- Email: [email protected]
Universal main magnetic focus ion source for production of highly charged ions
Nuclear Instruments and Methods in Physics Research B xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Universal main magnetic focus ion source for production of highly charged ions V.P. Ovsyannikov a, A.V. Nefiodov b,⇑, A.A. Levin a,c a
MaMFIS Group, Hochschulstr. 13, D-01069 Dresden, Germany Petersburg Nuclear Physics Institute, 188300 Gatchina, St. Petersburg, Russia c MaMFIS Lab, Shatelen Str. 26A, 194021 St. Petersburg, Russia b
a r t i c l e
i n f o
Article history: Received 26 October 2016 Received in revised form 10 May 2017 Accepted 11 May 2017 Available online xxxx Keywords: Atomic ions Ion source Smooth and rippled electron beams
a b s t r a c t A novel room-temperature compact ion source has been developed for the efficient production of atomic ions by means of an electron beam with energy Ee and current density je controllable within wide ranges (100 eV K Ee K 60 keV, 10 A/cm2 K je K 20 kA/cm2). In the first experiments, the X-ray emission of Ir64+ ions has been measured. Based on a combination of two different techniques, the device can operate both as conventional Electron Beam Ion Source/Trap and novel Main Magnetic Focus Ion Source. The tunable electron-optical system allows for realizing laminar and turbulent electron flows in a single experimental setup. The device is intended primarily for fundamental and applied research at standard university laboratories. Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction Nowadays there is a need to produce atomic ions of any elements of the periodic table in different charge states: from very low charged ions for modern lithography, fusion, astrophysics etc. to highly charged ions for atomic physics and accelerators. The electron beams required for such purposes should be characterized by current density je and energy Ee varying within wide ranges (10 A/cm2 K je K 10 kA/cm2, 100 eV K Ee K 100 keV). Satisfying these requirements in a single device is a very complex task [1–3]. Most of Electron Beam Ion Traps (EBITs) developed around the world operate stably in rather limited energy regimes. As characteristic examples of such devices one can mention the CoBIT with incident electron energy from 100 eV to 2.5 keV [4], EBIT with electron energy of up to 30 keV [5] at the Lawrence Livermore National Laboratory (LLNL) and LLNL SuperEBIT with Ee 200 keV [6]. 2. Techniques for production of highly charged ions At present, two methods for the production of highly charged ions by electron beams are known. The conventional technology is realized in the Electron Beam Ion Sources and Traps (EBIS/Ts) [5,7], where the working gas is ionized by the smooth electron ⇑ Corresponding author. E-mail address: [email protected] (A.V. Nefiodov). URL: http://mamfis.net/ovsyannikov.html (A.V. Nefiodov).
beam propagating through a few (at least three) sections of the drift-tube assembly along the z axis (see Fig. 1(a)). Ions are radially confined by the space charge of the electron beam. In addition, the trapping potential well can be strengthened by means of the variable inner diameter of the drift-tube segments. Axial ion-trapping potentials are created by voltages applied to the outermost drifttube electrodes. The extraction of ions from the trap is realized by decreasing the potential barrier in the direction of output. In the extraction regime, the EBIT is transformed into the EBIS. In the EBIT, the central section of drift tube is equipped with the slits for registration of the characteristic radiation of ions. In order to increase the current density, the electron beam is compressed by the axially symmetric magnetic field BðzÞ. In the EBIS, the characteristic length Ltrap of ion trap ranges from 0.7 m to 1.5 m, while the electron current density falls between 100 and 500 A/cm2. In the EBIT, the length of ion trap is reduced down to Ltrap 2–5 cm and the current density je is estimated to be at the level of about 2–10 kA/cm2. In the second method, highly charged ions are produced in the local ion traps formed by crossovers of the rippled electron beam. The up-to-date technology is realized in the Main Magnetic Focus Ion Source (MaMFIS), in which the crossover of the electron beam appears in the main focus of the thick magnetic lens [8,9] (see Fig. 1(b)). In order to extract the ions from the source, the rippled electron beam is transformed into the smooth flow by means of reducing potential of the focusing (Wehnelt) electrode. The depth of the axial potential well DU trap is estimated as follows
http://dx.doi.org/10.1016/j.nimb.2017.05.017 0168-583X/Ó 2017 Elsevier B.V. All rights reserved.
