A Possible Path Forward Current A Possible Path Forward Current Polarimeter Upgrades EffortsPolarimeter Upgrades Efforts

Based on a proposal by Boris Morozov

- Our experience this year- New detector test this year- The Proposed Test Plan- Detectors and Front-End- Front-End Logic and Digitizer Logic- Digitizers and Trigger Features

PProblems we faced lately with the present system

RHIC CNI polarimeters• Experienced Large changes in leakage current (> 4μA)• Poor resolution (>50 KeV)• “Dead layer” or other instability during with rate issues• Low dynamic range of the Preamps (~11MeV)• Possible Noise pick up due to long distance (~100m) between Preamp

and Shaper• 8-bit WFD limits dynamic range (limits ramp measurement at 250 GeV)• FPGA code limitations: Coupling between the time (T0) and amplitude

measurements

AGS CNI polarimeter• A significant jump in polarization when new detectors were installed• Some WFD digitizer had strong (and uncontrolled) dependence on the

external clock wave form

The Jet• Odd calibration data• Can we reduce the background and reach a lower pt?

What About the Jet?

Significant background specially at low energy!

Odd calibration behaviorWhy do we not see a much cleaner peak before cuts are applied?

New Detector Tests Atoian, Gill, Morozov

• Compare BNL and Hamamatsu large area (1cm x 1cm) Si and strip PIN photodiode detectors. Results show a several advantages to use these devices instead of the strip detectors

• A factor of ~2 better resolution (21 KeV vs. 43 KeV) which allows us to measure elastic carbons at ~ t=-0.005 GeV/c2 at higher analyzing power

• ~ 20 times less bias current after 4 months working on the RHIC beam (0.23A vs. 4 A)

• Simplify the readout electronics as well as DAQ• Did not experience a timing or mass shifts vs rate

5

The Test Plan

• Install two sets of 8-single strip Hamamatsu detectors at the 45 degree location in the AGS polarimeter

• Install new 16 channels of commercial amplifier and shaper system• Trigger Circuitry for the ADC gating and TDC start time• A new set of ADC and TDC system read through VME• Cables are already in place need to be terminated• Need a new DAQ system• This represents a prototype for the RHIC p-Carbon CNI polarimeter

Orders have been placed for the components and expect to have them in hand for the AGS polarized proton start up in late January

• Install similar single strip detectors in the Jet to replace the equivalent of two Jet detectors

• These will be readout in a similar manner to the current Jet system• Allows in situ comparison to the current system• These have to be installed prior to RHIC startup November 20?

Detectors & FrontEndDetectors & FrontEndDetectors: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/cm28 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(5g/cm2)

11

3344

55

66

2212 Si-strips 12 Si-strips detectorsdetectors

32cm32cm8 Si single 8 Si single PIN detectorsPIN detectors

Target axis

Beam axis

Front-End & Digitizer LogicFront-End & Digitizer Logic

Beam

Target

Digitizers & Trigger FeaturesDigitizers & Trigger FeaturesDigitizers: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 wereused for trigger

- protection against multiple pulsing - bunch time synchronization - “Prompt” suppression at the beginning of the bunch.

Backup

Carbon Spectroscopy Carbon Spectroscopy rangerange

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:

EbeamGeV

RecoilAnglerad

RecoilEnergyMeV

/t/(GeV/c)2

T.o.Fns/32cm

2.4 0.0136 0.2 0.0045 169.2

2.4 0.0371 1.5 0.0335 61.8

24 0.0043 0.2 0.0045 169.2

24 0.0119 1.5 0.0335 61.8

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 targetaxis , 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.

Angular Straggling due to Angular Straggling due to MSMS

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/cm2 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 GeV2) is the lowest possible value.

Ebeam = 24 GeV

Errors include AngularStragglin&EnergyResolution

Abacus Count Rate Abacus Count Rate EstimationEstimation

Beam:Energy (Ebeam) = 24 GeVIntensity (Ibunch) = 2.5*1011 protons/bunchFull width (Wbeam) = 0.25 cm

Target: Thickness = 5μg/cm2

Number of nuclei (Nt) = 5*10-6 / 19.9*10-24 = 2.5*1017 /cm2

Full width (Wtarget) = 0.0125 cm

Target efficiency (Teff) = Wtarget / Wbeam = 5*10-2

Luminosity: Luminosity (L) = Ibunch x Nt x Teff = 2.5*1011 x 2.5*1017 x 5*10-2 ≈ 3*1027 /cm2/bunch

Cross-section pC->pC: Average Cross-section (Selastic) ≈ 3 * 10-24 cm2/(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 (Adet) ≈ 1*10-4 Count Rate: Revolution Time (Trev) = 2.7 μs Ramp Time (Tramp) = 0.450 s Count Rate per detector (Rdet) = L x Selastic x Δt x Adet = 3*1027 x 3*10-24 x 0.03 x 1*10-4 ≈ ≈ 3*10-2 events/bunch/det or ≈ 1*104 events/s/det or ≈ 4.5 *103 events/ramp/det

Pile-upPile-up and Dead Time Losses Estimationand 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*Rdet=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.

Cost EstimationCost Estimation

Item Price/item Qty Total

Detector (S3588-09) ~$20 20 ~$400

Ceramic board ~$150 2 ~$300

ADC (MADC32) $6625 1 $6625

Preamps (MSI8) $3082 2 $6164 (One MSI available)

TDC (V767A) ~$4000 1 ~$4000

Shaper (MSCF-16) $8892 1 $8892

VME crate (6023/611) $7783 1 $7783

VME-PC interface (SiS3104/1104) $5500 1 $5500

Twisted Cable (16 pairs, 100m) ~$1500 1 $1500

Labor Cost ? ?

Total Cost ~$41000/~$29000

Blue – available for test’10 set up

SummarySummarySingle 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.