Characterization of the Catania VIS for H2 + a) Jose R. Alonso, Luciano Calabretta, Daniela Campo, Luigi Celona, Janet Conrad, Ruben Gutierrez Martinez, Richard Johnson, Francis Labrecque, Matthew H. Toups, Daniel Winklehner, and Lindley Winslow Citation: Review of Scientific Instruments 85, 02A742 (2014); doi: 10.1063/1.4850736 View online: http://dx.doi.org/10.1063/1.4850736 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/85/2?ver=pdfcov Published by the AIP Publishing Articles you may be interested in High current H2 + and H3 + beam generation by pulsed 2.45 GHz electron cyclotron resonance ion sourcea) Rev. Sci. Instrum. 85, 02A943 (2014); 10.1063/1.4850717 MICROWAVE CHARACTERIZATION OF TYPICAL AUSTRALIAN WOODBASED BIOMASS MATERIALS AIP Conf. Proc. 1096, 1558 (2009); 10.1063/1.3114143 Characterization of Soils Using Microwave Radiation AIP Conf. Proc. 1017, 300 (2008); 10.1063/1.2940648 Plasma and Beam Production Experiments with HYBRIS, a Microwaveassisted H− Ion Source AIP Conf. Proc. 925, 164 (2007); 10.1063/1.2773657 NearField Microwave and Embedded Modulated Scattering Technique (MST) for Dielectric Characterization of Materials AIP Conf. Proc. 657, 443 (2003); 10.1063/1.1570169
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REVIEW OF SCIENTIFIC INSTRUMENTS 85, 02A742 (2014)
Characterization of the Catania VIS for H2 +a) Jose R. Alonso,1,b) Luciano Calabretta,2 Daniela Campo,1 Luigi Celona,2 Janet Conrad,1 Ruben Gutierrez Martinez,3 Richard Johnson,4 Francis Labrecque,4 Matthew H. Toups,1 Daniel Winklehner,1 and Lindley Winslow3 1
Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Laboratori Nazionali del Sud, INFN, Catania, Italy 3 University of California Los Angeles, Los Angeles, California 90095, USA 4 Best Cyclotron Systems, Inc., Vancouver, British Columbia V6P 6T3, Canada 2
(Presented 12 September 2013; received 30 August 2013; accepted 4 November 2013; published online 23 January 2014) The Catania VIS 2.46 GHz source has been installed on a test stand at the Best Cyclotron Systems, in Vancouver, Canada, as part of the DAEδALUS and IsoDAR R&D program. Studies to date include optimization for H2 + /p ratio and emittance measurements. Inflection, capture, and acceleration tests will be conducted when a small test cyclotron is completed. © 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4850736] I. INTRODUCTION
The DAEδALUS and IsoDAR experiments require high-current beams for important neutrino measurements.1–3 DAEδALUS needs 800 MeV protons at a peak current of 10 mA, while IsoDAR will use 60 MeV protons also at 10 mA. Cyclotrons are planned as the source of these particles, for reasons of compactness and cost-effectiveness. 10 mA is about a factor of five greater than the present best cyclotron currents: PSI’s 590 MeV cyclotron delivers ∼2 mA, about what is also available from the highest-current commercial isotope-producing cyclotrons. We will inject and accelerate H2 + ions instead of bare protons. Perveance arguments4 indicate that space-charge effects for 5 mA of H2 + (equivalent to 10 mA of protons) at 70 keV injection energy are equivalent to those of 2 mA of protons at the typical 30 keV injection energy. Capture efficiency in the central region of a compact cyclotron is typically 10%, calling for an ion source current of 50 mA; but if the beam can be effectively pre-bunched at the cyclotron RF frequency a factor of two improvements could be obtained, dropping current requirement to 25 mA. Space charge is important at these current levels. Because of the geometry and field configurations around the spiral inflector, modeling this behavior is difficult. Most efficient is to experimentally test the performance of H2 + beams during injection and acceleration in a compact cyclotron. II. ION SOURCE TECHNOLOGY