Please cite this article in press as: V.P. Ovsyannikov et al., Universal main magnetic focus ion source for production of highly charged ions, Nucl. Instr. Meth. B (2017), http://dx.doi.org/10.1016/j.nimb.2017.05.017
2
V.P. Ovsyannikov et al. / Nuclear Instruments and Methods in Physics Research B xxx (2017) xxx–xxx
Fig. 1. Principle schemes of EBIS/T (a) and MaMFIS (b). The potentials U 1 ; U 2 , and U 3 are applied, respectively, to the sections S1 ; S2 , and S3 of drift tube, U C is the potential at electron collector. The z axis is directed along electron beam. Depth of the potential well DU trap is equal to difference of the maximum and minimum potentials (DU trap ¼ U 1 U 2 ).
DU trap ¼
PU 1 rmax pffiffiffiffiffiffi ln : 2g r min
2pe0
ð1Þ
Here rmax and rmin are, respectively, the maximum and minimum values of the electron-beam radius, e0 is the permittivity of free space, g ¼ e=m is the absolute value of the electron chargeto-mass ratio, U 1 is the accelerating potential of the first section of drift tube integrated with the anode relative to the potential
change properties of the electron beam, namely, it can provide a rippled electron beam for high values of energy Ee and current density je as well as a smooth flow for low values of Ee and je . This is achieved by changing the magnetic field Bc on the cathode surface and geometry of the electron gun. For a number of cases, it is sufficient to change a position of the cathode relative to the anode of the electron gun and, respectively, relative to the magnetic field.
of the cathode, P ¼ Ie =U 3=2 is the perveance of the electron beam, 1 and Ie is the electron current. An advantage of the MaMFIS for the production of highly charged ions is extremely high value of the electron current density: the attained je exceeds 10 kA/cm2 at length of ion trap of about 1 mm. A small size of Ltrap is compensated by a miniature size of the ion source. It allows one to reduce the distance between ion trap and X-ray detector and accordingly to increase the geometric efficiency of the detector. In the first experimental tests of the device performed at the Institute for Atomic and Molecular Physics of the Justus-Liebig University Giessen, the X-ray emission of Ir64+ ions was successfully measured [8,10–12]. 3. Basics of universal MaMFIS Efficient ionization of light, moderate, and heavy ions is possible in a single apparatus by combination of the EBIS/T and MaMFIS techniques. It has been realized in the Universal MaMFIS (UniMaMFIS) with the cathode position adjustable in a focusing magnetic field [9]. The electron-optical system of the device allows one to
Fig. 2. MaMFIS running mode (a) and EBIS/T running mode (b). BðzÞ is distribution of the focusing magnetic field along the z axis of electron beam.
Please cite this article in press as: V.P. Ovsyannikov et al., Universal main magnetic focus ion source for production of highly charged ions, Nucl. Instr. Meth. B (2017), http://dx.doi.org/10.1016/j.nimb.2017.05.017
V.P. Ovsyannikov et al. / Nuclear Instruments and Methods in Physics Research B xxx (2017) xxx–xxx
The focusing magnetic field is created by permanent magnets. Accordingly, the axial distribution BðzÞ can be changed discretely. In Fig. 2, schematic diagrams of operation of the device in both running modes are shown. In the MaMFIS running mode, the magnetic field at the cathode is chosen to be nearly zero (Bc 0 G). The distance between the cathode and anode is equal to d1 for highvoltage ionization in the local ion trap with an extremely high electron current density (je J 10 kA/cm2). In the EBIS/T running mode, the magnetic field Bc at the cathode is of a significant value (Bc 1 kG). The cathode–anode distance is equal to d2 ðd2 < d1 Þ for lowvoltage ionization in the potential ion trap with a relatively low current density (10 A/cm2 K je K 100 A/cm2). In the both running modes, the UniMaMFIS operates at room temperature.
