1. 1 August 20091 CNI Carbon Polarimeter for AGS G. Atoian, H. Huang, Y. Makdisi, B. Morozov, A. Zelenski - Introduction - Detectors and Front-End - Front-End Logic and Digitizer Logic - Digitizers and Trigger Features - Carbon Spectroscopy Range - Angular Straggling - Count Rate Estimation - Pile up and Dead time loss Estimation - Cost - Time Table - Summary

2. 2 August 20092 Introduction Large changes in leakage current (> 4μA) Poor resolution (>50 KeV) Probably “Dead layer” instability during run Low dynamic range of the Preamps (~11MeV) Noise pick up due to long distance (~100m) between Preamp and Shaper Result's dependence on detector-to-detector!! Small solid angle 8-bit WFD limits dynamic range FPGA code limitations Some problems with present system: Besides that, AGS polarimeter showed several “puzzles” during run’09. For example, it gave “high” polarization results with detectors with a small leakage current, while detectors with large leakage current gave a reasonable polarization value. Some WFD digitizer had strong (and uncontrolled) dependence on the external clock wave form. Proposed system is based on Hamamtsu single PIN Photodiode. The detectors (and FrontEnd) have been tested on Tandem and RHIC’09 runs. It showed a good and stable performance. Trigger are based on time filtering and decoupled from the amplitude measurement. DAQ system are built around 11-bits conventional Peak Sensing ADC and dead-time less TDC. A simple and mature software technique could be applied to such system. This kind of setup could be viewed as a prototype for future RICH CNI Carbon polarimeters.

3. 3 August 20093 Detectors & FrontEnd Detectors: Hamamtsu Single PIN photodiode for direct detection (S3588-09) Each detector has 30mm x 3mm active area and ~300 μm thickness and placed along the beam axis. The typical dead layer is 60 μg/cm2 8 detectors/per port placed on the existing (+/- 45°) vacuum ports. Front End: Charge sensing Preamps/Shapers (MSI-8 & MSCF- 16) connected to the detectors through the 0.5 m long low capacitance coax. The Shaper has two outputs: Digital (Time,CFD) – min delay 5ns with CFD –Walk: for 30ns input risetime, max 1ns (dynamic range 100:1) Analog – σ = 100 - 400 ns. PZ compensation: range 4 μs - ∞ Dynamic range: - 33 MeV Shaper has remote control capability. Ultra thin Carbon ribbon Target (5  g/cm 2 ) 1 3 4 5 6 2 12 Si-strips detectors 32cm 8 Si single PIN detectors Target axis Beam axis

4. 4 August 20094 Front-End & Digitizer Logic Beam Target

5. 5 August 20095 Digitizers & Trigger Features Digitizers: The Peak sensing ADC(MADC-32) is used for deposit energy measurement -11 bits - 0.8 μs dead time - 10 ns Time Stamp - VME The Dead Time-less TDC (V767A) is used for TOF - 0.6 ns bin width - 10 ns double pulse resolution - VME Triggers: The Shaper time filtering output with CFD discriminator & fast NIM logic were used for trigger - protection against multiple pulsing - bunch time synchronization - “Prompt” suppression at the beginning of the bunch.

6. 6 August 20096 Carbon Spectroscopy range According to Tandem results one can detect 0.2 MeV carbon recoil by using Hamamtsu PIN Photodiode with MIPs noise cut (~80 KeV for 300μm). Assuming that, for AGS beam energies the pC -> pC kinematic gives: Ebeam GeV RecoilAngle rad RecoilEnergy MeV /t/ (GeV/c) 2 T.o.F ns/32cm 2.40.01360.20.0045169.2 2.40.03711.50.033561.8 240.00430.20.0045169.2 240.01191.50.033561.8 At recoil angle of 37mrad the literal displacement will be 12mm at 32cm target-detector distance. Hamamatsu S3588 has 3mm X 30mm sensitive area. By setting detector at centre of the target axis, one can cover this angular interval (the recoil energy is ~1.5 MeV) The analyzing power varies from ~ 0.035 to ~0.02 at /t/ range of [0.0045 – 0.0335] (GeV/c) 2. It should be noted: - unlike RHIC, there is no T.o.F. limitation at that range; - “prompt” events can be fully rejected at flattop (bunch length ~30ns) and ~45% at injection (140ns); - measurement range can be extended down to ~0.002 (GeV/c) 2 by minimizing electronic noises.

