ECRIS2010 - List of Keywords (electron)

Paper	Title	Other Keywords	Page
MOCOBK04	Recent Activities at the ORNL Multicharged Ion Research Facility (MIRF)	ion, ECR, plasma, permanent-magnet	23
	F.W. Meyer, M.E. Bannister, S. Deng, I.N. Draganić, J.W. Hale, P.R. Harris, C.C. Havener, H.F. Krause, C.R. Vane ORNL, Oak Ridge, Tennessee, USA
	Funding: Sponsored by the Office of Fusion Energy Sciences and the Office of Basic Energy Sciences of the U.S. DOE under contract No. DE-AC05-00OR22725 with UT_Battelle. We report on recent upgrades of the ORNL Multicharged Ion Research Facility, and our activities in the area of ECR ion source diagnostic measurements. The upgrades include installation of a new all permanent magnet ECR ion source [1] on a high voltage platform that increases our high energy beam production capability to 250keV/q, and installation of a floating beamline fed by a 10 GHz CAPRICE ECR ion source for producing decelerated ion beams to energies as low as a few eV/q range. The primary application of all the produced ion beams is to study fundamental collisional interactions [2] of multicharged ions with electrons, atoms, and surfaces. We also summarize recent diagnostic measurements of the ECR plasma potential and other plasma parameters using an in-situ Langmuir probe installed in the ECR edge plasma and complementary measurements [3] using an external beam deceleration method. [1] D. Hitz et al. , “An All-Permanent Magnet ECR Ion Source for the ORNL MIRF Upgrade Project,” AIP Conference Proceedings 749, 123 (2005), Woodbury, NY. [2] F.W. Meyer, “ECR-Based Atomic Collision Physics Research at ORNL MIRF,” in Trapping Highly Charged Ions: Fundamentals and Applications, J. Gillaspy, ed., Nova Science Pub., New York, 2000, pp. 117-164. [3] P.R. Harris and F.W. Meyer, Rev. Sci. Inst. 81, 02A310 (2010).
	Slides MOCOBK04 [2.645 MB]

MOCOCK05	Multigan®: a New Multicharged Ion Source Based on Axisymetric Magnetic Structure	ion, ECRIS, plasma, extraction	37
	L. Maunoury, P. Delahaye, M. Dubois, P. Jardin, P. Lehérissier, M. Michel, J.Y. Pacquet GANIL, Caen, France S. Biri ATOMKI, Debrecen, Hungary X. Donzel, G. Gaubert, R. Leroy, A.C.C. Villari PANTECHNIK, BAYEUX, France C. Pierret CIMAP, Caen, France
	Standard ECR ion sources have radial magnetic field created by a multi-pole, e.g. hexapole or higher order, which fills all space in the center of the source structure. Based on the Monogan® ECRIS [1] concept, a new multicharged ECR ions source has been designed with a large opening space in the center of the source structure. This particular design allows, in a first approach, direct radial contact with the ECR plasma, allowing positioning of probes and targets for radioactive beam production very close to the plasma region. Secondly, the absence of a multi-pole allows considering extremely high magnetic fields with significantly smaller structural constraints. This source is combining the advantages of the axisymetric magnetic feature of Monogan® with higher frequencies. This paper will describe the magnetic structure calculation as well as the mechanical design and stresses of a full permanent magnet ion source using this concept. This source will be the first prototype of such an ECR ion source. Finally, using TrapCad code [2], an estimation of the electronic energy distribution has been calculated and thus, the performance of the source has been deduced. The beam formation and extraction were also roughly calculated taking into account magnetic and electric fields. [1] P. Jardin et al., Review of Scientific Instruments, 73, 789 (2002). [2] L. Maunoury et al., Plasma Sources Science and Technology , 18, 015019 (2009).
	Slides MOCOCK05 [5.532 MB]

