An alternative to the LBS measurement line for Linac4 Reconstructing the longitudinal emittance

1. An alternative to theLBS measurement line for Linac4 Reconstructing the longitudinal emittance JBLallement Linac4 BCC meeting – 25/07/2013 LBS line alternative – L4 BCC meeting - 25/07/2013 – JB Lallement

2. Present solution : LBS upgrade • Solution presented in October 2012 (BCC -36). • Adaptation of the present LBS line to the Linac4 beam. • 2 L4T bending magnets • 2 L4T quadrupoles • 1 SEM-Grid • 1 BCT • 1 dedicated beam dump LBS line alternative – L4 BCC meeting - 25/07/2013 – JB Lallement

3. Present solution : Drawbacks • Feasible but : • Expensive • Time consuming • A planning headache • Integration issues not solved yet J. Humbert LBS line alternative – L4 BCC meeting - 25/07/2013 – JB Lallement

4. Alternative solutions • Use of a spectrometer (LBS like) in a different location: • In the Linac4 tunnel • After BHZ.20 • In the PSB underground • In allcases need dedicated line (switching magnet) and a beam dump, civil engineering etc... • Use another method: • Reconstruct the longitudinal emittance with a classical BSM • Use a Laser stripping diagnostic (not ready to propose a workable solution) LBS line alternative – L4 BCC meeting - 25/07/2013 – JB Lallement

5. Why reconstructing the longitudinal emittance? The beam is characterized by its 6 D emittance: Horizontal, Vertical and longitudinal emittances X’ Y’ E E X Y Φ Φ What we are looking for !!! ΔE ΔΦ LBS line alternative – L4 BCC meeting - 25/07/2013 – JB Lallement

6. Reconstructing the longitudinal emittance The longitudinal emittance can be determined like in the transverse case using the “ 3 grids method” or the “ 3 gradients method”. X’ X’ X’ X X X Quad Quad This technique will be used at 50,100, 160 MeV and in the LBE line. LBS line alternative – L4 BCC meeting - 25/07/2013 – JB Lallement

7. Reconstructing the longitudinal emittance Let’s replace the quadrupole by a cavity and the grid by a BSM. We measure the bunch length at 352.2 MHz. E E E Φ Φ Φ Cavity Cavity The space charge effect are taken into account in the reconstruction with the “Forward method”. LBS line alternative – L4 BCC meeting - 25/07/2013 – JB Lallement

8. Reconstructing the longitudinal emittance: Location • What do we need? • A BSM (bunch shape monitor). • A cavity : The “debuncher”. • Find a location and some settings to do the measurement. • Some free space to locate the BSM. • Some reasonable distance from the cavity (level arm). • The beam should still be “small” (RMS phase < 50-60°). BHZ.20 Debuncher J. Humbert LBS line alternative – L4 BCC meeting - 25/07/2013 – JB Lallement

9. Reconstructing the longitudinal emittance: Location Proposed layout Present layout Two changes induced in the sector 6 (plateau): Steerer and support position. -> No impact on the beam dynamics ! LBS line alternative – L4 BCC meeting - 25/07/2013 – JB Lallement

10. Reconstructing the longitudinal emittance We can vary both the amplitude and the phase of the cavity : “3 Phase-Ampl method”. Have to make sure that the cavity has a measurable effect on the beam phase. Scanning the amplitude (red: OFF, green: 0.7 MV “nominal”, blue: 1.2 MV) Horizontal bend Cavity Vertical step BHZ.20 Scanning the phase (red: 90°, green: -90°, blue: 0°-180°) LBS line alternative – L4 BCC meeting - 25/07/2013 – JB Lallement

11. Reconstructing the longitudinal emittance Factor of 2 Max and Min phase ! LBS line alternative – L4 BCC meeting - 25/07/2013 – JB Lallement

12. Reconstructing the longitudinal emittance: Cavity characteristic RMS beam phase at BSM vs cavityparameters Depending mainly on the input beam parameters and distance between the cavity and the diagnostic. The cavity effect on the bunch length is clearly measurable! Expected resolution at the BSM < 15 keV for 1° (conservative). For the LBS, 100 keV/mm LBS line alternative – L4 BCC meeting - 25/07/2013 – JB Lallement

13. Experience in other Labs: SNS and J-PARC A. Aleksandrov, SNS A. Feschenko, D. Jeon, et al., INR, SNS M. Ikegami, J-PARC A. Feschenko, D. Jeon, et al., INR, SNS “LINAC4 … Uniquely positioned to carry out many valuable physics studies.”, D. Jeon LBS line alternative – L4 BCC meeting - 25/07/2013 – JB Lallement

14. Our recent experience: 3 MeV test stand ! BSM RFQ BU.2 varrying BU.1 fixed BU.3 OFF Measurement Reconstruction LBS line alternative – L4 BCC meeting - 25/07/2013 – JB Lallement

15. Our recent experience: 3 MeV test stand ! BSM RFQ Reconstruction Measurement BU.2 varrying BU.1 fixed BU.3 OFF Expected : 21 keV Reconstructed : 22 keV Reconstruction technique and diagnostic performance were validated ! LBS line alternative – L4 BCC meeting - 25/07/2013 – JB Lallement

16. Input from diagnostic and RP Beam aperture increased to 100 mm Quadrupole shielding? Ok for mid 2015 Cost approx. 170 kCHF (U. Raich, A. Feschenko) Tungsten melting point = 3680 K 400 µs, 40 mA, 1 Hz (F. Zocca) • Approx. 1% of the beam intercepted by the 100 µm wire. Assuming 100% stripping • -> around 30 W losses in BHZ.20 (400µs, 40 mA) • Quite often during commissioning (we can reduce the pulse length). • Limited to few minutes every week during operation. • Effects could be mitigated by having a thicker chicane in L2 tunnel. LBS line alternative – L4 BCC meeting - 25/07/2013 – JB Lallement

17. Solution LBE-BSM • LBE as foreseen (back on the left) and a BSM in the L4T sector 6 (keep the present LBS for ions ≠location?). • Many issues suddenly solved (disappeared) and cost drastically reduced. • Replacing [2 bends, 2 quads, 1 BCT, 1 SEMgrid, 1 beam dump, etc …] by [1 BSM]. • Integration issue solved. • No civil engineering and transport (PSB wall, PS access etc…). • Having the LBE, we keep a beam dump at PSB injection. J. Humbert LBS line alternative – L4 BCC meeting - 25/07/2013 – JB Lallement

18. Any question? LBS line alternative – L4 BCC meeting - 25/07/2013 – JB Lallement

19. Reconstructing the longitudinal emittance Let’s replace the quadrupole with a cavity and the grid by a BSM. Cavity E Φ LBS line alternative – L4 BCC meeting - 25/07/2013 – JB Lallement