1. October 4-5, 2010 1 Electron Lens Overall Design Alexander Pikin October 4, 2010 Electron Lens

2. October 4-5, 2010 2 Outline 1.Structure of the electron lens 2.Electron beam properties, electron gun simulations, design and operation modes 3.Electron collector 4.Magnetic structure and control 5.Electron beam diagnostics 6.Summary

3. October 4-5, 2010 3 Structure of the E-Lens Drift tube 3 Solenoid GS1 Electron gun Superconducting magnet Electron collector Drift tube 3 Solenoid GS2 Solenoid GSBSolenoid CSB Solenoid CS2 Solenoid CS1 Electron beam volume Drift tube 4 BPM Drift tube 1 Vacuum system BPM Drift tube 5 Drift tube 9 Drift tube 10 Electron collector Drift tube 7 Drift tube 8 Drift tube 6 Drift tube 2Electron gun 2x Ion Pump Cryopump Gate valve Ceramic HV break Ion pumps

4. October 4-5, 2010 4 Electron beam 1. Electron beam parameters: I el = 0.0 – 1.5 A, E el = 2.0 – 8.0 keV 2. Required shape of radial current density profile - Gaussian : Solution: generating required emission current density on the cathode of the electron gun and have electron beam fully magnetically confined from the cathode to the electron collector (Similar to Fermi Lab). σ cath =1.28 mm 3. Required range of σ in the center of SC solenoid: σ=0.28mm – 0.78 mm ( for E p =250 – 100 GeV) For a fully magnetically confined electron beam B-dependence of the beam σ : B cath – magnetic field on the cathode Reasonable range of magnetic fields: B cath = 0.2 – 0.8 T B center = 2.5 – 6.0 T 4. Required transverse displacement of e-beam from axis in any direction: Δr = 5.0 mm

5. October 4-5, 2010 5 Electron gun model 1. Electron gun is immersed in a controlled magnetic field of a gun solenoid coil 2.The emission density profile is formed by cathode surface and control electrode Electrostatic model :

6. October 4-5, 2010 6 Electron trajectory simulations near electron gun I el =0.6A, U an = 6.1 kV, different M-fields 8.0 kGs4.0 kGs 2.0 kGs 1.0 kGs

7. October 4-5, 2010 7 Emission density profile simulations (3 σ beam) The electron beam has to have Gaussian profile with r/σ≈3: overlapping the proton beam.

8. October 4-5, 2010 8 Gun electric field For I el =1.5 A U an =13.4 kV E max = 7.2 kV/mm Kilpatric safety factor = 2.5

9. October 4-5, 2010 9 Electron gun design Cathode Control electrode Anode Drift tube IrCe cathode prototype (G. Kuznetsov, Budker Institute, Novosibirsk) Requirements: 1.Precision (<0.05 mm) and reproducibility of assembly 2.High-vacuum compatibility 3.Easy replacement with minimum time loss 4.Life time >20,000 hours for current I el = 1.0 A Manufactured parts: Reduced vacuum aperture Installation spring (2 total) Gun assembly Anode Feed Thru Supporting legs (3 total) HV Feed Thru’s Anode modulator (prototype):

10. October 4-5, 2010 10 Electron gun operation modes There will be three main operation modes of the electron gun: 1.Continuous mode for head-on compensation of proton beam. 2.Pulsed mode with short pulses (0.5 μs, positive or negative) and frequency f=100 Hz for adjustment the transverse position of the electron beam in a main solenoid using pick-up beam position monitors. 3.Pulsed mode with pulses 1.0 - 10 μs and frequency 0.1 -1.0 Hz for imaging the transverse profile of the electron beam on a detector at the entrance into electron collector. Output pulses of the prototype anode modulator (Amplitude is 15 kV)

11. October 4-5, 2010 11 Electron collector: concept 1.Electrons are collected on inner cylindrical surface: simpler design, cheaper manufacturing. 2. Efficient magnetic shielding: reduces flux of secondary electrons, reduces diameter of electron beam at the entrance into electron collector (vacuum separation) 3. Open geometry on the rear: allows separate vacuum pumping of EC volume, access for direct visualization of the electron beam profile from the back, ability to measure extracted ion current.