TUCOBK01	Preglow Phenomenon Origins and its Scaling for Ecris	plasma, radiation, ion, ECR	87
	I. Izotov, V. Sidorov, V. Skalyga, V. Zorin IAP/RAS, Nizhny Novgorod, Russia
	Preglow effect investigation is one of topical directions of ECR ion sources development at present. Preglow is of interest for efficient short-pulsed multi-charged ion source creation. Particularly, such source of intense beams of short-living radioactive isotopes multi-charged ions is one of key elements in “Beta-Beam” European project [1]. Use of Preglow-generating regime of an ECRIS operation is a promising way of pulsed high-intense multi-charged ion beams production with much shorter edges in comparison with usual operation regime. The first theoretical investigations of Preglow phenomenon were performed in references [2,3]. Present work describes modified model of ECR discharge development in a magnetic trap of the ECRIS as a continuation of [2,3]. Numerical simulations made with the updated model allow authors to propose more physical and intuitive explanation of Preglow phenomenon origins. Obtained dependences of Preglow characteristics on experimental conditions offer a scaling for a wide range of ECRISes. [1] (ONLINE) http://beta-beam.web.cern.ch/beta-beam/task/diverse/mandate.htm [2] T. Thuillier et al, Rev. of Sci. Instrum., 79, 02A314, 2008. [3] I. Izotov et al, IEEE Trans. Plasma Sci. 36, 1494, 2008.
	Slides TUCOBK01 [0.928 MB]

TUCOBK03	Time Evolution of Plasma Potential in Pulsed Operation of ECRIS	plasma, ion, ion-source, 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]

TUCOBK04	Micropulses Generation in ECR Breakdown Stimulated by Gyrotron Radiation at 37.5 GHz	ion, plasma, ECR, ion-source	96
	V. Skalyga, S. Golubev, I. Izotov, S. Razin, V. Sidorov, A. Vodopyanov, V. Zorin IAP/RAS, Nizhny Novgorod, Russia
	Present work is devoted to experimental and theoretical investigation of possibility of short pulsed (< 100 μs) multicharged ion beams creation. The possibility of quasi-stationary generation of short pulsed beams under conditions of quasi-gasdynamic plasma confinement was shown in recent experiments. Later another way of such beams creation based on “Preglow” effect was proposed. In present work it was demonstrated that in the case when duration of MW pulse is less then formation time of “Preglow” peak, realization of a regime when ion current is equal to zero during MW pulse and intense multicharged ions flux appears only when MW ends could be possible. Such pulses after the end of MW were called "micropulses". In present work generation of micropulses was observed in experiments with ECR discharge stimulated by gyrotron radiation @ 37,5GHz, 100 kW. In this case pulses with duration less than 30 μs. Probably the same effect was observed in GANIL where 14 GHz radiation was used and pulses with duration about 2 ms were registered. In present work it was shown that intensity of such micropulse could be higher than intensity of “Preglow” peak at the same conditions but with longer MW pulse. The generation of micropulses of nitrogen and argon multicharged ions with current of a few mA and length about 30 μs after MW pulse with duration of 30-100 μs was demonstrated. The low level of impurities, high current density and rather high average charge make possible to consider such micropulse regime as perspective way for creation of a short pulsed ion source.
	Slides TUCOBK04 [3.473 MB]

TUPOT002	Enhancement of ECR Performances by Means of Carbon Nanotubes Based Electron Guns	plasma, gun, ion, ECR	114
	F. Odorici, M. Cuffiani, L. Malferrari, R. Rizzoli, G.P. Veronese INFN-Bologna, Bologna, Italy G. Castro, L. Celona, G. Ciavola, N. Gambino, S. Gammino, D. Mascali, R. Miracoli, F.P. Romano INFN/LNS, Catania, Italy T. Serafino Università di Messina, Messina, Italy
	One of the main goals of the scientific community which deals with ECR Ion Sources is the optimization of the Eelectron Energy Distribution Function (EEDF) inside the plasma. The EEDF consists of three different populations (cold, warm and hot electrons): the cold and the warm populations are responsible of the stabilization and of the efficient ionization of the plasma respectively. The presence of the hot population is doubly detrimental: in high frequency sources they lead to the heating of LHe in the superconducting coils’ cryostat and are also useless for the generation of high intensity ion beams, because of their small cross section. Therefore the injection of additional electrons inside the plasma may increase the density of cold and warm electrons, enabling at the same time to reduce the number of the high energy ones. The CANTES experiment tested the use of carbon nanotubes (CNTs) to emit electrons in presence of strong applied electric fields, in order to provide additional electrons to the plasma core. This technique was used with the Caesar ECR ion source, at INFN-LNS, demonstrating that the total extracted ion current is increased and that a relevant reduction of the number of “high energy” electrons (above 100 keV) can be obtained. This last result is even more important, because CNTs may be an effective and reliable tool to permit the operation of ECRIS at large power and high frequencies without any detrimental effect on the source stability and reliability coming from hot electrons. Details of the construction of CNTs based electron gun and their behaviour in plasma environments are presented. Preliminary results in terms of performances of the Caesar ECR ion source and possible future applications will be also discussed.
	Poster TUPOT002 [1.914 MB]