50 mA CW of protons are readily obtainable from multicusp,5, 6 and from non-resonant microwave7, 8 sources. All these will also produce H2 + . Re-tuning these proton sources can increase the yield of H2 + , but achieving 50 mA may not be easy. Decreasing discharge power increases the a) Contributed paper, published as part of the Proceedings of the 15th Interna-
tional Conference on Ion Sources, Chiba, Japan, September 2013. b) Author to whom correspondence should be addressed. Electronic mail:
[email protected]. 0034-6748/2014/85(2)/02A742/3/$30.00
fraction of H2 + , however, total current decreases. Ehlers and Leung5 reported an 82% H2 + fraction for 30 mA in a multicusp source. Newer work by Peng et al.9 with a 2.45 GHz microwave source will be mentioned later. III. VIS AND BEST CYCLOTRON SYSTEMS
The VIS developed at Catania and Saclay10 is a 2.45 GHz non-resonant ECR source with a permanent magnet collar that has produced 40 mA of proton current. In a test stand at LNSINFN (Catania), 15 mA of H2 + was observed, by adjustments of only the inlet gas pressure and microwave power. This source and supporting equipment were shipped to Vancouver and mounted on a new test stand at the development labs of Best Cyclotron Systems, Inc., in a collaborative project between MIT, LNS-INFN, and Best for the development of high-current q/A = 0.5 beams suitable for axial injection into compact cyclotrons. LNS-INFN provided the source and LEBT; Best the beam line infrastructure and diagnostics and a small 1 MeV cyclotron. The central region design, including the spiral inflector and first-turn channel geometry, was supported by MIT, which also contributed project management and coordination with funds from a NSF EAGER Grant. IV. BEST TEST STAND
Fig. 1 shows the test stand. The source, seen in the inset, is in the high-voltage cage behind an x-ray shield. The VIS is simple to set up and use: microwave power is transferred via an insulated waveguide, and permanent magnet material provides the fields. The only control at high-voltage is for the gas feed valve. The plasma chamber is a water-cooled copper cylinder, 100 mm long by 90 mm diameter and originally equipped with two boron-nitride end caps. The cap at the extraction end was removed for this experiment, leaving a stainless steel surface, as a test to increase recombination and possibly enhance H2 + production. A 6 mm aperture headed a standard four-electrode accel-decel extraction configuration.
85, 02A742-1
© 2014 AIP Publishing LLC
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02A742-2
Alonso et al.
FIG. 1. Photo of test stand at the Best Cyclotron Systems’ development lab in Vancouver, Canada. The ion source, also seen in inset, is in the highvoltage cage at far right behind the shield, the test cyclotron is on the left. Total length of the test stand is ∼5 m.
Microwave power is provided by a Sairem 2 kW 2.45 GHz magnetron, with flexible operation in CW or (arbitrarily shaped) pulsed mode. A 100 kV, 100 mA FuG Elektronik GmbH supply provides the standoff potential. Tests were run at 60 kV. The leakage current from this supply was our principal means of measuring the total ion current extracted from the source. A 44 cm effective-length, 10 cm bore Danfysik solenoid (blue cylinder in Fig. 1) located 50 cm from the extraction point provides primary focusing, and also the means of separating protons from H2 + ions. The test stand, originally configured for H− , did not allow for a bend to analyze the beam. P/H2 + separation was accomplished via solenoid focusing. Three six-way ISO-160 vacuum T’s located between 1.5 and 2.5 m from the solenoid provide space for placement of diagnostics, and a collimator-beamstop pair. A Bergoz 100 mm bore DCCT is the primary current monitor. While the cyclotron magnet and central region components were available, the final magnet shims and RF system, including the upstream RF buncher, had not arrived during our first testing campaign. We report here on initial results of source commissioning and beam characterization. Inflection and capture/acceleration tests will be conducted in 2014.
