Minimisation of Ion Feedback in Triple GEM Structures

Transcription

1 Minimisation of Ion Feedback in Triple GEM Structures Sven Lotze Sabine Blatt Martin Killenberg Joachim Mnich Astrid Münnich Stefan Roth Manfred Tonutti Adrian Vogel Michael Weber III Physikalisches Institut B ECFA Study of Physics and Detectors for a Linear Collider st Workshop Montpellier November 23 Sven Lotze Minimisation of Ion Feedback in Triple GEM Structures

2 Chamber Parameters and Parametrisation I K I GEMK I GEMA I D I Hole I T Cathode d d D T E D E E Hole T U GEM Three GEM voltages and four electric fields outside the GEMs (7 chamber parameters) determine charge transfer I GEM2K I GEM2A I GEM3K I GEM3A I A I Hole2 I T2 I Hole3 I I Anode d T2 d I E E E E I Hole2 T2 Hole3 U U GEM2 GEM3 By parametrisation of measured transfer coefficients quantities like ion feedback ( and eff Gain ( be calculated from a ) ) can set of these parameters Sven Lotze Minimisation of Ion Feedback in Triple GEM Structures 2

3 Charge Transfer Coefficients Collection Efficiency Extraction Efficiency Gain (single GEM) collected into hole before GEM extracted from GEM in GEMhole in GEMhole collected into hole GEMs Anode primary Effective Gain Sven Lotze Minimisation of Ion Feedback in Triple GEM Structures 3

4 Charge Transfer Test Setup 2 3 ( )( ) * +* 4mm 2mm 2mm 2mm HV Power Supply Range ADC DBCC SY 27 Interlock CAMAC Crate NIM Crate 8x 8x Current ADC RS 232 PCCPI GEM Pickup Cathode Anode Fe 55 Source Linux Sven Lotze Minimisation of Ion Feedback in Triple GEM Structures 4

5 Parametrisation of Ion Extraction Efficiency 9 8 Primary Ion Extraction Efficiency Measurement TDRGas at B=4T Fitted Parametrisation Field Ratio (E ext E hole ) Sven Lotze Minimisation of Ion Feedback in Triple GEM Structures 5

6 : ; 9 Parametrisation of Transfer Coefficients Electron Collection Efficiency Ion Collection Efficiency Measurement TDR Gas at B=4T Fitted Parametrisation Field Ratio (E ext E hole ) Measurement TDR Gas at B=4T Fitted Parametrisation Field Ratio (E ext E hole ) Electron Extraction Efficiency * Parallel Plate Gain Primary Ion Extraction Efficiency Measured Data Fitted Parametrisation Field Ratio (E ext E hole ) Measurement TDRGas at B=4T Fitted Parametrisation Field Ratio (E ext E hole ) Gain (single GEM) Secondary Ion Extraction Efficiency Measurement TDRGas at B=4T st try Measurement TDRGas at B=4T 2nd try Fitted Parametrisation (average) U GEM [V] Measurement TDRGas at 4T Fitted Parametrisation Field Ratio (E ext E hole ) Sven Lotze Minimisation of Ion Feedback in Triple GEM Structures 6

7 A @G F E A Boundary conditions for the parameters The drift field is determined by the peak in the drift velocity of the chosen gas; here <>= BDC The other fields are stable up to B C The induction field (next to the anode) is set to the maximum stable field; this maximizes extraction efficiency from GEM3 and has no adverse effects GEMs can be operated at up to Approximately all primary electrons have to be multiplied in the first GEM so statistics are not degraded The effective gain of the triple GEM structure as a whole is determined by the readout electronics; here F is used Sven Lotze Minimisation of Ion Feedback in Triple GEM Structures 7

8 Used Method for Finding Minimum IF Parameter space spanned by five parameters (keeping drift and induction fields fixed) is scanned stepwise with a C program At every point calculated ion feedback effective gain and corresponding parameters are written to hard disk (root tree) Then the obtained data set can be searched for minima or displayed graphically (with root macros) Sven Lotze Minimisation of Ion Feedback in Triple GEM Structures 8

9 KL MN Distribution Ion Feedback vs ugem3 vs IF Eff Ion Feedback U GEM3 [V] Sven Lotze Minimisation of Ion Feedback in Triple GEM Structures 9

10 U TS Ion Feedback vs OQPR etrans2 vs IF Eff Ion Feedback Transfer Field 2 [Vcm] Sven Lotze Minimisation of Ion Feedback in Triple GEM Structures

11 U TS Measurement vs Parametrisation: OQPR 3 25 Minimum Ion Feedback Parametrisation Induction Field = 8 Vcm Measurement Transfer Field 2 [Vcm] Sven Lotze Minimisation of Ion Feedback in Triple GEM Structures

12 U TS Measurement vs Parametrisation: OQPR 3 25 Minimum Ion Feedback Parametrisation Induction Field = 6 Vcm Measurement Parametrisation Induction Field = 8 Vcm Measurement Transfer Field 2 [Vcm] Sven Lotze Minimisation of Ion Feedback in Triple GEM Structures

13 ] ]d ]f Qualitative Results Influence of Individual Parameters: X <>=WV : fixed to 2 Vcm Y[Z\ : small influence on ion feedback allows variation of effective gain ba` <_^ V YcZ\ : maximal for minimum ion feedback : small influence on ion feedback allows variation of effective gain d ba` <e^ V : explicit minimum of ion feedback at low not yet verified in measurements d ba` <e^ V predicted YcZ\ : maximal for minimum ion feedback kx ml a hji <>g a : maximal for minimum ion feedback Sven Lotze Minimisation of Ion Feedback in Triple GEM Structures 2

14 Test Chamber in 5T Magnet Sven Lotze Minimisation of Ion Feedback in Triple GEM Structures 3

15 Influence of B Field 6 5 Effective Ion Feedback B [T] Sven Lotze Minimisation of Ion Feedback in Triple GEM Structures 4

16 n Influence of Effective Gain 6 45 Eff Ion Feedback Eff Ion Feedback Voltage GEM Voltage GEM Eff Gain Sven Lotze Minimisation of Ion Feedback in Triple GEM Structures 5 [V] U GEM

17 F f o q p J d r f q p F J q s Conclusion Summary The qualitative influence of the individual chamber parameters on the ion feedback is understood The minimum ion feedback depends strongly on the maximal reachable fields and GEM voltages A magnetic field of 4 T decreases ion feedback by a factor of d An ion feedback 25 with gas Ar93CH 5CO B=4 T as foreseen for the TESLA TPC is stable for (stability test wo magnetic field) 2 and 2 h Setting with IF 25 works in our TPC The goal of seems unrealistic check if higher ion feedback or lower effective gain are acceptable Check how settings optimized for IF affect dedx etc Sven Lotze Minimisation of Ion Feedback in Triple GEM Structures 6