Gasdynamic Ion Research Articles

Kinetic whistler instability in a mirror-confined plasma of a continuous ECR ion source

Kinetic instabilities in a dense plasma of a continuous electron cyclotron resonance (ECR) discharge in a mirror magnetic trap at the Gasdynamic Ion Source for Multipurpose Operation (GISMO) setup are studied. We experimentally define unstable regimes and corresponding plasma parameters, where the excitation of electromagnetic emission is observed, accompanied by the precipitation of energetic electrons from the magnetic trap. A comprehensive experimental study of the precipitating electron energy distribution and plasma electromagnetic emission spectra, together with theoretical estimates of the cyclotron instability increment proves that under the experimental conditions, the observed instability is related to the excitation of whistler-mode waves, which are a driver of losses of energetic electrons from the magnetic trap. The results of this study are important for the further development of the GISMO electron cyclotron resonance ion source facility and for the improvement of its parameters as an ion source. Also, this research on plasma kinetic instabilities is of fundamental interest and provides experimental tools to simultaneously study plasma electromagnetic activity and corresponding changes in a resonant electron energy distribution.

Energy distribution and bremsstrahlung spectra of energetic electrons escaping from the ECR plasma with high energy input

Electron energy distribution function (EEDF) is an important characteristic that defines the processes of plasma confinement and ionization. Understanding such processes is crucial for the proper tuning of ion sources. In the ECR plasma, the EEDF is significantly non-Maxwellian, and the exact shape remains still unknown. As the initial step towards the EEDF resolving, the energy distribution of the electrons lost from the magnetic mirror trap was directly measured in a wide range of neutral gas pressures and gyrotron powers along with bremsstrahlung spectra. A series of experiments were performed on the newly constructed Gasdynamic Ion Source for Multipurpose Operation (GISMO) facility allowing record-breaking specific energy input into the plasma. Obtained distributions showed unconventional behavior as the function of source parameters. The EEDF shape and the bremsstrahlung spectra showed a threshold qualitative change with the gyrotron power presumably as a result of the development of kinetic instabilities.

Status of a point-like neutron generator development

In this paper we report on a high current density ion beam profile diagnostics with a slit-based system as a reliable method, capable of high thermal load applications. The task arose in frames of a point-like neutron source development for neutron radiography. In previous research, it was suggested to construct such a system as a D-D neutron generator based on the high current gasdynamic ion source, which utilises the plasma of electron cyclotron resonance discharge sustained by powerful millimeter wave gyrotron radiation. This device is able to produce focused D+ beams with a characteristic diameter of 1 mm, total current above 100 mA, and current density at a level of several A/cm2. Study of such intense beams profile to obtain the best focusing efficiency and minimize neutron producing area appeared to be a challenging task. The paper also demonstrates the possibility of fast neutron imaging with a point-like powerful neutron generator (neutron yield on the level of 1010 s−1).

Измерения эмиттанса газодинамического электронно-циклотронного резонансного источника ионов

Advantages of using a gasdynamic electron cyclotron ion source in a proton accelerator based compact neutron source DARIA are discussed. It is experimentally demonstrated that the gasdynamic proton source is able to provide ion beams with 100 mA current, duration from 100 microseconds and longer at repetition rate up to 1 kHz. Emittance of the ion beams produced by the gasdynamic ion source was measured using a “pepper-pot” method for two extraction electrodes geometries: “spherical” and flat parallel. It is shown that the normalized 4 rms emittance value for both electrode configurations in the range of extraction voltage from 41 t 48 kV does not exceed 2 mm mrad.

Windowless gas dynamic ion beam cooler and buncher

In this paper the concept of the windowless gas dynamic ion beams cooler and buncher is proposed. This ion beam cooler/buncher has a very simple design, it is ultra-compact having a total length of only 20 cm including the extremely small-sized RF-buncher of 18 mm length. It consists of diverging supersonic nozzle having the inner tube on the axis that allows direct injection of primary ion beam into supersonic carrier gas jet and three simple differentially pumped RF funnels connected through the small diverging nozzles. In the new design there is no need for big and highly expensive vacuum pumps for maintaining the required vacuum levels around the cooler.The realization of this cooler/buncher concept will allow the fast and highly efficient deceleration, cooling and bunching ion beams with primary energies up to 300 keV without the need for high-voltage platforms. The feasibility of this concept for production of high-quality continuous and pulsed ion beams in wide range of masses and having a very small transverse and longitudinal emittance is demonstrated by results of detailed gas dynamic and ion-trajectory simulations which are presented and discussed.

Status of the gasdynamic ion source for multipurpose operation (GISMO) development at IAP RAS.

A new experimental facility named GISMO (Gasdynamic Ion Source for Multipurpose Operation) was constructed at the IAP RAS to continue investigations in the field of gasdynamic ion sources. The source utilizes 28 GHz/10 kW gyrotron radiation for heating magnetically confined plasma. Magnetic field configuration provided by a fully permanent magnet system is much like a simple mirror trap. The GISMO source is aimed at the production of bright ion beams with hundreds of milliamperes current. The facility has been tested for continuous-wave (CW) operation with 2 kW of heating power to check durability of a microwave injection system and the plasma chamber. A 2-electrode extraction system with an integrated Einzel lens was designed for a formation of CW high current beam with up to 100 kV accelerating voltage. The first results on ion beam production at GISMO are presented together with the general progress status of the facility.

