Grisham, L.R.

Hahto, S.K.

Hahto, S.T.

Kwan, J.W.

Leung, K.N.

Hahto, S. K.

Hahto, S. T.

Kwan, J. W.

Leung, K. N.

Grisham, L. R.

UNT Digital Library

 1Journal: Review of Scientific Instruments  Title: Negative chlorine ions from multicusp RF ion source for heavy ion fusion applications  Running title: Cl- ions from multicusp ion source  Authors:  S. K. Hahto*, S. T. Hahto , J. W. Kwan and K. N. Leung  Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720   L. R. Grisham Plasma Physics Laboratory Princeton University, Princeton, NJ 08543  The author would like to submit the manuscript electronically.                                                 * email: skhahto@lbl.gov  2Negative chlorine ions from multicusp RF ion source for heavy ion fusion applications  S. K. Hahto, S. T. Hahto , J. W. Kwan and K. N. Leung  Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720   L. R. Grisham Plasma Physics Laboratory Princeton University, Princeton, NJ 08543  Abstract Use of high mass atomic neutral beams produced from negative ions as drivers for inertial confinement fusion has been suggested recently. Best candidates for the negative ions would be bromine and iodine with sufficiently high mass and electron affinity. These materials require a heated vapor ion source. Chlorine was selected for initial testing because it has similar electron affinity to those of bromine and iodine, and is available in gaseous form. An experiment was set up by the Plasma and Ion Source Technology Group in Lawrence Berkeley National Laboratory to measure achievable current densities and other beam parameters by using an RF driven multicusp ion source1,2. Current density of 45 mA/cm2 was achieved with 99.5 % of the beam as atomic negative chlorine at 2.2 kW of RF power. An electron to negative ion ratio as low as 7 to 1 was observed, while the ratio of positive and negative chlorine ion currents was 1.3. This in addition to the fact that the front plate biasing had almost no effect to the negative chlorine ion and  3electron currents indicates that a very high percentage of the negative charge in the extraction area of the ion source was in form of Cl- ions. A comparison of positive and negative chlorine ion temperatures was conducted with the pepper pot emittance measurement technique and very similar transverse temperature values were obtained for positive and negative chlorine ions.  Motivation for the experiment Neutral heavy atoms produced from negative ions have been proposed as drivers for inertial confinement fusion3 . The best candidates for these ions seem to be4 bromine (mass 81, electron affinity 3.63 eV) and iodine (mass 127, electron affinity 3.06 eV). These elements have to be heated to a vapor, and the ion source would have to be operated at elevated temperatures to prevent the condensation of the vapor on cold surfaces. For an initial estimate of achievable negative ion current densities from bromine and iodine, chlorine was used because it has a very similar electron affinity (3.61 eV). It is readily available in gaseous form, which enables the test to be carried out using an already existing ion source by just modifying the gas lines to be compliant with corrosive gases.  Experimental setup The negative chlorine ion production experiment was conducted in Lawrence Berkeley National Laboratory’s Plasma and Ion Source Technology Group. In figure 1, a schematic diagram of the set up is presented. A 15 cm long by 10 cm diameter multicusp type source chamber with 20 cusp lines was used. A movable magnetic dipole filter with 135 gauss peak field and Full Width At Half Maximum of 2.4 cm was installed through  4the back plate of the source. This filter separates the ion source into a discharge and an extraction region. A 12.56 MHz, 2.2 kW RF power supply with accompanying matching network and a quartz coated RF antenna were used in the tests. The RF power supply and the matching network were floated at high voltage to enable proper shielding of the antenna legs in order to reduce the RF noise. The negative ion extractor and the faraday cup were designed and optimized for a 10 – 20 kV extraction voltage range. The first part of the extractor is a high voltage plasma electrode with a single aperture. It is insulated from the ion source body to enable biasing of the plasma electrode relative to the ion source. Ions are extracted by a water cooled, grounded ion extractor with permanent magnets attached to it for the removal of electrons from the ion beam. A movable, secondary-electron-suppressed faraday cup was installed for the ion beam current measurement. An einzel lens matches the ion beam to a magnetic mass spectrometer, which is used to analyze the extracted ion species. A 500 l/s turbomolecular pump is installed in the extraction chamber. A smaller 150 l/s turbo pumps the volume of the magnetic mass spectrometer. Chlorine gas was fed to the ion source through a gas line constructed from stainless steel, and the ion source and the gas line were located inside a ventilated hood to prevent any escape of chlorine gas. No cesium or other additives were introduced into the plasma chamber in any of the measurements.  