High current density ion-beam extraction

2020

ECR Ion Sources are deemed to be among the most performing ion sources feeding particle accelerators, cyclotrons in particular. Improvements of their performances strictly depend on the knowledge of plasma physics in compact magnetic traps. The paper will comment on the results obtained by the INFN-LNS team and international collaborators by means of a multi-diagnostics setup able to monitor the evolution in space and time of several plasma parameters, simultaneously with beam extraction and analysis in the LEBT, in single vs. double frequency operations, including the RF power and magnetic field scalings, and exploring regimes dominated by plasma turbulence. The results are relevant for the operations of existing ion sources and for the design of new ones. Compact magnetic traps fashioned in a similar way of ECRISs can be considered as an experimental environment by itself: we are exploring this opportunity relying to the in-plasma measurements of radionuclides lifetimes (in particular, beta-decaying elements): CosmoChronometers or nuclei involved in the s-process nucleosynthesis are among the case studies, opening new perspectives in the nuclear astrophysics field.

Physica Scripta, 1995

This paper surveys the ongoing physics experiments at the Electron Beam Ion Trap (EBIT) facility at NIST, with particular attention paid to the underlying physical principles involved. In addition, some new data on the performance of our EBIT are presented, including results related to the determination of the trap width, ion temperature, and number of highly charged ions in the trap.

Physical Review Special Topics - Accelerators and Beams, 2010

The use of electrostatic ion beam traps require to set many potentials on the electrodes (ten in our case), making the tuning much more difficult than with quadrupole traps. In order to obtain the best trapping conditions, an analytical formula giving the electrostatic potential inside the trap is required. In this paper, we present a general method to calculate the analytical expression of the electrostatic potential in any axisymmetric set of electrodes. We use conformal mapping to simplify the geometry of the boundary. The calculation is then performed in a space of simple geometry. We show that this method, providing excellent accuracy, allows to obtain the potential on the axis as an analytic function of the potentials applied to the electrodes, thus leading to fast, accurate and efficient calculations. We conclude by presenting stability maps depending on the potentials that enabled us to find the good trapping conditions for O 4+ at much higher energies than what has been achieved until now.

IEEE Symposium Conference Record Nuclear Science 2004., 2004

The conventional way of trapping ions is based on the uses of RF or magnetic fields, like in Paul or Penning traps. In such traps the ions are stored with approximately zero kinetic energy. In many applications a well-defined ion beam is needed especially in collision experiment, where the initial direction of a beam is critical for reaction product measurements and a well defined field free region is required at the collision place. In the last few years we have developed a new type of electrostatic ion trap for ion beams of a few keV per charge, with no mass limit. The ions are injected through a stack of electrodes, which are used as an electrostatic mirror. The ions are confined in a region of few tens of centimeters by two electrostatic mirrors, located on opposite sides. The stability criterion of such a trap can be demonstrated to be similar to the one existing for optical resonator. The dynamics of such trapped ion beam was studied for various potentials on the electrostatic mirrors. Two modes of operation where found. In the first mode a self bunching effect was observed where the ion-ion Coulomb interaction generates a single bunch with constant length along the whole trapping time. This mode of operation can be used for Fourier mass spectrometry. A second mode, where the Coulomb interaction enhances the correlation between the ion position and momentum, enables phase space manipulation of the stored ion beam.

Fusion Engineering and Design, 2010

An ion extractor system has been designed for the steady state superconducting tokamak (SST-1) neutral beam injector (NBI) for an experiment using a prototype ion source with fully integrated regulated high voltage power supply (RHVPS) and data acquisition and control system (DACS) developed at Institute for Plasma Research (IPR) to obtain experience of NB operation. The extractor system is capable of extracting positive hydrogen ion beam of ∼10 A current at ∼20 kV. This paper presents the beam optics study for detailed design of an ion extraction system which could meet this requirement. It consists of 3 grid accel-decel system, each of the grid has 217 straight cylindrical holes of 8 mm diameter. Grids are placed on a specially designed G-10 block; a fiber reinforc plastic (FRP) isolator of outer diameter of 820 mm and 50 mm thickness. Provisions are made for supplying high voltage to the grid system through the embedded feed-throughs. Extractor system has been fabricated, mounted on the SST-1 neutral beam injector and has extracted positive hydrogen ion beam of 4 A at 20 kV till now.

