1. Understanding Extraction And Beam Transport In The ISIS H - Ion Source D. C. Faircloth, A.P Letchford, C. Gabor, S. Lawrie M. O. Whitehead and T. Wood ISIS J. Pozimski, S. Jolly, P. Savage and M. Woods Imperial College

2. Motivation The Front End Test Stand (FETS) project at ISIS requires a 70 mA 2 ms 50 Hz H - beam. Previous work has already demonstrated that these beam currents and duty cycles are possible. However the emittance of the ISIS ion source is very large. This presentation describes the steps being taken to reduce the emittance.

3. ISIS Operational Ion Source Penning H - ion source Surface Plasma Source (SPS) 45 mA through 0.6  10 mm aperture (750 mA/cm 2 ) 200-250  s, 50 Hz  1% d.f.  20 ml/min H 2  3 g/month Cs 20-30 day average lifetime 10mm

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

7. Platform Ground Pulsed Extract Power Supply Extraction Electrode, Coldbox and Analysing Magnet all Pulsed + 17kV - Platform DC Power Supply 35kV Post Extraction Acceleration Gap Laboratory Ground +- 18kV 35keV H - Beam

9. Diagnostics Vessel 2000 Ls -1 Turbo pump 860 mm

10. Diagnostics Vessel Beam Current Toriod X and Y Slit-Slit Emittance Scanners Buffer Gas Delivery System Diagnostic Dipole ISDR Diagnostics Retarding Potential Energy Analyzer

11. Diagnostics Vessel Beam Current Toriod X and Y Slit-Slit Emittance Scanners Movable Scintillator with Interchangeable Pepperpot or Profile Head Buffer Gas Delivery System Diagnostic Dipole Beam Shutter ISDR Diagnostics

12. 17 kV extract power supply 25 kV extract power supply Cold Box Refrigerator Chiller Circulator Ion Source Control Racks and Power Supplies 35 kV Insulator ISDR

13. X-Emittance Scanner Y-Emittance Scanner Pepperpot and Profile Measurement Diagnostics Vessel Mark Trev

15. 17 kV Extract Potential -60 0-3030 0 50 100 -50 -100 x (mm) x ‘(mRads) -60 0-3030 0 50 10 0 -50 - 10 0 y (mm) y ‘(mRads) 0.84 πmm-mRad norm rms 0.92 πmm-mRad norm rms 57 mA Beam Current The Present Situation

16. Profile Measurements for Different Extraction Voltages

17. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 17 kV Extraction Voltage 35 kV Platform Voltage 18 kV Post Acceleration Voltage 47 mA Beam Current

18. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 16 kV Extraction Voltage 35 kV Platform Voltage 19 kV Post Acceleration Voltage 42 mA Beam Current

19. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 15 kV Extraction Voltage 35 kV Platform Voltage 20 kV Post Acceleration Voltage 40 mA Beam Current

20. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 14 kV Extraction Voltage 35 kV Platform Voltage 21 kV Post Acceleration Voltage 38 mA Beam Current

21. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 13 kV Extraction Voltage 35 kV Platform Voltage 22 kV Post Acceleration Voltage 35 mA Beam Current

22. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 12 kV Extraction Voltage 35 kV Platform Voltage 23 kV Post Acceleration Voltage 32 mA Beam Current

23. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 11 kV Extraction Voltage 35 kV Platform Voltage 24 kV Post Acceleration Voltage 28 mA Beam Current

24. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 10 kV Extraction Voltage 35 kV Platform Voltage 25 kV Post Acceleration Voltage 25 mA Beam Current

25. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 9 kV Extraction Voltage 35 kV Platform Voltage 26 kV Post Acceleration Voltage 21 mA Beam Current

26. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 8 kV Extraction Voltage 35 kV Platform Voltage 27 kV Post Acceleration Voltage 17 mA Beam Current

27. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 7 kV Extraction Voltage 35 kV Platform Voltage 28 kV Post Acceleration Voltage 13 mA Beam Current

28. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 6.5 kV Extraction Voltage 35 kV Platform Voltage 28.5 kV Post Acceleration Voltage 12 mA Beam Current

29. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 6 kV Extraction Voltage 35 kV Platform Voltage 29 kV Post Acceleration Voltage 10 mA Beam Current

30. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 5.5 kV Extraction Voltage 35 kV Platform Voltage 28.5 kV Post Acceleration Voltage 9 mA Beam Current

31. At normal operating conditions (17 kV Extraction Voltage) the beam is collimated into a round beam by the post acceleration electrodes. The beam is asymmetrically focused in the horizontal plane.

32. Profile Measurements for Different Extraction Voltages Keeping Post Acceleration Voltage Constant at 18 kV

33. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 17 kV Extraction Voltage 35 kV Platform Voltage 18 kV Post Acceleration Voltage 44 mA Beam Current

34. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 16 kV Extraction Voltage 34 kV Platform Voltage 18 kV Post Acceleration Voltage 43 mA Beam Current

35. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 15 kV Extraction Voltage 33 kV Platform Voltage 18 kV Post Acceleration Voltage 41 mA Beam Current

36. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 14 kV Extraction Voltage 32 kV Platform Voltage 18 kV Post Acceleration Voltage 37 mA Beam Current

37. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 13 kV Extraction Voltage 31 kV Platform Voltage 18 kV Post Acceleration Voltage 34 mA Beam Current

38. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 12 kV Extraction Voltage 30 kV Platform Voltage 18 kV Post Acceleration Voltage 31 mA Beam Current

39. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 11 kV Extraction Voltage 29 kV Platform Voltage 18 kV Post Acceleration Voltage 28 mA Beam Current

40. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 10 kV Extraction Voltage 28 kV Platform Voltage 18 kV Post Acceleration Voltage 25 mA Beam Current

41. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 9 kV Extraction Voltage 27 kV Platform Voltage 18 kV Post Acceleration Voltage 21 mA Beam Current

42. Profile Measurements For Different Post Acceleration Voltages Keeping Extraction Voltage Constant

43. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 10 kV Extraction Voltage 35 kV Platform Voltage 25 kV Post Acceleration Voltage 25.2 mA Beam Current

44. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 10 kV Extraction Voltage 33 kV Platform Voltage 23 kV Post Acceleration Voltage 24.8 mA Beam Current

45. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 10 kV Extraction Voltage 31 kV Platform Voltage 21 kV Post Acceleration Voltage 24.6 mA Beam Current

46. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 10 kV Extraction Voltage 29 kV Platform Voltage 19 kV Post Acceleration Voltage 24.2 mA Beam Current

47. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 10 kV Extraction Voltage 27 kV Platform Voltage 17 kV Post Acceleration Voltage 23.8 mA Beam Current

48. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 10 kV Extraction Voltage 25 kV Platform Voltage 15 kV Post Acceleration Voltage 23.2 mA Beam Current

49. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 10 kV Extraction Voltage 23 kV Platform Voltage 13 kV Post Acceleration Voltage 22.8 mA Beam Current

50. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 10 kV Extraction Voltage 21 kV Platform Voltage 11 kV Post Acceleration Voltage 22.6 mA Beam Current

51. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 10 kV Extraction Voltage 19 kV Platform Voltage 9 kV Post Acceleration Voltage 22.2 mA Beam Current

52. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 10 kV Extraction Voltage 17 kV Platform Voltage 7 kV Post Acceleration Voltage 21.6 mA Beam Current

53. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 10 kV Extraction Voltage 15 kV Platform Voltage 5 kV Post Acceleration Voltage 21.4 mA Beam Current

54. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 10 kV Extraction Voltage 13 kV Platform Voltage 3 kV Post Acceleration Voltage 20.8 mA Beam Current

55. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 10 kV Extraction Voltage 11 kV Platform Voltage 1 kV Post Acceleration Voltage 20.6 mA Beam Current

56. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 10 kV Extraction Voltage 9 kV Platform Voltage -1 kV Post Acceleration Voltage 18.0 mA Beam Current

57. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 10 kV Extraction Voltage 7 kV Platform Voltage -3 kV Post Acceleration Voltage 17.2 mA Beam Current

58. Increasing the Extraction Voltage Larger Beam Higher Beam Currents Increasing the Post Acceleration Voltage Smaller Beam Small Increase in Beam Current

59. Post Acceleration Electrode Modifications

60. New Post Acceleration Electrode Designed with Variable Gap Length

63. Standard 55mm Post Acceleration Gap 10mm Post Acceleration Gap XYXY Slit-Slit Emittance Scans 34 mA 13 kV Extraction Voltage 39 mA 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0

64. Standard 55mm Post Acceleration Gap 10mm Post Acceleration Gap XYXY Slit-Slit Emittance Scans 24 mA 10 kV Extraction Voltage 26 mA 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0

65. Standard 55mm Post Acceleration Gap 10mm Post Acceleration Gap XYXY Slit-Slit Emittance Scans 16 mA 8 kV Extraction Voltage 18 mA 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0

66. Work is Ongoing Different Post Acceleration Gap Lengths Will be Tested

67. Extraction Electrode Modifications Standard Gap 2.3 mm Standard Jaw Gap 2.1 mm

68. Extraction Electrode Modifications Decrease Jaw Gap to 1.1 mm

69. Beam Currents = 10 mm Post Ac. Gap / 1.1 mm Ext. Jaws = 10 mm Post Ac. Gap / 2.1 mm Ext. Jaws = 55 mm Post Ac. Gap / 2.1 mm Ext. Jaws ε x = 0.9 ε y = 0.9  mm-mRads rms Normalized ε x = 0.2 ε y = 0.3  mm-mRads rms Normalized

70. Axi-Symmetric Extraction To simplify matters a new circular aperture plate with the same area as the slit and a new circular extraction electrode have been manufactured. 4 mm Diameter 2.7 mm Diameter

71. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 17 kV Extraction Voltage 35 kV Platform Voltage 18 kV Post Acceleration Voltage 11.5 mA Beam Current

72. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 13 kV Extraction Voltage 35 kV Platform Voltage 22 kV Post Acceleration Voltage 7.2 mA Beam Current

73. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 10 kV Extraction Voltage 35 kV Platform Voltage 25 kV Post Acceleration Voltage 5.8 mA Beam Current

74. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 8 kV Extraction Voltage 35 kV Platform Voltage 27 kV Post Acceleration Voltage 4.6 mA Beam Current

75. Severe Defocusing in the vertical plane is now obvious

76. Multi Beamlett Extraction To study beam transport an aperture plate with 5 separate 1 mm diameter holes has been constructed. This will help understand the effect of transport through the 90° sector magnet.

77. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 17 kV Extraction Voltage 35 kV Platform Voltage 18 kV Post Acceleration Voltage 33 mA Beam Current

78. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 13 kV Extraction Voltage 35 kV Platform Voltage 22 kV Post Acceleration Voltage 27 mA Beam Current

79. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 10 kV Extraction Voltage 35 kV Platform Voltage 25 kV Post Acceleration Voltage 18 mA Beam Current

80. 2.5 mA/cm 2 2.0 1.5 1.0 0.5 0.0 8 kV Extraction Voltage 35 kV Platform Voltage 27 kV Post Acceleration Voltage 13 mA Beam Current

81. Work is still on going… Aperture plates with individual holes in each of the 5 positions are currently being tested. This will give an indication of how space charge affects transport. Different gap settings will be tested.

82. A new detailed modelling study using CST studio is underway. Scott Lawrie

83. Summary Work is still ongoing but it is clear that the present extraction and transport arrangement on ISIS is sub-optimal and improvements will yield higher output currents and lower emittances. It may be necessary to install electrostatic focusing as part of the extraction system. Redesign of 90° sector magnet may be required.

84. Thank you for your attention