PRODUCTION AND NEUTRALIZATION OF NEGATIVE IONS AND BEAMS: 11th International Symposium on the Production and Neutralization of Negative Ions and Beams
925(2007); http://dx.doi.org/10.1063/1.2773640View Description Hide Description
We present here some recent advances in the field of atom‐molecule and electron‐molecule collisions involving hydrogen and its isotopes. For the first topic the possibility of exploiting our large and complete hydrogen database by a suited scaling law is explored with the purpose of obtaining databases of hydrogen isotopes. In the electron‐molecule case, resonant dissociative attachment and ro‐vibrational excitation cross sections for the so‐called 14 eV resonance are derived.
925(2007); http://dx.doi.org/10.1063/1.2773641View Description Hide Description
We present here an account on the progress of kinetic simulation of non equilibrium plasmas in conditions of interest for negative ion production by using the 1D Bari code for hydrogen plasma simulation. The model includes the state to state kinetics of the vibrational level population of hydrogen molecules, plus a PIC/MCC module for the multispecies dynamics of charged particles. In particular we present new results for the modeling of two issues of great interest: the time filtering and the Cs addition via surface coverage.
925(2007); http://dx.doi.org/10.1063/1.2773642View Description Hide Description
The work concerns the simulation of negative ion formation and acceleration in a radio‐frequency discharge for neutral beam injection system for ITER, with particular emphasis on the IPP negative ion source. To generate intense beams of negative ions and to optimize the negative ion source, understanding of transport properties of negative ions H− is indispensable. To study this effect, we have developed a 1D(z)‐3V Particle‐in‐Cell electrostatic model of the production and extraction regions. The motion of charged particles (e, H+, and H−) in their self‐consistent electric field and of neutral particles (H(n=1,2,3) and H2( , ν=0,…,14)) is simulated. Surface and volumetric processes involving plasma and neutral systems have been included by using different Monte Carlo Collision methods. Comparisons between numerical and experimental results have been done in order to validate the code.
Electron Temperature Control in Plasmas with Mesh Grid Bias and its Application to Hydrogen Negative Ion Production925(2007); http://dx.doi.org/10.1063/1.2773643View Description Hide Description
Volume production of hydrogen negative ions, H−, is studied in pure hydrogen plasmas using a grid bias method for plasma parameter control. The purposes of the present study are as follows: One is to investigate the possibility of controlling plasma parameters, in particular electron temperature Te , with a grid bias method in DC discharge plasmas: the other, to realize efficient negative ion production in H2 plasmas and to discuss the difference in Te control and H− production between the grid bias method and the usual magnetic filter method. Relationship between the extracted H− ion currents and plasma parameters is discussed. It is confirmed that both high and low Te plasmas are produced in the separated regions when the grid is negatively biased. The negative ion production depends strongly on the grid potential and related plasma conditions.
925(2007); http://dx.doi.org/10.1063/1.2773644View Description Hide Description
Production and transport processes of H0 atoms are numerically simulated to obtain the H0 atom density. A three‐dimensional transport code using a Monte Carlo method has been applied to analyze the local density of H0 atoms in the large “JAEA 10 ampere negative ion source” under Cs‐seeded condition. In this study, the production rate of H0 atoms through the dissociation process of H2 molecules is estimated from single probe characteristics of the Langmuir probe measurement. In the code, the energy relaxation process of H0 atoms is also taken into account. The results show that the existence of high‐energy electrons and the energy relaxation process of H0 atoms affect the H0 atom density.
925(2007); http://dx.doi.org/10.1063/1.2773645View Description Hide Description
The development of a RF driven negative‐ion source currently in progress at IPP Garching has made remarkable progresses during the last years. Optimization of the source strongly depends on the understanding of the physics of generation, destruction and extraction of negative ions. Numerical model calculations can provide important information needed for the improvement of this understanding. Since negative ions are mainly produced on Cesium covered surfaces of the source, and have a survival length in the range of a few cm, models for the region close to the plasma grid are of particular interest. The plasma in this region is affected by magnetic filter fields. Another important feature is biasing of the plasma grid which strongly influences the co‐extracted electron current. The different effects are treated in two separate models. Their current status is presented: a particle‐in‐cell‐code (PIC) is used to study the influence of filter fields and bias voltage on the plasma flow onto the plasma grid. The motion of the charged particles due to their own and externally applied electric field is simulated in a self‐consistent way. In the second code the survival probability of negative ions produced on the surface of the plasma grid is estimated using test‐particles. The Monte‐Carlo technique is applied for the treatment of inelastic and elastic collisions.