I. Measurements with oxygen The experimental set-up was tested first with an oxygen plasma. Positive and negative ion beams were extracted and analyzed to make sure the set-up worked for both polarities. It was noticed that the electron beam focused into a small spot on the electron  5dump and started melting it. The water cooling of the electron dump was improved, after which the extraction worked well. Current density, defined by dividing the measured faraday cup ion current with the extraction aperture area, of 5.7 mA/cm2 for O- and 22 mA/cm2 for O+ was measured at 2.0 kW of RF power. The electron-to-ion ratio was 300. In figure 2 (a) the measured positive and negative atomic oxygen ion current and the electron current are plotted as a function of extraction voltage at 1.5 kW of RF power and 10 mTorr of source pressure. For figure 2 (b) the measured atomic negative oxygen current is plotted as a function of source pressure and RF power. The extraction aperture diameter and the extraction gap were 1.5 mm and 5.5 mm, respectively. The ratio of the O+ and O- current densities was 4. At 1.5 kW of RF input power, 40 % of the ions were O+ in the positive beam and 90 % were O- in the negative beam. Positive and negative oxygen spectrums are presented at figure 3.  II. Measurements with chlorine After testing the system with oxygen, chlorine operation was started. A positive chlorine ion spectrum is presented in figure 4. Some impurities can be seen in the spectrum, mainly nitrogen and oxygen. About 82% of the beam was atomic chlorine ions. The initial tests were carried out with a 1.5 loop transverse quartz antenna with the tip of the antenna 35 mm away from the filter rod center plane. The filter rods were 13 mm from the plasma electrode. This was the same set-up which was used for oxygen measurements. A negative chlorine ion spectrum with the same RF power can be seen in figure 5. The spectrum is noticeably clean, as 99.5 % of the beam is atomic Cl-, with the  6two peaks corresponding to the 76 % and 24 % natural abundance of chlorine isotopes 35 and 37, respectively. Only about 0.5 % of the beam is molecular Cl2-  ions.  In figure 6 (a), the measured Cl- and Cl+ ion currents and the electron current are plotted as a function of extraction voltage at 1.0 kW of RF power and 25 mTorr of source pressure. Cl- and Cl+ ion currents saturate at 7 kV and 13 kV, respectively. The higher saturation voltage of Cl+ is due in part to the higher total positive ion density at the extraction region of the plasma chamber. In figure 6 (b) the Cl- current density is plotted as a function of RF power and source pressure. The data were taken with a 2 mm extraction aperture and a 4.5 mm extraction gap. The Cl- current density has a maximum at 30 mTorr source pressure, and increases linearly with RF power. The maximum achieved current density of 45 mA/cm2 was measured at 2.2 kW of RF power and 28 mTorr source pressure. Biasing of the front plate has been reported in the literature to increase the negative ion yield and to reduce the electron yield from volume plasma source5. With oxygen this effect was clear. The O- ion current increased by 20 % and the electron current decreased by 25 % when the front plate voltage was increased from 0 to 15 V. With higher voltages the ion current started to go down while the electron current also continued decreasing. With chlorine this effect was much smaller. When the front plate was biased from 0 to 35 V, the Cl- current hardly changed, and the electron current decreased by less than 5 %. This is probably due to the fact that most of the negative charge in the extraction region of the ion source is chlorine ions and only a few percent are electrons. Figures 7 (a) and (b) show the measured negative ion and electron currents as a function of front plate bias for oxygen and chlorine.  