How to control the local beam density at the nTOF target

1. How to control the local beam density at the nTOF target Lau Gatignon / AB-ATB-SBA Thanks to Rende Steerenberg, Olav Berrig, Paolo Cenniniand many others for input and help Local beam density control

2. How to control the local beam density at the nTOF target 1) Beam optics / spot 2) Parasitic vs dedicated cycle 3) Bunch width 4) Intensity limitation Local beam density control

3. An increased beam spot will decreasethe local energy density in the target • Increase the beta function in the beam opticsNote that the b function is proportional to size2 If the size is doubled in each plane, the density decreases ~ x4 at least if the beam spot is not too small compared to the shower size • It is ‘easy’ to increase the b-value by up to 16x/planeThis reduces the density by roughly a factor 16! • Intermediate solutions can be found ‘easily’ Please note that TT2 optics has changed since 2004 (QKE58) Many thanks to Olav Berrig for preparing and providing the optics files with the new matching TT2-FTN Local beam density control

4. The focusing and steering options are the following: ID IF IHZ IVT For matchingto TT2 line Local beam density control

5. The original optics, up to 2004, with QKE58 Local beam density control

6. 7 x 3 mm2 RMS Local beam density control

7. Old FTN optics after re-matching w/o QKE58 kqde=-0.10914, kqfo=0.15441 Local beam density control

8. 7 x 3 mm2 RMS Local beam density control

9. Increase the spot by factor 2 / plane (b x4) kqde=-0.050722, kqfo=0.0590044 Local beam density control

10. 12 x 6 mm2 RMS Local beam density control

11. Increase the spot by factor 4 / plane (b x16) kqde=-0.00666 ; kqfo = 0.01388 Local beam density control

12. 19 x 11 mm2 RMS Local beam density control

13. How to choose final optics? • → There is a relatively free choice in increase of the beam spot by up to a factor ~4 in each planeThis would typically reduce the deposited energy density by about a factor of ~16 • The shape of the beam impact can be influenced as welle.g. increase the vertical spot and decrease the horizontal one • Simulations (FLUKA) can evaluate the impact of the increased beam spot on the neutronics and on the heating of the target • There is also the possibility to change the beam impact point from timeto time (e.g. once or twice per shift). But is the beam isvery large, room for maneuver is limited Local beam density control

14. Parasitic nTOF cycles are attractive The PS serves many users: LHC, SPS, EASTA, EASTB, EASTC, MD, AD, nTOF,… The basic PS period is 1.2 seconds and each user requiresone or two basic PS periods The SPS cycle is much longer and therefore an overall supercycle is defined to serve e.g. LHC, NA, CNGS and MDA typical supercycle was 16.8 s in 2007, 48 s in 2008! Local beam density control

15. There is heavy demand on supercycles Some (random) example in 2007: • Each EASTA, B, C serve the East experimental area and take two PS basic periods each.There are many EAST cycles per s.c. • A dedicated nTOF cycles takes1 PS basic period nTOF Local beam density control

16. Dedicated nTOF cycle Parasitic ( on any EAST) cycle East nTOF • nTOF can be served with: • dedicated cycles (up to 7 1012 ppp) • parasitic cycles (up to 4 1012 ppp) Parasitic cycles cannot be so intensethey perturb the 10x smaller bunch for the EAST But there are many EAST cycles available ‘for free’ As they are less intense, one may get the protons morefavorably distributed over time (less strongly peaked) Local beam density control

17. The bunch width can be lengthened, but is this useful? Normally the bunch length is shortened by “Bunch Rotation”: Courtesy Rende Steerenberg VRF phasejump by 180o after some delay VRF phasejump by 180o and wait few ms Result: bunch length (4s) from 50-60 nsec to ~25 nsec momentum spread from 1.6 to ~3.2 permille Local beam density control

18. Dedicated nTOF cycle Parasitic ( on any EAST) cycle Bunch rotation can (or not) be applied both in dedicated and parasitic cycles Rotate back(if needed) Bunch rotation (or not???) Bunch rotation (or not???) Bunch rotation Local beam density control

19. 4 s ~48 nsec, hence 1s ~12 nsec Before bunch rotation: Local beam density control

20. 4 s ~22 nsec, hence 1s ~6 nsec After bunch rotation: Local beam density control

21. 15 nsec resolution The bunch width degrades the TOF resolution and hence also the energy resolution Is this worth it? Doubling the time resolution of the proton beam extends this problemto almost 10x lower values. Local beam density control

22. There are ways to limit the intensity from the PS • One may limit the maximum intensity per PS pulseThis is done by sending the beam on the internal dump in case the intensity per shot exceeds a threshold (BCT at injection) • One may restrict the RMS current (by software) This would need monitoring of the current in a BCT (FESA modifs) and a modification to two rectifiers to allow fast switching of the beam settings to go onto the D3 dump. Plus the implementation of a software surveillance task.Is this important? • A hardware solution is in principle also possibleBased on a direct BCT reading or image current in a wire in the nTOF control room Local beam density control

23. Conclusions • It is possible toincrease the beam spotby up to 4xin each plane, thus reducing deposited energy density • It seems better for the target to take as much as possibleof the total integrated intensity fromparasitic cycles • It is possible to double the bunch width, but this hasa negative impact on the energy resolution • There are easy ways toprohibit excessive fluxesper shot.If really necessary one may also restrict the RMS flux Local beam density control