Research of the Negative Ion Source Based on Reflective Discharge with and without Addition of Cesium925(2007); http://dx.doi.org/10.1063/1.2773646View Description Hide Description
This paper is the review of researches of the physical processes in the negative ion source based on reflective discharge accomplished in Institute of physics of NAS of Ukraine. The dependences of the negative ion current on the pressure in the discharge chamber and the discharge current are experimentally measured. The theoretical model which takes into account all main processes occurring in the source is developed, and calculated dependences of ion current on gas pressure and discharge current are obtained. On a basis of the experiments and theoretical calculations, the existence in the source of two spatially separated areas with fast and slow electrons is shown. It leads to high efficiency of generation of H− ions. The influence of cesium on processes of negative ion formation is studied. It is shown both theoretically and experimentally that cesium in a volume cannot lead to improvement of the source characteristics. The increase of ion current density and gas efficiency obtained in the experiments is connected with the recharge processes of fast atoms and positive ions of hydrogen on the anode of the discharge chamber.
925(2007); http://dx.doi.org/10.1063/1.2773647View Description Hide Description
This paper covers the recent work carried out at the Rutherford Appleton Laboratory (RAL) on the ISIS Ion Source Development Rig (ISDR). The development of a retarding potential energy analyzer is described and a measured energy spread of 17.6 eV ± 1.5 eV from the ion source is reported. Variation in energy spread versus discharge current is shown. The development of a pepperpot emittance scanner to study emittance variation along the beam axis is discussed.
925(2007); http://dx.doi.org/10.1063/1.2773648View Description Hide Description
The HERA RF‐Volume Source is the only source that has delivered routinely an H− current of 40 mA without Cs. The current has now been improved to 60 mA. While for HERA operation a pulse length of less than 200 μsec is necessary, operation with a pulse length of 3 msec was demonstrated at DESY in cooperation with SNS, FNAL and CERN.
The physics of the extraction plasma region has been the subject of very detailed investigations with special sets of collars and different materials. Tests with plasma chambers of different sizes have been done. Significant changes have since been made in the source design. A more efficient RF coupling to the plasma was developed. Together with a new funnel system this source delivers higher H− currents and a lower H− /electron ratio. The high voltage and vacuum technology was improved and a new electron dump technique was introduced. The steps to a new improved source design are described in this paper.
925(2007); http://dx.doi.org/10.1063/1.2773649View Description Hide Description
The US Spallation Neutron Source (SNS) has recently begun producing neutrons and is currently on track to becoming a world‐leading facility for material science based on neutron scattering. The facility is comprised of an H− ion source, a linear accelerator, an accumulator ring, a liquid‐Hg target and a suite of neutron scattering instruments. Over the next several years the average H− current from the ion source will be increased in order to meet the baseline facility requirement of providing 1.4 MW of beam‐power to the target and the SNS power upgrade power requirement of 2+ MW on target. Meeting the latter goal will require H− currents of 70–100 mA with an RMS emittance of 0.20–0.35 π mm mrad and a ∼7% duty‐factor. To date, the RF‐driven‐multicusp SNS ion source has only been able to demonstrate sustained operation at 33 mA of beam current at a ∼7% duty‐factor. This report details our efforts to develop variations of the current ion source which can meet these requirements. Designs and experimental results are presented for helicon plasma drivers, high‐power external antennas, glow‐discharge plasma guns and advanced Cs systems.
925(2007); http://dx.doi.org/10.1063/1.2773650View Description Hide Description
The polarized negative light ion source at the Cooler Synchrotron COSY in Jülich is based on the colliding beams principle. Using an intense pulsed neutralized cesium beam for the charge exchange with a pulsed highly polarized hydrogen beam intensities of 50 μA have been achieved at the end of 2005. The steady improvement has lead to a gain of a factor of three in the total charge contained in one pulse, compared to the record value achieved in 2001. This report sums up the characteristics of the ion source and its components in their present mode of operation and describes the ongoing efforts for still higher beam intensities.
925(2007); http://dx.doi.org/10.1063/1.2773651View Description Hide Description
A 2.45 GHz electron cyclotron resonance test stand based on a pure volume H− negative ion production is presently running at CEA Saclay. This negative ion source (ECRIN) is working in pulsed mode, up to 10 ms at 10 Hz. Several modifications allowed increasing the extracted H− current from the source. Those results will be summed up in the first part. With the experience collected from this source, a second one using a multi‐cups magnetic structure is under development. Magnetic calculations and simulations showed that an octupolar configuration could allow improving the H− ion production. Those simulations will be discussed and the new set up will also be presented. The source is now being assembled on a new test bench, called BETSI, for light ion source development based on permanent magnet structure.
925(2007); http://dx.doi.org/10.1063/1.2773652View Description Hide Description
An increase of beam intensity and brightness is essential for future upgrades of existing CERN proton accelerator facilities. A first step can be an injection of H− ions from a new higher energy H− linear accelerator called Linac4 into the Proton Synchrotron Booster (PSB). A second step could be the complete replacement of the PSB by a high‐power linear accelerator, called SPL, injecting directly into the Proton Synchrotron (PS). Both injection scenarios require a high performance, high reliability negative hydrogen ion source. This paper will present the challenging source requirements and the two approaches to fulfill them.