7The effects of ion source chamber pressure and filter magnet position on the extractable negative chlorine and electron currents can be seen in figures 8 (a) and (b). Electron current goes down from 74 mA to 16 mA when the source pressure was increased from 15 to 30 mTorr. The ion current increased from 0.95 mA at 15 mTorr to 1.05 mA at 25 mTorr, and started to decrease at higher pressures. When the magnetic filter rods were moved from 11 mm to 21 mm away from the plasma electrode, the ion current went down from 0.8 mA to 0.6 mA, while the electron current had a minimum of 8.8 mA at 16 mm. The data in figure 8 were taken with a 2 mm extraction aperture and 2.0 kW of RF power for figure 8 (a) and 1.5 kW and 30 mTorr of source pressure for figure 8 (b).  The transverse temperatures of the positive and negative chlorine ions were determined by a pepper pot measurement. The ion beam was shot through a mask with 0.2 mm holes to a target foil. Transverse temperature of the beam was determined from the marks in the foil in parallel and transverse directions to the electron filter magnetic field. The exposures were done using 1.5 kW of RF power and 30 mTorr of source pressure for both positive and negative chlorine ions. The temperatures measured in the parallel and transverse directions to the magnetic field for the negative chlorine were 0.3 eV and 0.5 eV, respectively. For positive chlorine the temperatures were 0.2 eV and 0.5 eV. The ion temperature is larger in the transverse direction as the magnetic field deflects the ions. The relatively bigger temperature in the direction transverse to the magnetic field for positive chlorine can be explained by the large molecular chlorine ion component in the positive beam.    8Acknowledgement  This work is supported by the U.S Department of Energy under contract number DE-AC03-76SF00098 and by the Finnish Academy of Science and Letters.  9                                        ION EXTRACTOR PLASMA ELECTRODE EXTR. APERTURE ELECTRON DUMP  10O+, 1500 W, 15 kV, 10 mT-1012345670 5 10 15 20 25 30 35magnet current  (A)analyzer current (arb. units)O+O2+O-, 1500 W, 15 kV, 7mT-30-25-20-15-10-50-35-30-25-20-15-10-50magnet current (A)analyzer current (arb. units)O-OH-O2-(a) (b)  1151015201000120014001600180020000.010.020.030.040.050.060.070.080.090.0100.0110.0I(PA)P(mT)RF(W)               0204060801001201401600 3 6 9 12HV (kV)Ion current (PA)4042444648505254Electron current (mA)O+O-electron(a) (b)  12  Cl +, 1.5 kW, 12 kV, 15 mT-0.500.511.522.533.544.50 5 10 15 20 25 30 35 40mangnet current (A)Analyzer current(arb.units)35Cl+37Cl+Cl2+ 13                     Cl-, 1.5 kW, 15 kV, 30 mT-70-60-50-40-30-20-100-42-37-32-27-22-17-12-7-2magnet current (A)analyzer current (arb. units)35Cl-37Cl-Cl2- 14                   00.10.20.30.40.50.60.70.80 3 6 9 12 15 18Extraction voltage (kV)Ion current (mA)012345678910Electron current (mA)Cl-Cl+electron2025303510001400180022001215182124273033363942current density (mA/cm2 )pressure (mT)RF (W)(a) (b)  15 v               O-, 7 kV, 1.5 kW, 10 mT, 1.5 mm aperture0102030405060700 5 10 15 20 25 30Front plate bias(+V)O-  current ( PA)051015202530354045electron current (mA)Ion currentelectron currentCl-, 15 kV, 2.0 kW, 20 mT, 2 mm aperture0.50.70.91.11.31.51.71.92.12.32.50 10 20 30 40 50Front plate bias (+V)Cl-  current (mA)1516171819202122232425electron current (mA)Ion currentElectron current(a) (b)  160.940.960.9811.021.041.0610 15 20 25 30 35Source pressure (mTorr)Ion current (mA)01020304050607080Electron current (mA)Cl-electron             00.10.20.30.40.50.60.70.80.910 12 14 16 18 20 22Filter position from front plate (mm)Ion current (mA)05101520253035Electron current (mA)Cl-electron(a) (b)  17Figure 1: Schematic of the set up Figure 2: (a) O-, O+ and electron currents as a function of the extraction voltage, (b) O- current as a function of the source pressure and RF power. Figure 3: (a) positive and (b) negative oxygen spectrums Figure 4: Positive chlorine ion spectrum Figure 5: Negative chlorine ion spectrum. Figure 6: (a) Cl-, Cl+ and electron currents as a function of the extraction voltage, (b) Cl- current as a function of the source pressure and RF power. Figure 7: Effect of the front plate bias voltage on negative ion and electron currents for (a) oxygen and (b) chlorine. Figure 8: Negative chlorine and electron currents as a function of (a) source pressure, (b) magnetic filter position.  18References (1)  K. N. Leung, Rev. Sci. Instrum. 65, 1165 (1994).  (2)  Q. Ji, T. J. King, K. N. Leung and S. B. Wilde, Rev. Sci. Instrum. 73, 822 (2002)  (3)  L. R. Grisham, Nucl. Instrum. Methods A 464, 315 (2001).  (4)  L. R. Grisham, Evaluation of Negative Ion Driver Concepts for Heavy Ion Fusion, to be published in Fusion Science and Technology, (2003).  (5) K. N. Leung, K. W. Ehlers and R. V. Pyle, Rev. Sci. Instrum. 56, 11 (1985).   

