TESLA DAMPING RING RF DEFLECTORS DESIGN F.Marcellini & D. Alesini

SUMMARY THE CTF3 RF TW DEFLECTOR: FROM DESIGN TO OPERATION WITH THE BEAM COMPARISON OF DEFLECTION EFFICIENCY OF π/2, 2π/3 AND 4π/5 MODES, SCALING RESULTS OBTAINED BY LENGELER FOR 2.855GHz STRUCTURES HFSS AND MAFIA SIMULATIONS OF THE SINGLE CELL DEVELOPED FOR BOTH π/2 AND π/3 MODES: CHARACTERISTIC PARAMETERS AND DISPERSION CURVES OBTAINED.

OUR EXPERIENCE WITH RF DEFLECTOR FOR CTF3 1. STUDY AND NUMERICAL SIMULATIONS 2. MECHANICAL DRAWING 3. CONSTRUCTION 4. MEASUREMENTS

1 st turn - 1 st bunch train from linac 2 nd turn 3 rd turn 4 th turn 5. RESULTS OF RECOMBINATION TESTS ENLARGING THE IRIS APERTURE, CURRENT INCREASES FROM FIRST TO LAST TURN OF RECOMBINATION WITH NEGLIGIBLE LOSSES. FOUR STEPS BUNCH TRAIN RECOMBINATION

In this paper, for the first time, TW deflecting structures were studied. Three different modes (π/2, 2π/3, 4π/5) tuned at the same RF frequency (2.855GHz) were completely characterized as a function of the cell dimensions. βDβD ω/c π/22π/34π/5π 0 Typical dispersion curve of a periodically loaded structure. The three modes considered by the Lengeler analysis are pointed out. The π/2 mode presents the higher group velocity v g (higher tangent slope).

As a first step we have done an analogous analysis by scaling the Lengeler results with frequency (1.3 GHz in our case). For each considered mode we have fixed the energy of the beam, the angle of deflection and the RF power feeding the structure. Two different values have been supposed (9 MW is the max output power of the klystrons developed for TESLA). Therefore the length of the structure (L) is directly linked to its efficiency (shunt impedance per unit length). L, together with the group velocity (v g ), determines the filling time according to the formula: The power dissipated along the deflector due to resistive losses are also evaluated. In the following plots, the behaviour of each of these quantities as a function of the iris radius (a), are plotted. The same evaluations have been repeated, for each of the three modes, varying the thickness (t) of the iris. However only results for t=11.53 mm have been shown. t/2

 /2 MODE Deflection = 0.5 mrad f RF = 1.3 GHz Disk thickness = mm Cell length = mm

 /3 MODE Deflection = 0.5 mrad f RF = 1.3 GHz Disk thickness = mm Cell length = 76.9 mm

 /5 MODE Deflection = 0.5 mrad f RF = 1.3 GHz Disk thickness = mm Cell length = 92.2 mm

Reduction of the effective kick when the deflector is fed by a 3 MHz detuned excitation.

E.M. FIELDS ON THE AXIS OF THE SIMULATED STRUCTURE (HFSS)  /2  /3 a [mm]41.8 b [mm] D [mm] INPUT GEOMETRY FOR SIMULATIONS E H

mode  /2 (f≈1.3GHz) HFSSMAFIA Series impedance Quality factor Attenuation Group velocity * c = Equivalent deflecting voltage P = RF power p d = rms dissipated power per unit length w = rms stored energy per unit length  /2 MODE PARAMETERS FROM SIMULATION RESULTS

mode  /3 (f≈1.3GHz) HFSSMAFIA Series impedance Quality factor Attenuation Group velocity * c0.041 * c  /3 MODE PARAMETERS FROM SIMULATION RESULTS = Equivalent deflecting voltage P = RF power p d = rms dissipated power per unit length w = rms stored energy per unit length

Dispersion curves calculated by MAFIA 2D simulations have been performed to evaluate the dispersion curve of both the considered modes. Their slopes at 1.3 GHz indicate that the group velocity is close to its maximum reachable value.

Magnitude of E field Fields distribution in the volume of the cell has also been evaluated from simulations. In particular, the peak values for the electric field are localized in correspondence of the irises, as it is shown in the plot. The resulting values are listed below for input power of both 9 MW (single frequency input mode) and 27 MW (triple frequency input mode).  /2 Epeak 10 P RF 27 MW 5.7 P RF 9 MW  /3 Epeak 9.3 P RF 27 MW 5.4 P RF 9 MW