- Email: [email protected]
Investigation of resonant inner-shell processes with an electron beam ion trap
ARTICLE IN PRESS
Radiation Physics and Chemistry 75 (2006) 1749–1752 www.elsevier.com/locate/radphyschem
Investigation of resonant inner-shell processes with an electron beam ion trap Nobuyuki Nakamuraa,, Hirotsugu Tobiyamaa, Hiroaki Noharaa, Daiji Katob, Hirofumi Watanabec, Fred J. Currelld, Shunsuke Ohtania a
Institute for Laser Science, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan b National Institute for Fusion Science, Toki, Gifu 509-5292, Japan c Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan d Queen’s University Belfast, Belfast BT7 1NN, UK Accepted 27 July 2005
Abstract The collision processes of highly charged ions with electrons have been studied with an electron beam ion trap. Resonant inner-shell processes such as dielectronic recombination and resonant excitation double autoionization were investigated by observing the number ratio of extracted ions with adjacent charge states. r 2006 Elsevier Ltd. All rights reserved.
1. Introduction Resonant excitation and recombination are important processes in electron–ion interactions (Mu¨ller, 1999). In the interactions with highly charged ions (HCIs), a free electron is captured with a large probability and simultaneously a bound electron is excited to form a doubly excited state resonantly. This unstable intermediate state may decay by photon emission: dielectronic recombination (DR), or by emission of two electrons due to successive autoionization: resonant excitation/double autoionization (REDA). In this paper, we present an observation of these resonant processes using an electron beam ion trap (EBIT) (Marrs et al., 1988). An EBIT is suitable for studying such collision processes of HCIs with electrons because it has a mono-energetic and unidirectional electron beam interacting with trapped HCIs. By Corresponding author. Tel.: +81 424 43 5709; fax: +81 424 85 8960. E-mail address: [email protected] (N. Nakamura).
observing X-ray spectra or charge state distributions while controlling the electron beam energy, one can investigate various electron–HCI collision processes including the resonant processes described above.
2. Experiments The present experimental procedure is similar to those of DeWitt et al. (1993) and Ali et al. (1991) and is very effective for measurement of the electron-energy dependence of extracted-ion yields from an EBIT (or an electron beam ion source) in studying the DR processes of HCIs. In the present studies, an electron beam ion trap in Tokyo (Tokyo EBIT) (Nakamura et al., 1997) has been used. In the trap region of the EBIT, HCIs are produced and confined with a narrow charge-state distribution. At the charge equilibrium, the ionization balance for trapped HCIs is determined by the rates for ionization and recombination processes. Then, the number ratio for the abundance of adjacent charge-state
0969-806X/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.radphyschem.2005.07.032
ARTICLE IN PRESS N. Nakamura et al. / Radiation Physics and Chemistry 75 (2006) 1749–1752
CX nq1 sre q þ hsq i ¼ , ion nq sq1
(1)
where sre is the recombination cross section for q q ! q 1, sion q1 the electron impact ionization (EI) cross section for q 1 ! q, and hsCX q i the effective charge exchange cross section (Marrs et al., 1994) for collisions with the residual gas. In this expression, other loss terms for ions of charge state q such as the escape factor from the trap are not included. When there is no resonant process, the ratio nq1 =nq varies slowly with electron energy. Since hsCX q i can be excluded by observing the gas pressure dependence and by extrapolating it to zero neutral density, sion q1 can be obtained by normalizing sre to a reliable theoretical value of the q radiative recombination (RR) cross section. When the interaction energy of electrons matches (to with in the beam energy width of about 50 eV) a resonant energy where ionization or recombination is enhanced, the charge-state distribution can change drastically. Therefore, the abundance ratio of ions with neighbouring charge states in the trap should also change when this condition is fulfilled. For example, at an electron beam energy at which DR is possible, sre q can be represented as the sum of two components, sRR and q sDR q , and the ratio nq1 =nq is thus enhanced. Since the amount enhancement corresponds to the ratio ion DR sDR can be obtained by using the experimenq =sq1 , sq tally determined ionization cross section sion q1 , assuming the latter is slowly varying. The ion number ratio can be obtained by measuring the intensity of ions extracted from the EBIT. The trapped ions are heated through successive electron collisions so that they can finally escape from the trap. Ions which escape axially towards the electron collector can be extracted into an HCI beam line (Shimizu et al., 2000). The efficiency of extraction and transmission in the beam line might be different depending on the charge state of the extracted ions. However, it is considered to be almost the same for adjacent charge states for very high q (Lo´pez-Urrutia et al., 2004) because they have quite close values of charge-to-mass ratio. In the present study, the measurements were repeated with different experimental conditions and we could not find any significant difference for the ion ratios for the same pairs of adjacent charge states. Although more careful examination may be needed to check the absolute systematic errors, it is assumed here that the extracted ion intensity ratio gives the ion number ratio inside the trap. The energy of electrons interacting with HCIs is determined by the potential difference between the cathode and the interaction region in the central DT.
