Development of Floating Strip Micromegas Detectors

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1 Development of Floating Strip Micromegas Detectors Jona Bortfeldt LS Schaile Ludwig-Maximilians-Universität München Science Week, Excellence Cluster Universe December 2 nd 214

2 Introduction Why Detector R&D for High Energy Physics? ATLAS muon spectrometer: New Small Wheel High-Lumi-LHC: high-rate background O 2 khz/cm2 large-area Micromegas detectors O m2 Jona Bortfeldt (LMU Mu nchen) Development of Floating Strip Micromegas 2/12/14 2

3 Introduction Why Detector R&D for Medical Physics? ˆ tumor irradiation with ions: accurate dose deposition Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 3

4 Introduction Why Detector R&D for Medical Physics? ˆ tumor irradiation with ions: accurate dose deposition ˆ ions with known initial energy, higher than in therapy ˆ residual energy measurement energy loss contrast ˆ Micromegas: track single particles with accuracy <.5 mm ions head tumor tracking Micromegas range telescope Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 3

5 Introduction The Micromegas Detector charged particle Ar:CO2 ion iza tio n cathode mesh pillars copper anode strips 6mm.5kV/cm.47mm/ns 128μm 39kV/cm 25μm gas amplification 13 to 14 charge signal on strips single strip readout spatial resolution O(5µm) timing O(ns) thin amplification gap & fine segmentation fast drain of positive ions high-rate capable COMPASS: precision tracker, high flux CAST: photon detector, good energy resolution, low background T2K: TPC readout, large area Jona Bortfeldt (LMU Mu nchen) Development of Floating Strip Micromegas 2/12/14 4

6 Floating Strip Micromegas Principles Floating Strip Micromegas cathode -8V challenge: discharges mesh pillars copper anode strips 25μm Ar:CO 2 15μm 6mm 128μm.5kV/cm -5V 39kV/cm ˆ charge density e/.1 mm 2 (Raether limit) ˆ conductive channel potentials equalize ˆ non-destructive, but dead time efficiency drop voltage [V] 6 55 standard Micromegas time [ms] Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 5

7 Floating Strip Micromegas Principles Floating Strip Micromegas cathode mesh pillars copper anode strips 25μm voltage [V] Ar:CO μm floating strip MM 6mm 128μm standard Micromegas -3V.5kV/cm 39kV/cm +5V large R small C time [ms] challenge: discharges ˆ charge density e/.1 mm 2 (Raether limit) ˆ conductive channel potentials equalize ˆ non-destructive, but dead time efficiency drop idea: minimize the affected region ˆ floating copper strips: ˆ strip can float in a discharge ˆ individually connected to HV via 22MΩ ˆ capacitively coupled to readout electronics via pf HV capacitor ˆ only two or three strips need to be recharged optimization in dedicated measurements & detailed simulation Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 5

8 Floating Strip Micromegas Principles Discharge Study with Floating Strip Micromegas cathode +HV 1k 22M 22M 22M 22M anode strips mesh ˆ alpha source induces discharges ˆ voltage drop on one to three strips recharge current ˆ global high voltage drop affects all strips ˆ voltage signal on seven neighboring strips discharge topology 22MΩ 1nF 15pF Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 6

9 Floating Strip Micromegas Principles Optimization of the Floating Strip Principle ˆ standard Micromegas (approximate): 1 kω 3 V drop, dead time 8 ms ˆ intermediate: 1 MΩ 2 V drop, dead time 1 ms ˆ floating strip: 22 MΩ.5 V drop negligible cathode -3V SMD capacitor 15pF ground mesh +594V signal signal copper strips SMD resistor measured average voltage pulse Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 7

10 Floating Strip Micromegas Principles Detailed Investigation of the Global Voltage Drop discharges / 1mV ˆ measure voltage drop of common HV potential ˆ discrete structure probably corresponds to discharge of one, two or three strips ˆ how can we show this? investigate discharge topology develop simulation compare predicted with measured voltage drop maximum voltage drop [V] Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 8