TUPOT009	Measurements of Bremsstrahlung Radiation and X-Ray Heat Load to Cryostat on SECRAL	radiation, ion, ECR, plasma	134
	H. Zhao, Y. Cao, X.X. Li, D. Xie, W.H. Zhang, X.Z. Zhang, H.W. Zhao, Y.H. Zhu IMP, Lanzhou, People's Republic of China W. Lu Graduate School of the Chinese Academy of Sciences, Beijing, People's Republic of China
	Measurement of Bremsstrahlung radiation from ECR plasma can yield certain information of the ECR heating process and a plausible estimate of the X-ray heat load to the cryostat of a superconducting ECR source which needs seriously addressed. With a newly-developed collimation system, which defines a narrower spatial range of the measurement and provides an effective shielding from the background, a systematic measurement of the Bremmstrahlung emitted axially from the SECRAL (Superconducting ECR Ion Source with Advanced design in Lanzhou) plasma were carried out recently. The spectral temperature Tspe, a relative index of mean energy of the plasma hot electrons, was derived through linear fitting of the spectra in semi-logarithm coordinates. This article will present and discuss the evolutions of the X-ray flux and the hot electron energy with various source parameters, such as heating frequency, RF power and magnetic field configuration. And possible solutions to reduce the X-ray heat load induced by Bremsstrahlung radiation are proposed and discussed.
	Poster TUPOT009 [1.581 MB]

TUPOT011	Measurement of the Diamagnetic Current on the LBNL 6.4 GHz ECR Ion Source	plasma, ECR, ECRIS, 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	plasma, simulation, ion, ECR	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]

TUPOT014	Optimized Extraction Conditions From High Power ECRIS by Dedicated Dielectric Structures	plasma, ion, extraction, ECRIS	147
	L. Schächter, S. Dobrescu IFIN, Magurele- Bucuresti, Romania K.E. Stiebing IKF, Frankfurt-am-Main, Germany
	The MD-method of enhancing the ion output from ECR ion sources is well established and basically works via two mechanisms, the regenerative injection of cold electrons from an emissive dielectric layer on the plasma chamber walls and via the cutting of compensating wall currents, which results in an improved ion extraction from the plasma. As this extraction from the plasma becomes a more and more challenging issue for modern ECRIS installations with high microwave power input, a series of experiments was carried out at the 14 GHz ECRIS of the Institut für Kernphysik in Frankfurt/Main, Germany (IKF). In contrast to our earlier work, in these experiments emphasis was put on the second of the above mechanisms namely to influence the sheath potential at the extraction by structures with special dielectric properties. Two different types of dielectric structures, Tantalum-oxide and Aluminum oxide (the latter also being used for the MD-method) with contrastingly different electrical properties were mounted on the extraction electrode of the IKF-ECRIS, facing the plasma. For both structures an increase of the extracted ion beam currents for middle and high charge states by 60-80 % was observed. The method is able to be applied also to other ECR ion sources for increasing the extracted ion beam performances.
	Poster TUPOT014 [0.510 MB]

