Charge Breeding Experiences with an ECR and an EBIS for CARIBU

Transcription

1 Charge Breeding Experiences with an ECR and an EBIS for CARIBU Richard Vondrasek ATLAS, Physics Division Argonne National Laboratory Implementation of ECR charge breeding at Argonne Development and installation of EBIS charge breeder 1

2 ATLAS Argonne Tandem Linac Accelerator System New CARIBU Space 18 x 8.7 m 2

3 ECR charge breeder design For grounded tube penetration, reshaped the iron to maximize B inj (1.3 T) and maintain symmetric magnetic field Linear motion stage with 3 cm of travel Open hexapole allows radial RF injection and provides direct pumping of plasma chamber Multiple frequency operation Klystron: GHz, 2 kw TWTA: GHz, 0.5 kw Turbo pumps at injection and extraction tanks of ion source Base pressure of 2.0e-8 mbar 50 kv high voltage isolation All components constructed of 6061 aluminum Pumping RF 3

4 ECR charge breeder diagnostics CARIBU beams 1 + or Stable beams 65kV power supply ΔV power supply n + 4

5 Injected ion penetration Symmetric iron Asymmetric iron Looked at two cases Symmetric iron with no cut outs for waveguides and RF is launched radially Asymmetric iron which has cut outs for axial RF launch 5

6 Injected ion penetration Symmetric iron Asymmetric iron Cs + ions, V 1+ : 30 kv, ΔV: -10 V 3D field calculations - Computer Simulation Technology Electromagnetic Studio Simulations utilized running conditions for coils, hexapole, and potentials No plasma or collision effects included in simulation 6

7 Injected ion penetration Symmetric iron cases Particle % 60 Cs Sym Cs Asym K Sym K Asym Asymmetric iron cases Na Sym Na Asym Position (in) 133 Cs +, 39 K +, 23 Na + ions V 1+ : 30 kv, ΔV: -10 V 7

8 Low-A performance Potassium and sodium produced from surface ionization source Base pressure: 3.7 x 10-8 mbar Helium plasma: ~9.0 x 10-8 mbar Adding oxygen reduced breeding efficiency Using He-3 vs. He-4 made no difference in efficiency Ion Charge State Efficiency (%) A/Q 23 Na 39 K Helium plasma 5 s Response of 39 K 10+ beam current to pulsing an incoming K + beam with an intensity of 17 ena. Beam is pulsed with electrostatic steerer immediately after the surface ionization source. Oxygen plasma 8

9 Charge breeding results TWT frequency shift with Cesium GHz 53 W W GHz 73 W W 85 Rb 20+ Two-frequency heating with Xenon 10% 11.5% Kept GHz constant at 331 W, varied GHz power level 9

10 Charge breeding performance Ion Charge State Efficiency (%) A/Q 23 Na K Kr Rb Ru (1+) t 1/2 = 11.6 s 135 Te (1+) t 1/2 = 19.0 s Xe Xe Cs Cs Cs (1+) t 1/2 = 24.8 s 142 Cs (1+) t 1/2 = 1.69 s 143 Cs (1+) t 1/2 = 1.79 s 143 Ba (2+) t 1/2 = 14.3 s 144 Ba (2+) t 1/2 = 11.5 s 146 Ba (2+) t 1/2 = 2.22 s

11 Charge breeding time 132 Xe + Electrostatic deflector 0.35 t breeding = t creation + t extraction 132 Xe Deflector Voltage (kv) % Xe 29+ Intensity 0.05 t breeding 1.3 sec Time (sec)

12 Breeding efficiency and rise time RF frequency Xe-132 from RF discharge source Oxygen plasma, single-frequency heating TWTA only GHz: 300 W GHz: 310 W Efficiency (%) Avg: 36 msec/q Rise Time (msec) Avg: 6 msec/q Charge State 0 12

13 ECR contamination from air During 144 Ba 28+ run we encountered a background beam of 36 Ar 7+ with small amounts of 72 Ge 14+, 108 Cd 21+, 180 Hf Ar 7+ CARIBU ON Source of Ar-36 O-ring permeation 17 Viton o-rings with cumulative leak rate of 3.0e-5 torr-l/s 72 Ge Cd Ba Hf 35+ CARIBU OFF 13

14 ECR contamination from surfaces Extraction Platform Atomic Atomic Charge M 0/δM Threshold: δ Bρ Voltage, kvvoltage, kv # or Symb. Mass (p+n) State Include Radioactive ba Ions y/n (default - y): n (Optional) Calculate Ion Atomic Number: Central Ion Mass: Magnet Radius, m: Total flight time, nsec.: 56 Beam Rigidity, kg-m: Mag. Field, kg: Upper Bρ, kg-m: Lower Bρ, kg-m: ID Mass Q Abund. Br, kg-m B, kg δβ M0/DM dtime, ns Zn Ba Ba ********** Lower Probability Contaminants ********** Mg Ti Ge Se Kr Zr Mo Ru Ru Pd In Sn Sn Te Te Te Xe Xe Xe Cs La Ce Pr Nd Sm Eu Gd Dy Dy Er Er Yb Hf W W Os Ir Pt Hg Tl Pb Bi U U Ti Zn Mo Zr Sn Xe 26+ Ba-146: 10 4 pps 3% of total beam current 146 Ba Ir Hg

15 Background reduction Chemical Element % Present Solid species surface and bulk contamination Plasma chamber liners Sand blasting High-pressure rinsing CO 2 snow cleaning High-purity aluminum coating Magnesium (Mg) Silicon (Si) Titanium (Ti) Chromium (Cr) Manganese (Mn) Iron (Fe) Copper (Cu) Zinc (Zn) Aluminium (Al) Balance 15