11 Floating Strip Micromegas Principles Discharge Topology - Expected Amplitude Correlation expected correlation amplitude strip only 2 only 3 ˆ measure voltage signal on neighboring strips ˆ two reasons for signals on strips: ˆ discharge onto strip ˆ capacitive coupling from neighboring strips 4... amplitude strip 3 Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 9

12 Floating Strip Micromegas Principles Discharge Topology - One Strip voltage channel 2 [V] L23L 1L2 23L L12L L1 12L 2L3 2L34L 34L 3L4 3L45L 45L voltage channel 3 [V] ˆ discharges on separate strips distinguishable ˆ substructure quantitatively described by simulation amplitude strip expected correlation only only 3 amplitude strip 3 Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 1

13 Floating Strip Micromegas Principles LTSpice Detector Simulation mesh strip mesh C ms C asas strip C coupl HV C slsl C slg R vd1 R vd2 C cable U strip mesh C asas strip R hv C slsl detector HV C hvg C hvcoupl 1MΩ U hv ˆ consider the involved capacitances e.g. between neighboring strips, coupling capacitors, cable capacitance... ˆ simulate discharges (blue switch) Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 11

14 Floating Strip Micromegas Principles Optimum Configuration: Global Voltage Drop discharges / 1mV 22 2 simulation: one strip measurement 18 simulation: two strips 16 simulation: three strips maximum voltage drop [V] ˆ good agreement between simulation and measurement ˆ only two free parameters ˆ response time of HV supply: 5 ms ˆ voltage difference between strips at which leakage stops: 22 V ˆ peaks correspond indeed to discharge of one, two or three strip Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 12

15 Floating Strip Micromegas Principles floating strip principle works ˆ discharges: negligible effect on common high-voltage ˆ discharges are localized measurements ˆ muon tracking in high-rate background ˆ tracking of high-energy pions ˆ tracking of ions at highest rates Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 13

16 PM Measurement: MIP Tracking in High-Rate Background Cosmic Muon Tracking under High-Rate Background Irradiation 3 trigger scintillators vacuum-flange PM Kapton window z x questions: mm Gassiplex APV25 proton beam APV25 mm2 APV25 mm3 Gassiplex mm1 floating strip Micromegas 3 trigger scintillators cosmic muon reference reference reference reference PM scintillator ˆ muon 55 khz background ˆ efficiency ˆ spatial resolution ˆ stability floating strip Micromegas ˆ active area: cm 2 ˆ 128 strips, 3 µm width, 5 µm pitch ˆ 1 mm drift gap reference tracking system ˆ two non resistive Micromegas ˆ two resistive Micromegas ˆ 2 3 trigger scintillators proton background irradiation ˆ 2 MeV protons, 55 khz ˆ lateral beam spot: 6.5 cm 2 ˆ traverse detector signal on all strips Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 14

17 Measurement: MIP Tracking in High-Rate Background Distinguishing Cosmic Muon and Proton Background Signals Cosmic Muon + Proton Event charge [adc channels] time [25ns] 5 2 muon strip number two event classes: ˆ only muon ˆ coincident muon and proton direct influence on signal ˆ proton produces coincident signals on many strips ˆ muon signal shape similar to proton ˆ use reference track for cluster selection Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 15

18 Measurement: MIP Tracking in High-Rate Background Cosmic Muon Tracking in High-Rate Background events /.4mm residual distribution muons proton contamination Entries 2784 χ 2 / ndf / 96 p 9.1 p1.589 p p x = predicted position - measured position [mm] ˆ muon detection in background possible ˆ occasionally background misinterpreted as muon spatial resolution [µm] spatial resolution no p irradiation µ, with p irrad. µ + p, with p irrad E amp [kv/cm] ˆ no indirect effects as e.g. space charge ˆ only deterioration if muon and proton are coincident efficiency ˆ expectation for complete blinding: ε irrad /ε no irrad =.617 ˆ ε irrad /ε no irrad =.79 ˆ limited by strip anode stability ˆ discharge rate.17 Hz ˆ inefficiency: minimum ionizing particle tracking in high-rate background possible Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 16

Measurement: 12 GeV Pion Tracking 5 48 cm 2 Micromegas in 12 GeV Pion Beam @ H6 SPS floating-strip Micromegas, x-readout steel frame, rotation, translation 6 standard Micromegas, x-readout 2