TUPOT018	Sheath Formation of a Plasma Containing Multiply Charged Ions, Cold and Hot Electrons, and Emitted Electrons	ion, plasma, resonance, ion-source	159
	H.J. You NFRI, Daejon, Republic of Korea
	A model of sheath formation was extended to a plasma containing multiply charged ions (MCIs), cold and hot electrons, and secondary electrons emitted either by MCIs or hot electrons. The present study was motivated by the fact that the secondary electron yields are strongly dependent on the charge state of the ions and on the incident energy of electrons. Therefore, the contributions of the secondary electron emissions on the sheath formation would be severe in ECRIS plasmas where the charge state of ions is high and highly energetic electrons exist. In the model, modification of the “Bohm criterion” was given; thereby the sheath potential drop and the critical emission condition were analyzed. The model calculations were made mainly on the effects of the emitted electrons on the variations of the sheath potential drop, the particle and heat flux to the wall, by which some explanations for the effect of secondary electrons in ECR ion sources are given.
	Poster TUPOT018 [0.259 MB]

WECOAK02	Some Considerations About Frequency Tuning Effect in ECRIS Plasmas	plasma, ion, simulation, resonance	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	plasma, ECR, ion, ECRIS	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]

WECOAK05	Maximum Bremsstrahlung Energy Versus Different Heating Limits	resonance, plasma, ECRIS, photon	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]

THCOAK02	Kinetic Plasma Simulation of Ion Beam Extraction from an ECR Ion Source	ion, simulation, ECR, ion-source	194
	S.M. Elliott, E.K. White Thin Film Consulting, Longmont, Colorado, USA J. Simkin Vector Fields Ltd., Oxford, United Kingdom
	Designing optimized ECR ion beam sources can be streamlined by the accurate simulation of beam optical properties in order to predict ion extraction behavior. The complexity of these models, however, can make PIC-based simulations time-consuming. In this paper, we first describe a simple kinetic plasma finite element simulation of extraction of a proton beam from a permanent magnet hexapole electron cyclotron resonance (ECR) ion source. Second, we analyze the influence of secondary electrons generated by ion collisions in the residual gas on the space charge of a proton beam of a dual-solenoid ECR ion source. The finite element method (FEM) offers a fast modeling environment, allowing analysis of ion beam behavior under conditions of varying current density, electrode potential, and gas pressure.
	Slides THCOAK02 [0.821 MB]

Paper

Title

Other Keywords

Page

MOCOBK04

Recent Activities at the ORNL Multicharged Ion Research Facility (MIRF)

ion, ECR, plasma, permanent-magnet

23

F.W. Meyer, M.E. Bannister, S. Deng, I.N. Draganić, J.W. Hale, P.R. Harris, C.C. Havener, H.F. Krause, C.R. Vane
ORNL, Oak Ridge, Tennessee, USA

Funding: Sponsored by the Office of Fusion Energy Sciences and the Office of Basic Energy Sciences of the U.S. DOE under contract No. DE-AC05-00OR22725 with UT_Battelle.
We report on recent upgrades of the ORNL Multicharged Ion Research Facility, and our activities in the area of ECR ion source diagnostic measurements. The upgrades include installation of a new all permanent magnet ECR ion source [1] on a high voltage platform that increases our high energy beam production capability to 250keV/q, and installation of a floating beamline fed by a 10 GHz CAPRICE ECR ion source for producing decelerated ion beams to energies as low as a few eV/q range. The primary application of all the produced ion beams is to study fundamental collisional interactions [2] of multicharged ions with electrons, atoms, and surfaces. We also summarize recent diagnostic measurements of the ECR plasma potential and other plasma parameters using an in-situ Langmuir probe installed in the ECR edge plasma and complementary measurements [3] using an external beam deceleration method.
[1] D. Hitz et al. , “An All-Permanent Magnet ECR Ion Source for the ORNL MIRF Upgrade Project,” AIP Conference Proceedings 749, 123 (2005), Woodbury, NY.
[2] F.W. Meyer, “ECR-Based Atomic Collision Physics Research at ORNL MIRF,” in Trapping Highly Charged Ions: Fundamentals and Applications, J. Gillaspy, ed., Nova Science Pub., New York, 2000, pp. 117-164.
[3] P.R. Harris and F.W. Meyer, Rev. Sci. Inst. 81, 02A310 (2010).