3
4. Computer simulations of electron trajectories The theoretical basis for the UniMaMFIS is provided by the theory of focusing the electron beam with an arbitrary magnetic field at the cathode [13–15]. According to this theory, for a particular distribution of the focusing magnetic field there is a set of electron guns with different geometry of electrodes, which emit either rippled or smooth electron beams depending on magnitude of the magnetic field at the cathode. In Fig. 3, the computer simulations of electron trajectories for the electron gun with cathode of 1 mm in diameter and variable cathode–anode distance for the designed device are presented. Fig. 3(a) corresponds to such position of the cathode, that magnetic flux of the focusing field does not pass through the cathode surface. In this case, a rippled electron beam can be formed. Fig. 3(b) presents partially immersed gun forming a smooth electron beam, when significant part of magnetic flux passes through the cathode surface. In this case, the ratio of the magnetic flux through the cathode to that through the cross section of electron beam is the best one for acquiring the optimal electron flow with a constant radius. In Fig. 3(c), it is shown such position of the cathode, that the magnetic flux through the cathode surface is equal to the magnetic flux through the cross section of the electron beam (fully immersed gun). In this case, the electron beam is rippled with a small amplitude. The given simulations of the electron trajectories in electron gun demonstrate that by changing the position of cathode relative to the focusing magnetic field and geometry of the electron gun it is possible to implement operational regimes of the MaMFIS and EBIS/T in a single device. 5. Prototype of UniMaMFIS The prototype of the device has been designed for the electron beam energy of 8–42 keV at current 30–50 mA (see Fig. 4). The first
Fig. 3. Electron trajectories for the electron gun with variable cathode–anode distance. Equipotentials are drawn by blue lines. (a) Rippled electron beam (Ie ¼ 200 mA, Ee ¼ 30 keV, Bc ¼ 100 G). (b) Smooth electron beam for the optimal relation between magnetic field at the cathode and the maximum focusing magnetic field (Ie ¼ 200 mA, Ee ¼ 12 keV, Bc ¼ 1 kG). (c) Low rippled electron beam for significant value of magnetic field at the cathode (Ie ¼ 20 mA, Ee ¼ 1 keV, Bc ¼ 2 kG).
Fig. 4. General view of the prototype MaMFIS.
Please cite this article in press as: V.P. Ovsyannikov et al., Universal main magnetic focus ion source for production of highly charged ions, Nucl. Instr. Meth. B (2017), http://dx.doi.org/10.1016/j.nimb.2017.05.017
4
V.P. Ovsyannikov et al. / Nuclear Instruments and Methods in Physics Research B xxx (2017) xxx–xxx
measurements of the X-ray emission spectra from cathode material (Ir and Ce) are performed for two positions of cathode at 8.9 kV and 30 kV voltages of electron gun (see Fig. 5). The results of these experiments are discussed in more details in a selectedtopics report at 18th International Conference on the Physics of
Table 1 Project parameters of UniMaMFIS. Operational regime
EBIS/T
MaMFIS
Ee (keV) Ie (mA) je (A/cm2) Ltrap (cm)
0.1–20 10–200 10–500 2
20–60 200 20000 0.1
Highly Charged Ions (HCI 2016) [16]. The maximum current density achieved experimentally is about 10 kA/cm2. 6. Upgraded version of UniMaMFIS We have aimed at development of a room-temperature handsize device with stepless adjustment of the cathode position suitable for the efficient production of low-, moderate-, and highcharge-state ions with the ionization energies of up to about 30 keV. In comparison with the prototype, the upgraded UniMaMFIS (see Fig. 6) operates in a wider energy range and allows for fine tuning of the cathode–anode distance. The project parameters of the ion source are given in Table 1. The expected yield of, for example, Xe52+ ions is estimated at the level of about 300 ions per second at the running frequency of 10 Hz. 7. Summary We have developed a novel room-temperature compact ion source for the efficient production of atomic ions by an electron beam. The device can operate within wide ranges of electron energy and current density both as EBIS/T and novel MaMFIS. The ion source allows one to produce both relatively low charged ions with ionization energy of about a few tens of eV and highly charged ions with ionization energy of up to a few tens of keV. The electron-optical system of the device is tunable. It can form either smooth electron beam with current density of about a few hundreds of A/cm2 or rippled electron beam with high current density in crossovers (local ion traps). The device can be used at standard university laboratories for investigation of fundamental and applied problems related to physics of atomic ions and their characteristic radiation. Fig. 5. X-ray emission spectra from ions of Ir and Ce for the electron energies Ee of 8.9 keV and 30 keV.
