The ISIS Hˉ Ion Source and Development Program

1. The ISIS Hˉ Ion Source and Development Program Dan Faircloth

2. Talk Outline • ISIS Ion Source • Research + Development Program - Infrastructure Changes - Thermal Modeling - Electromagnetic modeling • Discussion and Summary

3. The ISIS Ion Source Penning H- ion source Surface Plasma Source (SPS) 35 mA through 0.610 mm aperture 200-250 s, 50 Hz  1% duty cycle  20 ml/min H2  3 g/month Cs • 0.17  mm mrad (665 keV, 35 mA, rms) 20-30 day average lifetime

4. Ion Beam Extract Electrode Penning Pole Pieces Discharge Region Aperture Plate Ceramic Anode Source Body Copper Spacer Cathode Mica 10mm Mounting Flange

5. H2 Gas Pulse ~200μs 50A Discharge Pulse ~600μs 17kV Extract Pulse ~250μs 35mA H- Beam Mode of Operation Time

6. The Ion Source Assembly

7. Research and Development Program Goals for ISIS upgrades and future accelerators: • Double output current 35mA → 70mA • Increase pulse length 200μs → 1 or 2 ms • Improve emittance • Maximise lifetime

8. Prototype Designs Prototype Designs Testing + Experimental Work FINALISED DESIGNS Development Strategy Infrastructure Changes New Source Flange New Power Supplies Separate Penning Field Thermal Studies Improved Temperature Control Longer Duty Cycles Better Start-up Electromagnetic Studies Improved Extraction and Transport Higher Beam Current Lower Emittance

9. Infrastructure Changes

10. The ISDR duplicates the equipment on the ISIS and allows ion source development work without affecting ISIS operations. HV platforms modified to accommodate new extract regulator. This will allow longer duty cycles and higher extract potential, which will provide higher beam current. The Ion Source Development Rig

11. Top Loading Ion Source Ion Source Assembly Flange and Magnet Assembly

12. In the present arrangement the Penning Field is generated by pole tip extensions on the 90° analyzing magnet. Separate Penning Field So the Penning Field could not be easily varied.

13. To allow separate control of the Penning field the pole tip extensions were removed…

14. To allow separate control of the Penning field the pole tip extensions were removed… And a separate magnetic circuit was added, consisting of a winding, yoke and pole pieces.

16. Thermal Studies

17. Thermal Modelling 3D Finite Element Model of the Ion Source using ALGOR software Experimental test rig set up on the ISDR to measure radiation functions and convection coefficients to be applied to the surfaces of the model. Computational fluid dynamic modelling of the cooling channels was conducted by Oxford University to validate the cooling system.

18. 600 520 440 360 280 200 Steady State Temperatures

19. Transient Results for Present Ion Source Double Duty Cathode Surface ΔT= 73 ºC Head HTC 1200 Wm-2C-1 (7.2ms-1 Air Flow) Flange HTC 500 Wm-2C-1 ( 0.09Lmin-1 Water) Mica Thickness Halved ΔT= 39 ºC Anode Surface 1000μs duty

22. Allows better cooling of the Cathode through the flange Increase Duty Cycle by Reducing Mica Thickness

23. Maximum discharge length obtained 1750μs

24. So try increasing aperture width Carefully file the slit wider from 0.6mm to 0.8mm Increase beam current How? Increase extract voltage not currently possible

25. Typical 0.6mm wide aperture

26. Increase aperture width to 0.8mm 70mA beam current

27. Electromagnetic Studies

28. MAFIA Model of Extractionand 90º Sector Magnet

29. 17 keV normalised Hrms= 0.03  mm mrad Vrms= 0.16  mm mrad Correctly Terminated Sector Magnet Field 0T 0.5T 0T 0.5T 17 keV normalised Hrms= 0.04  mm mrad Vrms= 0.16  mm mrad Inadequately Terminated Sector Magnet Field in the Current Arrangement

30. Terminated Extract Terminated Pierce Extract 17 keV normalised Hrms= 0.07  mm mrad Vrms= 0.05  mm mrad 17 keV normalised Hrms= 0.04  mm mrad Vrms= 0.16  mm mrad 17 keV normalised Hrms= 0.03  mm mrad Vrms= 0.03  mm mrad Extract Geometry Modifications Existing Extract

31. New Pole Pieces, Coldbox Insert and Extract Electrodes Manufactured

32. Pierce Extract Geometry H = 0.62 π mm mrad (norm) V = 0.73 π mm mrad (norm) New Extract Electrode Results Standard Extract Geometry H = 0.89 π mm mrad (norm) V = 0.97 π mm mrad (norm)

33. Discussion • Development Rig Infrastructure changes allow testing of new source designs • Separating the Penning Field allows: • Improved start-up • The source to run at different settings • Improved discharge stability

34. Discussion • Increasing the discharge length: • Requires decreasing the thickness of the mica to increase cooling • Leads to reduced beam current • But beam current may be increased by widening the aperture slit or increasing the extract voltage

35. Discussion • New analyzing magnet arrangement allows beam to be produced horizontal and on axis • New extract electrode arrangement improves beam emittance

36. Future Work • Complete study of new extract electrodes • Longer extract pulse • Higher extract voltage • Further investigation of aperture width • Cathode heating element • x2 size source? • Lifetime studies

37. Summary • The ISIS H- ion source is one of the world leading operation ion sources. • A comprehensive R+D program is continuing to increase the source’s duty cycle, output current, emittance and reliability to meet the requirements of future accelerators.

38. Acknowledgements Mark Whitehead Trevor Wood John Thomason Reg Sidlow Work funded by European Union HPNIS Network Contract No. HPRI-CT-2001-50021