1. NEW DRIVERS FOR FUTURE LINEAR COLLIDERS SEVENTEENTH LOMONOSOV CONFERENCE ON ELEMENTARY PARTICLE PHYSICS Moscow, August 20 - 26, 2015 Ivan Spassovsky Laboratory of Applied Math. and Physics Fusion Division Energy Department ENEA, FRASCATI

2. Research Center ENEA Frascati Villa Aldobrandini Frascati Downtown ENEA

3. FTU TOKAMAK SPARC Free-electron Laser

4. REAL ESTATE PRICE vs. the SIZE OF LINEAR ACCELERATORS If the driving frequency is 3 GHz Final energy - 1 TeV Accelerating Gradient – 35 MeV/m Facility Length – 30 km Number of RF drivers - 4000 Who is going to give us that much land where people would like to work and live?! If we would like to reach: Final energy - 50 TeV Accelerating Gradient – 50 MeV/m(probably possible @11GHz) Facility Length – 1000 km Number of RF Drivers – Who knows!?

5. WHY TO DRIVE LINEAR COLLIDERS WITH MM WEVES Fill Time Peak Microwave Power per Unit Length Total Microwave Pulse Energy Kilpatrick Breakdown Limit

6. HIGHER FREQUENCY WOULD BE A SOLUTION The choice of the driver’s frequency depends on: 1. The type of operation – pulsed hot structure 2. The accelerating gradient – up to 300 MeV/m if possible 3. The existing RF sources – how reliable and efficient they are – the efficiency at least 50 %

7. DIFICULTIES and CHALANGES 1. Realization of High-Power RF Sources with stable amplitude and phase 2. Complicate design and fabrication 3. Limited experimental track record

8. High-Frequency, Low & Mid Power, Long-Pulse Sources 1.Gyroklystron – 94 GHz, 10KW average power 2.Gyro-TWT – from 60 to 90 GHz, several kW RF Power (both operate as amplifiers) 3.Klystron – 100-500 kW, ms range, at 6-8 GHz 4.Low-Power, Long-Pulse, High-Efficiency Gyrotron – 1 MW, 1s pulse, cylindrical, Quasioptical and coaxial oscillator 5.Low-Power, High-Efficiency Cyclotron 6.Autoresonance Maser – from 100-400GHz, 1MW, @several ms. Operates as an amplifier and an oscillator, as well.

9. Low-Frequency, Short-Pulse, High-Power Sources 1.Klystron (amplifier)– up to 3, 5 and 11 GHz, 50 MW 2.Gyroklystron (amplifier)– 17GHz, 10 MW, 34 GHz, several MW, projects 3.Magnicon (amplifier)– 11 GHz, 50 MW 4.Free electron laser- 17 GHz, 20 MW, Oscillator version 5.High-power, Short-Pulse, Low efficiency Gyrotron oscillator(6-8%)–50 MW 6.Low-efficiency High-Power, Cyclotron Autoresonance Maser(<10%) 10-50GHz, tens of Megawatts, osc&ampl..

10. GOALS 1. Design and fabrication of 1 MW, 250 GHz, Long Pulse, RF Amplifier 2. Design and fabrication of efficient pulse compressor 3. Design and fabrication of Short RF Structure 4. Design, fabrication and test of RF ACCELERATING STRUCTURE, propagating TM modes 5.Design, fabrication and test of the RF UNDULATOR, propagating TE modes

11. CARM Cyclotron Autoresonance Maser Is a very promising RF source driven by relativistic energy beam at low current

12. POTENTIAL ADVANTAJES 1. High efficiency due to “auto-resonant” compensation 2. Comparable efficiency with klystrons and more stable against the excitation of parasitic modes 3. Operation far from cutoff should reduce fields at cavity walls 4. Operation at lower values of magnetic field.

13. POSSIBLE OBSTACLES I) Difficulty in making mode-selective high-k z cavities (quasioptical or Bragg reflector cavities required) ii) Requirement for a very low axial velocity spread (e.g., Δp z /p z < 1%) iii) Stability of gyrotron and gyro-BWO modes (if waveguide cavity is used) iiii) limited experimental track record, consisting mostly of short-pulse, high-voltage, and high- current oscillators

14. MAIN PROJECT PARAMETERS Operating Frequency – 250 GHz Pulse Duration: Phase I – up to 10 us Phase II – up to 100 us Phase III – from ms to CW operation Output Power – 1 MW Efficiency: Without Depressed Collector - 20 -25% With Depressed Collector – above - 45-50 %

15. PROJECT ASSEMBLY

16. MODULATOR DESIGN Technical Specification Output Voltage 500 – 700 kV (it must be finely tunable, with rough steps of 10 kV and fine steps of 1 kV) Load Resistance Resistive load in the range between 23,33 kΩ and 35kΩ (20 A < I max < 30 A) Pulse Length Stage 1: The Pulse Length should be variable from 5 µs up to 100 µs; for specific design of pulse transformer parameters the Pulse Length should be considered 100 µs Repetition Frequency minimum 1 Hz at 100 µs up to about 10Hz at 5 µs Voltage Variation during Flattop<0.1% 700V (key Parameter) Overshoot<2% Rise-Time< 1 µs Energy into arc<10 J (Voltage of arc =100 V) Pulse to Pulse stability<0.1% Ripple<0.1%

17. ELECTRON BEAM PARAMETERS 1. Beam Radius inside the cavity– 3.1 to 3.5mm - tunable (depends on the operating mode) 2. Beam Energy – 500 to 700 keV (variable) 3. Relativistic factor γ – 2 to 2.4 4. Beam Current – 5 to10 A (variable) 5. Pitch Ratio - α (v ┴ /v װ )~ 1/ γ - 0.45 to 0.55 (tunable) 6. Longitudinal Velocity Spread Δp z /p z - < 0.5%

18. START to END ELECTRON BEAM SIMULATION

19. BRAGG CAVITY Central blue part – L- 20 cm, R - 0.75 cm Upstream reflector – L - 50 cm, R – 0.75 cm Downstream reflector – L - 16 cm, R – 0.75 cm Groves: Period – 600 um, Depth – 45 um upstream mirror downstream mirror slotted cavity flange

20. TEST PARTS Converter option 1: Rough size at 250 GHz: radius = 2.25 mm, length ~ 22 mm, ripple depth ~ 0.1 mm, ripple period ~ 2 mm Technology: @ 250 GHz: idroforming/electroforming; scaled mockup: platelet technology probably viable. feasible

21. PERMANENT MAGNETS Gun coil: Inner Radius – 45 cm Length – 15 cm Max. Magnetic Field – 0.5 T Main magnet coil: Inner Radius – 6 cm Length at max. field – 50 cm Max. Magnetic Field – 7 T

22. WHAT MORE TO BE DONE 1. Design tool to simulate Particle-Wave Interaction 2. RF output system design 3. Vacuum system design 4. Depressed collector design 5. MASHINNING, ASSEMBLING and TESTING COST OF THE PROJECT IS ABOUT 10 ME CURRENTLY SUPPORTED BY ENEA-EUROATOM