ECRIS2010 - List of Authors (Tarvainen, O.A.)

Paper

Title

Page

Time Evolution of Plasma Potential in Pulsed Operation of ECRIS

93

O.A. Tarvainen, H. A. Koivisto, T. Ropponen, V.A. Toivanen
JYFL, Jyväskylä, Finland
Y. Higurashi, T. Nakagawa
RIKEN Nishina Center, Wako, Japan

The time evolution of plasma potential has been measured in pulsed operation mode with electron cyclotron resonance ion sources at JYFL and RIKEN. Three different ion sources with microwave frequencies ranging from 6.4 to 18 GHz were employed for the experiments. The plasma potential during the preglow and afterglow transients was compared with steady state conditions. The plasma potential was observed to increase 25-75 % during the preglow and 10-30 % during the afterglow. We describe the experimental procedure and present the results of the study in detail.

Slides TUCOBK03 [0.973 MB]

TUPOT011

Measurement of the Diamagnetic Current on the LBNL 6.4 GHz ECR Ion Source

140

J.D. Noland, J.Y. Benitez, M. Kireeff Covo, D. Leitner, C.M. Lyneis
LBNL, Berkeley, California, USA
O.A. Tarvainen
JYFL, Jyväskylä, Finland
J. Verboncoeur
UCB, Berkeley, California, USA

Two standard plasma diagnostics (x-ray spectroscopy and measurement of the diamagnetic current) have been employed at the LBNL 6.4 GHz ECR. These diagnostics are combined with time resolved current measurements to study the plasma breakdown, build up and decay times, as well as electron heating. Individual charged particles in a magnetized plasma orbit in such a way that the magnetic field produced by their motion opposes any externally applied magnetic field. When a charged particle density gradient exists in a plasma, a net current arises. This “diamagnetic” current is proportional to the time-rate-of-change of the perpendicular component of the plasma pressure, and can be measured with a loop of wire as the plasma ignites or decays. Another common plasma diagnostic that is used to characterize an ECR plasma is measurement of the x-ray spectra created when energetic electrons scatter off of plasma ions. The x-ray spectra provide insight on the relative abundance of electrons of different energies, and thus the electron energy distribution function. The x-ray spectra can also be used to estimate the total x-ray power produced by the plasma. In this paper diamagnetic loop diagnostics and set-up is described in detail. In addition, diamagnetic loop and low energy x-ray measurements (few keV to 100 keV) taken on the LBNL 6.4 GHz ECR ion source are presented and discussed.

Poster TUPOT011 [1.522 MB]

TUPOT013

Influence of Initial Plasma Density and Mean Electron Energy on the Preglow Effect

146

I. Izotov, V. Sidorov, V. Skalyga, V. Zorin
IAP/RAS, Nizhny Novgorod, Russia
H. A. Koivisto, O.A. Tarvainen, V.A. Toivanen
JYFL, Jyväskylä, Finland

The investigation of the Preglow effect is driven with the aim of creating a short-pulsed multicharged ion source. Recent experimental investigations have revealed strong influence of seed electrons, i.e. initial plasma density, on the amplitude and duration of the Preglow peak [1]. Present work, consisting of experiments and simulations, is dedicated to further investigation of the Preglow dependence on initial plasma density and electrons energy. Experimental investigation was performed at University of Jyväskylä (JYFL) with the A-ECR type ECRIS operated with 14 GHz frequency. Helium was used for the study. An initial ionization degree of the gas was varied by changing the pulse duration and duty factor. Time-resolved ion currents of He⁺ and He²⁺ were recorded. Calculations were made by using 0-dimensional model described in references [2], [3] and based on the balance equations for the particles confined in the magnetic trap. Results of simulation are compared with experimental Preglow peaks and discussed. Good agreement between experimental data and simulation encourages us to conduct a further study, aimed at optimizing the Preglow by tuning source parameters and initial plasma conditions.
[1] O. Tarvainen et al, Rev. Sci. Instrum., 81, 02A303, 2010.
[2] T. Thuillier et al, Rev. Sci. Instrum., 79, 02A314, 2008.
[3] I. Izotov et all. IEEE Trans. Plasma Sci. 36, 1494, 2008.

Poster TUPOT013 [0.569 MB]

WECOAK01

Characterization of the Microwave Coupling to the Plasma Chamber of the LBL ECR Ion Source.