Negative chlorine ions from multicusp RF ion source for heavy ion fusion applications

eScholarship - University of California

Lawrence Berkeley National LaboratoryRecent WorkTitleNegative chlorine ions from multicusp RF ion source for heavy ion fusion applicationsPermalinkhttps://escholarship.org/uc/item/58f2p3ggJournalReview of Scientific Instruments, 74(6)AuthorsHahto, S.K.Hahto, S.T.Kwan, J.W.et al.Publication Date2002-12-02eScholarship.org Powered by the California Digital LibraryUniversity of California 1Journal: Review of Scientific Instruments  Title: Negative chlorine ions from multicusp RF ion source for heavy ion fusion applications  Running title: Cl- ions from multicusp ion source  Authors:  S. K. Hahto*, S. T. Hahto , J. W. Kwan and K. N. Leung  Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720   L. R. Grisham Plasma Physics Laboratory Princeton University, Princeton, NJ 08543  The author would like to submit the manuscript electronically.                                                 * email: skhahto@lbl.gov  2Negative chlorine ions from multicusp RF ion source for heavy ion fusion applications  S. K. Hahto, S. T. Hahto , J. W. Kwan and K. N. Leung  Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720   L. R. Grisham Plasma Physics Laboratory Princeton University, Princeton, NJ 08543  Abstract Use of high mass atomic neutral beams produced from negative ions as drivers for inertial confinement fusion has been suggested recently. Best candidates for the negative ions would be bromine and iodine with sufficiently high mass and electron affinity. These materials require a heated vapor ion source. Chlorine was selected for initial testing because it has similar electron affinity to those of bromine and iodine, and is available in gaseous form. An experiment was set up by the Plasma and Ion Source Technology Group in Lawrence Berkeley National Laboratory to measure achievable current densities and other beam parameters by using an RF driven multicusp ion source1,2. Current density of 45 mA/cm2 was achieved with 99.5 % of the beam as atomic negative chlorine at 2.2 kW of RF power. An electron to negative ion ratio as low as 7 to 1 was observed, while the ratio of positive and negative chlorine ion currents was 1.3. This in addition to the fact that the front plate biasing had almost no effect to the negative chlorine ion and  3electron currents indicates that a very high percentage of the negative charge in the extraction area of the ion source was in form of Cl- ions. A comparison of positive and negative chlorine ion temperatures was conducted with the pepper pot emittance measurement technique and very similar transverse temperature values were obtained for positive and negative chlorine ions.  Motivation for the experiment Neutral heavy atoms produced from negative ions have been proposed as drivers for inertial confinement fusion3 . The best candidates for these ions seem to be4 bromine (mass 81, electron affinity 3.63 eV) and iodine (mass 127, electron affinity 3.06 eV). These elements have to be heated to a vapor, and the ion source would have to be operated at elevated temperatures to prevent the condensation of the vapor on cold surfaces. For an initial estimate of achievable negative ion current densities from bromine and iodine, chlorine was used because it has a very similar electron affinity (3.61 eV). It is readily available in gaseous form, which enables the test to be carried out using an already existing ion source by just modifying the gas lines to be compliant with corrosive gases.  