TUNERS FOR SRF CAVITIES A Comparative Study – Mechanical Characteristics Presented by N. Dhanaraj

1.3 GHz Tuner Comparison – Mechanical Specifications* TypeEnd Lever tunerSlim blade tuner A.K.ATTF tuner or Saclay tunerModified blade tuner LocationCavity endcoaxial CuBe screw specsM12 x 1.5 mmM12 x 1.5 mm (max. specified) CuBe screw coatingBalinit-C (tungsten carbide)Lamcoat (tungsten disulfide) Nut coatingBalinit-C (tungsten carbide) Axial force on driving screw at max. elongation409 N (calculated) 1600 N (loaded) and 2000 N (unloaded) (literature) Max. cavity elongation2 mm1.8 mm (12 screw turns) Tuner stiffness100 KN/mm (measured) KN/mm Coarse/slow tuning range± 400 kHz~ 600 kHz * Various sources

What is the axial force required to yield the thread Bolt tensile force required to yield entire thread cross section is F = A t S y ~ Pi/4 (0.9 d) 2 S y, S y = 28 ksi F = 17.6 KN for thread pitch 1 mm F = 15.7 KN for thread pitch 1.5 mm

End Lever Tuner – Saclay Tuner I P=δ K cavity R1 R2Force on CuBe screw (F) Simplification of Lever Equivalent Mathematical Model

End Lever Tuner – Saclay Tuner I (contd.) Force Calculation: Known parameters: Mechanical advantage range reported – 1:17 to 1:25 Solution: Stiffness of cavity (Kcav) = 3473 N/mm Max. elongation (δ) = 2 mm Load exerted by cavity (P) = δ * Kcav = 6946 N Therefore, Axial force on CuBe screw (F) = P / mechanical adv. Ratio = 6946 / 17 = N (Max.) If mechanical adv. 1:25 considered, then F = 277 N (min)

Blade Tuner – INFN Design and FEA Results FEA Results: Axial Force reported 2000 N (unloaded). Axial Force reported 1600 N (loaded), corresponds to 1.8 mm of maximum elongation and 12 turns of the CuBe screw. Inference: Considering 1.5 mm pitch of the CuBe screw,10 turns of screw required to produce a tuner displacement or elongation of 1.5 mm.

Blade Tuner – FNAL Measurements C. Grimm, N. Dhanaraj, D. Passarelli 10 Turns => 0.87 mm, 1mm pitch

Blade Tuner – FNAL Torque Measurements Torque measured using torque wrench: 2.9 Nm at 0.8 mm displacement or elongation of cavity. Axial force calculation from measured torque Torque = k. axial force. Diameter of screw Where k is the friction factor, 0.35 for Tungsten carbide on copper. Assume 50 % friction reduction using Lamcoat. Therefore, Axial force on screw = Torque / k. Diameter F = 2900/0.175 * 12 = 1381 N

Blade Tuner – FNAL FEA (unloaded) FEA Parameters: FNAL modified Tuner geometry Non-linear Material Properties (as per ASME, Div. 2) Mesh 1.32e6 nodes, 1mm elements on 66 mm long blades Displacement controlled analysis Large Deformation Model

Blade Tuner – FNAL FEA Force Results

Blade Tuner – FNAL Results FEA – 10 Turns 1 mm Measured – 10 Turns 0.95 mm

Acknowledgement Tom Peterson Chuck Grimm Bob Wands Donato Passarrelli Tuner Folks SRF DD