19 Measurement: 12 GeV Pion Tracking 5 48 cm 2 Micromegas in 12 GeV Pion H6 SPS floating-strip Micromegas, x-readout steel frame, rotation, translation 6 standard Micromegas, x-readout 2 resistive-strip Micromegas, x- & y-readout 3 trigger scintillators, y-readout pion beam Gassi Gassi Gassi APV Gassi APV Gassi Gassi APV floating strip Micromegas ˆ 192 strips, 15 µm width, 25 µm pitch ˆ 8 mm drift gap ˆ x-y- and angular scans z x tracking system: ˆ six non resistive Micromegas ˆ two resistive Micromegas ˆ 2 3 trigger scintillators questions: ˆ efficiency ˆ spatial resolution ˆ homogeneity ˆ inclined track reconstruction Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 17

20 Measurement: 12 GeV Pion Tracking 5 48 cm 2 Micromegas in 12 GeV Pion H6 SPS floating-strip Micromegas, x-readout steel frame, rotation, translation 6 standard Micromegas, x-readout 2 resistive-strip Micromegas, x- & y-readout 3 trigger scintillators, y-readout pion beam Gassi Gassi Gassi APV Gassi APV Gassi Gassi APV floating strip Micromegas ˆ 192 strips, 15 µm width, 25 µm pitch ˆ 8 mm drift gap ˆ x-y- and angular scans z x track accuracy [µm] position z [mm] tracking system: ˆ six non resistive Micromegas ˆ two resistive Micromegas ˆ 2 3 trigger scintillators questions: ˆ efficiency ˆ spatial resolution ˆ homogeneity ˆ inclined track reconstruction Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 17

21 Measurement: 12 GeV Pion Tracking Pulse Height pulse height vs E amp pulse height vs E drift pulse height [adc channels] 8 middle, middle top, right top, left cathode mesh E drift pulse height [adc channels] anode E amp 2 middle, middle E amp [kv/cm] ˆ exponential rise as expected (Townsend theory) ˆ gas gain can be selected over wide range as needed ˆ 37.5 kv/cm ˆ= 48 V 1 top, right top, left E drift [kv/cm] E drift <.4 kv/cm: ˆ low charge separation ˆ low drift velocity large E drift > 1. kv/cm: ˆ low electron mesh transparency Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 18

22 Measurement: 12 GeV Pion Tracking Efficiency & Drift Field efficiency vs E drift inefficient spots pillars efficiency hit position x [mm] E amp =37.5kV/cm E amp =36.7kV/cm E amp =35.9kV/cm E drift [kv/cm] hit position y [mm] optimum value: (95 ± 2)%, limited by mesh supporting pillars Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 19

23 Measurement: 12 GeV Pion Tracking Determining the Spatial Resolution floating strip Micromegas resid σ SR σ track σ SR,i ˆ resid = x track x meas ˆ doing this for many tracks residual distribution ˆ σ resid = σ 2 track + σ2 SR z x track reference Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 2

24 Measurement: 12 GeV Pion Tracking Spatial Resolution & Drift Field spatial resolution [µm] E amp =37.5kV/cm E amp =36.7kV/cm E amp =35.9kV/cm ˆ optimum value: (49 ± 2)µm ˆ no strong dependence on absolute pulse height ˆ resolution number of electrons, entering the amplification gap + low diffusion E drift [kv/cm] spatial resolution better 5 µm Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 21

25 Measurement: 12 GeV Pion Tracking Track Inclination Reconstruction in a Single Detector Plane cathode 8mm ϑ z cluster= t v drift mesh x cluster rise time fit time [25ns] linear fit to data points strip simulated signals method: ˆ arrival time drift distance ˆ measure arrival time of charge cluster on strip signal timing t ˆ linear fit to time-strip data points track inclination alternative hit position charge [adc channels] % 5% 9% 4 t t F time [25ns] p F charge [arb. units] strip 5 strip 6 strip 7 strip 8 strip 9 strip 1 strip time [s] systematics: ˆ capacitive coupling of signals onto neighboring strips ˆ simulation with parameter-free LTSpice detector model Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 22