Acknowledgments The authors are grateful to A. Müller for giving opportunity to test the MaMFIS at the laboratory of Institute of Atomic and Molecular Physics (Justus-Liebig University Giessen), to A. Borovik Jr. for his support in X-ray measurements, and to O.K. Kultashev and V. Kogan for their contribution to computer simulation of the electronic optics. References
Fig. 6. General view of the upgraded UniMaMFIS.
[1] A. Lapierre, M. Brodeur, T. Brunner, S. Ettenauer, A.T. Gallant, V. Simon, M. Good, M.W. Froese, J.R. Crespo López-Urrutia, P. Delheij, S. Epp, R. Ringle, S. Schwarz, J. Ullrich, J. Dilling, Nucl. Instrum. Methods A 624 (2010) 54. [2] S.W. Epp, J.R. Crespo López-Urrutia, M.C. Simon, T. Baumann, G. Brenner, R. Ginzel, N. Guerassimova, V. Mäckel, P.H. Mokler, B.L. Schmitt, H. Tawara, J. Ullrich J. Phys. B 43 (2010) 194008. [3] M.C. Simon, M. Schwarz, S.W. Epp, C. Beilmann, B.L. Schmitt, Z. Harman, T.M. Baumann, P.H. Mokler, S. Bernitt, R. Ginzel, S.G. Higgins, C.H. Keitel, R. Klawitter, K. Kubicˇek, V. Mäckel, J. Ullrich, J.R. Crespo López-Urrutia, J. Phys. B 43 (2010) 065003. [4] H.A. Sakaue, N. Nakamura, E. Watanabe, A. Komatsu, T. Watanabe, J. Instrum. 5 (2010) C08010. [5] M.A. Levine, R.E. Marrs, J.R. Henderson, D.A. Knapp, M.B. Schneider, Phys. Scr. T22 (1988) 157. [6] D.A. Knapp, R.E. Marrs, S.R. Elliott, E.W. Magee, R. Zasadzinski, Nucl. Instrum. Methods A 334 (1993) 305.
Please cite this article in press as: V.P. Ovsyannikov et al., Universal main magnetic focus ion source for production of highly charged ions, Nucl. Instr. Meth. B (2017), http://dx.doi.org/10.1016/j.nimb.2017.05.017
V.P. Ovsyannikov et al. / Nuclear Instruments and Methods in Physics Research B xxx (2017) xxx–xxx [7] E.D. Donets, USSR Inventor’s Certificate No. 248860, 16 March (1967); Bull. OIPOTZ 23 (1969) 65. [8] V.P. Ovsyannikov, Main Magnetic Focus Ion Trap, new tool for trapping of highly charged ions, arXiv e-print (arXiv:1403.2168) (2014). [9] V.P. Ovsyannikov, A.V. Nefiodov, O.K. Kultashev, Method and device for the production of highly charged ions, Int. Patent Appl. WO 2016/142481 A1. [10] V.P. Ovsyannikov, A.V. Nefiodov, A. Borovik Jr., A. Müller, J. Phys.: Conf. Ser. 635 (2015) 022021. [11] V.P. Ovsyannikov, A.V. Nefiodov, Nucl. Instrum. Methods B 367 (2016) 1.
5
[12] V.P. Ovsyannikov, A.V. Nefiodov, Nucl. Instrum. Methods B 370 (2016) 32. [13] I.V. Alamovsky, Electron Beams and Electron Guns. Moscow, Soviet radio Publ., 1966, 456 p. (in Russian). [14] K. Amboss, IEEE Trans. Electr. Dev. 16 (1969) 897. [15] R. Becker, Nucl. Instrum. Methods 187 (1981) 255. [16] A. Borovik, Jr., J. Dreiling, R. Silwal, E. Takács, J. Gillaspy, R. Lomsadze, V. Ovsyannikov, K. Huber, S. Schippers, A. Müller, Yu. Ralchenko, Dielectronic recombination processes in highly-charged heavy ions observed in ion traps, Book of abstracts, HCI-2016, ST10, p. 44.
