1. After Protons from RCS 1 st DeeMe Collaboration Meeting Dec. 10, 2012 Kazami Yamamoto J-PARC Center Accelerator Division

2. Contents DeeMe request of ＲＣＳ performance Source of After Proton Measurement system of After Proton Principle Setup Preliminary result Conclusion

3. DeeMe request of ＲＣＳ performance ->Required rate of after proton : < 10 -18 ->Correspond to less than few protons within 1 hour = 9*10 4 shot(Rep. = 25Hz) (1 pulse ～ 1*10 14 protons) ->It is impossible to measure such slight protons by ordinary monitors ->In order to develop new measurement system, we considered what particle becomes after proton ①High Power ： 1MW ->Demonstrated more than 500kW-eq. output with 181 MeV injection. ->Space charge force at 500 kW operation with 181 MeV injection is equivalent to more than 1.5MW operation with 400 MeV injection. ②No proton existence after extraction(=No after proton)

4. RCS STR+BPM To 3-N BT STR+BPM QFLQDL Pulse KM 1~3 Pulse KM 4~8 Begin Ext. Ins Source of After Proton Layout of Extraction Line Magnetic field by the Kicker First BunchSecond bunch Time structure of extraction beam and after proton Halo->after proton Σ KM Kick angle ≈ 17 mrad 1 8 Naive estimation: If the rest proton exists and extracts without pulse kicker magnets, a particle needs to have an inclination (x’) ≧ 17 mrad  An emittance of ≈ 2200  mm mrad!  4 times of the RCS physical aperture (486  mm mrad) or 7 times of the RCS collimator aperture (324  mm mrad).

5. Source of After Proton （ Con’t ） We estimated the possible initial conditions that the proton can extract with no kicker excitation. As a result, the protons that has 2500  mm-mrad. emittance can partially extract. however, some particles hit the branch chamber. →We can catch the existence of after proton by monitoring scintillator signals near this point! 324  Normal operation Red: Kicker, septum OFF Green:Kicker, septum ON 1000  2500  Red: Kicker, septum OFF Green:Kicker OFF, septum ON Red: Kicker, septum OFF Green:Kicker OFF, septum ON Kicker always off Beam outer ellipse (H) at the “begin Ext. INS”. (324 ~ 5000  mm mrad)

6. Measurement system of After Proton -Principle- Estimation of scattered proton trajectory by G4BeamLine -> Assume 324 ～ 5000  mm-mrad. emittance uniform beam Ratio of the number of the proton that hit the outside scintillator to the number of the proton that pass through the 3NBT line N[scintillator hit]/N[Pass through 3NBT]=ε=0.025 scintillator

7. Measurement system of After Proton -Setup- Two scintillators are arranged along the beam line. →Detect after proton that is scattered to the outside of 3NBT line. When the signals coincide, that event is considered after proton. Al plate is put between two scintillators in order to reduce the low energy β background. Beam direction Third septum magnet

8. Measurement system of After Proton -Preliminary Result- Fitting the signals at after proton region: f(t) = p2 + exp( p0+ p1*t) ->p1 agreed the decay constant of muon. Perhaps, these signals were caused by the positrons produced by muon decay. If above signals were caused by the positrons, then these were neglect and after proton rate was estimated to R_AP < 1.1e-18 From the signal analysis during off-beam timing, it can be considered that at least 40% event would be independent of the beam. Then, R_AP After proton rate meets requirement (< 1e-18). If we carefully considered that the signals were caused by not the positron but the after proton, R_AP<4e-17 The maximum momentum of above positron is 53MeV/c. In this summer shutdown period, we installed additional iron plate(10cm thickness) in order to eliminate the positrons. (However, there is no data yet.) Loss by first bunch Loss by second bunch After proton region Time[sec]

9. Conclusion As a result of the after proton measurement, we found that the after proton rate was 10 -17 level even if we supposed bad case. We will try to specify the origin of signals and improve accuracy in the future. We will prepare a data acquisition system for the after proton estimation during DeeMe physics run.