Linac4 BCC Meeting 43 - H - stripping test - 23 rd April 2013

1. H0/H- current monitor F. Zocca, F. Roncarolo, B. Cheymol, A. Ravni, S. Burger, G.J. Focker, J. Tan BE/BI Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

2. Outline • H0/H- current monitor overview: • Concept & specifications • Geometry & beam dynamics • Material • Sensitivity & expected signals • Status & on-going developments • Importance of the “half-chicane section” test for instrumentation • Other advantages in case of test implementation in L4T line (after bending) F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

3. H0/H- current monitor concept B.Goddard et al., 2010 H0/ H- current monitor needed in front of the dump - to allow efficient setting up of the injection - to monitor the efficiency of the stripping foil (detect degradation and failure) The H0/H- current monitors are supposed to be plates intercepting the H0 and H- ions and acting as a Faraday cup for the stripped electrons (stripping & collection) F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

4. Functional specifications • Robust and simple (lifetime ≈ 20 years, no maintenance) • Radiation dose of 0.1-1.0 MGy per year • Vacuum level 10-8 mbar with beam • Withstand the BSW4 pulsed magnetic field of 0.4T and at the same time do not perturb the field by more than ≈ 1 % • Transverse dimensions (including support structure) not exceeding dump dimensions • Sensitive areas maximized to cover as much as beam halo as possible • Withstand the heat load in normal operation condition and a full Linac4 pulse load (2.5×1013 H- ions), in case of failure of the stripping foil, on a one-off basis, several times per year • Dynamic range: 5×107 – 5×1012 ions (for H- and H0 alike) • Absolute accuracy ± 20 %, relative accuracy ± 10 % • Time resolution: integral over the full injection time (few ms – 100 ms) – however higher resolution is welcome F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

5. Monitor geometry preliminary proposal Top view Missing on the front frame only Signal plates Polarization frames F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

6. Beam envelopes SiC Dump 110 mm + 30 mm Pol. Frames Courtesy of C.Bracco Separation H0/H- = 10.8 mm Separation H0/H+ = 2.8 mm Distance dump edge/ H0 beam = 0.5 mm F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

7. Plates material: titanium Requirements: good enough conductivity (for signal read-out) but compatible with BSW4 field quality, low thermal load, low neutron yield (low activation), high signal level Fully acceptable Among low-Z conductive materials, titanium is the only one with acceptable impact on the BS4 field quality thanks to the relatively “low” conductivity Acceptable (not ideal) Not acceptable * taking into account losses due to electron backscattering and secondary emission F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

8. Charge signal estimate Proton energy = 160 MeV  electron energy = 87 keV Q (e/H-) = -2*(1-h) + 2*SEYP + 2*SEYBS + YD h = fraction of backscattered electrons (e- energy range ≈ 1-87 keV) SEYP = Secondary Emission Yield of the Proton (e- energy range ≈ 1-20eV) (SEY of H- entering the plate = SEY of proton exiting) SEYBS = Secondary Emission Yield of one BackScattered electron YD = fraction of “delta-rays” electrons emitted by the plate owing to collisions with the proton beam (e- energy range ≈ 100-400 keV) Q (e/H0) = - (1-h) + SEYP + SEYBS + YD F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

9. Polarization rings: E-field effect View from the top CST Particle Studio tracking simulation Electron energy range = 10-30 eV Isotropic angular distribution Stationary condition No space charge frame (- 1000 V) monitor plates frame (- 1000 V) E-field map on the monitor plates Effect due to the missing lateral frame Simulations including surrounding beam pipe F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

10. E-field + B-field effect (BSW4 magnet 0.4T) Uniform vertical B-field of 0.4 T Stationary condition, no space charge 10 mm Secondary emission electrons (10 eV - 30eV) Curvature radius for 30eV electrons ≈ 30 mm Backscattered electrons (60 keV – 90 keV) Curvature radius for 90keV electrons ≈ 2.6 mm “Delta-rays” electrons (125 keV – 375 keV) Curvature radius for 375 keV electrons ≈ 6 mm F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

11. Expected signals • Stripping foil of ≈ 200 mg/cm2 : • H- stripped to H0 ≈ 1 % , • H- stripped to H+ ≈ 10-6 level BUT assume that 1% of H- from the LINAC4 beam will miss the foil and impact the dump •  nominal number of particles hitting the monitor perinjection =2.5 × 1011 for H0 and H- alike Desired dynamic range = 5 × 107- 5 × 1012 particles (for H- and H0 alike) F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

12. Status Almost finalized: • Material choice • Design principle • Theoretical study of sensitivity – range of expected signals On-going developments: • Final dimensions (w.r.t. dump size & beam dynamics simulations) • Mechanical support • Final integration in the system (design office) • Simulation of the impact on the BSW4 field (by magnet group) • Cables type and quantity • Read-out electronics F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

13. What is important to test • Operational check including mechanical integration issues, thermic and mechanical stress (beam heat load and magnetic field) • Impact on the BSW4 field quality – beam positions & envelopes • Sensitivity to H- and H0 ions: effect of the E-field and of the B-field on the secondary electron suppression (and eventually on the backscattering effect suppression) • Read-out electronics: noise level and amplitude of picked-up induced signals on the plates  decision between charge integration or current read-out mode • Control signals for start/stop read-out according to injection start/stop • Calibration procedure of the H- and H0 currents: with unstrippedH- beam of known intensity, profiting from BLMs for H0…? • Interlock reaction (protecting the injection system) • Long-term stability of the measured signals F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

14. The presence of the bending magnet L4T.MBH.0250… … allows us for a more complete test of the laser-wire scanner Test of the stripping unit (≈ 20 cm) 40 cm long slot allocated between the steerers L4T.MCHV.0115 and L4T.MCHV.0135 for installing a laser station + profile monitor via stripped electron counting F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

15. Conclusions • “Half-chicane section” test is of extreme importance for instrumentation commissioning • Despite the relatively simple working principle, many issues need to be checked for the H0/H- current monitor, regarding • - mechanical integration • - measurement sensitivity & read-out electronics • - interlock system • Beam instrumentation developments (laser wire emittance meter) would much profit from the presence of the bending section  we strongly support the option of the “half-chicane section” test in the L4T line F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013