Please cite this article in press as: V.P. Ovsyannikov et al., Universal main magnetic focus ion source for production of highly charged ions, Nucl. Instr. Meth. B (2017), http://dx.doi.org/10.1016/j.nimb.2017.05.017
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Universal main magnetic focus ion source for production of highly charged ions V.P. Ovsyannikov a, A.V. Nefiodov b,⇑, A.A. Levin a,c a
MaMFIS Group, Hochschulstr. 13, D-01069 Dresden, Germany Petersburg Nuclear Physics Institute, 188300 Gatchina, St. Petersburg, Russia c MaMFIS Lab, Shatelen Str. 26A, 194021 St. Petersburg, Russia b
a r t i c l e
i n f o
Article history: Received 26 October 2016 Received in revised form 10 May 2017 Accepted 11 May 2017 Available online xxxx Keywords: Atomic ions Ion source Smooth and rippled electron beams
a b s t r a c t A novel room-temperature compact ion source has been developed for the efficient production of atomic ions by means of an electron beam with energy Ee and current density je controllable within wide ranges (100 eV K Ee K 60 keV, 10 A/cm2 K je K 20 kA/cm2). In the first experiments, the X-ray emission of Ir64+ ions has been measured. Based on a combination of two different techniques, the device can operate both as conventional Electron Beam Ion Source/Trap and novel Main Magnetic Focus Ion Source. The tunable electron-optical system allows for realizing laminar and turbulent electron flows in a single experimental setup. The device is intended primarily for fundamental and applied research at standard university laboratories. Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction Nowadays there is a need to produce atomic ions of any elements of the periodic table in different charge states: from very low charged ions for modern lithography, fusion, astrophysics etc. to highly charged ions for atomic physics and accelerators. The electron beams required for such purposes should be characterized by current density je and energy Ee varying within wide ranges (10 A/cm2 K je K 10 kA/cm2, 100 eV K Ee K 100 keV). Satisfying these requirements in a single device is a very complex task [1–3]. Most of Electron Beam Ion Traps (EBITs) developed around the world operate stably in rather limited energy regimes. As characteristic examples of such devices one can mention the CoBIT with incident electron energy from 100 eV to 2.5 keV [4], EBIT with electron energy of up to 30 keV [5] at the Lawrence Livermore National Laboratory (LLNL) and LLNL SuperEBIT with Ee 200 keV [6]. 2. Techniques for production of highly charged ions At present, two methods for the production of highly charged ions by electron beams are known. The conventional technology is realized in the Electron Beam Ion Sources and Traps (EBIS/Ts) [5,7], where the working gas is ionized by the smooth electron ⇑ Corresponding author. E-mail address: [email protected] (A.V. Nefiodov). URL: http://mamfis.net/ovsyannikov.html (A.V. Nefiodov).
beam propagating through a few (at least three) sections of the drift-tube assembly along the z axis (see Fig. 1(a)). Ions are radially confined by the space charge of the electron beam. In addition, the trapping potential well can be strengthened by means of the variable inner diameter of the drift-tube segments. Axial ion-trapping potentials are created by voltages applied to the outermost drifttube electrodes. The extraction of ions from the trap is realized by decreasing the potential barrier in the direction of output. In the extraction regime, the EBIT is transformed into the EBIS. In the EBIT, the central section of drift tube is equipped with the slits for registration of the characteristic radiation of ions. In order to increase the current density, the electron beam is compressed by the axially symmetric magnetic field BðzÞ. In the EBIS, the characteristic length Ltrap of ion trap ranges from 0.7 m to 1.5 m, while the electron current density falls between 100 and 500 A/cm2. In the EBIT, the length of ion trap is reduced down to Ltrap 2–5 cm and the current density je is estimated to be at the level of about 2–10 kA/cm2. In the second method, highly charged ions are produced in the local ion traps formed by crossovers of the rippled electron beam. The up-to-date technology is realized in the Main Magnetic Focus Ion Source (MaMFIS), in which the crossover of the electron beam appears in the main focus of the thick magnetic lens [8,9] (see Fig. 1(b)). In order to extract the ions from the source, the rippled electron beam is transformed into the smooth flow by means of reducing potential of the focusing (Wehnelt) electrode. The depth of the axial potential well DU trap is estimated as follows
http://dx.doi.org/10.1016/j.nimb.2017.05.017 0168-583X/Ó 2017 Elsevier B.V. All rights reserved.
