Slac Gun (140 keV)

1. Injector and positron source scheme. A.Variola, O.Dadoun, F Poirier, R.Chehab, P Lepercq, R.Roux, J.Brossard A.Variola Frascati SuperB meeting

2. In SLAC we proposed Polarised e+ upgrade Luminosity loss ? Energy 80-100 MeV LER Damping ring Energy TBA Injector and Positron driver 300-600 MeV Bypass Line for e- Matching Slac Gun (140 keV) Linac 6.4-6.7 GeV Damping ring Energy TBA Capture section 200-300MeV Bunchers Positron Converter HER ….but now see R.Boni talk A.Variola Frascati SuperB meeting

3. Needed injection rates: • new scheme =>from J.Seeman and R Boni Talk=>Δn PS ≈ 2 – 2.5•109 …. @ PS output • ~ 333 pC/bunch • Taking a factor 2 => 600 pC exit capture section A.Variola Frascati SuperB meeting

4. From SLAC…this is always valid • Before to start I would like to stress that: -In Dafne production at 200 MeV drive beam and efficiency at the linac end is ~ 1.2 % -The accepted yield scales ~ linearly with the energy so @ 600 MeV one can expect 3.6% - If the Slac gun provides 10 nC = 6.2 1010 electrons => At the Linac end: 2.25 109 - This already fits the SuperB requirements but the Dafne system is very close to a QWT, very good for energy selection but not for acceptance. Moreover the capture system is @ 3 GHz!!! - If the DR acceptance is big we can suppose to capture with an AMD that is much more efficient also if we increase the captured energy spread. A.Variola Frascati SuperB meeting

5. @SLAC ws - Future activity • 1 Solve the discrepancies between codes (we are progressing) • 2 Have a final estimation in L band • 3 Introduce the SLAC Constant Grad section • 4 Study a Const imp section to increase the acceptance • Give a final estimation and solution (we hope for December-Frascati) A.Variola Frascati SuperB meeting

6. L band / Geant and Parmela 600 MeV case – AMD 6 T, 50 cm, r=2cm Y (cm) AMD input – G4 = 8569 positrons AMD output – G4 But we want yield : 8569/1.58= 5423 e- (=nb of positrons entering the AMD / production yield e-/e+) X (cm) With this sample, we have a yield of 59.7% for the AMD (=3235/5423) A.Variola Frascati SuperB meeting

7. AMD (6 T – 50 cm) exit X’ (rad) Population Energy (MeV) X (cm) A.Variola Frascati SuperB meeting

8. ACS – L band • ACS: Accelerating Capture Section • 1.3 GHz, aperture 1.8 cm • Input sz=1cm (random gaussian distributed) Round beam i.e. sx=~sy, sx’=~sy’ A.Variola Frascati SuperB meeting

9. ACS – L band • ACS: Accelerating Capture Section • 1.3 GHz, aperture 1.8 cm X’ (rad) Energy (MeV) f (deg) X (cm) A.Variola Frascati SuperB meeting

10. S - Band • SLAC type TW cavities: • 1 tank is constituted of 85 travelling wave structures • 1 tank = 3.01 m • In total 6 tanks are used here to bring the positrons at least up 250 MeV • For the simulation with Parmela, the ACS is then constructed with one single file containing the 6 tanks (but here the gradient is not decreasing in the fourth tank…need POISSON files) • Or the ACS is constructed with 2 files containing each 3 tanks. The second file takes as input the output of the first file (losses of particles are observed at junction of tanks 1 and 2!). A.Variola Frascati SuperB meeting

11. ACS – S band • 2.8 GHz, aperture 0.95 cm • SLAC type constant aperture • Input sz=1cm** (case with 6 tanks in 1 file) *In the case of the S-band ACS it is here the end of the first trwave i.e. at 7.9 cm after the beginning of the ACS (for Parmela simulation we have: drift+cell+half a trwave). Note: the nb of particles at the end of the first tank, i.e. at ~3.01m, is 527. ** Random gaussian distribution A.Variola Frascati SuperB meeting

12. ACS – S band • 2.8 GHz, aperture 0.95 cm • SLAC type constant aperture • Input sz=1cm (case with 6 tank in 1 file) X’ (rad) Energy (MeV) X (cm) f (deg) A.Variola Frascati SuperB meeting

13. ACS – S band • 2.8 GHz, aperture 0.95 cm • SLAC type constant aperture • Input sz=1cm (case with 3 tanks separated in 2 files) A.Variola Frascati SuperB meeting

14. Summary => Yield For S-Band, the case with 6 tanks in 1 file is chosen * End of tank **Explanation: 1857 positrons/ 5423 electrons = 34.2%, 789 positrons/ 50000 electrons = 1.6% ^ in the case of 3 tanks in 2 files, yield: 246/5423 = 4.5% A.Variola Frascati SuperB meeting

15. Analyticalestimations (dependents from arbitrary, AMD length and field scan S band : matching more critical A.Variola Frascati SuperB meeting

16. Conclusions • L Band =>35% (3.5nC). We can loose more than a order of magnitude!!! • S Band => ~600 pC without any optimisation. Consistent with the initial boundary conditions • S Band Dafne => 1.6%. Consistent with the measured yield (good to validate simulations) • So : we want to be safe => L Band up to damping ring • S band works anyway…a little margin can be gained by: 1) increasing the energy (700 – 800 MeV) 2) New design of S band with larger diameter (lower gradient) 3) 2 GHz? Should be an occasion for CLIC synergies…..politically correct! • S Band Dafne good agreement. • In my point of view this scheme is viable, we have only to decide if we want to have a big margin or not • Next steps : 1) Solve the 1 / 2 tanks discrepancy 2) Optimisation of L/S band 3) Post acceleration up to 600 MeV (1 GeV?) The best test bench should be to send the SLAC gun here, in Frascati and mount it on Dafne. Is it feasible? Money, integration, manpower….. A.Variola Frascati SuperB meeting

17. Better configuration for capture L-Band: 1.9-2 cm RADIUS • 1st L BAND • We had problems of agreement between Geant and Parmela: Solved A.Variola Frascati SuperB meeting

18. Ps…we started also the simulation of the SLAC gun. We have already the results for the standard configuration Start at 15 nC since we found 30% lossesWe would like to propose some modifications in the future to optimize the line in the SuperB framework. Transv Long z DE Phase space A.Variola Frascati SuperB meeting