162

C.M. Lyneis, J.Y. Benitez, D. Leitner, J.D. Noland, M.M. Strohmeier
LBNL, Berkeley, California, USA
H. A. Koivisto, O.A. Tarvainen
JYFL, Jyväskylä, Finland

The characteristics of the microwave coupling of the 6.4 GHz ECR ion source were measured as a function of frequency, input power and time dependence. In addition the plasma diamagnetism and bremsstrahlung could be measured to help quantify the time dependence of the plasma build up and energy content. The LBL ECR plasma chamber, which has a diameter to wavelength ratio of 1.9 is not as over-moded as the 14 GHz AECR-U, which has a ratio greater than 3. This makes it possible to locate frequencies, where a single RF mode is predominately excited. For one of these modes we were able to demonstrate that with no plasma in the cavity, it is over-coupled and as the power is increased, the plasma density rises and the plasma loading increases it becomes under-coupled. By measuring the ratio of the incident to reflected power it is possible to show the microwave electric field levels saturate with increasing power. In the paper, the time dependence of the plasma loading and plasma diamagnetism as a function of input power and time are analyzed. The measurements of the plasma loading also provide insight into the dynamics of microwave heating in a multimode cavity.

Slides WECOAK01 [1.593 MB]

WECOAK05

Maximum Bremsstrahlung Energy Versus Different Heating Limits

175

H. A. Koivisto, V.P. Aho, P. Jones, P. Peura, J.H. Sarén, O.A. Tarvainen, V.A. Toivanen
JYFL, Jyväskylä, Finland

A comprehensive set of bremsstrahlung measurements have been performed at JYFL (University of Jyväskylä, Department of Physics) in order to understand the parameters affecting the time evolution of electron energy. In order to extend the understanding of electron heating, a new set of measurements with the JYFL 6.4 GHz ECRIS have been initiated to further study the parameters affecting the maximum bremsstrahlung energy. In the measurements the effect of magnetic field gradient, microwave power, plasma size and gas pressure were studied. In the analysis, main focus will be given to compare the results with different theoretical electron heating limits.

Slides WECOAK05 [0.739 MB]

WECOBK03

Fine Frequency Tuning of the PHOENIX Charge Breeder Used as a Probe for ECRIS Plasmas

184

T. Lamy, J. Angot, M. Marie-Jeanne, J. Médard, P. Sortais, T. Thuillier
LPSC, Grenoble Cedex, France
A. Galatà
INFN/LNL, Legnaro (PD), Italy
H. A. Koivisto, O.A. Tarvainen
JYFL, Jyväskylä, Finland

Fine frequency tuning of ECR ion sources is a main issue to optimize the production of multiply charged ion beams. The PHOENIX charge breeder operation has been tested in the range 13,75 - 14,5 GHz with an HF power of about 400 W. The effect of this tuning is analyzed by measuring the multi-ionization efficiency obtained for various characterized injected 1+ ion beams (produced by the 2.45 GHz COMIC source). The 1+/n+ method includes the capture and the multi ionization processes of the 1+ beam and may be considered as a plasma probe. The n+ spectra obtained could be considered, in first approach, as an image of the plasma of the charge breeder. However, in certain conditions it has been observed that the injection of a few hundreds of nA of 1+ ions (i.e.: Xe¹⁺) in the plasma of the charge breeder, is able to destroy the charge state distribution of the support gas (i.e.: up to 40 % of O⁶⁺ and O⁷⁺ disappears). The study of this phenomenon will be presented along with plasma potential measurements for various charge states. This study may help to understand the ECRIS creation (or destruction) of highly charged ions.

Slides WECOBK03 [7.745 MB]

TUPOT010

Effects of Microwave Frequency Fine Tuning on the Performance of JYFL 14 GHz ECRIS

137

V.A. Toivanen, V.P. Aho, J. Ärje, P. Jones, J.A. Kauppinen, H. A. Koivisto, P. Peura, O.A. Tarvainen
JYFL, Jyväskylä, Finland
L. Celona, G. Ciavola, S. Gammino
INFN/LNS, Catania, Italy
A. Galatà
INFN/LNL, Legnaro (PD), Italy
D. Mascali
CSFNSM, Catania, Italy
T. Ropponen
NSCL, East Lansing, Michigan, USA

Measurements have been carried out at Department of Physics, University of Jyväskylä (JYFL) to study the effects of microwave frequency fine tuning on the performance of JYFL 14 GHz electron cyclotron resonance ion source. The frequency was varied within an 85 MHz band around the normal operation frequency of 14.085 GHz. The radial bremsstrahlung emission was measured for plasma diagnostics purposes and mass separated ion beam currents extracted from the ion source were recorded at the same time. Also, beam quality studies were conducted by measuring the ion beam emittance and shape with and without enhanced space charge compensation. The obtained results are presented and possible origins of seen phenomena in measured quantities are discussed.