Slides MOCOBK04 [2.645 MB]

MOCOCK05

Multigan®: a New Multicharged Ion Source Based on Axisymetric Magnetic Structure

ion, ECRIS, plasma, extraction

37

L. Maunoury, P. Delahaye, M. Dubois, P. Jardin, P. Lehérissier, M. Michel, J.Y. Pacquet
GANIL, Caen, France
S. Biri
ATOMKI, Debrecen, Hungary
X. Donzel, G. Gaubert, R. Leroy, A.C.C. Villari
PANTECHNIK, BAYEUX, France
C. Pierret
CIMAP, Caen, France

Standard ECR ion sources have radial magnetic field created by a multi-pole, e.g. hexapole or higher order, which fills all space in the center of the source structure. Based on the Monogan® ECRIS [1] concept, a new multicharged ECR ions source has been designed with a large opening space in the center of the source structure. This particular design allows, in a first approach, direct radial contact with the ECR plasma, allowing positioning of probes and targets for radioactive beam production very close to the plasma region. Secondly, the absence of a multi-pole allows considering extremely high magnetic fields with significantly smaller structural constraints. This source is combining the advantages of the axisymetric magnetic feature of Monogan® with higher frequencies. This paper will describe the magnetic structure calculation as well as the mechanical design and stresses of a full permanent magnet ion source using this concept. This source will be the first prototype of such an ECR ion source. Finally, using TrapCad code [2], an estimation of the electronic energy distribution has been calculated and thus, the performance of the source has been deduced. The beam formation and extraction were also roughly calculated taking into account magnetic and electric fields.
[1] P. Jardin et al., Review of Scientific Instruments, 73, 789 (2002).
[2] L. Maunoury et al., Plasma Sources Science and Technology , 18, 015019 (2009).

Slides MOCOCK05 [5.532 MB]

TUCOBK01

Preglow Phenomenon Origins and its Scaling for Ecris

plasma, radiation, ion, ECR

87

I. Izotov, V. Sidorov, V. Skalyga, V. Zorin
IAP/RAS, Nizhny Novgorod, Russia

Preglow effect investigation is one of topical directions of ECR ion sources development at present. Preglow is of interest for efficient short-pulsed multi-charged ion source creation. Particularly, such source of intense beams of short-living radioactive isotopes multi-charged ions is one of key elements in “Beta-Beam” European project [1]. Use of Preglow-generating regime of an ECRIS operation is a promising way of pulsed high-intense multi-charged ion beams production with much shorter edges in comparison with usual operation regime. The first theoretical investigations of Preglow phenomenon were performed in references [2,3]. Present work describes modified model of ECR discharge development in a magnetic trap of the ECRIS as a continuation of [2,3]. Numerical simulations made with the updated model allow authors to propose more physical and intuitive explanation of Preglow phenomenon origins. Obtained dependences of Preglow characteristics on experimental conditions offer a scaling for a wide range of ECRISes.
[1] (ONLINE) http://beta-beam.web.cern.ch/beta-beam/task/diverse/mandate.htm
[2] T. Thuillier et al, Rev. of Sci. Instrum., 79, 02A314, 2008.
[3] I. Izotov et al, IEEE Trans. Plasma Sci. 36, 1494, 2008.

Slides TUCOBK01 [0.928 MB]

TUCOBK03

Time Evolution of Plasma Potential in Pulsed Operation of ECRIS

plasma, ion, ion-source, 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]

TUCOBK04

Micropulses Generation in ECR Breakdown Stimulated by Gyrotron Radiation at 37.5 GHz