The electron energy was scanned by controlling the voltage at the electron gun, with respect to laboratory earth. In order to ensure the charge equilibrium condition was maintained, the scan was performed very slowly ð10 s=stepÞ. The voltage of the central drift tube was fixed to þ3 kV throughout the experiment while the final DT was set a further 50 V above this value, fixing the axial trapping voltage for the ions.
3. Results and discussion 3.1. KLL DR for He- to C-like iodine An intermediate doubly excited state having low principal quantum numbers for both excited electrons formed in electron interactions with high q, high Z (atomic number) HCIs, would usually predominantly decay radiatively. Therefore, the observed nq1 =nq spectra in these resonant interactions would be expected to show peak structures corresponding to enhancement at the resonant energies. Fig. 1 shows the electron energy dependence of nq1 =nq : the number ratio between adjacent charge states of highly charged iodine ions extracted from the
10 e- + Iq+
8
Li/He (sHeDR) (x1/5)
6
4 Be/Li (sLiDR) B/Be (sBeDR)
2
C/B (sBDR) N/C (sCDR)
0
500 K-alpha cut
19.5
20
20.5
21
0 21.5
X-ray counts
ions can be expressed in terms of cross sections for relevant e–HCI collision processes
Ratio between adjacent ions
1750
Electron energy (keV) Fig. 1. Number ratio between adjacent charge states of highly charged iodine ions extracted from the Tokyo-EBIT as a function of electron energy. The ratios are raised by 0.5, 1.0, 1.5, and 5 for C/B, B/Be, Be/Li and Li/He, respectively, for clarity. K-a X-ray intensity is also plotted.
ARTICLE IN PRESS N. Nakamura et al. / Radiation Physics and Chemistry 75 (2006) 1749–1752
3.2. REDA in Na-like iodine As well as DR, resonant ionization, e.g. REDA, can cause a sharp electron energy dependence in the ion number ratio. By extending Eq. (1) to include REDA and DR contributions, the ion number ratio can be expressed by the following formula: REDA sion nq q1 þ sq1 ¼ RR , CX nq1 sq þ sDR q þ hsq i
(2)
where sion q1 is the (non-resonant) ionization cross section including direct and indirect (e.g. excitation autoionization) processes, sREDA is the REDA cross section, and q1 sRR and sDR are the RR and the DR cross section, q q respectively. Thus, DR should decrease the ion ratio nq =nq1 whereas REDA increases the ratio. In general, the radiative decay rates have a strong Z dependence (proportional to Z 4 ). For intermediate doubly excited states formed in the resonant interaction with relatively low q HCIs, the DR rates can be strongly suppressed due to decreasing Zeff (effective atomic number). Therefore, in ionic systems like Na-like ions, strong relative enhancement of the cross section due to REDA can be expected. Fig. 2 shows the electron energy dependence of the number ratio of Ne-like and Na-like iodine ions extracted from the Tokyo-EBIT. A great number of structures which correspond to DR for Ne-like ions and REDA for Na-like ions can be observed. In the figure, the theoretical ionization cross section for Na-like Xe calculated by Chen and Reed (1993) is also plotted. The energy scale for the theoretical cross section was scaled by Z2 and shifted for comparison. Since the dotted line indicates the ionization cross section without REDA, the DR contribution is considered to appear below the dotted line whereas the REDA contribution appears above the dotted line. Although the overall agreement
4 Ratio between Na-like and Ne-like I ions
Tokyo-EBIT. Lots of structures corresponding to KLL DR processes are observed. In the figure, X-ray counts for the K-a line are also plotted as a function of electron energy. Because it is difficult to resolve the K-a X-ray emission for different (isonuclear) charge states with an ordinary Ge detector, contributions from several charge states are superimposed. On the other hand, the charge state has been clearly resolved for the extracted ions, so that the presence of DR resonances for each charge state can be deduced. However, in practice, in order to determine the DR cross section, contributions from escape and multiple charge exchange have to be treated carefully. For example, the dips in the C/N ratio appearing at electron energies of around 20.5 and 20:8 keV are considered to be the artifacts due to these contributions. Analysis to include these effects are on going.
