ECRIS2010 - Table of Session: WECOAK (Plasma & Beam Investigations)

Paper

Title

Page

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]

WECOAK02

Some Considerations About Frequency Tuning Effect in ECRIS Plasmas

165

D. Mascali, G. Castro, L. Celona, G. Ciavola, N. Gambino, S. Gammino, R. Miracoli, L. Neri
INFN/LNS, Catania, Italy
F. Maimone
GSI, Darmstadt, Germany

During the last years many experiments have demonstrated that slight variations in microwave frequency used to heat and sustain the plasma of ECRIS may strongly influence their performances (frequency tuning effect) both in terms of extracted current and mean charge state. Theoretical investigations revealed that this phenomenon can be correctly explained assuming that the plasma chamber works as a resonant cavity: standing waves are excited inside of it, and their spatial structure considerably changes even with slight variations of the pumping frequency. Therefore some particular modes present a higher electric field on the resonance surface, that is the only region in which the energy transfer from waves to electrons occurs. Experimental measurements carried out on microwave discharge plasmas at high density (up to 10¹¹ cm^-3) featured that even if the absorption of electromagnetic energy at the ECR surface is evident, the stochastic nature of the wave-electron interaction allows the wave to be reflected at the extraction flange, thus forming a standing wave. The model here proposed, and based on PIC and MonteCarlo collisional simulations, puts in evidence that the frequency tuning effect in ECRIS has a global influence on plasma properties: it strongly affects both ion and electron dynamics. Electron heating, electron density distribution, ion formation and acceleration at resonance surface, beam formation are determined by the particular mode excited inside the cavity. This means that the frequency tuning will be an important tool for future ECRIS for the optimization of the beam quality (emittance, etc.).

Slides WECOAK02 [4.765 MB]

WECOAK03

Studies of the ECR Plasma in the Visible Light Range

168

S. Biri, R. Rácz
ATOMKI, Debrecen, Hungary
J. Pálinkás
DU, Debrecen, Hungary

In order to investigate experimentally ECR plasmas one way is to record their optical spectra or photos in the infra-red, visible light (VL), ultra-violet or X-ray regions. The measurements and analysis of photos and spectra taken in any of these regions are usually affordable tasks. The non-destroying nature of this method is certainly an advantage, but the drawback is that the recorded information in most cases means integration over a specific line-of-sight in the plasma volume. Recently high resolution VL plasma photographs were taken at the ATOMKI-ECRIS using an 8 megapixel digital camera. Plasmas were generated from eight gases (He, methane, N, O, Ne, Ar, Kr, Xe) and from their mixtures. The analysis of the photo series gave us many qualitative and numerous valuable physical information on the nature of ECR plasmas [1, 2]. It is a further challenging task to understand the colors of this special type of plasmas. The colors can be determined by the VL electron transitions of the plasma atoms and ions. Through the examples of He and Xe we analyze the physical processes which effects the characteristic colors of these plasmas.
[1] Rácz R., Biri S., Pálinkás J.: Electron cyclotron resonance plasma photos. Rev. Sci. Instrum. 81 (2010) 02B708.
[2] Rácz R., Biri S., Pálinkás J.: ECR Plasma Photographs as Plasma Diagnostic. Submitted to Plasma Sources Science and Technology.

Slides WECOAK03 [1.573 MB]

WECOAK04

Bremsstrahlung and Ion Beam Current Measurements With SuSI ECR Ion Source

171

T. Ropponen, D.G. Cole, G. Machicoane, A. Stolz, L.T. Sun, L. Tobos
NSCL, East Lansing, Michigan, USA

The Superconducting Source for Ions (SuSI) at the National Superconducting Cyclotron Laboratory at Michigan State University is a fully superconducting 3rd generation ECR ion source. The axial magnetic field is generated by six solenoid magnets which allow to control the magnetic field characteristics, such as resonance locations, mirror ratios and magnetic field gradients, almost independently. In addition, a collimation scheme in the SuSI beam line after the analyzing magnet has been developed to optimize the ion beam production from the ion source within a given acceptance. These aspects make SuSI an excellent tool for ECRIS research and development. In this paper we will focus on the bremsstrahlung and ion beam current measurements where the gradient on the magnetic field is changed while keeping the Bmin and axial plasma length as constants. We will also show how the shift of the extraction side resonance location affects the extracted ion beam currents and radiation spectra and, finally, we will discuss about the effect of flatB mode with a modern superconducting ECR ion source on the ion beam production and radiation levels.