Rev. Sci. Instrum. 85, 02A742 (2014)
FIG. 2. Current detected on beam stop 10 cm behind a 20 mm collimator, 2.5 m downstream from the focusing solenoid. Peak widths are due to collimator size, not beam width. Protons peak at 190 A, H2 + at 280 A. For 600 W of microwave power, ratio of protons to H2 + is about 1 to 1, and overall H2 + current is maximized. Extraction voltage was lowered to 40 kV to accommodate the current limit in the solenoid magnet.
In an attempt to increase the maximum H2 + current, the extraction aperture was increased to 8 mm. H2 + current did go up, to 10–12 mA. The front surface of the plasma chamber was changed, from stainless steel to copper and back to boron nitride with little effect on total beam.
B. Space-charge neutralization
The collecting surfaces (collimator and beam stop) just downstream of the DCCT were not magnetically suppressed, so there is no control over secondary electron current. In an attempt to make the sum of currents on the collimator and beamstop equal the DCCT reading, a 50 V bias was placed on both collimator and stop. This did lead to consistency in current readings, but also had a significant effect on the beam size, as shown in Fig. 3. These photos, through a window about 50 cm upstream of the collimator, imply that the 50 V is sufficient to draw the neutralizing electrons away from the beam, even from 50 cm away. The effect is repeatable and instantaneous with application/removal of the bias. Greatest effect is seen for bias on the collimator, as would be expected, but biasing the stop also had an effect on the beam envelope.
V. SOURCE CHARACTERIZATION A. H2 + optimization
VIS is optimized for protons at about 1400 W of microwave power. We found H2 + efficiency highest at around 400–600 W. Below that the discharge could be unstable, depending on gas pressure. This pressure seemed to have only a small effect on the H2 + to proton ratio. Proton current rose roughly monotonically with RF power, while H2 + output was relatively flat. Hence, optimum ratio of protons to H2 + occurs at the lower end of the power scale. Maximum H2 + current was of the order of 4–5 mA. Fig. 2 shows a scan of current on the beam stop vs solenoid current, showing that one can indeed cleanly separate protons from H2 + .
FIG. 3. (a) Beam profile 50 cm upstream of collimator with bias on collimator OFF. (b) Beam profile with bias ON. Beam size increases from ∼3 mm to ∼15 mm diameter, likely due to removal of space-charge compensating electrons from beam.
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02A742-3
Alonso et al.
Rev. Sci. Instrum. 85, 02A742 (2014)
The lack of complete coverage of the ellipses, as well as their overlap, makes extraction of emittance values difficult, however, estimates indicate a rms normalized emittance of approximately 0.4 π mm mrad. This value is high compared to earlier characterization work of the VIS source (
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP: 130.18.123.11 On: Mon, 22 Dec 2014 14:09:04
REVIEW OF SCIENTIFIC INSTRUMENTS 85, 02A742 (2014)
Characterization of the Catania VIS for H2 +a) Jose R. Alonso,1,b) Luciano Calabretta,2 Daniela Campo,1 Luigi Celona,2 Janet Conrad,1 Ruben Gutierrez Martinez,3 Richard Johnson,4 Francis Labrecque,4 Matthew H. Toups,1 Daniel Winklehner,1 and Lindley Winslow3 1
Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Laboratori Nazionali del Sud, INFN, Catania, Italy 3 University of California Los Angeles, Los Angeles, California 90095, USA 4 Best Cyclotron Systems, Inc., Vancouver, British Columbia V6P 6T3, Canada 2
(Presented 12 September 2013; received 30 August 2013; accepted 4 November 2013; published online 23 January 2014) The Catania VIS 2.46 GHz source has been installed on a test stand at the Best Cyclotron Systems, in Vancouver, Canada, as part of the DAEδALUS and IsoDAR R&D program. Studies to date include optimization for H2 + /p ratio and emittance measurements. Inflection, capture, and acceleration tests will be conducted when a small test cyclotron is completed. © 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4850736] I. INTRODUCTION