1751
3
Ionization CS for Na-like Xe (horizontal scale was scaled by Z2 and shifted)
Experiment Ne/Na
2
1
0 4
4.5
5 5.5 6 6.5 Electron energy (keV)
7
7.5
Fig. 2. Number ratio of Ne-like and Na-like iodine ions extracted from the Tokyo-EBIT. The theoretical ionization cross section for Na-like xenon calculated by Chen and Reed (1993) is also plotted after scaling and shifting of the electron energy scale.
between experiment and the theory is found, complications introduced by the superposition of DR and REDA makes the comparison difficult. The detailed analysis by calculating both the REDA and DR contributions is ongoing and will be published elsewhere.
4. Conclusion We have studied the resonant processes in electron–HCI collisions such as DR and REDA using the Tokyo electron beam ion trap by measuring the number ratio of extracted ions. The effectiveness and efficiency of the present method to study these processes has been demonstrated. Although the present study was done only for iodine ions, the method can be applied for any other ions. Thus a systematic study for observing the Z-dependence is on-going.
Acknowledgement This work has been supported by the CREST program ‘‘Creation of Ultrafast, Ultralow Power, Super-performance Nanodevices and Systems’’ in the Japan Science and Technology Agency and Japan–UK Research Cooperative Program in Japan Society for the Promotion of Science, and has been performed under the activity of the 21st Century Center of Excellence (COE) Program ‘‘Innovation in Coherent Optical Science’’ at the University of Electro-Communications. N. Nakamura acknowledges the support of the Matsuo Foundation.
ARTICLE IN PRESS 1752
N. Nakamura et al. / Radiation Physics and Chemistry 75 (2006) 1749–1752
References Ali, R., Bhalla, C.P., Cocke, C.L., Schulz, M., Stockli, M., 1991. Dielectronic recombination and electron-impact excitation of heliumlike argon. Phys. Rev. A 44, 223. Chen, M.H., Reed, K.J., 1993. Indirect contributions to electron-impact ionization of kr24þ , kr25þ , and xe43þ . Phys. Rev. A 47, 1874. DeWitt, D.R., Schneider, D., Chen, M.H., Schneider, M.B., Church, D., Weinberg, G., Sakurai, M., 1993. Dielectronic recombination cross sections of fluorinelike xenon. Phys. Rev. A 47 (3), R1597. Lo´pez-Urrutia, J.C., Braun, J., Brenner, G., Bruhns, H., Lapierre, A., Martı´ nez, A.G., Mironov, V., Orts, R.S., Tawara, H., Trinczek, M., Ullrich, J., 2004. Optimization of the charge state distribution of the ion beam extracted from an ebit by dielectronic recombination. Rev. Sci. Instrum. 75, 1560.
Marrs, R.E., Levine, M.A., Knapp, D.A., Henderson, J.R., 1988. Measurement of electron-impact–excitation cross sections for very highly charged ions. Phys. Rev. Lett. 60, 1715. Marrs, R.E., Elliott, S.R., Knapp, D.A., 1994. Production and trapping of hydrogenlike and bare uranium ions in an electron beam ion trap. Phys. Rev. Lett. 72, 4082. Mu¨ller, A., 1999. Atomic Physics with Heavy Ions. Springer, Berlin, p. 272 (Chapter 12). Nakamura, N., Asada, J., Currell, F.J., Fukami, T., Motohashi, K., Nagata, T., Nojikawa, E., Ohtani, S., Okazaki, K., Sakurai, M., Shiraishi, H., Tsurubuchi, S., Watanabe, H., 1997. An overview of the Tokyo electron beam ion trap. Phys. Scr. T73, 362. Shimizu, H., Currell, F., Ohtani, S., Sokell, E., Yamada, C., Hirayama, T., Sakurai, M., 2000. Characteristics of the beam line at the Tokyo electron beam ion trap. Rev. Sci. Instrum. 71 (2), 681.