ion, plasma, ECR, ion-source

96

V. Skalyga, S. Golubev, I. Izotov, S. Razin, V. Sidorov, A. Vodopyanov, V. Zorin
IAP/RAS, Nizhny Novgorod, Russia

Present work is devoted to experimental and theoretical investigation of possibility of short pulsed (< 100 μs) multicharged ion beams creation. The possibility of quasi-stationary generation of short pulsed beams under conditions of quasi-gasdynamic plasma confinement was shown in recent experiments. Later another way of such beams creation based on “Preglow” effect was proposed. In present work it was demonstrated that in the case when duration of MW pulse is less then formation time of “Preglow” peak, realization of a regime when ion current is equal to zero during MW pulse and intense multicharged ions flux appears only when MW ends could be possible. Such pulses after the end of MW were called "micropulses". In present work generation of micropulses was observed in experiments with ECR discharge stimulated by gyrotron radiation @ 37,5GHz, 100 kW. In this case pulses with duration less than 30 μs. Probably the same effect was observed in GANIL where 14 GHz radiation was used and pulses with duration about 2 ms were registered. In present work it was shown that intensity of such micropulse could be higher than intensity of “Preglow” peak at the same conditions but with longer MW pulse. The generation of micropulses of nitrogen and argon multicharged ions with current of a few mA and length about 30 μs after MW pulse with duration of 30-100 μs was demonstrated. The low level of impurities, high current density and rather high average charge make possible to consider such micropulse regime as perspective way for creation of a short pulsed ion source.

Slides TUCOBK04 [3.473 MB]

TUPOT002

Enhancement of ECR Performances by Means of Carbon Nanotubes Based Electron Guns

plasma, gun, ion, ECR

114

F. Odorici, M. Cuffiani, L. Malferrari, R. Rizzoli, G.P. Veronese
INFN-Bologna, Bologna, Italy
G. Castro, L. Celona, G. Ciavola, N. Gambino, S. Gammino, D. Mascali, R. Miracoli, F.P. Romano
INFN/LNS, Catania, Italy
T. Serafino
Università di Messina, Messina, Italy

One of the main goals of the scientific community which deals with ECR Ion Sources is the optimization of the Eelectron Energy Distribution Function (EEDF) inside the plasma. The EEDF consists of three different populations (cold, warm and hot electrons): the cold and the warm populations are responsible of the stabilization and of the efficient ionization of the plasma respectively. The presence of the hot population is doubly detrimental: in high frequency sources they lead to the heating of LHe in the superconducting coils’ cryostat and are also useless for the generation of high intensity ion beams, because of their small cross section. Therefore the injection of additional electrons inside the plasma may increase the density of cold and warm electrons, enabling at the same time to reduce the number of the high energy ones. The CANTES experiment tested the use of carbon nanotubes (CNTs) to emit electrons in presence of strong applied electric fields, in order to provide additional electrons to the plasma core. This technique was used with the Caesar ECR ion source, at INFN-LNS, demonstrating that the total extracted ion current is increased and that a relevant reduction of the number of “high energy” electrons (above 100 keV) can be obtained. This last result is even more important, because CNTs may be an effective and reliable tool to permit the operation of ECRIS at large power and high frequencies without any detrimental effect on the source stability and reliability coming from hot electrons. Details of the construction of CNTs based electron gun and their behaviour in plasma environments are presented. Preliminary results in terms of performances of the Caesar ECR ion source and possible future applications will be also discussed.

Poster TUPOT002 [1.914 MB]

TUPOT009

Measurements of Bremsstrahlung Radiation and X-Ray Heat Load to Cryostat on SECRAL

radiation, ion, ECR, plasma

134

H. Zhao, Y. Cao, X.X. Li, D. Xie, W.H. Zhang, X.Z. Zhang, H.W. Zhao, Y.H. Zhu
IMP, Lanzhou, People's Republic of China
W. Lu
Graduate School of the Chinese Academy of Sciences, Beijing, People's Republic of China

Measurement of Bremsstrahlung radiation from ECR plasma can yield certain information of the ECR heating process and a plausible estimate of the X-ray heat load to the cryostat of a superconducting ECR source which needs seriously addressed. With a newly-developed collimation system, which defines a narrower spatial range of the measurement and provides an effective shielding from the background, a systematic measurement of the Bremmstrahlung emitted axially from the SECRAL (Superconducting ECR Ion Source with Advanced design in Lanzhou) plasma were carried out recently. The spectral temperature Tspe, a relative index of mean energy of the plasma hot electrons, was derived through linear fitting of the spectra in semi-logarithm coordinates. This article will present and discuss the evolutions of the X-ray flux and the hot electron energy with various source parameters, such as heating frequency, RF power and magnetic field configuration. And possible solutions to reduce the X-ray heat load induced by Bremsstrahlung radiation are proposed and discussed.

