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Tevatron IPM

Tevatron IPM. Primary signal, electron transport, amplification, detection…. Overview. Primary signal levels (# of electrons) Electron transport to detector Separation of protons and pbars Amplification and detection Avoiding parasitic signals. IPM schematic. High voltage plate.

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Tevatron IPM

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  1. Tevatron IPM Primary signal, electron transport, amplification, detection… Andreas Jansson - Tevatron IPM review

  2. Overview • Primary signal levels (# of electrons) • Electron transport to detector • Separation of protons and pbars • Amplification and detection • Avoiding parasitic signals Andreas Jansson - Tevatron IPM review

  3. IPM schematic High voltage plate Electron source (e-gen or hot wire) I+ Electron suppression grid Microchannel plate 5-10kV (60-120 kV/m) B RF screen e- ~1kV ~100V Anode board Andreas Jansson - Tevatron IPM review “Faraday cage”

  4. Estimation of ionization • Tev gas composition: • 42% H2 • 42% H2O • 16% N2 • Production rate (Sauli) • H2 5.9 cm-1 • H2O 15 cm-1 (est) • N2 10 cm-1 • Gives 1.3 10-2 cm-1 torr-1, or about 1000e for a 10 cm detector at 3 108 torr and 2.7 1011 protons. Andreas Jansson - Tevatron IPM review

  5. Electron Transport • Simulated electron transport in E+B field, to understand and minimize peak broadening. • Home-cooked Mathematica code adapted from a program by A Hahn Andreas Jansson - Tevatron IPM review

  6. Electron energy distribution • Energy distribution MC generator from A. Hahn. • Distribution approximately 1/T2. • Sharply peaked at low energies, long tail which essentially generates background. Fig. from A. Hahn Andreas Jansson - Tevatron IPM review

  7. Transverse displacement B=0.2 T, E=100kV/m Andreas Jansson - Tevatron IPM review

  8. Signal time structure B=0.2 T, E=100kV/m Andreas Jansson - Tevatron IPM review

  9. Magnetic field spec • 0.2 T is adequate for protons at flat-top (worst case). • Field uniformity should be 1% or better. • Field must be compensated (less than 0.1 mm residual orbit distortion). Fig. from A. Hahn Andreas Jansson - Tevatron IPM review

  10. Magnet designs • Electro- vs Permanent magnet • Electromagnet preferred since field can be varied and turned off • 2 vs 3-bump • Limited by tolerances, use simpler 2-bump. • Single “Self-compensating” vs separate C-magnets • Cheaper to use commercially available c-magnets Fig. from V. Kashikin Andreas Jansson - Tevatron IPM review

  11. How to separate p’s and pbars • Helix separation is barely enough, and helix is undergoing modifications • Don’t rely on helix for separation! • Time separation is 0-198ns, depending on location, and collection time typically 2-3ns. • Time gating can be used! • Implies single bunch resolution Andreas Jansson - Tevatron IPM review

  12. How to gate? • MCP too slow for single bunch gating (recharge time ~100us, according to Burle)! • Gating clearing voltage is impractical (~10000V). • Partially gated clearing voltage would simply act as a delay. • Use fast readout electronics (gated integrator)! Andreas Jansson - Tevatron IPM review

  13. MCP gain limitations • The output current from the MCP should be limited to 10% of the bias current to avoid ‘field distortion saturation’. • “Extended dynamic range” MCPs have bias currents of 4-14 uA/cm2 (at maximum gain). • This gives a max signal per bunch on a 0.25 mm by 10 cm anode strip of 0.4-1.3 106 electrons (60-200fC). • Effectively limits gain to ~10000 for the expected signal levels (if using high end plates). Andreas Jansson - Tevatron IPM review

  14. Main Injector IPM results Turn# saturation Andreas Jansson - Tevatron IPM review

  15. Single vs Dual plate • Current IPMs (at Fermilab) use dual plates (Chevron). • For a given gain, a Chevron saturates at a smaller signal (smaller voltage). • A single plate can deliver ~10000 gain. • Use single plate! Andreas Jansson - Tevatron IPM review

  16. MCP electrons are collected on anode strips Electric field of beam can couple directly to anode strips! Such signals would be capacitively coupled and average to zero. How big are they? Parasitic beam signals Measurements on booster IPM Andreas Jansson - Tevatron IPM review

  17. Avoiding parasitic signals • Faraday cage and RF screening mesh give significant overall reduction (any effect on desired signals?). • Avoid any low frequency (< 200 MHz) resonances in anode strips/cabling. • Change HV capacitors (used for shorting HV detector components to ground at high frequencies) to surface mounted . Andreas Jansson - Tevatron IPM review

  18. Summary • Fairly good understanding of where the issues are • Some tests still to be done • MCP test stand • Gain uniformity, test calibration device, effect of RF screening mesh… • RF coupling • Try to remove all resonances from the Booster can. • Repeat tests on RR IPMs that were recently removed. Andreas Jansson - Tevatron IPM review

  19. Bonus slides Just in case Andreas Jansson - Tevatron IPM review

  20. Booster IPM measurements L=0.7 uH Residual: 10 pC L=0.07 uH Residual: 2 fC Andreas Jansson - Tevatron IPM review

  21. Proton/pbar space separation • Although the helix separation has improved, there is still significant overlap in the projected profiles • Helix can change again(?). • Don’t rely on helix alone to separate beams!  = 20  mm mrad p/p = 7.5 10-4 Andreas Jansson - Tevatron IPM review

  22. Proton pbar time separation • Time difference between protons and pbars are in the range 0-198 ns, depending on location. • Collection time 2-3 ns. • Gate on single bunches! Andreas Jansson - Tevatron IPM review

  23. Higher saturation limit, due to higher operating voltage Cheaper Simpler Same plate lifetime as for Chevron Larger gain dispersion Limited gain, but: Much smaller primary signals would be limited by statistics (esp. pbars), hence it is better to boost too low primary signals with injected gas. Pros and cons of single plate Andreas Jansson - Tevatron IPM review

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