Cairo University Electrical Engineering – Faculty of Engineering Cyclotrons Yasser Nour El-Din Mohammed Group 2 - Accelerators and Applications Supervisors B.N. Gikal O.B. Borisov Flerov Laboratory of Nuclear Reactions

Cairo University Electrical Engineering – Faculty of Engineering 2 Outlines Introduction. AVF Cyclotrons. Cyclotrons U400, U400M. Resonators and Dees Beam Extraction.

Cairo University Electrical Engineering – Faculty of Engineering 3 Introduction Electric field used for acceleration. Magnetic field used for bending/deflection. No energy change – Can't accelerate. In homogeneous magnetic field B, the particle has a circular orbit of radius R. “For constant q and m, and uniform B, the angular frequency ω remain constant independent of particle speed (Energy)” R

Cairo University Electrical Engineering – Faculty of Engineering 4 Classical Cyclotron

Cairo University Electrical Engineering – Faculty of Engineering 5 Problem of Classical Cyclotron Increasing energy and therefore increasing mass “m” (Relativistic particles) requires rising B as radius of beam circle increase to keep angular frequency (and so frequency of Dees voltage) constant. But increasing magnetic field B with radius r will make axial instability. Axial Stability Condition: -1 < k < 0 where:

Cairo University Electrical Engineering – Faculty of Engineering 6 Problem of Classical Cyclotron – cont. One solution is : Azimuthally varying field (AVF)

Cairo University Electrical Engineering – Faculty of Engineering 7 AVF Radial-sector Cyclotrons Strong field B h in the “hills” and weak field B v in the “valleys” leads to a scalloped not circular orbit, which crosses the sector edges at a small “Thomas angle” κ. Radial v r and azimuthal B θ components yield an axial restoring focusing force F z (θ). As a result there is a positive edge-focusing effect when both entering and leaving a hill, each edge acting as a thin focusing lens with a focal length given by

Cairo University Electrical Engineering – Faculty of Engineering 8 AVF Spiral-sector Cyclotrons D. Kerst 1956 suggested to use spiral sectors to increase axial focusing. edge-crossing angles: k + ε : strong focusing lens. or k - ε : weak defocusing lens. Focal Length becomes: Spiral angle ε

Cairo University Electrical Engineering – Faculty of Engineering 9 U400 Straight Sector Cyclotron Parameters of U400 cyclotron R pole = 200 cm 4 sectors (45 o straight boundaries) B o = T W = MeV/n Dee Voltage = 80 kV Freq. Range = 5.48 – 12.2 Mhz

Cairo University Electrical Engineering – Faculty of Engineering 10 U400M Spiral Sector Cyclotron Parameters of U400M cyclotron R pole = 200 cm 4 sectors (45 o, max spiral angle ~ 40 o ) B o = T A/Z = W = MeV/n

Cairo University Electrical Engineering – Faculty of Engineering 11 Cyclotron System Accelerating Structure (Dees) RF Resonator Magnetic Field Ion Source Power Supply Beam Extraction Vacuum system Control System

Cairo University Electrical Engineering – Faculty of Engineering 12 RF Resonators and Dees Resonator is the source of the accelerating electric field. The Dees are (capacitive) electrodes, inserted into the magnet gap, usually in the ‘valley’ of the pole plates. A shorted coaxial part (inductive part) extends to the outside of the magnet yoke, thus completing the structures to λ/4 resonators.

Cairo University Electrical Engineering – Faculty of Engineering 13 RF resonators and Dees Dee positioned in 2 Vally regions. First half gap focusing Second half gap defocusing Total focusing effect in the gap (Phase focusing)

Cairo University Electrical Engineering – Faculty of Engineering 14 Cyclotron System Accelerating Structure (Dees) RF Resonator Magnetic field Ion Source Power Supply Beam Extraction Vacuum system Control System

Cairo University Electrical Engineering – Faculty of Engineering 15 Beam Extraction – Charge Exchange Method Accelerated ion with charge Z 1 passes trough a thin carbon foil ( µg/cm 2 ). The charge ion after foil is equal Z 2 because of the electrons stripping. Z 2 / Z 1 – called ratio of charge- exchange. After stripping foil the ion with charge Z 2 have a more rigidty and can be extracted from the cyclotron.

Cairo University Electrical Engineering – Faculty of Engineering 16 Extraction from U400 Cyclotron

Cairo University Electrical Engineering – Faculty of Engineering 17 Extraction from U400M Cyclotron

Cairo University Electrical Engineering – Faculty of Engineering 18 Charge Stripping Foil

Cairo University Electrical Engineering – Faculty of Engineering 19 Cyclotron System Accelerating Structure (Dees) RF Resonator Magnetic field Ion Source Power Supply Beam Extraction Vacuum system Control System

Cairo University Electrical Engineering – Faculty of Engineering 20 Thanks