925(2007); http://dx.doi.org/10.1063/1.2773653View Description Hide Description
The High Intensity Neutrino Source (HINS) program at Fermilab (formerly the Proton Driver) aims to develop a multi‐mission linear accelerator (LINAC) capable of accelerate H− ions to 8 GeV. This paper touches on the ion source requirements for the HINS and discusses long pulse length testing of three ion sources which appear to have the capability of meeting these requirements.
925(2007); http://dx.doi.org/10.1063/1.2773654View Description Hide Description
A multicusp ion source with modular design was developed at LBNL for production of H− ions. The source consists of a front plate, two multicusp front chambers, a quartz flange with external 3‐loop RF antenna and a rear multicusp chamber. The source has LaB6 sputtering target at the rear chamber to lower the work function of the surfaces by coating them with LaB6 and an external cesium oven on the front plate. The front plate also has an integrated collar and filter magnets to cool plasma near the extraction. The collar also enables the use of cesium and LaB6 surface effects. The rear chamber is equipped with three vacuum feed‐throughs for operation with two gases and a pressure measurement.
Current density of over 10 mA/cm2 of H− has been measured with e/I− ratio being ∼100 when the source was operated with only 1000 W of cw RF power. Negative ion production was enhanced using cesium, Xe gas mixing and LaB6 deposition to the source surfaces. When the front plate with filter magnets is removed, the source produces large amounts of H+. Current density of 110 mA/cm2 with 1800 W RF power at 2.3 Pa source pressure was measured with over 90 % atomic species. A long operation lifetime is excepted as the external RF antenna is not exposed to plasma.
925(2007); http://dx.doi.org/10.1063/1.2773655View Description Hide Description
The comparison of cesiated sources for H−, like Camembert‐III and the SNS source with the non‐cesiated DESY source leads to an interesting conclusion how volume production of H− ions might be performed in the DESY source: The generation of vibrationally highly excited H2 — molecules is also possible by protons with energies of some tenth of eV. This may solve the dilemma of volume production how to provide enough high energy electrons for the creation of excited molecules and how to completely suppress them in the region, where H− ions are born by atachment of low energy electrons to excited molecules. An H− ion source, which uses protons to generate the vibrationally excited molecules, needs an intense proton beam of some tenth of eV injected to a plasma with low electron energy and high hydrogen pressure. This may be achieved by the direct coupling of two plasma generators. The proton beam will be accelerated by the potential fall in the sheath of the first plasma generator and by the bias to the second one. Space charge limitations of a drifting beam thus may be avoided resulting in a high intensity proton beam at optimum low energy.
925(2007); http://dx.doi.org/10.1063/1.2773656View Description Hide Description
A Surface Plasma Source (SPS) with plasma generation by a saddle type antenna is discussed. The following features of the helicon discharge with a saddle type antenna in magnetic field are identified: efficient plasma generation in resonant condition, low gas density, strong separation of plasma from the wall, possibility to control plasma flux distribution by magnetic field configuration. Applications of saddle type antenna in SPS for accelerators for Homeland Security and for Neutral Beam Injectors (NBI) are considered.
925(2007); http://dx.doi.org/10.1063/1.2773657View Description Hide Description
A two‐stage ion source concept was presented a few years ago, consisting of a proven H− ion source and a 2.45‐GHz Electron Cyclotron‐Resonance (ECR) type ion source, here used as a plasma cathode. This paper describes the experimental development path pursued at Lawrence Berkeley National Laboratory, from the early concept to a working unit that produces plasma in both stages and creates a negative particle beam. Without cesiation applied to the second stage, the H− fraction of this beam is very low, yielding 75 micro‐amperes of extracted ion beam current at best. The apparent limitations of this approach and envisaged improvements are discussed.
925(2007); http://dx.doi.org/10.1063/1.2773658View Description Hide Description
Helicon plasma generators are widely used for plasma processing applications due to their long life‐time and capability of creating high‐density plasmas efficiently. The aim of the helicon plasma generator‐assisted negative ion source project at Los Alamos Neutron Science Center (LANSCE) is to use these features for producing intense beams of H− ions. Our development work builds upon pioneering experiments previously conducted at Lawrence Berkeley National Laboratory (LBNL) with a 2.45 GHz electron cyclotron resonance plasma generator. In the new approach a helicon plasma generator is used as a plasma cathode injecting electrons into a multi‐cusp H− ion source. The secondary source can be operated without filaments or any other consumable parts and, consequently, the life‐time of the ion source can be extended significantly. The development of the ion source is aimed to meet the beam production goals of the LANSCE 800 MeV linear accelerator refurbishment project i.e. 20 mA of H− beam with normalized area emittance (95 % of the beam) less than 1.1 π⋅mm⋅mrad and a duty factor of 12 %. The operation principle of the source, the test stand design and the status of the development work will be presented in this article.