Radiation Physics and Chemistry 75 (2006) 1749–1752 www.elsevier.com/locate/radphyschem
Investigation of resonant inner-shell processes with an electron beam ion trap Nobuyuki Nakamuraa,, Hirotsugu Tobiyamaa, Hiroaki Noharaa, Daiji Katob, Hirofumi Watanabec, Fred J. Currelld, Shunsuke Ohtania a
Institute for Laser Science, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan b National Institute for Fusion Science, Toki, Gifu 509-5292, Japan c Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan d Queen’s University Belfast, Belfast BT7 1NN, UK Accepted 27 July 2005
Abstract The collision processes of highly charged ions with electrons have been studied with an electron beam ion trap. Resonant inner-shell processes such as dielectronic recombination and resonant excitation double autoionization were investigated by observing the number ratio of extracted ions with adjacent charge states. r 2006 Elsevier Ltd. All rights reserved.
1. Introduction Resonant excitation and recombination are important processes in electron–ion interactions (Mu¨ller, 1999). In the interactions with highly charged ions (HCIs), a free electron is captured with a large probability and simultaneously a bound electron is excited to form a doubly excited state resonantly. This unstable intermediate state may decay by photon emission: dielectronic recombination (DR), or by emission of two electrons due to successive autoionization: resonant excitation/double autoionization (REDA). In this paper, we present an observation of these resonant processes using an electron beam ion trap (EBIT) (Marrs et al., 1988). An EBIT is suitable for studying such collision processes of HCIs with electrons because it has a mono-energetic and unidirectional electron beam interacting with trapped HCIs. By Corresponding author. Tel.: +81 424 43 5709; fax: +81 424 85 8960. E-mail address: [email protected] (N. Nakamura).
observing X-ray spectra or charge state distributions while controlling the electron beam energy, one can investigate various electron–HCI collision processes including the resonant processes described above.
2. Experiments The present experimental procedure is similar to those of DeWitt et al. (1993) and Ali et al. (1991) and is very effective for measurement of the electron-energy dependence of extracted-ion yields from an EBIT (or an electron beam ion source) in studying the DR processes of HCIs. In the present studies, an electron beam ion trap in Tokyo (Tokyo EBIT) (Nakamura et al., 1997) has been used. In the trap region of the EBIT, HCIs are produced and confined with a narrow charge-state distribution. At the charge equilibrium, the ionization balance for trapped HCIs is determined by the rates for ionization and recombination processes. Then, the number ratio for the abundance of adjacent charge-state
0969-806X/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.radphyschem.2005.07.032
ARTICLE IN PRESS N. Nakamura et al. / Radiation Physics and Chemistry 75 (2006) 1749–1752
CX nq1 sre q þ hsq i ¼ , ion nq sq1
(1)
where sre is the recombination cross section for q q ! q 1, sion q1 the electron impact ionization (EI) cross section for q 1 ! q, and hsCX q i the effective charge exchange cross section (Marrs et al., 1994) for collisions with the residual gas. In this expression, other loss terms for ions of charge state q such as the escape factor from the trap are not included. When there is no resonant process, the ratio nq1 =nq varies slowly with electron energy. Since hsCX q i can be excluded by observing the gas pressure dependence and by extrapolating it to zero neutral density, sion q1 can be obtained by normalizing sre to a reliable theoretical value of the q radiative recombination (RR) cross section. When the interaction energy of electrons matches (to with in the beam energy width of about 50 eV) a resonant energy where ionization or recombination is enhanced, the charge-state distribution can change drastically. Therefore, the abundance ratio of ions with neighbouring charge states in the trap should also change when this condition is fulfilled. For example, at an electron beam energy at which DR is possible, sre q can be represented as the sum of two components, sRR and q sDR q , and the ratio nq1 =nq is thus enhanced. Since the amount enhancement corresponds to the ratio ion DR sDR can be obtained by using the experimenq =sq1 , sq tally determined ionization cross section sion q1 , assuming the latter is slowly varying. The ion number ratio can be obtained by measuring the intensity of ions extracted from the EBIT. The trapped ions are heated through successive electron collisions so that they can finally escape from the trap. Ions which escape axially towards the electron collector can be extracted into an HCI beam line (Shimizu et al., 2000). The efficiency of extraction and transmission in the beam line might be different depending on the charge state of the extracted ions. However, it is considered to be almost the same for adjacent charge states for very high q (Lo´pez-Urrutia et al., 2004) because they have quite close values of charge-to-mass ratio. In the present study, the measurements were repeated with different experimental conditions and we could not find any significant difference for the ion ratios for the same pairs of adjacent charge states. Although more careful examination may be needed to check the absolute systematic errors, it is assumed here that the extracted ion intensity ratio gives the ion number ratio inside the trap. The energy of electrons interacting with HCIs is determined by the potential difference between the cathode and the interaction region in the central DT.
