GSI Helmholtzzentrum fr Schwerionenforschung Gmb H Response function

GSI Helmholtzzentrum für Schwerionenforschung Gmb. H Response function measurements and simulations for the integral monitor chambers GSI Biophysics Uli Weber Bernd Voss, Christian Graeff, Christoph Schuy, Sulaiman Aqra Workshop on Medical Accelerator Design and Diagnostics (OMA) 11. 12. 2018 , GSI Darmstadt GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Motivation: Improvement of Detectors for Beam Monitoring (raster scanning) • Upgrade of Cave M (therapy pilot project, C. Graeff et. al) • • Improvement of scanning speed (factor 10 intended ) Processing of the beam spots within 100 µs (min. time) GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Scanning feed back system (simplified representation ) 3 Ionization chambers Scanner magnets Scanner control magnet power supplies GSI Helmholtzzentrum für Schwerionenforschung Gmb. H amplifier

New Scanning System @ GSI The response time from the beam monitors was identified as a relevant bottle-neck for a speed-up § Beam Intensity detectors (Parallel plate ionization chambers) § Position sensitive detectors (MWPS’s) Main reason is the signal delay caused by the slowly drifting positive ions, that gives ca. 50% of the signal from the detectors GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Intensity controlled raster scanning Slow Synchrotron extraction (always strong ripple) 12 C, 300 Me. V/u Ni ions t ) o p s am e b s / m 0 0 (1 m y t i ns a e t c s in t s m a a e b F st a f s e r i equ r ng i n n GSI Helmholtzzentrum für Schwerionenforschung Gmb. H r u s ea t n e em

Parallel plate Ionization chambers: Response for a short beam pulse + + + Beam pulse - + - - - IA(t) + - + electrons - + - - ions - t + 10 mm GSI Helmholtzzentrum für Schwerionenforschung Gmb. H dgap/v+ dgap/v-

Detector Test Setup in Cave M Beam monitoring detectors Detector stack (test stack) Beam nozzle Fast current amplifiers Fast oscilloscope MWPCs 2 x filled with: Ar/CO 2 , He GSI Helmholtzzentrum für Schwerionenforschung Gmb. H Parallel plate Ionization chambers 4 x filled with: Ar/CO 2 , N 2 , He , Air

IC signals from short ion-beam pulses Beam parameters: • GSI Synchrotron ; Cave M • Fast extraction (Kicker) ; beam pulse < 1 µs • 12 C , 300 Me. V/u ; ≈106 ions Detectors: • 4 parallel plate ionization chambers filled with different gases: • • Ar-CO 2 (80 -20%) Helium Air N 2 Stanford-Instruments fast current amplifiers SR 570 (104 - 107 V/A) GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Response function for a short beam pulse (fast beam extraction: t < 1 µs) Ar-CO 2 fast electron signal UIC = -2000 V slow ion signal Beam pulse GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Response function for a short beam pulse (fast beam extraction: t < 1 µs) UIC = -500 V fast electron signal Beam pulse GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Response function for a short beam pulse (fast beam extraction: t < 1 µs, 12 C, 300 Me. V/u) UIC = -2000 V Slow ion signal Beam pulse GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Response function for a short beam pulse (fast beam extraction: t < 1 µs, 12 C, 300 Me. V/u) Slow signal from positive ions UIC = -2000 V Beam pulse GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Response function for a short beam pulse for 4 different gases (Ar/CO 2 , N 2 , He , Air) UIC = -500 V He Ar-CO 2 N 2 Air GSI Helmholtzzentrum für Schwerionenforschung Gmb. H t - 80% [µs] 271 µs 542 µs 585 µs 599 µs t - 80% normalized to Helium 100% 200% 215% 221%

Response function for a short beam pulse for 4 different gases (Ar/CO 2 , N 2 , He , Air) UIC = -1000 V He Ar-CO 2 N 2 Air GSI Helmholtzzentrum für Schwerionenforschung Gmb. H t - 80% [µs] 122 µs 232 µs 269 µs 286 µs t - 80% normalized to Helium 100% 190% 220% 234%

Response function for a short beam pulse for 4 different gases (Ar/CO 2 , N 2 , He , Air) UIC = -2000 V He Ar-CO 2 N 2 Air GSI Helmholtzzentrum für Schwerionenforschung Gmb. H t - 80% [µs] 55 µs 114 µs 124 µs 135 µs t - 80% normalized to Helium 100% 207% 225% 245%

