Advances in Depressed Collectors for High Efficiency Linear

Advances in Depressed Collectors for High Efficiency Linear Beam Microwave Devices Lalit Kumar Microwave Tube Research & Development Centre, BE Complex, Jalahalli, Bangalore Carterfest, Daresbury, 14 July, 2010 EM-Power to Empower Defence MTRDC

CARTERFEST-2010 Heartiest Felicitations to Prof. Dr. Richard Geoffrey Carter From Lalit Kumar and Colleagues MTRDC, Bangalore, India Microwave Research Group, Lancaster University, May, 1994 EM-Power to Empower Defence MTRDC

Multi-stage Depressed Collectors (MSDCs) l Linear Beam Device Efficiency Range: 5 -60 % l Spent Beam- significant amount of Electrical Energy Recovery – by Collector Voltage Depression Energy Efficient Microwave Devices – Green Devices EM-Power to Empower Defence MTRDC

Multi-stage Depressed Collector: The Beginning The Heils proposed MDC in 1935 A. Arsenjeva Heil & O. Heil, Zeitschrift fuer Physik, 95, pp. 752 -762, 1935 MTRDC EM-Power to Empower Defence

MSDC Advantages: l Design Goals High Device Efficiency Reduced Prime Power l Reduced Payload - weight & cost l Reduced Heat Dissipation – Longer Life l l Reduced X- Ray Emission Disadvantages: l Power Supply • Soft-landing of electrons • Prevent Rapid divergence - large radial velocities • Reduce space charge forces –add vanes • Reduce Backstreaming - Suppress Secondaries • Lower Noise – • Prevent Cavity- & Virtual cathode Oscillations – Curb Degassing Complex l Heavy l l • Energy Sorting of Electrons • EMI- shielding Increased Noise • Good Thermal Management EM-Power to Empower Defence MTRDC

Work at Lancaster: 1990 -91, 1994 3 - D Package for Depressed Collectors- LKOBRA (Based on KOBRA 3 -INP) Modeling of asymmetric Collectors 3 -D TWT Interaction Theory Review EM-Power to Empower Defence MTRDC

3 -D Simulation of Asymmetric Collectors (LKOBRA) 3 -stage Hyperbolic Collector Primary electrons Tilted E-Field Okoshi’s Collector # Tilted E-Field Thales Collector # Secondary Electrons MTRDC EM-Power to Empower Defence

LKOBRA: Trajectory Analysis in MSDC Simulation Trajectory Sorting by Energy class Particle sorting in Kinetic /Potential Energy space Kinetic Energy Plot PE Plot EM-Power to Empower Defence MTRDC

Work in India • At CEERI Pilani • At MTRDC, Bangalore EM-Power to Empower Defence MTRDC

Detailed Modelling of Secondary Electron Emission Effects in PIERCE Ø Automatic initiation of Secondaries: Ø True, Elastic and Inelalistic - individually or simultaneously. Ø User Assigned Number of trajectories Ø Realistic Cosine Distribution: for all classes Ø The space charge of the secondaries included Ø Several generations of secondaries Ø Under-current cutoff criterion to discard low current secondaries Ø Detailed analysis of primary and secondary electron trajectories Ø at each iteration EM-Power to Empower Defence MTRDC

Secondary Emission Model in PIERCE. • Modified Vaughan’s formula for angular dependence of the total SEE yield (Rao & Kumar) max( ) = max(0) (1+Ks ( 2 +L 4)/2 – Where max( ) is the maximum yield for primary angle 0, – Ks is a surface smoothness parameter and L is an empirical parameter. L = 0. 25 • Similar Formula for Backscattered yield ( ) with the constants for copper as: parameter Backscattered yield( ) Ksv 0. 5 Ks 1. 6 L 0. 25 K : v<10, 1<v 3. 6, v>3. 6 0. 45, 0. 08, 0. 14 • for normal incidence, • An empirical formula (by Arnal et al. ) modified to include primary energy dependence ( valid above 500 e. V ) = (Vmax/Vi)( /Z) 2(-9/Z) , Z is the atomic number, is a constant,

Simulation of Collector with Secondaries using PIERCE EM-Power to Empower Defence MTRDC

4 -Stage Collector for a Micro-TWT (MTRDC) Primary Trajectories alone Secondary Trajectories alone Collector Analysis: Parameter / Stage 4 -stage Collector Piece parts I II IV Stage Voltages wrt Cathode (V) 2800 2400 1600 1200 Current (m. A) 10. 6 40. 5 54. 5 63. 3 Power Dissipated (W) 15. 83 76. 8 147. 2 196. 3 Power Recovered (W) 5. 0 18. 3 17. 7 46. 1 Total Power Entering the Collector (W) 523. 68 Total Power Recovered by collector (W) 436. 29 Total Power Dissipated in Collector (W) 87. 38 Back Streaming Current (m. A) 27. 3 Efficiency ( Primary Electrons) % 83. 31 Efficiency ( Secondary Electrons) % 75. 3 EM-Power to Empower Defence MTRDC

PIC SIMULATION OF 3 -STAGE COLLECTOR (MAFIA) Stage Voltages V Trajectories Nos. Current A Power (Rec) W Power (loss) W Body 4300 0 0 1 2870 25 -0. 0437 62. 555 37. 159 2 2000 48 -0. 0839 193. 04 80. 265 3 910 23 -0. 0402 136. 43 32. 672 96 -0. 16795 392. 03 150. 19 Total EM-Power to Empower Defence MTRDC

3 D Simulation of TEF Collector in CST Studio Electric Field & Primaries EM-Power to Empower Defence Secondaries MTRDC

Thermal Analysis of Collectors 2 -stage Collector 4 -stage collector EM-Power to Empower Defence MTRDC

4 -Stage Radiation Cooled Collector for a Space-TWT Developed by CEERI & Bharat Electronics, Designed Jointly with MTRDC using PIERCE Simulation with Primary trajectories Simulation with secondary trajectories EM-Power to Empower Defence MTRDC

Helix TWT Collectors (MTRDC) 2 -stage Axi-symmetric Collector 2 --stage TEF Collector 4 -stage Ceramic Envelope Collector

CC-TWT COLLECTORS (MTRDC) SDC EM-Power to Empower the Defence 2 -stage-MDC MTRDC

Gyrotron Collector Concepts l l l Separation of the paths of : the spent beam and the RF Wave A Narrow width Hollow Beam Minimal Axial velocity Spread The spent beam energy- Predominantly transverse Unwinding of the spent beam Ø Ø Large-orbit gyrotron: unwinding by a non-adiabatic transition by a magnetic cusp. Small orbit gyrotrons: Adiabatic expansion, followed by a non-adiabatic transition. EM-Power to Empower Defence MTRDC

Collectors for Gyro-Amplifiers (MTRDC) Beam Trajectories simulation in PIERCE ( MTRDC) Average Heat Distribution along Collector EM-Power to Empower Defence MTRDC

XII IEEE Int. Vacuum Electronics Conference (IVEC-2011) , 21 -24 February, 2011, Welcome to IVEC-2011 Bangaloe Bangalore, India Organisers: IEEE- EDS Chapter, Bangalore Section Vacuum Electron Devices & Applications Society The Institution of Electronics & Telecomm Engineers Defence Research & Development Organisation Tutorials: Exhibition: General Chair: 1. Microwave Tubes 2. High Power Microwaves * Industrial Products * Scientific Laboratories Dr. Lalit Kumar EM-Power to Empower Defence MTRDC

EM-Power to Empower Defence MTRDC