Experimental setup The negative chlorine ion production experiment was conducted in Lawrence Berkeley National Laboratory’s Plasma and Ion Source Technology Group. In figure 1, a schematic diagram of the set up is presented. A 15 cm long by 10 cm diameter multicusp type source chamber with 20 cusp lines was used. A movable magnetic dipole filter with 135 gauss peak field and Full Width At Half Maximum of 2.4 cm was installed through  4the back plate of the source. This filter separates the ion source into a discharge and an extraction region. A 12.56 MHz, 2.2 kW RF power supply with accompanying matching network and a quartz coated RF antenna were used in the tests. The RF power supply and the matching network were floated at high voltage to enable proper shielding of the antenna legs in order to reduce the RF noise. The negative ion extractor and the faraday cup were designed and optimized for a 10 – 20 kV extraction voltage range. The first part of the extractor is a high voltage plasma electrode with a single aperture. It is insulated from the ion source body to enable biasing of the plasma electrode relative to the ion source. Ions are extracted by a water cooled, grounded ion extractor with permanent magnets attached to it for the removal of electrons from the ion beam. A movable, secondary-electron-suppressed faraday cup was installed for the ion beam current measurement. An einzel lens matches the ion beam to a magnetic mass spectrometer, which is used to analyze the extracted ion species. A 500 l/s turbomolecular pump is installed in the extraction chamber. A smaller 150 l/s turbo pumps the volume of the magnetic mass spectrometer. Chlorine gas was fed to the ion source through a gas line constructed from stainless steel, and the ion source and the gas line were located inside a ventilated hood to prevent any escape of chlorine gas. No cesium or other additives were introduced into the plasma chamber in any of the measurements.  I. Measurements with oxygen The experimental set-up was tested first with an oxygen plasma. Positive and negative ion beams were extracted and analyzed to make sure the set-up worked for both polarities. It was noticed that the electron beam focused into a small spot on the electron  5dump and started melting it. The water cooling of the electron dump was improved, after which the extraction worked well. Current density, defined by dividing the measured faraday cup ion current with the extraction aperture area, of 5.7 mA/cm2 for O- and 22 mA/cm2 for O+ was measured at 2.0 kW of RF power. The electron-to-ion ratio was 300. In figure 2 (a) the measured positive and negative atomic oxygen ion current and the electron current are plotted as a function of extraction voltage at 1.5 kW of RF power and 10 mTorr of source pressure. For figure 2 (b) the measured atomic negative oxygen current is plotted as a function of source pressure and RF power. The extraction aperture diameter and the extraction gap were 1.5 mm and 5.5 mm, respectively. The ratio of the O+ and O- current densities was 4. At 1.5 kW of RF input power, 40 % of the ions were O+ in the positive beam and 90 % were O- in the negative beam. Positive and negative oxygen spectrums are presented at figure 3.  