Please cite this article in press as: V.P. Ovsyannikov et al., Universal main magnetic focus ion source for production of highly charged ions, Nucl. Instr. Meth. B (2017), http://dx.doi.org/10.1016/j.nimb.2017.05.017
2
V.P. Ovsyannikov et al. / Nuclear Instruments and Methods in Physics Research B xxx (2017) xxx–xxx
Fig. 1. Principle schemes of EBIS/T (a) and MaMFIS (b). The potentials U 1 ; U 2 , and U 3 are applied, respectively, to the sections S1 ; S2 , and S3 of drift tube, U C is the potential at electron collector. The z axis is directed along electron beam. Depth of the potential well DU trap is equal to difference of the maximum and minimum potentials (DU trap ¼ U 1 U 2 ).
DU trap ¼
PU 1 rmax pffiffiffiffiffiffi ln : 2g r min
2pe0
ð1Þ
Here rmax and rmin are, respectively, the maximum and minimum values of the electron-beam radius, e0 is the permittivity of free space, g ¼ e=m is the absolute value of the electron chargeto-mass ratio, U 1 is the accelerating potential of the first section of drift tube integrated with the anode relative to the potential
change properties of the electron beam, namely, it can provide a rippled electron beam for high values of energy Ee and current density je as well as a smooth flow for low values of Ee and je . This is achieved by changing the magnetic field Bc on the cathode surface and geometry of the electron gun. For a number of cases, it is sufficient to change a position of the cathode relative to the anode of the electron gun and, respectively, relative to the magnetic field.
of the cathode, P ¼ Ie =U 3=2 is the perveance of the electron beam, 1 and Ie is the electron current. An advantage of the MaMFIS for the production of highly charged ions is extremely high value of the electron current density: the attained je exceeds 10 kA/cm2 at length of ion trap of about 1 mm. A small size of Ltrap is compensated by a miniature size of the ion source. It allows one to reduce the distance between ion trap and X-ray detector and accordingly to increase the geometric efficiency of the detector. In the first experimental tests of the device performed at the Institute for Atomic and Molecular Physics of the Justus-Liebig University Giessen, the X-ray emission of Ir64+ ions was successfully measured [8,10–12]. 3. Basics of universal MaMFIS Efficient ionization of light, moderate, and heavy ions is possible in a single apparatus by combination of the EBIS/T and MaMFIS techniques. It has been realized in the Universal MaMFIS (UniMaMFIS) with the cathode position adjustable in a focusing magnetic field [9]. The electron-optical system of the device allows one to
Fig. 2. MaMFIS running mode (a) and EBIS/T running mode (b). BðzÞ is distribution of the focusing magnetic field along the z axis of electron beam.
Please cite this article in press as: V.P. Ovsyannikov et al., Universal main magnetic focus ion source for production of highly charged ions, Nucl. Instr. Meth. B (2017), http://dx.doi.org/10.1016/j.nimb.2017.05.017
V.P. Ovsyannikov et al. / Nuclear Instruments and Methods in Physics Research B xxx (2017) xxx–xxx
The focusing magnetic field is created by permanent magnets. Accordingly, the axial distribution BðzÞ can be changed discretely. In Fig. 2, schematic diagrams of operation of the device in both running modes are shown. In the MaMFIS running mode, the magnetic field at the cathode is chosen to be nearly zero (Bc 0 G). The distance between the cathode and anode is equal to d1 for highvoltage ionization in the local ion trap with an extremely high electron current density (je J 10 kA/cm2). In the EBIS/T running mode, the magnetic field Bc at the cathode is of a significant value (Bc 1 kG). The cathode–anode distance is equal to d2 ðd2 < d1 Þ for lowvoltage ionization in the potential ion trap with a relatively low current density (10 A/cm2 K je K 100 A/cm2). In the both running modes, the UniMaMFIS operates at room temperature.
