November 16th, 2017, Gyeongju, Korea Developments of Various Low Energy RF Linear Accelerators at KAERI & RTX Pikad Buaphad, Yujong Kim, Kibaek Song, Hyungdal Park, Sungsu Cha, Youngwoo Joo, Byeongchul Lee, and Siyoung Ryu Radiation Technology eXcellence, Daejeon, Korea Future Accelerator R&D Team, Nucleat Data Center, KAERI, Daejeo, Korea University of Science and Technology, Daejeon, Korea [email protected] Outline Introduction to Low Energy Electron Linac Developments of Industrial Electron Linac at KAERI & RTX 9/6 MeV Multi-Energy American S-band (=2856 MHz) Linac 9/6 MeV Dual Energy European S-band (=2998 MHz) Linac 6 MeV High Gradient European S-band (=2998 MHz) Linac Photocathode RF Gun Developments at KAERI Medical Electron Linac Developments at KAERI & RTX 6 MeV X-band (=9300 MHz) Linac 6 MeV Higher Gradient X-band (=9300 MHz) Linac Summary 2 Application of Low Energy Electron Accelerator Different mechanisms of radiation interaction with matter are used for different applications. Some applications use electron beam but most of the applications uses the bremsstrahlung (X-ray) radiations. X-rays penetrate deeper in matter than electron beam. 3 Low Energy RF Electron Linac System RF Accelerating Structure X-ray Target E-GUN Ion E-GUN Reflected Pump PS RF Circulator Forward RF Modulator (H.V. Pulse PS) Magnetron L-band: f ~ 1.5 GHz (l ~ 10 cm) Ion S-band: f ~ 3 GHz (l ~ 5 cm) Pump C-band: f ~ 5 GHz (l ~ 3 cm) X-band: f ~ 9-12 GHz (l ~ 1.5 cm) 4 What’s Important for Developing a Linac ? Reliability and Stability Performance to meet the Requirements Dose Rate Keeping an Energy with a Small Energy Spread High Capture of Injected Electron from Gun Low and High Current Capability The simpler is better Easy for Operating and Maintenance Low Radiation Loss 5 9/6 MeV American S-band RF Electron Linac RF Frequency = 2856 MHz 6 9/6 MeV American S-band RF Electron Linac E-beam energy : 9/6 MeV Penetration Depth (steel 380 mm @ 9 MeV, 30 Gy/min @ 1 m ) Spot size : < 2 mm Resolution Average power: > 1 kW Scan Speed (0.3 m/s, < 1-2 min @ 1 kW) Energy Switch mode None Destructive Testing RF Frequency = 2856 MHz Structure length ~ 0.57 m 7 9/6 MeV European S-band RF Electron Linac Structure length ~ 0.64 m European S-band to use a cheaper and low power (3.1 MW) magnetron8 6 MeV European S-band RF Electron Linac Beam Motion along 6 MeV Linac Structure - CST Particle Studio, PIC 9 6 MeV European S-band RF Electron Linac Structure length ~ 0.3 m 10 American S-band Photocathode RF Gun ● 1.6 RF-gun with Operation Frequency 2856 MHz, π-mode ● Mode Separation of 15.5 MHz For Ultrafast Applications (UED, UEM) 11 6 MeV X-band Linac for Medical Applications For the medical applications (CyberKnife & dual head gantry), we promised following parameters: RF Frequency ~ 9.3 GHz beam energy ≥ 6 MeV dose rate ≥ 500 cGy/min target spotsize ≤ 2 mm (FW) To supply those parameters, we are developing new X-band electron linacs. gun gap voltage ~ 20 kV peak current at gun exit ~ 100 - 200 mA peak energy at linac exit ~ 6 MeV beam capturing coefficient ~ 50% average beam power ~ 167 W for 500 cGy/min peak / average current at linac exit ≥ 50 - 100 mA / 28 µA for 500 cGy/min with a duty factor 0.0009 duty factor of L3 magnetron: ~ 0.0002 (2 MW) - 0.0008 (1.7 MW). duty factor of CPI magnetron: ~ 0.0018 (1.5 MW) 12 6 MeV X-band Linac We assume that energy gain at a half cell is 125 keV and energy gain at a full cell is 245 keV. The π-mode has been chosen as the operating mode since it provides the highest shunt impedance and it also gives the highest energy gain for a given power. With every acceleration, the electron bunch travels a greater distance in the same amount of time. Thus, the length of the cavities must also increase as the bunch velocity increases. õ ⁄̋ õ Â ƔÌ ̘̌ Ɣ ì ̘̌ ̶̴̡̣̩̹ ¹ ̋ 13 6 MeV X-band Linac KAERI & RTX teams designed an X-band linac structure with 24.5 cells. Bunching cells: 10.5 cells with energy gains of 