The electron energy was scanned by controlling the voltage at the electron gun, with respect to laboratory earth. In order to ensure the charge equilibrium condition was maintained, the scan was performed very slowly ð10 s=stepÞ. The voltage of the central drift tube was fixed to þ3 kV throughout the experiment while the final DT was set a further 50 V above this value, fixing the axial trapping voltage for the ions.
3. Results and discussion 3.1. KLL DR for He- to C-like iodine An intermediate doubly excited state having low principal quantum numbers for both excited electrons formed in electron interactions with high q, high Z (atomic number) HCIs, would usually predominantly decay radiatively. Therefore, the observed nq1 =nq spectra in these resonant interactions would be expected to show peak structures corresponding to enhancement at the resonant energies. Fig. 1 shows the electron energy dependence of nq1 =nq : the number ratio between adjacent charge states of highly charged iodine ions extracted from the
10 e- + Iq+
8
Li/He (sHeDR) (x1/5)
6
4 Be/Li (sLiDR) B/Be (sBeDR)
2
C/B (sBDR) N/C (sCDR)
0
500 K-alpha cut
19.5
20
20.5
21
0 21.5
X-ray counts
ions can be expressed in terms of cross sections for relevant e–HCI collision processes
Ratio between adjacent ions
1750
Electron energy (keV) Fig. 1. Number ratio between adjacent charge states of highly charged iodine ions extracted from the Tokyo-EBIT as a function of electron energy. The ratios are raised by 0.5, 1.0, 1.5, and 5 for C/B, B/Be, Be/Li and Li/He, respectively, for clarity. K-a X-ray intensity is also plotted.
ARTICLE IN PRESS N. Nakamura et al. / Radiation Physics and Chemistry 75 (2006) 1749–1752
3.2. REDA in Na-like iodine As well as DR, resonant ionization, e.g. REDA, can cause a sharp electron energy dependence in the ion number ratio. By extending Eq. (1) to include REDA and DR contributions, the ion number ratio can be expressed by the following formula: REDA sion nq q1 þ sq1 ¼ RR , CX nq1 sq þ sDR q þ hsq i
(2)
where sion q1 is the (non-resonant) ionization cross section including direct and indirect (e.g. excitation autoionization) processes, sREDA is the REDA cross section, and q1 sRR and sDR are the RR and the DR cross section, q q respectively. Thus, DR should decrease the ion ratio nq =nq1 whereas REDA increases the ratio. In general, the radiative decay rates have a strong Z dependence (proportional to Z 4 ). For intermediate doubly excited states formed in the resonant interaction with relatively low q HCIs, the DR rates can be strongly suppressed due to decreasing Zeff (effective atomic number). Therefore, in ionic systems like Na-like ions, strong relative enhancement of the cross section due to REDA can be expected. Fig. 2 shows the electron energy dependence of the number ratio of Ne-like and Na-like iodine ions extracted from the Tokyo-EBIT. A great number of structures which correspond to DR for Ne-like ions and REDA for Na-like ions can be observed. In the figure, the theoretical ionization cross section for Na-like Xe calculated by Chen and Reed (1993) is also plotted. The energy scale for the theoretical cross section was scaled by Z2 and shifted for comparison. Since the dotted line indicates the ionization cross section without REDA, the DR contribution is considered to appear below the dotted line whereas the REDA contribution appears above the dotted line. Although the overall agreement
4 Ratio between Na-like and Ne-like I ions
Tokyo-EBIT. Lots of structures corresponding to KLL DR processes are observed. In the figure, X-ray counts for the K-a line are also plotted as a function of electron energy. Because it is difficult to resolve the K-a X-ray emission for different (isonuclear) charge states with an ordinary Ge detector, contributions from several charge states are superimposed. On the other hand, the charge state has been clearly resolved for the extracted ions, so that the presence of DR resonances for each charge state can be deduced. However, in practice, in order to determine the DR cross section, contributions from escape and multiple charge exchange have to be treated carefully. For example, the dips in the C/N ratio appearing at electron energies of around 20.5 and 20:8 keV are considered to be the artifacts due to these contributions. Analysis to include these effects are on going.
