D. Gonzalez-Diaz, KEK, 19-01-2017 I. A contemporary recap II. - PowerPoint PPT Presentation

D. Gonzalez-Diaz, KEK, 19-01-2017

I. A contemporary recap II. Historical introduction III.Technological pillars / few things not to forget IV. Faster V. Bigger VI. Better

I. parallel plate geometries II. Cherenkov light + solid converters Limited by V fluctuations in the 0 multiplication and primary ionization statistics III. Multi-sampling Limited by primary statistics and electron diffusion D. Gonzalez-Diaz et al. arXiv:1606.08172v2 Limited by ionization mean free path and drift velocity R. de Oliveira arXiv:1503.05330v1

History of timing with gaseous detectors(I) 1956 E. K. Zavoisky and G. E. Smolkin, At. Energ. (USSR), 4(1956)46 [ ? ] track σ =100 ps readout trigger tails! chambers Long dead-time (time to reload the chamber capacitance after a spark was ~1-10ms)  . • Read-out was performed by optical means  . •

History of timing with gaseous detectors(II) 1970 1 mm Time resolution limited due to a relatively big gas gap  . • Discharge takes energy only from the locally affected area, limited by surface resistivity  . •

History of timing with gaseous detectors(III) 1978 0.1 mm High efficiency enforces operation at around 12bar  . • Time resolution consistently below 100ps  . •

History of timing with gaseous detectors(IV) 1981 1.5 mm Time resolution limited due to a relatively big gas gap  . • Avoids the necessity of using soviet technology (Bakelite plates used instead)  . • • In subsequent works, the authors introduced C 2 H 2 F 4 and SF 6 and a new operation mode (limited proportionality / saturated avalanche mode).

History of timing with gaseous detectors(V) 1996 3 mm Time resolution limited due to a relatively big gas gap  . • • Time resolution and efficiency can be improved with addition of more gaps. Each new gas gap behaves like a detector replica (i.e., a parallel current generator) improving avalanche statistics, and resistive plates can be simply left floating  .

History of timing with gaseous detectors (VI) 2000 0.3 mm Time resolution good due to small gap  . • Efficiency good due to large number of gaps  . • Standard materials, standard gases, standard pressure, standard 1GHz electronics  . •

History of timing with gaseous detectors (VIII) >2004 J. Wang et al. NIM A, 621(2010)151 [Tsinghua University] charged particle readout pads/strips -V +V Small improvements since 2000 in order to stablish reliable production techniques  . • 50-90ps achieved on large 2m-scale areas  . • • Technology stabilized.

I. The characteristics of the induced signal are only mildly affected by the resistive material (through its dielectric constant and thickness). II. The transition avalanche-streamer-filamentary discharge-spark is quenched down to the energy available in a small local area, provided the flow of current through the resistive electrode is limited. In practice big avalanches end as streamers, and stable operation of the amplification electronics is possible. III. The use of multiple gas gaps (acting in practice as parallel current generators) allows to keep the high efficiency characteristic of large gaps and the high time resolution characteristic of narrow ones . The associated reduction in the induced charge fluctuations improves both. IV. The use of electronegative gases helps at stabilizing le operation up to very high gains, even in the presence of strong Space-Charge effects. V. The maximum operating rate is limited by charge build-up and the characteristic time for the released charge to abandon the system, by conduction through the resistive electrodes. VI. Scalability is relatively easy due to use of common materials.

log( s / A ) 1GeV 10GeV 100GeV 1000GeV 10000GeV FOPI • technology introduced (100ps) 2000 ALICE HADES NIM A 443(2000)201 HARP E • simulations demonstrate operation under deep space-charge conditions STAR (barrel, MTD) NIM A 517(2004)54 CBM • ALICE module (50ps) R&D PHENIX NIMA 533 (2004)93 2005 EEE • warm RPCs NIM A 527(2004)471 year NIM A 555(2005)72 • 24-gap module (20ps) MPD NIM A 594(2008) 39 R&D • Chinese glass RPC 2010 NIM A 621(2010)151 • Electrostatic compensation NIM A 648 (2011) 52 BGO LEPS2 2015 • Ceramics RPC NIM A818 (2016) 45–50

SHOWER magnet detector high angle TOF inner MDCs (I-II) RPC wall hadron blind RICH outer MDCs (III-IV)

8 m 2

 0.27 mm × 4 gaps  minimum for good efficiency  Aluminum and glass, 2mm-thick electrodes  minimize amount of glass for maximum rate capability  try to keep good mechanics  Heat-tolerant materials fully shielded spring-loaded Aluminium Glass pressure plate HV & readout at the center

wall 1116 tRPC individual detectors 6 sectors x 2layers x 3columns x 31 cells gas box of one sector variable cell overlap for providing full angular coverage column (1-3) variable cell width for matching occupancy layer(1-2) row (1-31) detailed info in D.Gonzalez-Diaz 2006 JINST TH 003 and D.Belver et al. NIM A, 602(2009)687