The DAEδALUS and IsoDAR experiments require high-current beams for important neutrino measurements.1–3 DAEδALUS needs 800 MeV protons at a peak current of 10 mA, while IsoDAR will use 60 MeV protons also at 10 mA. Cyclotrons are planned as the source of these particles, for reasons of compactness and cost-effectiveness. 10 mA is about a factor of five greater than the present best cyclotron currents: PSI’s 590 MeV cyclotron delivers ∼2 mA, about what is also available from the highest-current commercial isotope-producing cyclotrons. We will inject and accelerate H2 + ions instead of bare protons. Perveance arguments4 indicate that space-charge effects for 5 mA of H2 + (equivalent to 10 mA of protons) at 70 keV injection energy are equivalent to those of 2 mA of protons at the typical 30 keV injection energy. Capture efficiency in the central region of a compact cyclotron is typically 10%, calling for an ion source current of 50 mA; but if the beam can be effectively pre-bunched at the cyclotron RF frequency a factor of two improvements could be obtained, dropping current requirement to 25 mA. Space charge is important at these current levels. Because of the geometry and field configurations around the spiral inflector, modeling this behavior is difficult. Most efficient is to experimentally test the performance of H2 + beams during injection and acceleration in a compact cyclotron. II. ION SOURCE TECHNOLOGY
50 mA CW of protons are readily obtainable from multicusp,5, 6 and from non-resonant microwave7, 8 sources. All these will also produce H2 + . Re-tuning these proton sources can increase the yield of H2 + , but achieving 50 mA may not be easy. Decreasing discharge power increases the a) Contributed paper, published as part of the Proceedings of the 15th Interna-
tional Conference on Ion Sources, Chiba, Japan, September 2013. b) Author to whom correspondence should be addressed. Electronic mail:
[email protected]. 0034-6748/2014/85(2)/02A742/3/$30.00
fraction of H2 + , however, total current decreases. Ehlers and Leung5 reported an 82% H2 + fraction for 30 mA in a multicusp source. Newer work by Peng et al.9 with a 2.45 GHz microwave source will be mentioned later. III. VIS AND BEST CYCLOTRON SYSTEMS
The VIS developed at Catania and Saclay10 is a 2.45 GHz non-resonant ECR source with a permanent magnet collar that has produced 40 mA of proton current. In a test stand at LNSINFN (Catania), 15 mA of H2 + was observed, by adjustments of only the inlet gas pressure and microwave power. This source and supporting equipment were shipped to Vancouver and mounted on a new test stand at the development labs of Best Cyclotron Systems, Inc., in a collaborative project between MIT, LNS-INFN, and Best for the development of high-current q/A = 0.5 beams suitable for axial injection into compact cyclotrons. LNS-INFN provided the source and LEBT; Best the beam line infrastructure and diagnostics and a small 1 MeV cyclotron. The central region design, including the spiral inflector and first-turn channel geometry, was supported by MIT, which also contributed project management and coordination with funds from a NSF EAGER Grant. IV. BEST TEST STAND
Fig. 1 shows the test stand. The source, seen in the inset, is in the high-voltage cage behind an x-ray shield. The VIS is simple to set up and use: microwave power is transferred via an insulated waveguide, and permanent magnet material provides the fields. The only control at high-voltage is for the gas feed valve. The plasma chamber is a water-cooled copper cylinder, 100 mm long by 90 mm diameter and originally equipped with two boron-nitride end caps. The cap at the extraction end was removed for this experiment, leaving a stainless steel surface, as a test to increase recombination and possibly enhance H2 + production. A 6 mm aperture headed a standard four-electrode accel-decel extraction configuration.
85, 02A742-1
© 2014 AIP Publishing LLC
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02A742-2
Alonso et al.
FIG. 1. Photo of test stand at the Best Cyclotron Systems’ development lab in Vancouver, Canada. The ion source, also seen in inset, is in the highvoltage cage at far right behind the shield, the test cyclotron is on the left. Total length of the test stand is ∼5 m.
