bwTW RF design update

RF design of a high-gradient medical linac accelerating structureStefano Benedetti, TERA Foundation1

CLIC Workshop, 03-07 February 2014, CERN1Project summary and goalsDesign the prototype of a high gradient 3 GHz proton accelerator operating in a backward Travelling Wave mode with 5pi/6 phase advance

2Compact sizeAcceptable BDRA general overview on the TULIP project will be given Thursday 6 at 2pm by Prof. Amaldi Cell design

Fixed geometry parametersIris thickness [mm]2Gap [mm]7Nose cone angle []65Bore radius [mm]2.5Nose inner radius [mm]1Nose outer radius [mm]2Corner inner radius [mm]1Corner outer radius [mm]1Number of cell12Cell length [mm]15.82Averaged accelerating parametersFrequency [GHz]2.9985Q7239Rshunt/Q [M/m]7395ZTT [M/m]53.5vg [c]2.926Es/Ea 3.86Hs/Ea [1/k]4.63Sc/Ea2 nose[ 1/k]0.26Sc/Ea2 slot [1/k]0.253Tuning by dimple tuners4

tuner

tuner4 dimples8 dimplesdrf /dimpleffmkHzkHzMHz551215861172249019176515314441726871375407158631126335313955711154 dimples8 dimplesdrf /dimpleffmkHzkHzMHz450-114-454-909370-94-375-750310-77-310-619270-65-261-522200-48-190-381A. Degiovanni

Tapered structureCoupling hole radii have been adjusted from cell to cell in order to get a group velocity between 0.4% and 0.2% of c in the tankCell diameter has been adjusted accordingly, to maintain the resonant frequency of 2.9985 GHzA precision of 1 m in the cell diameter has been reached

5Tank design

Rc01 -> acD01acD2=(acD01+acD02)/2acD11=(acD010+acD011)/21st and 12th cell diameters depend on the couplers design6Out cell coupling - preliminary

-47 dB

7In cell coupling - issues

Sc up to 40% higher than in the regular cells holesRegular coupling holes radius

But we affect the vg, so the Ez8By reducing the coupling holes radius closer to the coupling slot the problem is solvedIn cell coupling - preliminary

-44 dB

9Tank optimization10

Minimization of the SW pattern by adjusting the out-coupler

Final optimization of the in-coupler to get the final design of the tank

Electric field distribution

11P0PloadA bwTW structure12

P0PwPloadBeamModified Sc plot

The Sc/Ea^2 < 7e-4 A/V constraint is respected

13Reflection from input (red) and from output (brown)

14-67 dB-27 dBElectric field EZ 2.5 MW 15

Good agreement between the analytical and the simulated resultsTo reach the desired accelerating gradient Ea=EzT of 50 MV/m, the needed power is approximately 9 MWThe energy gain in the first tank will be of about 9-10 MeV

RF phase advance

The RF phase advance per cell is 150 at 2.9985 GHz 16To summarize17150o/cellcommentsf [GHz]2.9985S11 [dB]-67S120.549tf [ns]224Qavg 7239Gradient averaged over all cellsG12 [V/m]@Pin = 1 W111462 matching +10 regular cellsLacc = 189.84 mmPin [MW] @ 9What nextFew modifications to the geometry after the discussion with VDL but theoverall impact is negligible

Cells should be ready by the end of autumn at most

Low and high power tests on the structure to study overall performances and BDR

Thanks for your attention!Special thanks to KT for financing the project