Multiaperture Surface-Plasma Negative Ion Source: Beam Formation and - PowerPoint PPT Presentation

Multiaperture Surface-Plasma Negative Ion Source: Beam Formation and Transport through LEBT Yu. Belchenko, P. Deichuli, A.A. Ivanov, A. Sanin, O. Sotnikov Budker Institute of Nuclear Physics, Novosibirsk, Russia BINP source features  H- beam production  Beam transport through LEBT  ICIS 2017, October 17, Geneva

Negative-ion based Neutral Beam Injector (BINP scheme) Beam acceleration is produced after purifying from the co-streaming fluxes of primary and secondary particles (gas, fast neutrals, electrons, cesium, light) Negative ion beam is focused to a single-aperture 0.5-1 MeV accelerating tube. The stresses of the accelerator must be considerably reduced. PI Recuperator Neutralizer Acceleration tube 0.88 MV Ion Source Ion Separator Neutral Beam NI Recuperator LEBT 120 keV beam separation Yu.Belchenko, ICIS 2017, Geneva 2

BINP Multiaperture sources of Negative Ions Inductive RF sources with Surface-Plasma production of Negative Ions H 2 feed + ignitor ВЧ антенна RF discharge Cs feed Expansion Magnet Filter chamber PG EXG AG Correcting Magnet 9 А Source with 4 RF Drivers. 145 beamlets Source prototype with 1 RF Driver. 21 beamlets Yu.Belchenko, ICIS 2017, Geneva 3

New elements of the source: • Active temperature control of IOS grids (heating/cooling by hot f luid) • Cesium seed to PG periphery • Convex magnetic field in the IOS gaps Hot Central Grid Cold Peripheral Flange Plasma Grid with heating/cooling by hot fluid Cs distribution tube is attached to PG periphery Thermal carrier feedthrough Correction magnet to convex magnetic lines Extraction Grid with heating/cooling by hot fluid Yu.Belchenko, ICIS 2017, Geneva 4

Cesium systems with pellets Oven with Oven pellets Fan to control Internal oven cold point Thermocable SS tube Swagelok Connection Cs Oven at the top of PG flange Cs system scheme Yu.Belchenko, ICIS 2017, Geneva 5

Test Stand Faraday Main tank Cup Port Cryopump Н - Source HV Platform • Beam transport through LEBT with two large-aperture bending magnets and two cryopumps • Movable Faraday cup and Calorimeter, equipped by thermocouples and SEDs Yu.Belchenko, ICIS 2017, Geneva 6

Beam measurements scheme Faraday Calorimeter cup • H- beam was measured by Faraday Cup (at 1.6 m) and by calorimeter (at 3,5 m) IOS circuits currents I ex , I ac , I AG were measured to control H- beam current and electron load • Transported H - beam was scanned along calorimeter plane by change of magnet #1 and 2 field. • Yu.Belchenko, ICIS 2017, Geneva 7

New Properties RF discharge with Cesium seed through IOS heating improves HV conditioning distribution tube reduces Cs consumption Cold electrodes: 72 kV after 160 pulses, 0.5 G provides ~2 month work Hot electrodes: 82 kV after 50 pulses, Positive PG biasing decreases two times Convex magnetic field enhances IOS HV holding the electron current I AG to acceleration grid under wide experimental change of source parameters Yu.Belchenko, ICIS 2017, Geneva 8

H- beam and co-extracted electron currents 1.2 A, 85 keV, 1.6 s shot 0.8 A, 100 keV, 12 s shot RF discharge power 36 kW RF discharge power 22 kW ≈ 0.4 I FC H- beam current I b is compared (~1:1) with the co-extracted electron current I e • • Beam current is stable during the long pulse Yu.Belchenko, ICIS 2017, Geneva 9

H- beam at distance 1.6 m Comparison of outgoing beam current I b and beam current I FC , transported to FC plane Beam profile for current at FC plane ~ 1 A H- beam current I b , outgoing the source Divergence ± 60 x ± 50 mRad, and beam current I FC at Faraday cup plane FC ø 10, 100 and 170 mm vs acceleration voltage. • H- current I FC is ~ 20 % smaller, than beam current I b , outgoing from the source No saturation of I b and I FC currents growth was recorded with beam energy up to 100 keV. • • Currents rise with energy growth is caused by improved transmission, by decrease of H- ions stripping and by beam focusing to FC Yu.Belchenko, ICIS 2017, Geneva 10

H- beam at distance 1.6 m Dependences vs hydrogen filling pressure Normalizing to RF discharge power 25 kW The similar decrements for I b and I FC currents vs H 2 shows the dominant stripping of H- ions in the AG+GG area . Yu.Belchenko, ICIS 2017, Geneva 11