Chinese Physics C, 2011

The characteristics of the ion beam extraction and focused to a volume as small as possible were investigated with the aid of computer code SIMION 3D version 7. It has been used to evaluate the extraction characteristics (accel-decel system) to generate an ion beam with low beam emittance and high brightness. The simulation process can provide a good study for optimizing the extraction and focusing system of the ion beam without any losses and transported to the required target. Also, a study of a simulation model for the extraction system of the ion source was used to describe the possible plasma boundary curvatures during the ion extraction that may be affected by the change in an extraction potential with a constant plasma density meniscus has been done.

Review of Scientific Instruments, 2008

The efficiency of trapping ions in an electron-beam ion source ͑EBIS͒ is of primary importance for many applications requiring operations with externally produced ions: RIA breeders, ion sources, and traps. At the present time, the most popular method of ion injection is pulsed injection, when short bunches of ions get trapped in a longitudinal trap while traversing the trap region. Continuous trapping is a challenge for EBIS devices because mechanisms which reduce the longitudinal ion energy per charge in a trap ͑cooling with residual gas, energy exchange with other ions, and ionization͒ are not very effective, and accumulation of ions is slow. A possible approach to increase trapping efficiency is to slant the mirror at the end of the trap which is opposite to the injection end. A slanted mirror will convert longitudinal motion of ions into transverse motion, and, by reducing their longitudinal velocity, prevent these ions from escaping the trap on their way out. The trade-off for the increased trapping efficiency this way is an increase in the initial transverse energy of the accumulated ions. The slanted mirror can be realized if the ends of two adjacent electrodes, drift tubes, which act as an electrostatic mirror, are machined to produce a slanted gap, rather than an upright one. Applying different voltages to these electrodes will produce a slanted mirror. The results of two-dimensional ͑2D͒ and three-dimensional ͑3D͒ computer simulations of the ion injection into an EBIS are presented using simplified models of an EBIS with conical ͑2D simulations͒ and slanted ͑3D simulations͒ mirror electrodes.

2006

A high current, mixed ion electron flux with space charge compensation has been produced without using a traditional dedicated source of space charge neutralizing electrons. The source employs a dual stage discharge and extraction concept. The main gas discharge plasma was generated in the cavity of a hollow cathode, representing a non self sustained glow discharge supported by electrons injected from the plasma of an auxiliary glow discharge. An ion beam was extracted from the plasma of the main discharge by a single grid extractor. Beam ions were later decelerated to a required energy in the layer between the grid and the beam plasma. The ion beam current was measured using a collector located 30-60 cm away from the dischar ge system. For the electron component of the main dischar ge plasma to penetrate into the ion beam drift space through the grid, the potential barrier was reduced under the condit ions of the optimal extractor potential with respect to the hollow cathode. The space charge neutralization of the low energy ion beam lead to a decrease in the plasma potential in the drift space and an increase in ion beam current. At a main discharge current of 1 A and a main discharge voltage of 300 V, an ion beam current of up to 100 mA and an ion en ergy of 20-100 eV was obtained. An increase in the distan ce between the collector and the discharge system necessita ted a corresponding increase in the initial ion energy if the ion beam current needed to be kept constant. The formation of an ion beam with the desired energy was confirmed by ti me of flight measurements.

A large fraction of radioactive beams produced and delivered at TRIUMF's isotope separator and accelerator facility, ISAC, are using either a surface ion source or a resonant ionization laser ion source, which share a common design. To characterize the operation of the ion sources, simulations were performed to determine the ion beam optics and beam envelope properties of the extracted beam. Furthermore ion-optics calculations were performed to determine the transmission parameters through the mass separator magnet. Emittances are measured in the ISAC low energy beam line right after the mass separator. The recent addition of a channeltron to the Allison emittance meter scanner now allows us to measure emittances for ion beams with intensities as low as 10 5 ions/s. This is particularly useful for establishing high resolution, high throughput mass separator tunes for radioactive isotope beams. This paper discusses emittance measurements of low intensity beams, typical emittance scans for the surface ion source and the resonant laser ionized source for different source parameters. The observed results are compared to the simulations and discussed.

AIP Conference Proceedings, 2002

Electron Beam Ion Trap (EBIT) devices and their special features are reviewed with attention to applications in highly charged ion plasma research. EBIT properties are presented based on information extracted from a variety of experiments reported in the literature. Topics discussed include typical parameters (Debye length, Wigner-Seitz radius, Coulomb coupling parameter, density, temperature, etc.), magnetic trapping mode, ion cloud shape, rotation, and evaporative cooling. We conclude that the quantitative understanding of highly charged ion plasmas inside an EBIT requires improved modeling and advanced diagnostic techniques.