26 Measurement: 12 GeV Pion Tracking Track Inclination Measurement in a Single Detector Plane entries track inclination [ ] reconstructed angle [ ] angular resolution [ ] systematic effect track inclination [ ] ˆ track inclination reconstruction possible for angles 2 ϑ 4 with angular resolution ( ) +6 4 ˆ systematic effect understood calibration possible ˆ combined position reco possible (µtpc + centroid) Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 23

27 Measurement: Highest-Rate Ion Tracking Ion Tracking with Thin Micromegas at Highest HIT beams z particle beam y Micromegas, one-dimensional readout Micromegas 1, one-dimensional readout Micromegas 2, two-dimensional readout scattered particles scintillators + photomultipliers ˆ MeV/u to 43 MeV/u 2 MHz to 8 MHz ˆ 48 MeV to 221 MeV 8 MHz to 2 GHz ˆ thanks to S. Brons and the HIT accelerator team for the support floating strip Micromegas ˆ cm 2 doublet ˆ low material budget (FR4 + Cu 2 µm) APV25 frontend APV25 frontend APV25 frontend additional detectors APV25 frontend ˆ 9 9 cm 2 monitoring Micromegas with x-y-readout ˆ trigger on secondary charged particles Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 24

28 Measurement: Highest-Rate Ion Tracking Beam Characterization signal timing 12 C, Hz bunch spacing signals / ns bunch spacing [ns] micom micom 1 expected signal timing [25ns] ˆ good multihit resolution ˆ bunch spacing measureable ˆ bunch filling measureable beam energy [MeV/u] Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 25

29 Measurement: Highest-Rate Ion Tracking Signals at Lowest and Highest Rate 12 C, E = 43 MeV/u, 5 MHz p, E = 221 MeV, 2 GHz pulse height [arb. units] pulse height [arb. units] time [25ns] strip time [25ns] strips 3 particles clearly distinguishable single particle tracking possible integration over 8 coincident particles envelope of beam profile Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 26

30 Measurement: Highest-Rate Ion Tracking Pulse Height & Spatial Resolution for 88 MeV/u Carbon Ions pulse height [adc channels] C beam micom micom1 micom spatial resolution [µm] mean particle rate [Hz] ˆ up to 8 MHz single particle tracks visible but not all of them separable ˆ only 2% pulse height 8 MHz mean particle rate [Hz] ˆ highest rates: slight distortion of hit position by hits on adjacent strips ˆ limited by multiple scattering ˆ sufficient for medical application tracking of carbon ions at highest rates possible Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 27

31 Measurement: Highest-Rate Ion Tracking Detection Efficiency and Up-Time p, 221 MeV efficiency proton beam micom micom1 micom mean particle rate [Hz] single particle detection efficiency detector up-time no efficiency & up-time reduction in floating strip Micromegas Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 28

32 Measurement: Highest-Rate Ion Tracking Rate Capability & Multi-hit Resolution reconstructed hits per multi-event track finding algorithm number of hits in detector reconstr., measurement reconstr., simulation true, simulation mean particle rate [Hz] track distance r [mm] track inclination α [rad] ˆ reconstruction of all particles up to 1 MHz = 7 MHz/cm 2 ˆ Hough transform: d = x cos(α) + z sin(α) point in position space line in Hough space line in position space point in Hough space ˆ up to seven coincident tracks reconstructable Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 29

33 Summary Summary ˆ floating strip Micromegas were optimized and work ˆ discharges: ˆ behavior and topology understood special thanks to ˆ negligible influence on efficiency ˆ cosmic muon tracking in Otmar intensebiebel proton background possible ( 5 khz/strip) ˆ high-energy pion trackingralf using Hertenberger a 48 5 cm 2 floating strip Micromegas ˆ efficiency >.95 the hardware crew at LS Schaile ˆ spatial resolution < 5 µm ˆ homogeneous pulse height, Dorothee efficiency Schaile & position resolution ˆ medium-energy carbon ion DFG and proton tracking at highest rates ˆ separation of all particles at rates 1 MHz ˆ only 2% pulse height reduction at 8 MHz ˆ spatial resolution better Raphaela 18 µm at Bortfeldt all rates 8 MHz ˆ stable operation up to highest rates of 2 GHz floating strip Micromegas: versatile, discharge tolerant, high-rate capable tracking detectors with good spatial resolution Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 3