1751
3
Ionization CS for Na-like Xe (horizontal scale was scaled by Z2 and shifted)
Experiment Ne/Na
2
1
0 4
4.5
5 5.5 6 6.5 Electron energy (keV)
7
7.5
Fig. 2. Number ratio of Ne-like and Na-like iodine ions extracted from the Tokyo-EBIT. The theoretical ionization cross section for Na-like xenon calculated by Chen and Reed (1993) is also plotted after scaling and shifting of the electron energy scale.
between experiment and the theory is found, complications introduced by the superposition of DR and REDA makes the comparison difficult. The detailed analysis by calculating both the REDA and DR contributions is ongoing and will be published elsewhere.
4. Conclusion We have studied the resonant processes in electron–HCI collisions such as DR and REDA using the Tokyo electron beam ion trap by measuring the number ratio of extracted ions. The effectiveness and efficiency of the present method to study these processes has been demonstrated. Although the present study was done only for iodine ions, the method can be applied for any other ions. Thus a systematic study for observing the Z-dependence is on-going.
Acknowledgement This work has been supported by the CREST program ‘‘Creation of Ultrafast, Ultralow Power, Super-performance Nanodevices and Systems’’ in the Japan Science and Technology Agency and Japan–UK Research Cooperative Program in Japan Society for the Promotion of Science, and has been performed under the activity of the 21st Century Center of Excellence (COE) Program ‘‘Innovation in Coherent Optical Science’’ at the University of Electro-Communications. N. Nakamura acknowledges the support of the Matsuo Foundation.
ARTICLE IN PRESS 1752
N. Nakamura et al. / Radiation Physics and Chemistry 75 (2006) 1749–1752
References Ali, R., Bhalla, C.P., Cocke, C.L., Schulz, M., Stockli, M., 1991. Dielectronic recombination and electron-impact excitation of heliumlike argon. Phys. Rev. A 44, 223. Chen, M.H., Reed, K.J., 1993. Indirect contributions to electron-impact ionization of kr24þ , kr25þ , and xe43þ . Phys. Rev. A 47, 1874. DeWitt, D.R., Schneider, D., Chen, M.H., Schneider, M.B., Church, D., Weinberg, G., Sakurai, M., 1993. Dielectronic recombination cross sections of fluorinelike xenon. Phys. Rev. A 47 (3), R1597. Lo´pez-Urrutia, J.C., Braun, J., Brenner, G., Bruhns, H., Lapierre, A., Martı´ nez, A.G., Mironov, V., Orts, R.S., Tawara, H., Trinczek, M., Ullrich, J., 2004. Optimization of the charge state distribution of the ion beam extracted from an ebit by dielectronic recombination. Rev. Sci. Instrum. 75, 1560.
Marrs, R.E., Levine, M.A., Knapp, D.A., Henderson, J.R., 1988. Measurement of electron-impact–excitation cross sections for very highly charged ions. Phys. Rev. Lett. 60, 1715. Marrs, R.E., Elliott, S.R., Knapp, D.A., 1994. Production and trapping of hydrogenlike and bare uranium ions in an electron beam ion trap. Phys. Rev. Lett. 72, 4082. Mu¨ller, A., 1999. Atomic Physics with Heavy Ions. Springer, Berlin, p. 272 (Chapter 12). Nakamura, N., Asada, J., Currell, F.J., Fukami, T., Motohashi, K., Nagata, T., Nojikawa, E., Ohtani, S., Okazaki, K., Sakurai, M., Shiraishi, H., Tsurubuchi, S., Watanabe, H., 1997. An overview of the Tokyo electron beam ion trap. Phys. Scr. T73, 362. Shimizu, H., Currell, F., Ohtani, S., Sokell, E., Yamada, C., Hirayama, T., Sakurai, M., 2000. Characteristics of the beam line at the Tokyo electron beam ion trap. Rev. Sci. Instrum. 71 (2), 681.