Beam transport to calorimeter Group #3 Magnet 1 Magnet 2 Main Group C B Group #1 Main Group consists of H- beam + neutrals, produced by H- stripping in section C Group # 3 is produced by H- ions stripping in section B, after ions bending by magnet 1 Main Group and Group #3 are shifted with magnets field change Group 1 is produced by H- ions stripping in section A, before H- ions bending by magnets. It is not shifted by magnets field Yu.Belchenko, ICIS 2017, Geneva 12

H- beam transport to calorimeter Small income of neutral beam satellites were displayed at tank vacuum 3·10 -3 P a Y X Δ T ~ 70% of H- beam, outgoing the source were transported to calorimeter area 30 x 30 cm 2 (at energy 93 к eV) Yu.Belchenko, ICIS 2017, Geneva 13

X- profile of transported H- beam 3·10 -3 P a ΔT - temperature rise of central thermocouple vs H- beam shift during magnetic scan. X- profile shows the structure of beam main group. Profile asymmetry indicates a few income of atomic group #3 There is no atomic group #1 at calorimeter center Yu.Belchenko, ICIS 2017, Geneva 14

Power to calorimeter W vs X-shift 93 kV, 3·10 -3 P a Composition of 50 kW beam, entering calorimeter window at B 1 = 21,5 mT 47 kW main group, 1 kW group #3, ~2 kW atomic group #1 galo Yu.Belchenko, ICIS 2017, Geneva 15

Power to calorimeter W vs X-shift 93 kV, 3·10 -3 P a Composition of 12 kW beam, entering calorimeter window at B 1 = 15,5 mT 7 kW - left side of main group, 3 kW – left half of group #3, ~2 kW atomic group #1 galo Yu.Belchenko, ICIS 2017, Geneva 16

Power to calorimeter W vs X-shift 93 kV, 3·10 -3 P a Composition of 10 kW beam, entering calorimeter window at B 1 = 27,5 mT 8 kW - right part of main group, ~2 kW atomic group #1 galo Yu.Belchenko, ICIS 2017, Geneva 17

SEDs Oscillogram 93 kV, 3·10 -3 P a Beam main group is focused to the calorimeter center Left, Top, Right and Bottom SED positions at the periphery of Left SED shows little increase of atomic group #3 to the 10 s shot end calorimeter window Bottom SED shows a decrease of H- group to the pulse end (similar to those for the outgoing beam I b ) . Yu.Belchenko, ICIS 2017, Geneva 18

Y-profile of beam main group at calorimeter At tank vacuum 3·10 -3 P a Y- profile vs beam energy Y-profile (X=0) vs plasma grid potential 0.5 Pa 0.4 Pa Beam FWHM vs plasma grid potential Y-profile vs hydrogen filling pressure Yu.Belchenko, ICIS 2017, Geneva 19

H- ions stripping at poor vacuum Neutral Group #3 is clearly displayed at poor tank vacuum 7·10 -3 Pa X-distribution of the beam along calorimeter H- beam is separated from atomic Groups #1 and #3 ΔT - temperature rise of central thermocouple LS , RS , TS- secondary electron emission detectors At poor vacuum ~ 50% of H- ions beam enter the calorimeter window 24x24 cm 2 Yu.Belchenko, ICIS 2017, Geneva 20

Beam transport efficiency 93 kV, 3·10 -3 Pa I b At IOS exit At FC plane At calorimeter window At calorimeter area 24 x 24 cm 2 30 x 30 cm 2 NI NI Trans Main Trans Main Trans beam beam mission Group mission group mission 84 kW 72 kW 86% 47 kW 56% 60 kW 70% At optimal vacuum ~ 70% of H- ions beam enter the calorimeter area 30x30 cm 2 Yu.Belchenko, ICIS 2017, Geneva 21

Next Steps • To improve beam transport by beam energy increase to projected 120 kV • To gain beam production by RF discharge power increase • To accelerate the purified beam Yu.Belchenko, ICIS 2017, Geneva 22

Source and LEBT at 1 MeV stand BINP Test stand with 1 MeV platform and accelerating tube Yu.Belchenko, ICIS 2017, Geneva 23

Thank you attention !

Invitation to NIBS’18, Novosibirsk The 6th International Symposium NIBS'18 ( Negative Ions, Beams and Sources) will be held on September 3-7, 2018 at Budker Institute of Nuclear Physics, Novosibirsk, Russia . Symposium Topics: Fundamental processes and modelling H – and D – sources for fusion, accelerators and other applications Other Negative ion sources Beam formation and low energy transport Beam acceleration and neutralization Beam lines and facilities Applications Welcome to Novosibirsk !