3
4. Computer simulations of electron trajectories The theoretical basis for the UniMaMFIS is provided by the theory of focusing the electron beam with an arbitrary magnetic field at the cathode [13–15]. According to this theory, for a particular distribution of the focusing magnetic field there is a set of electron guns with different geometry of electrodes, which emit either rippled or smooth electron beams depending on magnitude of the magnetic field at the cathode. In Fig. 3, the computer simulations of electron trajectories for the electron gun with cathode of 1 mm in diameter and variable cathode–anode distance for the designed device are presented. Fig. 3(a) corresponds to such position of the cathode, that magnetic flux of the focusing field does not pass through the cathode surface. In this case, a rippled electron beam can be formed. Fig. 3(b) presents partially immersed gun forming a smooth electron beam, when significant part of magnetic flux passes through the cathode surface. In this case, the ratio of the magnetic flux through the cathode to that through the cross section of electron beam is the best one for acquiring the optimal electron flow with a constant radius. In Fig. 3(c), it is shown such position of the cathode, that the magnetic flux through the cathode surface is equal to the magnetic flux through the cross section of the electron beam (fully immersed gun). In this case, the electron beam is rippled with a small amplitude. The given simulations of the electron trajectories in electron gun demonstrate that by changing the position of cathode relative to the focusing magnetic field and geometry of the electron gun it is possible to implement operational regimes of the MaMFIS and EBIS/T in a single device. 5. Prototype of UniMaMFIS The prototype of the device has been designed for the electron beam energy of 8–42 keV at current 30–50 mA (see Fig. 4). The first
Fig. 3. Electron trajectories for the electron gun with variable cathode–anode distance. Equipotentials are drawn by blue lines. (a) Rippled electron beam (Ie ¼ 200 mA, Ee ¼ 30 keV, Bc ¼ 100 G). (b) Smooth electron beam for the optimal relation between magnetic field at the cathode and the maximum focusing magnetic field (Ie ¼ 200 mA, Ee ¼ 12 keV, Bc ¼ 1 kG). (c) Low rippled electron beam for significant value of magnetic field at the cathode (Ie ¼ 20 mA, Ee ¼ 1 keV, Bc ¼ 2 kG).
Fig. 4. General view of the prototype MaMFIS.
Please cite this article in press as: V.P. Ovsyannikov et al., Universal main magnetic focus ion source for production of highly charged ions, Nucl. Instr. Meth. B (2017), http://dx.doi.org/10.1016/j.nimb.2017.05.017
4
V.P. Ovsyannikov et al. / Nuclear Instruments and Methods in Physics Research B xxx (2017) xxx–xxx
measurements of the X-ray emission spectra from cathode material (Ir and Ce) are performed for two positions of cathode at 8.9 kV and 30 kV voltages of electron gun (see Fig. 5). The results of these experiments are discussed in more details in a selectedtopics report at 18th International Conference on the Physics of
Table 1 Project parameters of UniMaMFIS. Operational regime
EBIS/T
MaMFIS
Ee (keV) Ie (mA) je (A/cm2) Ltrap (cm)
0.1–20 10–200 10–500 2
20–60 200 20000 0.1
Highly Charged Ions (HCI 2016) [16]. The maximum current density achieved experimentally is about 10 kA/cm2. 6. Upgraded version of UniMaMFIS We have aimed at development of a room-temperature handsize device with stepless adjustment of the cathode position suitable for the efficient production of low-, moderate-, and highcharge-state ions with the ionization energies of up to about 30 keV. In comparison with the prototype, the upgraded UniMaMFIS (see Fig. 6) operates in a wider energy range and allows for fine tuning of the cathode–anode distance. The project parameters of the ion source are given in Table 1. The expected yield of, for example, Xe52+ ions is estimated at the level of about 300 ions per second at the running frequency of 10 Hz. 7. Summary We have developed a novel room-temperature compact ion source for the efficient production of atomic ions by an electron beam. The device can operate within wide ranges of electron energy and current density both as EBIS/T and novel MaMFIS. The ion source allows one to produce both relatively low charged ions with ionization energy of about a few tens of eV and highly charged ions with ionization energy of up to a few tens of keV. The electron-optical system of the device is tunable. It can form either smooth electron beam with current density of about a few hundreds of A/cm2 or rippled electron beam with high current density in crossovers (local ion traps). The device can be used at standard university laboratories for investigation of fundamental and applied problems related to physics of atomic ions and their characteristic radiation. Fig. 5. X-ray emission spectra from ions of Ir and Ce for the electron energies Ee of 8.9 keV and 30 keV.