12. October 4-5, 2010 12 Electron collector: simulation model Magnetic shield Drift tube Electron ReflectorBeam Position Monitor Electron Collector EC coil

13. October 4-5, 2010 13 Electron collector simulations Electron trajectories: I el 1.0 A, E el = 4.0 kV, B = 3.0 kGs

14. October 4-5, 2010 14 Electron collector engineering analysis Uniform heat load 50 watt/cm 2, total 73.5 kwatt Uniform heat load of 50W/cm 2 Total heat load of 73.5KW Heat transfer coefficient = 8770 W/m at 20⁰C Based on: Material OFC (UNS 10200) 20 cooling tubes @.6 gal/min, 32.2⁰C D=.245”=.0062m ∆T water =.6 gal/min*C P /q=22.7 ⁰C Calculated surface temperature of tube: ∆T=(T S -32.2)q C /(h C A) T S =119⁰C The simulated values of thermal stresses safety factors: 12 for the nominal heat Load 4.7 for the maximum heat load

15. October 4-5, 2010 15 Electron collector design EC coil High-voltage platform HV ceramic break Bellows 4-electrode beam position monitor Cooling tubes Electron reflector Electron collector Magnet shield Manufactured EC parts

16. October 4-5, 2010 16 E-lens test bench Goals: Tests of electron gun, electron collector, electron beam imaging, transverse beam control with dipole coils, tests of control programs

17. October 4-5, 2010 17 Magnetic structure of the E-Lens Superconducting solenoid Warm solenoid coils Dipole coils Extraction arm Injection arm Dipole coils Functions of magnetic structure: 1.Provide electron beam confinement in an interaction region 2.Electron beam deflection from injection arm to the main solenoid and to the extraction arm 3.Control of the electron beam diameter in the interaction region 4.Control of the electron beam position in the interaction region within radius of 5.0 mm from the axis

18. October 4-5, 2010 18 Main solenoid magnetic field distributions

19. October 4-5, 2010 19 Fringe magnetic field B_center=6T B_center=3T B_center=1T The magnetic field in the transition areas does not go below 3 kGs within the range of field in the center of main solenoid 1.0 - 6.0 T. Keeping the fringe magnetic field relatively high allows restrict transverse deflection of the electron beam and limit its diameter in the transition area.

20. October 4-5, 2010 20 Warm magnets Solenoid coil Dipole coil

21. October 4-5, 2010 21 Parameters of the “warm” magnets Parameter Gun coil (GS1) Gun-transition coil (GS2) Gun bending coil (GSB) X-Dipole coil (GSX) Y-Dipole coil (GSY) Conductor h_cond (mm)14.0 6.35 ID_water (mm)9.0 4.75 B_insul (mm)0.3 0.65 Dimensions ID (mm)173.48234.0480.0178.0193.0 OD (mm)553.08526.0859.6192.0207.0 Length (mm)262.8379.6262.8580.0 N_layers13101312 N_pancakes9139 Nominal regime M - field B (Gauss)8000.04468.03202.0190.0 (5mm) Power P (watt)58.025.645.01.41.7 Current I (A)1188.0731.0769.0239.0258.0 Total power consumed by all magnets in 2 E-lenses (kwatt)525.2 Maximum regime (nominal+40%) M - field B (Gauss)11200.06256.04482.0270.0270 Power P (watt)114.050.0882.93.4 Current I (A)1663.01023.01077.0334.0361 Total power consumed by all magnets in 2 E-lenses (kwatt)1029.6

22. October 4-5, 2010 22 Ion content control Ion presence in the interaction region would neutralize electric field of the electron beam and therefore ions have to cleared from the electron beam. With DC electron beam the proposed E-lens employs axial expulsion of ions from the interaction region to the electron collector using axial gradient of the electric field.

23. October 4-5, 2010 23 Beam position measurements The beam position monitors (BPMs) are designed using Fermilab prototype for our beam line. 2 BPMs will be used: 1 BPM on each end of uniform magnetic field (±100 cm from the median plane of main solenoid) for electron and ion beam measurements for overlapping the proton and electron beams. Bremsstrahlung sensors are considered for fine overlapping of electron and ion beams

24. October 4-5, 2010 24 Transverse beam profile measurements YAG Scintillator Pinhole scanner

25. October 4-5, 2010 25 Image processing Simulated electron beam image Simulated current density distribution

26. October 4-5, 2010 26 Summary 1.We have a design of the electron lens which satisfies the requirements to the electron beam profile, current and energy range and beam positioning laid out by Yun Luo based on beam dynamic simulations. This design is high-vacuum compatible and has an acceptable maintainability. 2.The actual operational range of electron gun, electron collector and magnetic structure has a comfortable safety margin of approx. 40%, limited by available electrical power and cooling water. 3.Diagnostic tools include beam position monitors in a beam line and scintillator/CCD camera combination for fast visualization and processing of the transverse electron beam profile. Other detector concepts of proton/electron beam overlapping are being considered and analyzed.