7. 7 August 20097 Angular Straggling due to MS Another limitation for low /t/ value comes from the Multiple Scattering in carbon target. The Carbon energy 0.15 MeV has Angular Straggling with σ =14mm for 5μg/cm 2 target. For 1 MeV recoil energy the angular straggling is σ = 1.5mm. The Angular Straggling is dominating factor to overall angular spread of low energy carbon recoils. The separated kinematic range elastic-inelastic (the first excited carbon state at 4.4 MeV) is ~0.15 MeV - >1.0 MeV. So, the kinematic restriction shows that the ~0.15 MeV carbon recoil energy (/t/=0.0034 GeV 2 ) is the lowest possible value. Ebeam = 24 GeV Errors include AngularStragglin&EnergyResolution

8. 8 August 20098 Abacus Count Rate Estimation Beam: Energy (E beam ) = 24 GeV Intensity (I bunch ) = 2.5*10 11 protons/bunch Full width (W beam ) = 0.25 cm Target: Thickness = 5μg/cm 2 Number of nuclei (N t ) = 5*10 -6 / 19.9*10 -24 = 2.5*10 17 /cm 2 Full width (W target ) = 0.0125 cm Target efficiency (T eff ) = W target / W beam = 5*10 -2 Luminosity: Luminosity (L) = I bunch x N t x T eff = 2.5*10 11 x 2.5*10 17 x 5*10 -2 ≈ 3*10 27 /cm 2 /bunch Cross-section pC->pC: Average Cross-section (S elastic ) ≈ 3 * 10 -24 cm 2 /(GeV/c) 2 at –t = 0.003÷0.03 interval /t/ range (Δt) = 0.03 (GeV/c) 2 Angular acceptance: Detector size = (0.3cm X 3cm) Target-Detector distance = 32cm Acceptance (A det ) ≈ 1*10 -4 Count Rate: Revolution Time (T rev ) = 2.7 μs Ramp Time (T ramp ) = 0.450 s Count Rate per detector (R det ) = L x S elastic x Δt x A det = 3*10 27 x 3*10 -24 x 0.03 x 1*10 -4 ≈ ≈ 3*10 -2 events/bunch/det or ≈ 1*10 4 events/s/det or ≈ 4.5 *10 3 events/ramp/det

9. 9 August 20099 Pile-up and Dead Time Losses Estimation There are two main drawbacks using conventional ADC: a possible pile-up and dead time losses. Assume that the rise time of the digitized pulse is ~150 ns (analog output). Signal to background ratio at ~50% prompts events suppression is ~ 1 (RHIC test results) So, the total raw rate per detector would be ~ 2*R det =20 KHz/det. It gives a pile-up of ~0.3%. MADC32 has 0.8 μs dead time and one gate for 8 channels. It will give ~6% losses at the rate of 10 KHz/det. It should be noted that the pile-up reduction is important, because pile-up “introduces” direct systematic shift to polarization value, while dead time losses increase the measurement time for given statistics only.

10. 10 August 200910 Cost Estimation ItemPrice/itemQtyTotal Detector (S3588-09)~$2020~$400 Ceramic board~$1502~$300 ADC (MADC32)$66251 Preamps (MSI8)$30822 $6164 (One MSI available) TDC (V767A)~$40001 Shaper (MSCF-16)$88921 VME crate (6023/611)$77831 VME-PC interface (SiS3104/1104)$55001 Twisted Cable (16 pairs, 100m)~$15001$1500 Labor Cost?? Total Cost~$41000/~$29000 Blue – available for test’10 set up

11. 11 TIME Table One year ago, we had a plan to set a test system for AGS. Some work (pulling cables, ceramic boards) has already been done. Also, we have all hardware to start software development right now. But goal is, as we understand, to set hardware in AGS tunnel for beginning of November’09. So, roughly, the time tables look like this: 1.Ordering Detectors, Preamps/Shapers and PC - Aug.,30? (usually delivery time - 4 weeks, PC - 2 weeks) 2.Pulling cables to electronics room and terminating them - Sep.,15 3.Setting necessary VME electronics with PC in DAQ room and starting development DAQ software - Sep.,15 4.Modifying r.f. shielding for two ports - Oct., 1 5.Mounting detectors to flanges and tested by using alpha source - Oct., 15 6.Mounting ports to AGS polarimeter and connecting detectors to DAQ - Nov., 1 7.Starting debuging DAQ - Nov., 15 Men-Power: Hardware ?? Software ??

12. 12 August 200912 Summary Single SI PIN Photodiode gives good performance in terms of the energy and time resolutions, dead layer uniformity, rate behavior and noise suppression. It is very robust set up, easy to handle and… also cheap. The conventional DAQ with modern Peak Sensing ADC (thanks to MADC32) is also simple and well suitable for our Purpose, especially, if one uses the shaper filtering and prompts noise suppression on the level of the events triggers. Besides that it is programming without any “magic touch” technique. Estimate less than 0.3 men-year for DAQ software development. The detectors set up and DAQ are based completely on commercial available devices. Summarized main features of the proposed system are: Good resolution (<25 KeV) Constant value of Dead Layer Large dynamic range of Preamps (33 MeV) Short distance (~2m from Preamps to Shaper) There are no dependence from detector-to-detector Large solid angle (~twice more compared to the present setup) 11-bits dynamic range Small leakage current (<0.2μA) Conventional fast ADC with 800ns dead time and dead-time less TDC.