Acknowledgments The authors are grateful to A. Müller for giving opportunity to test the MaMFIS at the laboratory of Institute of Atomic and Molecular Physics (Justus-Liebig University Giessen), to A. Borovik Jr. for his support in X-ray measurements, and to O.K. Kultashev and V. Kogan for their contribution to computer simulation of the electronic optics. References
Fig. 6. General view of the upgraded UniMaMFIS.
[1] A. Lapierre, M. Brodeur, T. Brunner, S. Ettenauer, A.T. Gallant, V. Simon, M. Good, M.W. Froese, J.R. Crespo López-Urrutia, P. Delheij, S. Epp, R. Ringle, S. Schwarz, J. Ullrich, J. Dilling, Nucl. Instrum. Methods A 624 (2010) 54. [2] S.W. Epp, J.R. Crespo López-Urrutia, M.C. Simon, T. Baumann, G. Brenner, R. Ginzel, N. Guerassimova, V. Mäckel, P.H. Mokler, B.L. Schmitt, H. Tawara, J. Ullrich J. Phys. B 43 (2010) 194008. [3] M.C. Simon, M. Schwarz, S.W. Epp, C. Beilmann, B.L. Schmitt, Z. Harman, T.M. Baumann, P.H. Mokler, S. Bernitt, R. Ginzel, S.G. Higgins, C.H. Keitel, R. Klawitter, K. Kubicˇek, V. Mäckel, J. Ullrich, J.R. Crespo López-Urrutia, J. Phys. B 43 (2010) 065003. [4] H.A. Sakaue, N. Nakamura, E. Watanabe, A. Komatsu, T. Watanabe, J. Instrum. 5 (2010) C08010. [5] M.A. Levine, R.E. Marrs, J.R. Henderson, D.A. Knapp, M.B. Schneider, Phys. Scr. T22 (1988) 157. [6] D.A. Knapp, R.E. Marrs, S.R. Elliott, E.W. Magee, R. Zasadzinski, Nucl. Instrum. Methods A 334 (1993) 305.
Please cite this article in press as: V.P. Ovsyannikov et al., Universal main magnetic focus ion source for production of highly charged ions, Nucl. Instr. Meth. B (2017), http://dx.doi.org/10.1016/j.nimb.2017.05.017
V.P. Ovsyannikov et al. / Nuclear Instruments and Methods in Physics Research B xxx (2017) xxx–xxx [7] E.D. Donets, USSR Inventor’s Certificate No. 248860, 16 March (1967); Bull. OIPOTZ 23 (1969) 65. [8] V.P. Ovsyannikov, Main Magnetic Focus Ion Trap, new tool for trapping of highly charged ions, arXiv e-print (arXiv:1403.2168) (2014). [9] V.P. Ovsyannikov, A.V. Nefiodov, O.K. Kultashev, Method and device for the production of highly charged ions, Int. Patent Appl. WO 2016/142481 A1. [10] V.P. Ovsyannikov, A.V. Nefiodov, A. Borovik Jr., A. Müller, J. Phys.: Conf. Ser. 635 (2015) 022021. [11] V.P. Ovsyannikov, A.V. Nefiodov, Nucl. Instrum. Methods B 367 (2016) 1.
5
[12] V.P. Ovsyannikov, A.V. Nefiodov, Nucl. Instrum. Methods B 370 (2016) 32. [13] I.V. Alamovsky, Electron Beams and Electron Guns. Moscow, Soviet radio Publ., 1966, 456 p. (in Russian). [14] K. Amboss, IEEE Trans. Electr. Dev. 16 (1969) 897. [15] R. Becker, Nucl. Instrum. Methods 187 (1981) 255. [16] A. Borovik, Jr., J. Dreiling, R. Silwal, E. Takács, J. Gillaspy, R. Lomsadze, V. Ovsyannikov, K. Huber, S. Schippers, A. Müller, Yu. Ralchenko, Dielectronic recombination processes in highly-charged heavy ions observed in ion traps, Book of abstracts, HCI-2016, ST10, p. 44.
Please cite this article in press as: V.P. Ovsyannikov et al., Universal main magnetic focus ion source for production of highly charged ions, Nucl. Instr. Meth. B (2017), http://dx.doi.org/10.1016/j.nimb.2017.05.017