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Ultrafast High-brightness Electron Source for Advanced Energy Systems

This article discusses the challenges and solutions in generating and preserving ultrafast high-brightness electron beams. It introduces a compact electron source design and presents simulation results and experimental setup plans.

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Ultrafast High-brightness Electron Source for Advanced Energy Systems

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  1. Ultrafast High-brightness Electron Source Advanced Energy Systems Inc. P.O. Box 7455, Princeton, NJ 08543-7455 Phone: (609) 514-0319 Fax: (609) 514-0318 E-mail: park@aesprin.com Jangho Park

  2. Introduction • Generation and preservation of ultrafast high-brightness electron beams is one of the major challenges in accelerator R&D. • In order to generate and preserve the ultrafast high-brightness electron beam, transverse and longitudinal space charge effects have to be considered. • Several approaches to achieving ultra-short bunches have been explored such as velocity bunching and magnetic compression. • However, each option suffers drawbacks (extra RF and bulky) in achieving a compact ultrafast high-brightness source. • A compact ultrafast high-brightness electron source is demanded for Ultrafast/Femtosecond Electron Diffraction (UED/FED) and advanced accelerator experiment.

  3. Bunch Lengthening • For a high-aspect-ratio (short bunch length) electron bunch, the asymptotic bunch length due to the space charge forces of a uniformly accelerated bunch, ignoring the drive laser duration and assuming prompt response from a copper cathode where the laser spot radius is kept constant, is expressed by: • Bunch lengthening due to the space charge is inversely proportion to the square of the bunch radius and the square of the accelerating field. • Bunch length stretches due to the longer path lengths of the outer particles compared with electrons closer to the axis. • Bunch lengthening due to the geometrical effects is proportional to the square of the beam radius.

  4. Rc=30mm R=3.35mm R=2.55mm R=4.25mm Gun Cavity Design • Gun Cavity Design Aspects • Higher Acceleration Field with x-band RF • Utilizing a curved cathode • Axisymmetry coupling • Copper cathode

  5. Cavity Field Configuration Axial Field Radial Field Cathode A: Curved, Rc=30mm Cathode C: Flat cathode

  6. Transverse Bunch Size Evolution Cathode A: Curved, Rc=30mm Cathode C: Flat cathode

  7. Beam Dynamics Results 25fs UV Cathode A: Curved, Rc=30mm Cathode B: Curved, Rc=40 mm, laser pulse shaping Cathode C: Flat cathode

  8. Beam Dynamics Results Cathode A: Curved, Rc=30mm Cathode B: Curved, Rc=40 mm, laser pulse shaping Cathode C: Flat cathode Beam dynamics simulation results at the z = 50 cm target location.

  9. 20.00 20.51 21.01 21.52 22.03 22.53 23.04 23.55 24.05 24.56 Temperature Results • 3-D ANSYS • 4.0x10-5 duty factor Mean Temperature of Gun 21.94 C 20C cooling water Cooling channels Temperature K

  10. Displacement Results

  11. Freq Shift • Frequency Shift determined from 3-D ANSYS original geometry eigenvalue solution and new geometry from displacements resulting from RF/Thermal loads. • Frequency Shift from Displacements: -159 kHz • Frequency shift from rf losses can be offset with cooling temperature

  12. Gun Assembly RF Input Vacuum Grille Vacuum Cross 2.75 CF Flanges Full Cell Cathode Cell Waveguide to Coax Transition Beamline Flange 1.33 Conflat Ding Holes For Tuning (4 per Cell)

  13. Cooling Arrangement RETURN FEED (2) RETURN INTERNAL PLENUMS

  14. Laser Solenoid RF In RF Window Ion Pump • Beam Viewer with Faraday Cup • Pin-hole • CTR Target Bucking Coil UV View Port • Beam Viewer Steerer Steerer E-beam Laser Mirror Gate Valve Camera RF Gun Linear motion Camera Interferometer IR View port Ion pump Linear motion Ion Pump 0 30 50 12.5 Z [cm] 150 Proposed Experimental Setup

  15. Proposed Experimental Setup

  16. Conclusions • AES is developing a ultrafast high-brightness electron source for FED experiments and advanced accelerator applications. • The ultrafast high-brightness electron beam from X-band curved cathode RF gun is feasible. • Numerical calculations are improved 5 to 10 times brighter than S-band PC gun. • Thermal-structural and RF frequency shift analysis shows that the design of this electron gun running at 4.0x10-5 duty factor is robust. • Planning installation and tests at ATF would start July 2013. • The ATF beam tests will include; • validate the source, • provide a useful data point on the bunch length and emittance. • This work was supported by DOE SBIR Phase I grant No. DE-SC0006210. The Phase II grant is anticipating in July 2012. • Thank You!!!

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