55cm length 13cm length overall cross-talk 0.4% overall resolution 77ps S 1 S 2 σ T [ps] S 3 S 4 S 5 S 6 A. Blanco et al., NIM A, doi.10.1016/2010.08.068 deterioration of resolution for a coincident track (around 100ps) distance (in rows) between primary and secondary hits

G. Kornakov et al., 2014 JINST 9 C11015

t= ∞ t t=0 Normal V R gap C gap E? E? g E 0 V V E = E = g g Resistive V R gap C gap E? E? g E R plate C plate σ , ε r d 0 C V V = plate E = E + C C g g plate gap transient! (in practice, few sec)

glass capacitance un-loaded, (‘AC limit’) (‘DC limit’) RPC capacitance loaded gap capacitance fully loaded V=V o V=V o V=V o V=V o C glass +- +- +- +- +- +- +- +- +- d E glass E glass = C tot /C glass V o /d E glass ~0 E glass R glass V o C gas g E gas E gas R gas Δ V o =1/3V o +- +- +- +- +- +- +- +- +- E glass E glass C glass R glass E gas E gas 2/3V o +- +- +- +- +- +- +- +- +- E glass E glass = C tot /C gas V o /g E gas = V o /3g E gas +- +- +- +- +- +- +- +- +- E glass E glass V=0 V=0 V=0 V=0 1/C tot =1/C glass +1/C gas +... R tot =R glass +R gas +...

V=V o V=V o V=V o V o V o V o - - - - ++++ + + o + Δ V 1 2/3V o 2/3V <V>=2/3V o - + ... + - - - o - Δ V 2 1/3V o <V>=1/3V o 1/3V - - - - - - - - - ++++++ 0 0 0 V=0 V=0 V=0 E. Cerron Zeballos et al., NIM A, 374(1996)132 * Indeed, it has not been possible to quantify the effect of the fluctuations on the plates’ potentials. But no practical difference has been observed between leaving them floating or fixing the potential…

Avalanche field ( E z =100 kV/cm , 0.3 mm gap) !! C. Lippmann, W. Riegler, NIM A 517(2004)54

Semi-quantitative derivation of the maximum attainable gain before streamers appear: 2 = x α x q e r 4 D ≅ e E ( x ) v πε av 2 4 r λ o = D v th α 3 x q e c c ≅ ≅ e E ( x ) E λ πε q av c o 2 4 r ≅ e v E o o mv α ≈ + ε + th 16 ln( [ eV ]) ln( [ cm ]) x x c c k c characteristic energy: α ≈ + ε g 16 ln( [ eV ] g [ cm ]) q E D k ε = = 2 e o mv k th Experimentally observed limit for ~ cm gap PPCs: v α ≈ g 20 The Raether limit , 1964 in equilibrium α g=25- 33 in tRPCs!

σ + σ 2 2 σ = v , noise v , avalanche T dV = ( V V ) th dt 1 . 28 Exact solution for a single σ = α − η T electron avalanche! ( ) v d W. Riegler et al., Nucl. Inst. Meth. A 500(2003)144

MC simulation consider only 1 gap V Δ V glass /R ∆ V ‘cell DC model’ I(t)=q δ (t) long transient behavior, 'equilibration time' simple circuit calculation average voltage drop in stationary conditions voltage fluctuations D. Gonzalez-Diaz et al., Nucl. Phys. B (Proc. Suppl) 158(2006)111 D. Gonzalez-Diaz et al., Nucl. Instr. Meth. A 602(2009)713

fluctuations around transient time average field the average field simple analytical estimate the DC limit must satisfy Campbell theorem τ for shot noise + φρ 1 ~ ln( 1 ) t eq a d = −  +  φρ ( ) E V I R 2 a d rms gap o   g q 1   2 rms q   E gap = 1 no dependence on the area A = − φρ − ( ) V d q E E 2 N o o gap g influenced (cell) by the shot! N = τφ A MC if we further assume that ( ) rms Egap /(E o -E gap ) − ~ q a V V t eq / τ gap th − Campbell theorem ( ) V V V Φ [Hz/cm 2 ] = + th o th E + φρ gap ( 1 ) g g a d Φ [Hz/cm 2 ] for float glass the DC model equilibration time typically for the typical values A>1mm 2 observed is ~2-3s. the importance is small. D. Gonzalez-Diaz et al., Nucl. Phys. B (Proc. Suppl) 158(2006)111

electrical ageing (material) avalanche ageing (material+gas) (dry) Next generation experiments From M. Morales, C. Pecharromán, PoS(RPC2012)024 Deposits observed for ~100mC/cm 2 but no degradation of performance! 300 Hz/cm 2 5 years 2pC Q/A = q x ϕ x Δ t = 100 mC/cm 2 S. Gramacho, L. Lopes et al., NIM A 602(2009)775