PREX- 2 Issues. April 11, Kent Paschke

Transcription

1 PREX- 2 Issues April 11, 2014 Kent Paschke

2 What We Learned in PREX-I What Worked: New Septum We now know how to tune it to optimize FOM A T false asymmetry A T is small (<1 ppm Pb, <10 ppm C) and A false will be small if P T is minimized HRS Tune We have a tune and good first-guess optics matrix for a tune optimized for the small detectors Fast Helicity Flipping We know how to control false asymmetries and monitor performance Lead Target Survival > 1 wk, 15 C Injector Spin Manipulation Second Wein and solenoid are calibrated and used for helicity reversal. Important cancellation for systematic beam asymmetries from the polarized source. New Detectors Suitable energy resolution achieved for 1 GeV electrons. <5% precision loss. 26 p.e. s Polarimetry at low energy Moller at 1.3%, Integrating Compton at 1.2% Beam Modulation System Fast beam kicks cancel low frequency noise and improve precision of beam position corrections Problems to resolve: Lead Target Septum Vacuum system Radiation damage in Hall

3 PREX-I Radiation Issues BPM MOLLER POLARIMETER EP Q1 Q2 RASTER BCM COMPTON POLARIMETER DIPOLE Q3 SHIELD HOUSE BEAM DUMP 2x photon signal with lead target ACCESS RAMP LimiAng aperture Failing electronics

4 Vacuum Chamber, Sieve Box beam Target Tungsten Plug: ~2kW, will require water cooling sieve box PREX-I: O-ring here at ~34.5 mrad Redesign area for all metal seals septum

5 Collimation, Beamline, Shielding HRS-L Tungsten beamline collimator collimator Septum Magnet HRS-R scattering chamber collimator sieve box

6 Vacuum System Metal Seals Rubber/plastic O-ring connecting sieve box to scattering chamber

7 Relative Silicon Damage vs. Neutron Energy 100 kev 10 MeV

8 PREX-I: Sources of Radiation photon neutron Photoproduction dominates, not spallation: soft energy spectrum quadratic in target thickness, not linear Neutrons from the target are NOT the problem - the 10% target radiation length is Even with W plug, significant spray into beam pipe and hall target area dump tunnel

9 Poly Shield Neutron Stopping Power simple geometry: target + collimator in spherical poly shield of various thickness 0-1 MeV 1-50 MeV

10 PREX- II: Shielding Strategy 30cm thick Polyethelene hut to moderate neutrons Maximize solid angle coverage of collimator Tungsten collimator down to 0.8 o so whatever gets past the plug gets to the dump Also need improved shielding of septum fringe field at the beampipe Concept ready for detailed design

11 Status Detailed simulaaon of HDPE shield Detailed simulaaon of collimaaon a) Concept is in design/engineering b) Iron concept to shield fringe field Concept ready for design Rakitha BeminiwaMha - Important ques1ons on b) - Ready for detailed design

12 Activation Studies Underway (Lorenzo Zana) Aluminum Vs Stainless Sieve Box alone (1 month decay, 28 days at 70 ua) Aluminum Stainless Sieve Box + collimator (1 month decay, 28 days at 70 ua) Goals: - guide materials choices - guide de- installa1on planning

13 Target Thickness and Uniformity G#H%47= Target uniformity degraded by beam damage. Target #3 "#$%&'(()*./01)257C>:>> Melted after >1week production 7C><>> 7C>>>> G#H%47< Created noise due to raster. Raster synched for lissajous period matching helicity flip, recovered width >CEA>> ),-./(%0045G8;"4=9 >CE:>> Conclusion: Target non-uniformity is NOT a problem G#H%47: >CE<>> >CE>>> >CAA>> > F 7> 7F E,2(JKLKG <> 7< '$)1405 Target #1 U%$17%2)05 G#H%4: "#$%&'(()*./01)237= Targets with thin diamond backing (4.5 % background) degraded fastest. T'$)1405 U%$17%2)05 Thick diamond (8%) ran well and did not melt at 70 ua. 7: 7C7>>> 7C>F>> 7C>>>> ),-./(%0045G8;"479 E,2(JKOQQ Never melted, or even degraded. Last 4 days at 70 ua >CEF>> >CE>>> > < : Summary: target design is PROVEN to be sufficient although maybe limited... maybe only 1 week per A T'$)1405 U%$17%2)05 :

