, diagnostics, and mechanical aspects.

Comparison between experiment and two simulation strategies for the extraction of focused ion beams

Computer simulation codes for the extraction of ion beams have been used for over three decades. Here we describe medium current extraction (∼1 mA) from a high density plasma source (>1012 cm−3) with a three electrode extraction system and compare the extracted current and the angular divergence with the results of two computer simulation programs. The first is called PBgun and is a commercially available ray tracing code; the second, called simulation d’extraction de faisceaux d’ions (SEFI) uses a particle-in-cell code to simulate the plasma and ion beam. It is the purpose of this article to ascertain whether these codes can adequately model the plasma/beam interface and hence successfully predict the extracted current and beam form across a broad range of extraction parameters. We found that SEFI could accurately predict the function of extracted current versus extraction voltage and that PBgun gave accurate simulations when the current or current density could be specified near the meniscus. Also for a thin plasma aperture and a fixed current at the meniscus, PBgun gave roughly 60% of the functional dependence of the extracted current on the extraction voltage and the other 40% on variations in the plasma pre-sheath. Both codes had some error from beam crossing near the axis which changed the amount of meniscus curvature predicted.

Micro-PHOENIX: Intense deuton beams production for SPIRAL II

The development of electron cyclotron resonance ion source (ECRIS) at LPSC Grenoble (previously ISN) covers a wide range of applications. Micro-PHOENIX is a compact source whose magnetic confinement is fully generated by permanent magnets. The extraction geometry has been specially designed to manage high currents with a double electrode extraction system to improve the beam characteristics at high voltage. The ECRIS can accept a microwave power frequency from 10 to 18 GHz. It has been installed as a universal injector on the new charge breeder test bench in order to perform the widest range of experiments including mono- or multicharged ion injections. To characterize the analyzed extracted beam, a new emittance meter based on electrostatic deflection plates has been set up and permits one to obtain online high resolution measurements. The first objective of the experiments was to fulfill the future SPIRAL II requirements. After a technical description of the Micro-PHOENIX ECRIS and its beam analysis system, the first experimental results obtained with a single puller electrode will be presented. Thus, a D+ intensity of 5 mA at 39 kV is easily delivered within a normalized rms emittance of 0.092 π mm mrad, which is well below the 0.2 π mm mrad limit assuring a 100% RFQ transport efficiency as computed for the LINAG project. A more extensive study of emittance versus plasma parameters is in progress.

Efficiency and transient time studies of an electron cyclotron resonance ion source for radioactive ion beam production at ISAC/TRIUMF

A 2.45 GHz electron cyclotron resonance (ECR) ion source with a single mode resonator is being developed to produce high efficient single charged ion beams from exiguous gaseous elements. The source is intended to produce short and long half-life radioactive ion beams as well as stable ion beams for low and high energy experiments at ISAC [J. M. Poutissou, Proceedings of the ISAC Workshop (1994)]. It is obvious that for the radioactive ion beam production, the gas and ion transient time and the overall ionization efficiency are the most important parameters. The transient time is measured using ultrafast peizoelectric gas valve which could operate up to a frequency of 2 kHz. A unique feature of the source is that the plasma chamber is considerably smaller (∼170 times) than its resonance cavity in order to minimize the transient time. Quartz tubes with various diameters (5–20 mm) and 80 mm long are tested as the plasma chamber and the results are discussed. The effect of the transfer tube length, which links the target and the ion source on the transient time is also described. An axially symmetric five electrode extraction system containing three multiaperture electrodes was used to extract the beam. The source, including ECR coils and extraction system is placed in the middle of a 60 cm×60 cm×90 cm vacuum box to simulate the ISAC target module conditions. The preliminary results of the molecular and ion transient time studies, beam efficiency studies are also presented in this article.

2D simulation and optimization of the volume H− ion source extraction system for the spallation neutron source accelerator

Abstract The low-energy beam transport system (LEBT) for the Spallation Neutron Source (SNS) is required to transport 35 mA of a 65 keV H − ion beam from the ion source to the RFQ accelerator entrance with a normalized rms emittance of less than 0.15 π mm mrad. A radio frequency driven, magnetically filtered multicusp ion source is under development at LBNL. The H − beam extraction from this ion source is being simulated utilizing the 2D-computer code IGUN [Rev. Sci. Instr. 63 (1992) 2756]. An H − ion extraction model is discussed. Computational results are presented for the H − ion beam emittance of a single aperture two electrode extraction system and for the tuning range of the low-energy beam transport system.

A microwave driven off-line ion source for ISAC at TRIUMF

An off-line microwave ion source (TE111 mode resonator at 2.45 GHz) is being developed to produce stable ion beams for ISAC commissioning as well as to produce intermediate and long half-life radioactive ion beams for initial experiments. Two different sources have been constructed and tested. In the standard source configuration the microwave power is injected and the beam is extracted on axis. In the second source microwave power is injected radially. In this case, the beam is extracted radially. Each of the sources is capable of handling gaseous, metallic and volatile compounds. A three electrode extraction system and a mass spectrometer with a resolution of 1600 are used to analyze the beams. The performance of the two sources is compared. In a number of parameters, efficiency, power requirements, tuning simplicity and lifetime, the radial source out performs the axial source. The test results with both sources are present.

Efficient ion beam extraction from a flowing plasma

A moving plasma with directed flow velocities v larger than the ion acoustic speed cs is used as a source of high-current ion beams in the 10–20-keV range of energies. Current densities up to 3 A/cm2 are obtained at the plasma boundary which is an order of magnitude larger than the limiting value of Bohm current in a stationary plasma. The observed current densities were proportional to v, unlike the Bohm current densities which are proportional to ion acoustic speed. Total ion currents up to ∼100 A were extracted from the plasma through a two electrode extraction system. Simple geometric shaping of the electrodes enabled an 8-cm-diam beam to be focused to ∼7 mm.

A Study of the Ion Beam Intensity and Divergence Obtained from a Single Aperture Three Electrode Extraction System

Experimental results are given for the perveance and beam divergence of a single aperture three electrode extraction system using helium ions at energies between 10 and 30 keV. The aperture radii, the electrode thicknesses, and the spacings were varied and from the results a preferred design was obtained for use in a multiaperture array. The most critical parameter was the ratio (S) of the radius of the first aperture to the distance between the first and second electrodes, the highest current density being obtained at values of this ratio less than 0.5. The optimum beam divergence observed corresponded to a Gaussian beam profile with a width (ω) of ± 1.2° at 2 m from the source. The measured perveance at small values of S and at minimum ω lay between 75% and 90% of the value predicted on the basis of a simple model using the Langmuir-Blodgett formula for the spherical diode.

Indium Ion Source

An ion source that utilizes a continuously oxygenated porous tungsten surface to generate indium ions is described. Indium vapor supplied to the back of the tungsten ionizer from a reservoir percolates through to the front surface where the indium is evaporated as ions. An accel-decel electrode extraction system is used to increase the ion current capability of the source. The ionizer and reservoir are designed to operate at temperatures in excess of 1000°C and at voltages up to 20 keV. The peak ion current attained was 0.57 mA at an ion energy of 10 keV.