Poster TUPOT010 [0.678 MB]

Paper	Title	Page
TUCOBK03	Time Evolution of Plasma Potential in Pulsed Operation of ECRIS	93
	O.A. Tarvainen, H. A. Koivisto, T. Ropponen, V.A. Toivanen JYFL, Jyväskylä, Finland Y. Higurashi, T. Nakagawa RIKEN Nishina Center, Wako, Japan
	The time evolution of plasma potential has been measured in pulsed operation mode with electron cyclotron resonance ion sources at JYFL and RIKEN. Three different ion sources with microwave frequencies ranging from 6.4 to 18 GHz were employed for the experiments. The plasma potential during the preglow and afterglow transients was compared with steady state conditions. The plasma potential was observed to increase 25-75 % during the preglow and 10-30 % during the afterglow. We describe the experimental procedure and present the results of the study in detail.
	Slides TUCOBK03 [0.973 MB]

TUPOT011	Measurement of the Diamagnetic Current on the LBNL 6.4 GHz ECR Ion Source	140
	J.D. Noland, J.Y. Benitez, M. Kireeff Covo, D. Leitner, C.M. Lyneis LBNL, Berkeley, California, USA O.A. Tarvainen JYFL, Jyväskylä, Finland J. Verboncoeur UCB, Berkeley, California, USA
	Two standard plasma diagnostics (x-ray spectroscopy and measurement of the diamagnetic current) have been employed at the LBNL 6.4 GHz ECR. These diagnostics are combined with time resolved current measurements to study the plasma breakdown, build up and decay times, as well as electron heating. Individual charged particles in a magnetized plasma orbit in such a way that the magnetic field produced by their motion opposes any externally applied magnetic field. When a charged particle density gradient exists in a plasma, a net current arises. This “diamagnetic” current is proportional to the time-rate-of-change of the perpendicular component of the plasma pressure, and can be measured with a loop of wire as the plasma ignites or decays. Another common plasma diagnostic that is used to characterize an ECR plasma is measurement of the x-ray spectra created when energetic electrons scatter off of plasma ions. The x-ray spectra provide insight on the relative abundance of electrons of different energies, and thus the electron energy distribution function. The x-ray spectra can also be used to estimate the total x-ray power produced by the plasma. In this paper diamagnetic loop diagnostics and set-up is described in detail. In addition, diamagnetic loop and low energy x-ray measurements (few keV to 100 keV) taken on the LBNL 6.4 GHz ECR ion source are presented and discussed.
	Poster TUPOT011 [1.522 MB]

TUPOT013	Influence of Initial Plasma Density and Mean Electron Energy on the Preglow Effect	146
	I. Izotov, V. Sidorov, V. Skalyga, V. Zorin IAP/RAS, Nizhny Novgorod, Russia H. A. Koivisto, O.A. Tarvainen, V.A. Toivanen JYFL, Jyväskylä, Finland
	The investigation of the Preglow effect is driven with the aim of creating a short-pulsed multicharged ion source. Recent experimental investigations have revealed strong influence of seed electrons, i.e. initial plasma density, on the amplitude and duration of the Preglow peak [1]. Present work, consisting of experiments and simulations, is dedicated to further investigation of the Preglow dependence on initial plasma density and electrons energy. Experimental investigation was performed at University of Jyväskylä (JYFL) with the A-ECR type ECRIS operated with 14 GHz frequency. Helium was used for the study. An initial ionization degree of the gas was varied by changing the pulse duration and duty factor. Time-resolved ion currents of He⁺ and He²⁺ were recorded. Calculations were made by using 0-dimensional model described in references [2], [3] and based on the balance equations for the particles confined in the magnetic trap. Results of simulation are compared with experimental Preglow peaks and discussed. Good agreement between experimental data and simulation encourages us to conduct a further study, aimed at optimizing the Preglow by tuning source parameters and initial plasma conditions. [1] O. Tarvainen et al, Rev. Sci. Instrum., 81, 02A303, 2010. [2] T. Thuillier et al, Rev. Sci. Instrum., 79, 02A314, 2008. [3] I. Izotov et all. IEEE Trans. Plasma Sci. 36, 1494, 2008.
	Poster TUPOT013 [0.569 MB]