14 Lead / Diamond Target Diamond The ladder will be built for 10 targets. If targets last only 1 week, this is more than enough LEAD Lead (0.5 mm) sandwiched by diamond (0.15 mm) Liquid He cooling (30 Watts)

15 Reviving Known Techniques

16 Optics Calibration Water Cell - 1% rela1ve measurement of Q 2 - H peak on O radia1ve tail - One- 1me only Can this go on a separate target mover? Gas Cell - Could mount on primary target mover, available for repeat measurements - Long, to allow sovware cut on windows. - Cross- sec1on vs angle presents complica1ons - H/He? Ne? Ar? Nilanga, Nickie Saylor

17 Moller Polarimetry High Field Iron Moller Target Align Magnet to beam Align Target Foil to Magnet - New Target Holder OpAcs design (new 4Q spectrometer at 1 GeV) Revive operaaon at 1 GeV (Detectors, DAQ, analysis) (Jim) (Roman)

18 Compton Polarimetry Brian Quinn Laser system - Green at 500W + - Must be revived, disassembled for upgrade DAQ - Old Saclay system is being re1red - rely on integra1ng DAQ (supplement with new coun1ng DAQ?) Photon Detector - Key challenge of integra1ng technique, well known PMT linearity Commission new beamline (Gaskell, UVa) (Michaels, CMU?) (CMU) (Gaskell, UVa, CMU )

19 Polarized Source / Accelerator Fast Flip 120Hz, 240Hz? Spot Size measurement PREX require 10-4 spot size asymmetry (UVa) Injector Spin ManipulaAon flip takes 1me, changes beam. Improve? AdiabaAc Damping Accelerator has refined techniques for delivering well matched beam. Revive exper1se?

20 Revive/Requalify PARITY DAQ - 4 crates, fast (low capacitance) cabling. Noise performance. - Fast event transfer to online monitor/feedback - switch to coun1ng mode BCM - Cri1cal reliance on old 1 MHz down- convertor - New electronics may prove as good. Beam studies? Spectrometer OpAcs Design - Significant changes to design not expected Detectors - Previous design works. - Linearity studies ModulaAon - Undesirable modifica1ons to interface for Qweak. recover. - Do magnet and power supplies remain aver upgrade? - Control sovware revive. Analysis Chain - online monitoring, prompt, post decoding, summaries. Beamline OpAcs Design - Control phase space to avoid mixing energy with difficult- to- measure angle. Septum - Previous design - need to rebuild damaged coils Q1 collimaaon - Previous design? Simplified or improved for acceptance? (Michaels) (?) (Nickie?) (UMass) (UVa?) (Michaels, UVa, +?) (Benesch?) (Michaels?)

21 Luminosity Monitors Qweak : large (few ppm) asymmetries in Lumi and background detectors correlated to main detectors Hall A luminosity monitors have always shown an asymmetry Can we show they don t correlate to the detectors? Linearity issues? Poten1ally important for MOLLER - lessons learned from QWeak may be (?) that you need to understand the lumi, or understand that you are independent of it. (who?)

22 Summary Vacuum Integrity New CollimaAon - engineering/design RadiaAon Shielding - two concepts, ready for design/engineering Target - Previous design works (with higher mul1plicity) Polarimetry - significant work, but technologies are proven OpAcs / Angle calibraaon - Improved by providing redundant techniques, repeatability? Large Range of reviving (improving?) previous technologies

23 Summary Vacuum Integrity New CollimaAon - engineering/design RadiaAon Shielding - two concepts, ready for design/engineering Target - Previous design works (with higher mul1plicity) Polarimetry - significant work, but technologies are proven OpAcs / Angle calibraaon - Improved by providing redundant techniques, repeatability? Large Range of reviving (improving?) previous technologies This list looks easy? Its a terrible list. This is a very challenging experiment. Past results do not guarantee future performance.

24 Summary Vacuum Integrity New CollimaAon - engineering/design RadiaAon Shielding - two concepts, ready for design/engineering Target - Previous design works (with higher mul1plicity) Polarimetry - significant work, but technologies are proven OpAcs / Angle calibraaon - Improved by providing redundant techniques, repeatability? Large Range of reviving (improving?) previous technologies This list looks easy? Its a terrible list. This is a very challenging experiment. Past results do not guarantee future performance.