Microwave power is provided by a Sairem 2 kW 2.45 GHz magnetron, with flexible operation in CW or (arbitrarily shaped) pulsed mode. A 100 kV, 100 mA FuG Elektronik GmbH supply provides the standoff potential. Tests were run at 60 kV. The leakage current from this supply was our principal means of measuring the total ion current extracted from the source. A 44 cm effective-length, 10 cm bore Danfysik solenoid (blue cylinder in Fig. 1) located 50 cm from the extraction point provides primary focusing, and also the means of separating protons from H2 + ions. The test stand, originally configured for H− , did not allow for a bend to analyze the beam. P/H2 + separation was accomplished via solenoid focusing. Three six-way ISO-160 vacuum T’s located between 1.5 and 2.5 m from the solenoid provide space for placement of diagnostics, and a collimator-beamstop pair. A Bergoz 100 mm bore DCCT is the primary current monitor. While the cyclotron magnet and central region components were available, the final magnet shims and RF system, including the upstream RF buncher, had not arrived during our first testing campaign. We report here on initial results of source commissioning and beam characterization. Inflection and capture/acceleration tests will be conducted in 2014.
Rev. Sci. Instrum. 85, 02A742 (2014)
FIG. 2. Current detected on beam stop 10 cm behind a 20 mm collimator, 2.5 m downstream from the focusing solenoid. Peak widths are due to collimator size, not beam width. Protons peak at 190 A, H2 + at 280 A. For 600 W of microwave power, ratio of protons to H2 + is about 1 to 1, and overall H2 + current is maximized. Extraction voltage was lowered to 40 kV to accommodate the current limit in the solenoid magnet.
In an attempt to increase the maximum H2 + current, the extraction aperture was increased to 8 mm. H2 + current did go up, to 10–12 mA. The front surface of the plasma chamber was changed, from stainless steel to copper and back to boron nitride with little effect on total beam.
B. Space-charge neutralization
The collecting surfaces (collimator and beam stop) just downstream of the DCCT were not magnetically suppressed, so there is no control over secondary electron current. In an attempt to make the sum of currents on the collimator and beamstop equal the DCCT reading, a 50 V bias was placed on both collimator and stop. This did lead to consistency in current readings, but also had a significant effect on the beam size, as shown in Fig. 3. These photos, through a window about 50 cm upstream of the collimator, imply that the 50 V is sufficient to draw the neutralizing electrons away from the beam, even from 50 cm away. The effect is repeatable and instantaneous with application/removal of the bias. Greatest effect is seen for bias on the collimator, as would be expected, but biasing the stop also had an effect on the beam envelope.
V. SOURCE CHARACTERIZATION A. H2 + optimization
VIS is optimized for protons at about 1400 W of microwave power. We found H2 + efficiency highest at around 400–600 W. Below that the discharge could be unstable, depending on gas pressure. This pressure seemed to have only a small effect on the H2 + to proton ratio. Proton current rose roughly monotonically with RF power, while H2 + output was relatively flat. Hence, optimum ratio of protons to H2 + occurs at the lower end of the power scale. Maximum H2 + current was of the order of 4–5 mA. Fig. 2 shows a scan of current on the beam stop vs solenoid current, showing that one can indeed cleanly separate protons from H2 + .
FIG. 3. (a) Beam profile 50 cm upstream of collimator with bias on collimator OFF. (b) Beam profile with bias ON. Beam size increases from ∼3 mm to ∼15 mm diameter, likely due to removal of space-charge compensating electrons from beam.
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP: 130.18.123.11 On: Mon, 22 Dec 2014 14:09:04
02A742-3
Alonso et al.
Rev. Sci. Instrum. 85, 02A742 (2014)
The lack of complete coverage of the ellipses, as well as their overlap, makes extraction of emittance values difficult, however, estimates indicate a rms normalized emittance of approximately 0.4 π mm mrad. This value is high compared to earlier characterization work of the VIS source (