34 Summary Summary ˆ floating strip Micromegas were optimized and work ˆ discharges: ˆ behavior and topology understood ˆ negligible influence on efficiency ˆ cosmic muon tracking in intense proton background possible ( 5 khz/strip) ˆ high-energy pion tracking using a 48 5 cm 2 floating strip Micromegas ˆ efficiency >.95 ˆ spatial resolution < 5 µm ˆ homogeneous pulse height, efficiency & position resolution ˆ medium-energy carbon ion and proton tracking at highest rates ˆ separation of all particles at rates 1 MHz ˆ only 2% pulse height reduction at 8 MHz ˆ spatial resolution better 18 µm at all rates 8 MHz ˆ stable operation up to highest rates of 2 GHz floating strip Micromegas: versatile, discharge tolerant, high-rate capable tracking detectors with good spatial resolution Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 3

35 Summary Summary ˆ floating strip Micromegas were optimized and work ˆ discharges: ˆ behavior and topology understood ˆ negligible influence on efficiency ˆ cosmic muon tracking in intense proton background possible ( 5 khz/strip) ˆ high-energy pion tracking using a 48 5 cm 2 floating strip Micromegas ˆ efficiency >.95 ˆ spatial resolution < 5 µm ˆ homogeneous pulse height, efficiency & position resolution ˆ medium-energy carbon ion and proton tracking at highest rates ˆ separation of all particles at rates 1 MHz ˆ only 2% pulse height reduction at 8 MHz ˆ spatial resolution better 18 µm at all rates 8 MHz ˆ stable operation up to highest rates of 2 GHz floating strip Micromegas: versatile, discharge tolerant, high-rate capable tracking detectors with good spatial resolution Thank you! Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 3

36 backup backup Discrete & Integrated Floating Strip Micromegas discrete cathode -3V ground SMD capacitor 15pF 6mm mesh +5V 128µm cathode mesh integrated 6mm 128μm -HV +HV signal copper strips SMD resistor 22MΩ copper strips copper strips resistor 1MΩ signal ˆ exchangable Rs and Cs optimization possible ˆ more complicated assembly soldering 2 for each strip ˆ space requirements due to HV sustaining components strip pitch limited to.5 mm ˆ anode strips: connected to HV via printable paste resistors ˆ readout strips: second layer of copper strips capacitive coupling through the board, intrinsically HV sustaining Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 31

37 backup backup Track Inclination Reconstruction Systematics: LTSpice-Simulation mesh strip mesh C ms C asas strip C asas mesh strip C coupl R hv HV C slsl C slsl C slg C cr C cc signal ˆ use LTSpice to simulate 16 neighboring strips, read out via charge-sens.-preamps ˆ consider mesh-anode strip, anode strip-ground, anode strip-anode strip, coupling, stripline-stripline and stripline-ground capacitance, no free parameter ˆ inject time dependent current on anode strips study signals on all other strips detector HV cathode C hvg C hvcoupl 1MΩ charge [arb. units].2.15 strip 5 strip 6 strip 7 strip 8 strip 9 strip 1 strip 11 mesh current time time [s] Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 32

38 backup backup Hough Transform Based Track Building x x 1 track with slope -b 1 & intersect a 1 a a 1 x 2 x 3 x 4 z 1 z 2 z 3 z b 1 b point in position space (z i,x i ) line in Hough space a = z i b + x i line in position space x = -b j z + a j point in Hough space (b j,a j ) ˆ for improved stability: use Hesse normal form as transform function ˆ up to seven valid tracks reconstructed per event Jona Bortfeldt (LMU München) Development of Floating Strip Micromegas 2/12/14 33

Full characterization tests of Micromegas with elongated pillars

University of Würzburg Full characterization tests of Micromegas with elongated pillars B. Alvarez1 Gonzalez, L. Barak1, J. Bortfeldt1, F. Dubinin3, G. Glonti1, F. Kuger1,2, P. Iengo1, E. Oliveri1, J.