rf design of a high-gradient medical linac accelerating structure
DESCRIPTION
RF design of a high-gradient medical linac accelerating structure. Stefano Benedetti, TERA Foundation. Project summary and goals. Design the prototype of a high gradient 3 GHz proton accelerator operating in a backward Travelling Wave mode with 5pi/6 phase advance. Compact size. - PowerPoint PPT PresentationTRANSCRIPT
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