Poster TUPOT009 [1.581 MB]

TUPOT011

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

plasma, ECR, ECRIS, 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

plasma, simulation, ion, ECR

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]

TUPOT014

Optimized Extraction Conditions From High Power ECRIS by Dedicated Dielectric Structures

plasma, ion, extraction, ECRIS

147

L. Schächter, S. Dobrescu
IFIN, Magurele- Bucuresti, Romania
K.E. Stiebing
IKF, Frankfurt-am-Main, Germany

The MD-method of enhancing the ion output from ECR ion sources is well established and basically works via two mechanisms, the regenerative injection of cold electrons from an emissive dielectric layer on the plasma chamber walls and via the cutting of compensating wall currents, which results in an improved ion extraction from the plasma. As this extraction from the plasma becomes a more and more challenging issue for modern ECRIS installations with high microwave power input, a series of experiments was carried out at the 14 GHz ECRIS of the Institut für Kernphysik in Frankfurt/Main, Germany (IKF). In contrast to our earlier work, in these experiments emphasis was put on the second of the above mechanisms namely to influence the sheath potential at the extraction by structures with special dielectric properties. Two different types of dielectric structures, Tantalum-oxide and Aluminum oxide (the latter also being used for the MD-method) with contrastingly different electrical properties were mounted on the extraction electrode of the IKF-ECRIS, facing the plasma. For both structures an increase of the extracted ion beam currents for middle and high charge states by 60-80 % was observed. The method is able to be applied also to other ECR ion sources for increasing the extracted ion beam performances.

Poster TUPOT014 [0.510 MB]

TUPOT018

Sheath Formation of a Plasma Containing Multiply Charged Ions, Cold and Hot Electrons, and Emitted Electrons

ion, plasma, resonance, ion-source

159

H.J. You
NFRI, Daejon, Republic of Korea

A model of sheath formation was extended to a plasma containing multiply charged ions (MCIs), cold and hot electrons, and secondary electrons emitted either by MCIs or hot electrons. The present study was motivated by the fact that the secondary electron yields are strongly dependent on the charge state of the ions and on the incident energy of electrons. Therefore, the contributions of the secondary electron emissions on the sheath formation would be severe in ECRIS plasmas where the charge state of ions is high and highly energetic electrons exist. In the model, modification of the “Bohm criterion” was given; thereby the sheath potential drop and the critical emission condition were analyzed. The model calculations were made mainly on the effects of the emitted electrons on the variations of the sheath potential drop, the particle and heat flux to the wall, by which some explanations for the effect of secondary electrons in ECR ion sources are given.

Poster TUPOT018 [0.259 MB]

WECOAK02

Some Considerations About Frequency Tuning Effect in ECRIS Plasmas

plasma, ion, simulation, resonance

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

plasma, ECR, ion, ECRIS

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]

WECOAK05

Maximum Bremsstrahlung Energy Versus Different Heating Limits

resonance, plasma, ECRIS, photon

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]

THCOAK02

Kinetic Plasma Simulation of Ion Beam Extraction from an ECR Ion Source

ion, simulation, ECR, ion-source

194

S.M. Elliott, E.K. White
Thin Film Consulting, Longmont, Colorado, USA
J. Simkin
Vector Fields Ltd., Oxford, United Kingdom

Designing optimized ECR ion beam sources can be streamlined by the accurate simulation of beam optical properties in order to predict ion extraction behavior. The complexity of these models, however, can make PIC-based simulations time-consuming. In this paper, we first describe a simple kinetic plasma finite element simulation of extraction of a proton beam from a permanent magnet hexapole electron cyclotron resonance (ECR) ion source. Second, we analyze the influence of secondary electrons generated by ion collisions in the residual gas on the space charge of a proton beam of a dual-solenoid ECR ion source. The finite element method (FEM) offers a fast modeling environment, allowing analysis of ion beam behavior under conditions of varying current density, electrode potential, and gas pressure.

Slides THCOAK02 [0.821 MB]