II. Measurements with chlorine After testing the system with oxygen, chlorine operation was started. A positive chlorine ion spectrum is presented in figure 4. Some impurities can be seen in the spectrum, mainly nitrogen and oxygen. About 82% of the beam was atomic chlorine ions. The initial tests were carried out with a 1.5 loop transverse quartz antenna with the tip of the antenna 35 mm away from the filter rod center plane. The filter rods were 13 mm from the plasma electrode. This was the same set-up which was used for oxygen measurements. A negative chlorine ion spectrum with the same RF power can be seen in figure 5. The spectrum is noticeably clean, as 99.5 % of the beam is atomic Cl-, with the  6two peaks corresponding to the 76 % and 24 % natural abundance of chlorine isotopes 35 and 37, respectively. Only about 0.5 % of the beam is molecular Cl2-  ions.  In figure 6 (a), the measured Cl- and Cl+ ion currents and the electron current are plotted as a function of extraction voltage at 1.0 kW of RF power and 25 mTorr of source pressure. Cl- and Cl+ ion currents saturate at 7 kV and 13 kV, respectively. The higher saturation voltage of Cl+ is due in part to the higher total positive ion density at the extraction region of the plasma chamber. In figure 6 (b) the Cl- current density is plotted as a function of RF power and source pressure. The data were taken with a 2 mm extraction aperture and a 4.5 mm extraction gap. The Cl- current density has a maximum at 30 mTorr source pressure, and increases linearly with RF power. The maximum achieved current density of 45 mA/cm2 was measured at 2.2 kW of RF power and 28 mTorr source pressure. Biasing of the front plate has been reported in the literature to increase the negative ion yield and to reduce the electron yield from volume plasma source5. With oxygen this effect was clear. The O- ion current increased by 20 % and the electron current decreased by 25 % when the front plate voltage was increased from 0 to 15 V. With higher voltages the ion current started to go down while the electron current also continued decreasing. With chlorine this effect was much smaller. When the front plate was biased from 0 to 35 V, the Cl- current hardly changed, and the electron current decreased by less than 5 %. This is probably due to the fact that most of the negative charge in the extraction region of the ion source is chlorine ions and only a few percent are electrons. Figures 7 (a) and (b) show the measured negative ion and electron currents as a function of front plate bias for oxygen and chlorine.  7The effects of ion source chamber pressure and filter magnet position on the extractable negative chlorine and electron currents can be seen in figures 8 (a) and (b). Electron current goes down from 74 mA to 16 mA when the source pressure was increased from 15 to 30 mTorr. The ion current increased from 0.95 mA at 15 mTorr to 1.05 mA at 25 mTorr, and started to decrease at higher pressures. When the magnetic filter rods were moved from 11 mm to 21 mm away from the plasma electrode, the ion current went down from 0.8 mA to 0.6 mA, while the electron current had a minimum of 8.8 mA at 16 mm. The data in figure 8 were taken with a 2 mm extraction aperture and 2.0 kW of RF power for figure 8 (a) and 1.5 kW and 30 mTorr of source pressure for figure 8 (b).  The transverse temperatures of the positive and negative chlorine ions were determined by a pepper pot measurement. The ion beam was shot through a mask with 0.2 mm holes to a target foil. Transverse temperature of the beam was determined from the marks in the foil in parallel and transverse directions to the electron filter magnetic field. The exposures were done using 1.5 kW of RF power and 30 mTorr of source pressure for both positive and negative chlorine ions. The temperatures measured in the parallel and transverse directions to the magnetic field for the negative chlorine were 0.3 eV and 0.5 eV, respectively. For positive chlorine the temperatures were 0.2 eV and 0.5 eV. The ion temperature is larger in the transverse direction as the magnetic field deflects the ions. The relatively bigger temperature in the direction transverse to the magnetic field for positive chlorine can be explained by the large molecular chlorine ion component in the positive beam.    8Acknowledgement  This work is supported by the U.S Department of Energy under contract number DE-AC03-76SF00098 and by the Finnish Academy of Science and Letters.  