125 - 245 keV Accelerating cells: 14 cells with 16 MV/m (coupler @ 14th cell) central frequency ~ 9.302 GHz length ~ 0.4 m unloaded Q0 ~ 11319 external Qext ~ 10197 coupling beta ~ 1.11 shunt impedance ~ 80 MΩ/m RF power for 6 MeV ~ 1.5 MW 14 6 MeV X-band Linac Beam Motion along 6 MeV X-band Linac Structure - CST Particle Studio, PIC Without considering the space charge effect, the phase motion of the electron with different initial phases and energy gain were calculated by solving the equation of motion. About 49% of the electrons can reach to the end of Linac structure, but only electrons with initial phase between 150º and 317º have the final energy to reach to 6 MeV. The capture efficiency of Linac structure is about 46% with energy spread of 9%. 15 X-band Linac ASTRA Simulation Optimization Results with 1,000,000 particles for 3 RF periods (108 ps × 3 = 324 ps) peak current ~ 3.6 pC/30 ps > 120 mA energy spread ~ 15% Transverse beam properties of first single head bunch 16 X-band Linac 3D Drawing 24.5 cells with 10 bunching cells central frequency ~ 9.302 GHz length ~ 0.4 m unloaded Q ~ 11319 coupling beta ~ 1.11 Rsh ~ 80 M Ω/m Power for 6 MeV ~ 1.5 MW Cell length ~ 16.1 mm Radius ~ 14.2 mm Gradient ~ 17 MV/m Weight ~ 8 kg 17 X-band Linac Fabrication - Cells Cells for X-band linac 18 X-band Linac Fabrication Brazed coupler cell for X-band linac Tuners for X-band linac 19 X-band Linac - Fabricated Linac SSS111111 Right After Fabrication KAERI did Great Design & Fabrication! π mode ~ 9.302 GHz with -5.0 dB 20 X-band Linac - Fabricated Linac SSS111111 After Final Tuning @ Tempearture = 30 degree KAERI did Great Tuning! π mode ~ 9312.31 MHz with -27 dB (0.2% reflection) 21 X-band Linac – Bead-pull Measurement 7 6 5 4 E (A.U) E 3 2 1 0 0 500 1000 1500 2000 2500 3000 position number 22 Photo of Assembled X-band Linac 23 RF Condition with 2.1 MW We could finish RF condition only with one day! 2.1 MW full power, 4 µs, 2 Hz, Vacuum ~ 1.0E-8 Torr This is a good indication of our great jobs! quiet vacuum << 1.0E-6 Torr green: forward yellow: reflected blue: modulator HV Beam On: -1 kV + Drive (50 V) Beam Off: -1 kV -50 V Faraday Cup Trigger 24 1st Beam from X-band Linac - Nov. 14th, 2014 We could get the first beam from the 6 MeV X-band linac on November 14th, 2014! 2.1 MW full power, 4 µs, 2 Hz, Vacuum ~ 1.0E-8 Torr Our X-band design worked! 25 Higher Gradient X-band Linac - RTX & KAERI An X-band linac with a higher gradient (~ 30 MV/m) is needed for the Dual-Head Gantry project (30% reduction of therapy time). KAERI & RTX have been developing the higher gradient X-band linac. 26 Higher Gradient X-band Linac - RTX & KAERI KAERI and RTX have been developing an higher gradient X-band linac! We assume that energy gain at a half cell is 240 keV and energy gain at a full cell is 500 keV. Bunching cells: 4.5 cells with energy gains of 240 - 500 keV Accelerating cells: 8 cells with 16 MV/m (coupler @ last cell) The length of beam pipe at half cell is 8 mm with a radius of 2.5 mm. However the beam pipe length at the last cell is 16.5 with a radius of 5 mm. 27 Higher Gradient X-band Linac - RTX & KAERI 28 Summary There are various growing user applications with MeV-range RF electron linacs. KAERI has successfully developed a 9/6 MeV multi-energy American S-band (=2856 MHz) electron linac for NDT applications. To reduce magnetron cost, KAERI also has successfully developed a 9/6 MeV dual energy and a 6 MeV European S-band (=2998 MHz) electron linacs for CIS and NDT applications. RTX already commercialized these accelerators for CIS and NDT applications. KAERI and RTX have successfully developed a 6 MeV X-band (=9300 MHz) electron linac for medical applications. KAERI and RTX finished design of a new 6 MeV X-band linac with a higher gradient of about 30 MV/m. Moreover KAERI and RTX finished design of a photocathode RF gun for ultrafast electron beam sciences (UED and UEM) with our collaborators (KRISS and GIST) 29.