Gasdynamic ECR ion source for negative ion production

H− ion sources are needed in various areas of accelerator technology, such as beam injection into cyclotrons and storage rings and as a part of neutral beam injectors for plasma heating in experimental facilities studying thermonuclear fusion. It was recently demonstrated that gasdynamic ion source based on ECR discharge in a simple mirror trap is very efficient for proton beam production [1]. Here we use the gasdynamic plasma source as the first stage driver of volumetric negative ion production through dissociative electron attachment (DEA) [2]. Experiments were performed with a pulsed 37 GHz / up to 100 kW gyrotron radiation in a dual-trap magnetic system, which consists of two identical simple mirror traps. The first trap was used for the plasma production under ECR condition. Dense hydrogen plasma flux from the first trap flows into the second trap through a perforated plate, which prevented the propagation of microwaves into the second one. The configuration helps to separate plasma volumes with “hot” and “cold” electrons. We present recent experimental results on this topic. A negative ion current density of 80 mA/cm2 through 1 mm plasma electrode was demonstrated.

First experiments with gasdynamic ion source in CW mode.

A new type of ECR ion source-a gasdynamic ECR ion source-has been recently developed at the Institute of Applied Physics. The main advantages of such device are extremely high ion beam current with a current density up to 600-700 emA/cm(2) in combination with low emittance, i.e., normalized RMS emittance below 0.1 π mm mrad. Previous investigations were carried out in pulsed operation with 37.5 or 75 GHz gyrotron radiation with power up to 100 kW at SMIS 37 experimental facility. The present work demonstrates the first experience of operating the gasdynamic ECR ion source in CW mode. A test bench of SMIS 24 facility has been developed at IAP RAS. 24 GHz radiation of CW gyrotron was used for plasma heating in a magnetic trap with simple mirror configuration. Initial studies of plasma parameters were performed. Ion beams with pulsed and CW high voltage were successfully extracted from the CW discharge. Obtained experimental results demonstrate that all advantages of the gasdynamic source can be realized also in CW operation.

New progress of high current gasdynamic ion source (invited).

The experimental and theoretical research carried out at the Institute of Applied Physics resulted in development of a new type of electron cyclotron resonance ion sources (ECRISs)-the gasdynamic ECRIS. The gasdynamic ECRIS features a confinement mechanism in a magnetic trap that is different from Geller's ECRIS confinement, i.e., the quasi-gasdynamic one similar to that in fusion mirror traps. Experimental studies of gasdynamic ECRIS were performed at Simple Mirror Ion Source (SMIS) 37 facility. The plasma was created by 37.5 and 75 GHz gyrotron radiation with power up to 100 kW. High frequency microwaves allowed to create and sustain plasma with significant density (up to 8 × 10(13) cm(-3)) and to maintain the main advantages of conventional ECRIS such as high ionization degree and low ion energy. Reaching such high plasma density relies on the fact that the critical density grows with the microwave frequency squared. High microwave power provided the average electron energy on a level of 50-300 eV enough for efficient ionization even at neutral gas pressure range of 10(-4)-10(-3) mbar. Gasdynamic ECRIS has demonstrated a good performance producing high current (100-300 mA) multi-charged ion beams with moderate average charge (Z = 4-5 for argon). Gasdynamic ECRIS has appeared to be especially effective in low emittance hydrogen and deuterium beams formation. Proton beams with current up to 500 emA and RMS emittance below 0.07 π ⋅ mm ⋅ mrad have been demonstrated in recent experiments.

High current proton source based on ECR discharge sustained by 37.5 GHz gyrotron radiation

Formation of hydrogen ion beams with high intensity and low transverse emittance is one of the key challenges in accelerator technology. Present work is devoted to experimental investigation of proton beam production from dense plasma (Ne > 1013 cm−3) of an ECR discharge sustained by 37.5 GHz, 100 kW gyrotron radiation at SMIS 37 facility at IAP RAS. The anticipated advantages of the SMIS 37 gasdynamic ion source over the current state-of-the-art proton source technology based on 2.45 GHz hydrogen discharges are described. Experimental result obtained with different extraction configurations i.e. single- and multi-aperture systems are presented. It was demonstrated that ultra bright proton beam with approximately 4.5 mA current and 0.03 π·mm·mrad normalized emittance can be produced with the single-aperture (1 mm in diameter) extraction, the corresponding brightness being 5 A/(π·mm·mrad)2. For production of high current beams a multi-aperture extractor was used resulting to a record of 200 mA / 1.1 π·mm·mrad normalized emittance proton beam. The species fraction i.e. the ratio of H+ to H2+ current was recorded to be > 90 % for all extraction systems. A possibility of further enhancement of the beam parameters by improvements of the extraction system and its power supply is discussed.

Ion beam formation in a gas-dynamic electron cyclotron resonance ion source

Generation of quasistationary flows of multicharged ions with a current density of up to 1A∕cm2 from a dense electron cyclotron resonance plasma confined in a magnetic trap under the quasi-gas-dynamic regime has been achieved [Golubev et al., Trans. Fusion Sci. Technol. 47, 345 (2005)]. This technique provides opportunities for extracting high current multicharged ion beams. The present research is concerned with experimental and theoretical investigations of two ion extraction systems for the gas-dynamic ion sources. (1) Single-aperture system. In this case, there is a principal possibility to obtain ion beams with low emittance by using a small-diameter aperture for extraction. Here we describe investigations aimed at creating nitrogen ion beams (the main ion in the spectrum is N2+) with currents of up to 6.5mA through a 1.5mm aperture in the plasma electrode. (2) Multiaperture system. Such systems provide significantly higher beam currents. First results of testing an extractor with five apertures are presented in this article.