Drift times Summary Gas U = -500 V U = -1000 V U = -2000 V t 80% µ (mobility) [ (cm/s) / (V/cm) ] ( literature values 1 -3) [µs] normalized to Helium He 5. 0 – 10. 0 271 100% 122 100% 55 100% Ar-CO 2 1. 2 - 1. 5 542 200% 232 190% 114 207% N 2 1. 3 585 215% 269 220% 124 225% Air 1. 4 599 221% 286 234% 135 245% 1) K. Kleinknecht, Detektoren für Teilchenstrahlung -. Berlin Heidelberg New York: Springer-Verlag, 2015. 2) F. Sauli, “Principles of operation of multiwire proportional and drift chambers, ” in Experimental Techniques in High-energy Nuclear and Particle Physics, World Scientific, 1991. 3) H. Kolanoski and N. Wermes, Teilchendetektoren - Grundlagen und Anwendungen. Berlin Heidelberg New York: Springer-Verlag, 2016. GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

IC signals from Photon LINAC pulses VARIAN true beam Δt<3µs Helium vs. Air @ 1000 V @ 100 V He He Air electron attachment e - + O 2 + + O- 2 GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Different gases Short-Pulse answer of IC @ 1800 V , amp = 107 V/A , 6 Me. V photons Helium vs. Ar. CO 2 vs. Nitrogen GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Different Amplifiers Short-Pulse answer of IC filled with Ar. CO 2 @ 1800 V, amp = 107 V/A FEMTO DLPCA-200 vs. Standford Instruments SR 570 GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Concept of Signal Simulation : GARFIELD + SPICE gas composition diffusion constant electron attachment Mobility µ GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

LT-SPICE circuit voltage source buffer – capacitor Garfield-Output I(t) @ electrodes Ionization chamber with capacity Output 2 -stage amplifier GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Signal simulation vs. measurement Ar. CO 2 ; U=500 V , amp = 107 V/A Mess. 450 µs Simul. 520 µs 80 % GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Signal simulation vs. measurement Helium ; U= 1800 V , amp = 107 V/A 50 µs 80 % GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Conclusion Biophysics intends designs of 10 x faster scanning system for treatment of moving organs • Beam-monitoring detectors are one of the bottlenecks Ø Ø • 50% of the signal (ions signal) are strongly delayed Electroncis delays on the top Helium decreases the delay of the detectors by factor of 2 -3 • drawback: Helium delivers only 10% of the signal of an Argon chamber (higher noise/signal ratio) • Higher Voltage decreases the delay: tdelay ~ 1 / Voltage • Fast amplifiers reduce the signal delay relevant • Oxygen absorbs the fast electrons (suppression of the fast electron part) • The signals of ionization chambers can be well simulated (time behavior well understood) (not yet perfectly, due to uncertainties of the mobility µ) GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Thank you … speed matte GSI Helmholtzzentrum für Schwerionenforschung Gmb. H rs

Reserve … GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Response function of the MWPC for 2 different gases (Ar/CO 2 and He) UIC = -1750 V GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Response function for a short beam pulse (fast beam extraction: t < 1 µs) Slow signal from positive ions UIC = -500 V Beam pulse GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Signal of drifting ions – charge induction on the electrodes Shockley-Ramo-Theorem (simplified) time derivative (1) (2) M. Nakhostin, Signal Processing for Radiation Detectors. WILEY, 2018. GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Calculation of the signal of an ion track : chain of ionized ions/electrons (simultaneously produced) particle track Ionisation chamber is(t) charge collection time for a single particle track: electrons ions t dgap/v+ (1) H. Kolanoski and N. Wermes, Teilchendetektoren - Grundlagen und Anwendungen. Berlin Heidelberg New York: Springer-Verlag, 2016. GSI Helmholtzzentrum für Schwerionenforschung Gmb. H dgap/v-

Spice simulation of the fast electron pulse UIC = -2000 V GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Delay by drift time (response for a short beam pulse) Theoretical time response GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Fast PIN-diode vs. Ionization chamber Ar. CO 2 (500 V) GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Fast PIN-diode vs. Ionization chamber Ar. CO 2 (500 V) GSI Helmholtzzentrum für Schwerionenforschung Gmb. H

Existing Beam monitors for scanning Parallel plate ionization chambers Vacuum Window Vacuum Beamline MWPC 1 3 x IC MWPC 2 Nozzle GSI Helmholtzzentrum für Schwerionenforschung Gmb. H Multi wire proportional chamber