Slides WECOAK04 [3.752 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]

Paper	Title	Page
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]

WECOAK02	Some Considerations About Frequency Tuning Effect in ECRIS Plasmas	165
	D. Mascali, G. Castro, L. Celona, G. Ciavola, N. Gambino, S. Gammino, R. Miracoli, L. Neri INFN/LNS, Catania, Italy F. Maimone GSI, Darmstadt, Germany
	During the last years many experiments have demonstrated that slight variations in microwave frequency used to heat and sustain the plasma of ECRIS may strongly influence their performances (frequency tuning effect) both in terms of extracted current and mean charge state. Theoretical investigations revealed that this phenomenon can be correctly explained assuming that the plasma chamber works as a resonant cavity: standing waves are excited inside of it, and their spatial structure considerably changes even with slight variations of the pumping frequency. Therefore some particular modes present a higher electric field on the resonance surface, that is the only region in which the energy transfer from waves to electrons occurs. Experimental measurements carried out on microwave discharge plasmas at high density (up to 10¹¹ cm^-3) featured that even if the absorption of electromagnetic energy at the ECR surface is evident, the stochastic nature of the wave-electron interaction allows the wave to be reflected at the extraction flange, thus forming a standing wave. The model here proposed, and based on PIC and MonteCarlo collisional simulations, puts in evidence that the frequency tuning effect in ECRIS has a global influence on plasma properties: it strongly affects both ion and electron dynamics. Electron heating, electron density distribution, ion formation and acceleration at resonance surface, beam formation are determined by the particular mode excited inside the cavity. This means that the frequency tuning will be an important tool for future ECRIS for the optimization of the beam quality (emittance, etc.).
	Slides WECOAK02 [4.765 MB]

WECOAK03	Studies of the ECR Plasma in the Visible Light Range	168
	S. Biri, R. Rácz ATOMKI, Debrecen, Hungary J. Pálinkás DU, Debrecen, Hungary
	In order to investigate experimentally ECR plasmas one way is to record their optical spectra or photos in the infra-red, visible light (VL), ultra-violet or X-ray regions. The measurements and analysis of photos and spectra taken in any of these regions are usually affordable tasks. The non-destroying nature of this method is certainly an advantage, but the drawback is that the recorded information in most cases means integration over a specific line-of-sight in the plasma volume. Recently high resolution VL plasma photographs were taken at the ATOMKI-ECRIS using an 8 megapixel digital camera. Plasmas were generated from eight gases (He, methane, N, O, Ne, Ar, Kr, Xe) and from their mixtures. The analysis of the photo series gave us many qualitative and numerous valuable physical information on the nature of ECR plasmas [1, 2]. It is a further challenging task to understand the colors of this special type of plasmas. The colors can be determined by the VL electron transitions of the plasma atoms and ions. Through the examples of He and Xe we analyze the physical processes which effects the characteristic colors of these plasmas. [1] Rácz R., Biri S., Pálinkás J.: Electron cyclotron resonance plasma photos. Rev. Sci. Instrum. 81 (2010) 02B708. [2] Rácz R., Biri S., Pálinkás J.: ECR Plasma Photographs as Plasma Diagnostic. Submitted to Plasma Sources Science and Technology.
	Slides WECOAK03 [1.573 MB]

WECOAK04	Bremsstrahlung and Ion Beam Current Measurements With SuSI ECR Ion Source	171
	T. Ropponen, D.G. Cole, G. Machicoane, A. Stolz, L.T. Sun, L. Tobos NSCL, East Lansing, Michigan, USA
	The Superconducting Source for Ions (SuSI) at the National Superconducting Cyclotron Laboratory at Michigan State University is a fully superconducting 3rd generation ECR ion source. The axial magnetic field is generated by six solenoid magnets which allow to control the magnetic field characteristics, such as resonance locations, mirror ratios and magnetic field gradients, almost independently. In addition, a collimation scheme in the SuSI beam line after the analyzing magnet has been developed to optimize the ion beam production from the ion source within a given acceptance. These aspects make SuSI an excellent tool for ECRIS research and development. In this paper we will focus on the bremsstrahlung and ion beam current measurements where the gradient on the magnetic field is changed while keeping the Bmin and axial plasma length as constants. We will also show how the shift of the extraction side resonance location affects the extracted ion beam currents and radiation spectra and, finally, we will discuss about the effect of flatB mode with a modern superconducting ECR ion source on the ion beam production and radiation levels.
	Slides WECOAK04 [3.752 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]