9                                        ION EXTRACTOR PLASMA ELECTRODE EXTR. APERTURE ELECTRON DUMP  10O+, 1500 W, 15 kV, 10 mT-1012345670 5 10 15 20 25 30 35magnet current  (A)analyzer current (arb. units)O+O2+O-, 1500 W, 15 kV, 7mT-30-25-20-15-10-50-35-30-25-20-15-10-50magnet current (A)analyzer current (arb. units)O-OH-O2-(a) (b)  1151015201000120014001600180020000.010.020.030.040.050.060.070.080.090.0100.0110.0I(PA)P(mT)RF(W)               0204060801001201401600 3 6 9 12HV (kV)Ion current (PA)4042444648505254Electron current (mA)O+O-electron(a) (b)  12  Cl +, 1.5 kW, 12 kV, 15 mT-0.500.511.522.533.544.50 5 10 15 20 25 30 35 40mangnet current (A)Analyzer current(arb.units)35Cl+37Cl+Cl2+ 13                     Cl-, 1.5 kW, 15 kV, 30 mT-70-60-50-40-30-20-100-42-37-32-27-22-17-12-7-2magnet current (A)analyzer current (arb. units)35Cl-37Cl-Cl2- 14                   00.10.20.30.40.50.60.70.80 3 6 9 12 15 18Extraction voltage (kV)Ion current (mA)012345678910Electron current (mA)Cl-Cl+electron2025303510001400180022001215182124273033363942current density (mA/cm2 )pressure (mT)RF (W)(a) (b)  15 v               O-, 7 kV, 1.5 kW, 10 mT, 1.5 mm aperture0102030405060700 5 10 15 20 25 30Front plate bias(+V)O-  current ( PA)051015202530354045electron current (mA)Ion currentelectron currentCl-, 15 kV, 2.0 kW, 20 mT, 2 mm aperture0.50.70.91.11.31.51.71.92.12.32.50 10 20 30 40 50Front plate bias (+V)Cl-  current (mA)1516171819202122232425electron current (mA)Ion currentElectron current(a) (b)  160.940.960.9811.021.041.0610 15 20 25 30 35Source pressure (mTorr)Ion current (mA)01020304050607080Electron current (mA)Cl-electron             00.10.20.30.40.50.60.70.80.910 12 14 16 18 20 22Filter position from front plate (mm)Ion current (mA)05101520253035Electron current (mA)Cl-electron(a) (b)  17Figure 1: Schematic of the set up Figure 2: (a) O-, O+ and electron currents as a function of the extraction voltage, (b) O- current as a function of the source pressure and RF power. Figure 3: (a) positive and (b) negative oxygen spectrums Figure 4: Positive chlorine ion spectrum Figure 5: Negative chlorine ion spectrum. Figure 6: (a) Cl-, Cl+ and electron currents as a function of the extraction voltage, (b) Cl- current as a function of the source pressure and RF power. Figure 7: Effect of the front plate bias voltage on negative ion and electron currents for (a) oxygen and (b) chlorine. Figure 8: Negative chlorine and electron currents as a function of (a) source pressure, (b) magnetic filter position.  18References (1)  K. N. Leung, Rev. Sci. Instrum. 65, 1165 (1994).  (2)  Q. Ji, T. J. King, K. N. Leung and S. B. Wilde, Rev. Sci. Instrum. 73, 822 (2002)  (3)  L. R. Grisham, Nucl. Instrum. Methods A 464, 315 (2001).  (4)  L. R. Grisham, Evaluation of Negative Ion Driver Concepts for Heavy Ion Fusion, to be published in Fusion Science and Technology, (2003).  (5) K. N. Leung, K. W. Ehlers and R. V. Pyle, Rev. Sci. Instrum. 56, 11 (1985).   

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Negative chlorine ions from multicusp RF ion source for heavy ion fusion applications

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