16 Background reduction Aluminum coating Cleaned chamber with CO 2 Used W coil with high-purity (99.999%) aluminum wire Source pressure: 5.0e-7 Torr Wall covered with 1 micron layer Vented to oxygen Not all surfaces were adequately coated 16

17 Background reduction CO 2 cleaning 40 Ar Cl F Fe

18 Background reduction CO 2 cleaning 35 Cl Ar 12+ After CO2 cleaning F: factor of 20 reduction Cl: factor of 4 reduction Fe: factor of 50 reduction Ar: 22% reduction 19 F Fe

19 Background reduction Aluminum coating 35 Cl Ar 12+ After CO2 cleaning F: factor of 20 reduction Cl: factor of 4 reduction Fe: factor of 50 reduction Ar: 22% reduction After aluminum coating F: factor of 160 reduction Cl: factor of 17 reduction Fe: Not detectable Ar: factor of 3 reduction 19 F 5+ 19

20 Reduction on target After coating 98 Mo Ta 37+ After coating 132 Xe W Ti 10+ Before coating Some contaminants were eliminated 100 Before coating Mo-98 was reduced by x5 (on target) New contaminants Ta-181 & W Ti Fe Mo Ce W 38+ Investigating new techniques 113 Cd Yb

21 Conformal coatings by Atomic Layer Deposition 1 μm All exposed surfaces coated Line-of-sight not required ZnO Si 200 nm 21

22 Atomic Layer Deposition of Al 2 O 3 Trimethyl Aluminum (TMA) CH 3 Al CH 3 CH3 CH 4 A) OH OH OH Al(CH 3 ) 3 CH Al CH 3 3 CH CH Al 3 CH3 Al CH 3 3 OH OH OH H 2 O CH 4 B) Al CH CH 3 3 CH CHAl 3 CH3 Al CH 3 3 OH OH OH H 2 O H 2 O OH Al CH CH OH OH 3 3 CH CHAl 3 CH3 Al CH 3 3 OH OH OH 1 ALD Cycle of TMA/H 2 O Deposits 1 Al 2 O 3 Monolayer Process can be done in situ Care has to be taken with exposed surfaces 22

23 Characteristics of ALD Process Al 2 O 3 Growth Rate (Å/Cycle) Thickness (Å) Growth Rate = 1.29 Å/Cycle TMA Exposure (Torr s) Al 2 O 3 ALD Cycles Self-terminating surface reactions Film thickness is linear with ALD cycles To achieve 1 micron thickness will require 7751 cycles at 1 minute/cycle Possible path to coating all surfaces responsible for source contamination with a surface which is beneficial to source performance 23

24 CARIBU Californium Rare Ion Breeder Upgrade 252 Cf source, gas catcher, isobar separator To low energy area Stable beam platform EBIS CHARGE BREEDER ECRCB ion source 1+ SOURCE HEAD 24

25 CARIBU system with RF cooler/buncher & MR-TOF Had to fit onto existing high voltage platform All electrostatic transport line 25

26 EBIS charge breeder Thermal insulation Water-cooled copper screen Based upon RHIC Test EBIS design EBIS was commissioned off-line EBIS has been moved on-line and we expect to have the EBIS system operational in May2016 Heater bars Steering coils EBIS design parameters Solenoid field 6 T IrCe cathode diameter Electron beam current Electron beam energy 4 mm 2.0 A 5 kev Electron beam radius 330 µm Electron beam density 577 A/cm 2 Normalized full acceptance Trap capacity π mm mrad 30 nc Injection time 10 µs Repetition rate 30 Hz Duty cycle 90 % 26

27 Charge bred cesium EBIS operational parameters Solenoid field Electron beam current Electron beam energy in trap 4 T 1.0 A 9.4 kev Electron beam radius 860 µm Electron beam density 170 A/cm 2 Trap pressure Repetition rate Breeding time ~3.0x10-10 Torr 5 Hz 10 ms Dipole First results in May % breeding efficiency into Cs

28 Charge bred cesium 28+ EBIS operational parameters Solenoid field 5 T Electron beam current 1.6 A Electron beam energy in trap 6.5 kev Electron beam radius 370 µm Electron beam density 385 A/cm 2 Trap pressure ~8.0x10-10 Torr 16 O Repetition rate 10 Hz 16 O C Breeding time 28 ms O N C 2+ Latest results several small leaks fixed, system baked out 28% breeding efficiency into 133 Cs

29 Ion injection and extraction EBIS is an inherently pulsed device Typical extraction pulse is µs REX-ISOLDE 15 minutes of delivered beam in every 24 hours of beam time Plenty of time between bunches to do other things Pulsed injection Continuous injection Courtesy of T. Baumann, NSCL, MSU 29

30 Multi-beam scheme Radioactive CARIBU Stable Up to 3% Duty Factor t Pulsed Deflector 96 % Duty Factor t ECR-2 EBIS t RFQ Achromatic LEBT The simultaneous acceleration of two beam species One stable from the ECR and one radioactive from CARIBU-EBIS A/q required to be within 1% of each other PII 30

31 Summary The ECR charge breeding program at ANL was successful Advanced the state of the art for ECR charge breeding Delivered 81 days of radioactive beams in final year Even with background, many successful experiments Installation of the EBIS charge breeder is progressing Demonstrated 28% breeding efficiency in off-line tests New high voltage platform is complete EBIS system should be operational in May