V. G. Zorin

Formation of multi-charged ions and plasma stability at quasigasdynamic plasma confinement in a mirror magnetic trap

It is known that an increase in plasma density in sources of multicharged ions leads to a substantial increase of ion current and slightly improves the ion distribution over charge states. The validity of this statement was verified in experiments with plasma densities not exceeding several units of 1012 cm−3. In the present work it is demonstrated experimentally that, for the electron densities exceeding 1013 cm−3, the regime of plasma confinement in a trap changes significantly and the quasigasdynamic regime of plasma confinement is realized. Comparison of numerical simulations and experimental data showed the essential influence of the anisotropy of electron velocity distribution in a plasma on the ion charge state distribution. This allows looking for the optimal conditions for the creation of highly charged ions in plasma. In this article we also address problems of plasma stability in an axisymmetric mirror trap under powerful microwave pumping. First experiments on ion extraction from a dense plasm...

Multiple ionization of metal ions by ECR heating of electrons in vacuum arc plasmas

A joint research and development effort has been initiated, whose ultimate goal is the enhancement of the mean ion charge states in vacuum arc metal plasmas by a combination of a vacuum arc discharge and electron cyclotron resonance (ECR) heating. Metal plasma was generated by a special vacuum arc mini-gun. Plasma was pumped by high frequency gyrotron-generated microwave radiation. The results have demonstrated substantial multiple ionization of metal ions. For a lead plasma, ECR heating increased the maximum attainable ion charge state from Pb2+ up to Pb6+. The confinement parameter was as high as ∼109 cm−3 s. Further increase of the ion charge states will be attained by increasing the vacuum arc plasma density and optimizing the ECR heating conditions.

Plasma creation by terahertz electromagnetic radiation

The results of experiments aimed at the study of the discharge in a focused beam of terahertz waves in argon under near-atmospheric pressures are presented. The range of electric fields and gas pressures, at which a breakdown occurs, is determined. The study of the discharge glow dynamics showed that the discharge starts at the maximum of the terahertz wave beam field and its front moved towards the radiation with the speed of about 105 cm/s into the region of the fields being significantly weaker than the breakdown value. Measurements of the ratio of wave transmission through the discharge allow one to conclude that the density of the plasma produced in the discharge exceeds 1015 cm−3. Some features of the terahertz discharge are discussed.

Study of pulsed electron cyclotron resonance ion source plasma near breakdown: The preglow

A careful study of pulsed mode operation of the PHOENIX electron cyclotron resonance (ECR) ion source has clearly demonstrated the reality of an unexpected transient current peak, occurring at the very beginning of the plasma breakdown. This regime was named the preglow, as an explicit reference to the afterglow occurring at the microwave pulse end. After the transient preglow peak, the plasma regime relaxes to the classical steady state one. Argon preglow experiments performed at LPSC are presented. A theoretical model of ECR gas breakdown in a magnetic trap, developed at IAP, showing satisfactory agreement with the experimental results is suggested.

Observation of pulsed fast electron precipitations and the cyclotron generation mechanism of burst activity in a decaying ECR discharge plasma

We have detected and investigated quasi-periodic series of pulsed energetic electron precipitations in the decaying plasma of a pulsed ECR discharge in a mirror axisymmetric magnetic trap. The observed particle ejections from the trap are interpreted as the result of resonant interaction between energetic electrons and a slow extraordinary wave propagating in the rarefied plasma across the external magnetic field. We have been able to explain the generation mechanism of the sequences of pulsed precipitations at the nonlinear instability growth phase in terms of a cyclotron maser model in which the instability threshold is exceeded through a reduction in electromagnetic energy losses characteristic of the plasma decay.

High current density ion beam formation from plasma of electron cyclotron resonance discharge

This article describes the research effort to obtain a quality ion beam with high currents from the dense plasma of the pulsed electron cyclotron resonance discharge pumped with high-power millimeter-wave radiation. The results of the experiments aimed at optimization of the two-electrode system for ion extraction are presented. Under the conditions, when the density of the ion current in the vicinity of the plasma electrode was 65–75 mA/cm2, the normalized emittance of the ion beam did not exceed 0.19 π mm mrad.

Scaling for ECR sources of multicharged ions with pumping at frequencies from 10 to 100 GHz

One of the major trends in the development of ECR sources of multicharged ions is an increase of the extracted ion current. The main factor affecting the current of an ion beam produced by such a source is, obviously, the density of the plasma from which ions are extracted. In the present article the mean ion charge, the ion current density, and the minimal microwave power required to sustain needed electron temperature are calculated for a broad range of plasma densities (up to 1014 cm−3, which corresponds to 90 GHz cutoff frequency of microwave pumping). The electron temperature is taken as granted and no effects due to instabilities are considered. The distinguishing future of the analysis performed is that it takes into account alteration of the regime of plasma confinement, which occurs as the plasma density is increased. If the plasma density exceeds a certain threshold, the classical Pastukhov’s regime of plasma confinement is replaced by the quasi-gas-dynamic regime. It is demonstrated, in particu...

High current density production of multicharged ions with ECR plasma heated by gyrotron transmitter

In order to study the possibilities to produce high currents of pulsed heavy ion beams dedicated to synchrotron injection, two new approaches of ECR devices are now underway. The basic principle consists in maintaining a functioning point of the source with the highest density as possible and a minimum confinement time for the production of a given charge state. It means that for a constant neτi product we try to maximize ne and minimize τi. For this purpose two experiments are in progress at ISN/Grenoblea and IAP/Nizhny Novgorod.b The first one consists of using a minimum |B| magnetic structure with a 1.8 mirror ratio characteristic value with a 28 GHz frequency injection. In this case we explore different functioning points up to 10 kW of UHF power. The second one consists of a simple mirror magnetic system (simple mirror ion source, SMIS) working at 37.5 GHz with a mirror ratio up to 3 (2.5 T) where we study discharges with a peak power up to 100 kW. We will show that, in spite of a very short rising t...

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 πmmmrad normalized emittance can be produced with the single-aperture (1 mm in diameter) extraction, the corresponding brightness being 5 A/(πmmmrad)2. For production of high current beams a multi-aperture extractor was used resulting to a record of 200 mA / 1.1 πmmmrad 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.

Multiaperture ion beam extraction from gas-dynamic electron cyclotron resonance source of multicharged ions.

Electron cyclotron resonance ion source with quasi-gas-dynamic regime of plasma confinement (ReGIS), constructed at the Institute of Applied Physics, Russia, provides opportunities for extracting intense and high-brightness multicharged ion beams. Despite the short plasma lifetime in a magnetic trap of a ReGIS, the degree of multiple ionization may be significantly enhanced by the increase in power and frequency of the applied microwave radiation. The present work is focused on studying the intense beam quality of this source by the pepper-pot method. A single beamlet emittance measured by the pepper-pot method was found to be approximately 70 pi mm mrad, and the total extracted beam current obtained at 14 kV extraction voltage was approximately 25 mA. The results of the numerical simulations of ion beam extraction are found to be in good agreement with experimental data.