WECOAK01	Characterization of the Microwave Coupling to the Plasma Chamber of the LBL ECR Ion Source.	162
	C.M. Lyneis, J.Y. Benitez, D. Leitner, J.D. Noland, M.M. Strohmeier LBNL, Berkeley, California, USA H. A. Koivisto, O.A. Tarvainen JYFL, Jyväskylä, Finland
	The characteristics of the microwave coupling of the 6.4 GHz ECR ion source were measured as a function of frequency, input power and time dependence. In addition the plasma diamagnetism and bremsstrahlung could be measured to help quantify the time dependence of the plasma build up and energy content. The LBL ECR plasma chamber, which has a diameter to wavelength ratio of 1.9 is not as over-moded as the 14 GHz AECR-U, which has a ratio greater than 3. This makes it possible to locate frequencies, where a single RF mode is predominately excited. For one of these modes we were able to demonstrate that with no plasma in the cavity, it is over-coupled and as the power is increased, the plasma density rises and the plasma loading increases it becomes under-coupled. By measuring the ratio of the incident to reflected power it is possible to show the microwave electric field levels saturate with increasing power. In the paper, the time dependence of the plasma loading and plasma diamagnetism as a function of input power and time are analyzed. The measurements of the plasma loading also provide insight into the dynamics of microwave heating in a multimode cavity.
	Slides WECOAK01 [1.593 MB]

WECOAK05	Maximum Bremsstrahlung Energy Versus Different Heating Limits	175
	H. A. Koivisto, V.P. Aho, P. Jones, P. Peura, J.H. Sarén, O.A. Tarvainen, V.A. Toivanen JYFL, Jyväskylä, Finland
	A comprehensive set of bremsstrahlung measurements have been performed at JYFL (University of Jyväskylä, Department of Physics) in order to understand the parameters affecting the time evolution of electron energy. In order to extend the understanding of electron heating, a new set of measurements with the JYFL 6.4 GHz ECRIS have been initiated to further study the parameters affecting the maximum bremsstrahlung energy. In the measurements the effect of magnetic field gradient, microwave power, plasma size and gas pressure were studied. In the analysis, main focus will be given to compare the results with different theoretical electron heating limits.
	Slides WECOAK05 [0.739 MB]

WECOBK03	Fine Frequency Tuning of the PHOENIX Charge Breeder Used as a Probe for ECRIS Plasmas	184
	T. Lamy, J. Angot, M. Marie-Jeanne, J. Médard, P. Sortais, T. Thuillier LPSC, Grenoble Cedex, France A. Galatà INFN/LNL, Legnaro (PD), Italy H. A. Koivisto, O.A. Tarvainen JYFL, Jyväskylä, Finland
	Fine frequency tuning of ECR ion sources is a main issue to optimize the production of multiply charged ion beams. The PHOENIX charge breeder operation has been tested in the range 13,75 - 14,5 GHz with an HF power of about 400 W. The effect of this tuning is analyzed by measuring the multi-ionization efficiency obtained for various characterized injected 1+ ion beams (produced by the 2.45 GHz COMIC source). The 1+/n+ method includes the capture and the multi ionization processes of the 1+ beam and may be considered as a plasma probe. The n+ spectra obtained could be considered, in first approach, as an image of the plasma of the charge breeder. However, in certain conditions it has been observed that the injection of a few hundreds of nA of 1+ ions (i.e.: Xe¹⁺) in the plasma of the charge breeder, is able to destroy the charge state distribution of the support gas (i.e.: up to 40 % of O⁶⁺ and O⁷⁺ disappears). The study of this phenomenon will be presented along with plasma potential measurements for various charge states. This study may help to understand the ECRIS creation (or destruction) of highly charged ions.
	Slides WECOBK03 [7.745 MB]

TUPOT010	Effects of Microwave Frequency Fine Tuning on the Performance of JYFL 14 GHz ECRIS	137
	V.A. Toivanen, V.P. Aho, J. Ärje, P. Jones, J.A. Kauppinen, H. A. Koivisto, P. Peura, O.A. Tarvainen JYFL, Jyväskylä, Finland L. Celona, G. Ciavola, S. Gammino INFN/LNS, Catania, Italy A. Galatà INFN/LNL, Legnaro (PD), Italy D. Mascali CSFNSM, Catania, Italy T. Ropponen NSCL, East Lansing, Michigan, USA
	Measurements have been carried out at Department of Physics, University of Jyväskylä (JYFL) to study the effects of microwave frequency fine tuning on the performance of JYFL 14 GHz electron cyclotron resonance ion source. The frequency was varied within an 85 MHz band around the normal operation frequency of 14.085 GHz. The radial bremsstrahlung emission was measured for plasma diagnostics purposes and mass separated ion beam currents extracted from the ion source were recorded at the same time. Also, beam quality studies were conducted by measuring the ion beam emittance and shape with and without enhanced space charge compensation. The obtained results are presented and possible origins of seen phenomena in measured quantities are discussed.
	Poster TUPOT010 [0.678 MB]