PREX Simulation Update

Transcription

1 PREX Simulation Update Rakitha Beminiwattha Syracuse University 1

2 Outline PREX-II Collimator Plastic Shielding for Neutrons PREX-II Background Radiation Effects of Septum Magnet Fringe Field Summary 2

3 PREX-II Collimator Design References : final summary at elog

4 PREX-II Collimator Prototype Design The collimator is placed about 85 cm from the target and intercepts scattered electrons from 0.78o to 3.8o A hybrid design where water cooled Copper-Tungsten inner cylinder (CW70) contained in a Tungsten rectangular box Estimated to deposit about 2.1 kw of energy Collimator will be water cooled 4

5 Specifications Comparison PREX-I collimator bore has a flat radius of cm (limit above 1.27 deg) PREX-II Prototype-4 (PT4) uses smaller (R1 = cm and R2 = cm) conical collimator bore (limit above 0.78 deg) W-box L=16.5 cm, W=22.7 cm (W R.L = 3.5 mm) CW70 cylinder R=5.1 cm L=10.5 cm (CW70 R.L = 5.6 mm) PREX-I collimator took only about 500 W of energy and radiated about 50 W back into the hall PREX-II collimator estimated to take about 2.1 kw but only radiate about 35 W back into the hall New design minimizes what radiated out to the hall 5

6 Specifications Comparison Radiated out through the Collimator Photons Neutrons E Range (MeV) E<10 E>10 E< <E<10 E>10 Passed to the Beamline from Collimator Interactions PREX-II PREX-I (W/uA) (W/uA) Photons Electrons + Positrons E Range PREX-II PREX-I (MeV) (W/uA) (W/uA) E< E> E<10 E> Total Electrons + Positrons Total E<10 E> Collimator Power Summary PREX-II PREX-I (W/uA) (W/uA) Intercepted Radiated out Into Beamline Deposited

7 Neutron Radiation Spectrum 1 < KineE < 20 MeV KineE < 1 MeV 7

8 Longitudinal Power Distribution (W/uA) PREX-I PREX-II 8

9 PREX-I Transverse (XY) Power Distribution Upstream Downstream 9

10 PREX-II Transverse (XY) Power Distribution Upstream Downstream 10

11 PREX-II Neutron Shielding Design References : elog 2939, 2941 and

12 PREX-II Neutron Shielding Design New collimator concentrates the neutron production to and around the collimator area Neutrons harmful to electronics and other sensitive equipments are around 0.1 to 10 MeV Apply polythene shielding to slow down and/or block harmful neutrons Initial plan was to completely surround the scattering chamber and vacuum box area polythene shielding (default shielding design) Started optimizing the shielding design by moving some parts into the scattering chamber vacuum (Proposed design) Less volume and better practical implementation of shielding 12

13 Default Design : Top View 13

14 Energy Deposit Plots for Default Design Transverse view Longitudinal view Front Shield 14

15 Energy Deposit Plots for Default Design Transverse view Longitudinal view Scattering Chamber Shield 15

16 Proposed Design : Top View 16

17 Proposed Design Copper absorber 17

18 Energy Deposit Plots for Proposed Design Transverse view Longitudinal view Front Shield 18

19 Energy Deposit Plots for Proposed Design Transverse view Longitudinal view Scattering Chamber Shield 19

20 Energy Deposit Plots for Proposed Design Transverse view Longitudinal view In Scattering Chamber Vacuum Shield with NO Absorber 20

21 Energy Deposit Plots for Proposed Design Transverse view Longitudinal view In Scattering Chamber Vacuum Shield with Absorber 21

22 Neutron Shielding Specifications The power deposit into the vacuum shielding must be minimized A 0.5 cm (0.4 R.L.) thick Copper absorber is placed in-front of the shielding With an absorber, power deposited into the shielding can be reduced from 10 W to 3 W at 100 ua (next slide table-1) See next slide table-2 for relative neutron shielding by default and proposed designs 22

23 Neutron Shielding Specifications Table-1 : Plastic Shielding Power Deposit Summary Shielding Area Scattering Chamber Scattering Chamber Attachment In Scattering Chamber Vacuum Total Proposed with CuProposed absorber (W/uA) (W/uA) Default (W/uA) n/a Table-2 : Reduction in Neutron Flux w.r.t PREX-I Neutrons Proposed PREX-II PREX-II with CuE Range Defalut Proposed absorber (MeV) (%) (%) (%) E< <E< >E>

24 PREX-II Hall Background Radiation References : elog

25 Hall Background Radiation The simulation is performed with full geometry for PREXI/II Looked at the radiation intercepted by a plane cylindrical detector (Hall Detector) at about the radius closer to where electronics are kept (At R=2300 cm centered at z=0 cm) Divided the hall into three regions based on vertex Z < Z < -110 cm (US of the target) < Z < 135 cm (from target to end of the septum pipe) < Z < 3400 cm ( from the end of the septum pipe to the dump) 25

26 Hall Background Radiation Comparison Radiation intercepted by the Hall Detector 26

27 Hall Background Radiation Comparison Radiation intercepted by the Hall Detector only from Region 2 27

28 Hall Background Radiation Comparison Neutron Radiation intercepted by the Hall Detector and they are concentrated to Region 2 28

29 Hall Background Radiation Comparison Neutron Radiation intercepted by the Hall Detector only from Region 2 29

30 Septum Magnet Fringe Field Simulation References : elog 2944 and

31 Septum Magnet Fringe Field Simulation The small angle scattered electrons traverse in the beam pipe are extremely sensitive to the fringe field generated in the septum pipe. The fringe field at each end of the septum pipe was modeled according to Paul Brindza's field presentations we believe this may not be the best model representation for the fringe field but gives us an idea about the fringe field Due to the fringe field, according to simulation the radiation in the hall has worsen By extending the magnetic shield by 30 cm at either ends of the septum pipe, radiation can be minimized to the the levels seen with no fringe field. The 30 cm is about the maximum length we can have if we modify the septum pipe installation (according to Alan Gavalya from engineering) 31

32 Septum Fringe Field Effects Fringe field effect on the hall radiation can be seen as an increase in hall radiation The following tables summarize the relative increase in radiation at Hall Detector with respect to PREX-II no fringe field simulation All vertices With with 30 Fringe cm extnd E. Range Field (%) (%) (MeV) E< Photons 500>E> E< Neutrons 0.1<E<10 50>E> E< Electrons + Positrons 500>E> Region 2 With with 30 Fringe cm extnd Field (%) (%) Region 3 With with 30 Fringe cm extnd Field (%) (%)

33 Septum Fringe Field Effects The following table summarizes the absolute power of the hall radiation at Hall Detector Total Power from all vertices PREX-II with PREX-II with E. Range PREX-II Fringe Field 30 cm extnd (MeV) (W/uA) (W/uA) (W/uA) E< Photons 500>E> E<0.10 Neutrons 0.1<E<10 50>E>10 E<10 Electrons + Positrons 500>E> E E E E E E E E E

34 Septum Fringe Field Effects The following tables summarize the absolute power of the hall radiation at Hall Detector based on vertex region Power from Region 2 (vertex range -110<z_0< 135 cm) PREX-II PREX-II with Fringe with 30 cm Field extnd E. Range PREX-II (W/uA) (W/uA) (MeV) (W/uA) E< Photons 500>E> E<0.10 Neutrons 0.1<E<10 50>E>10 E<10 Electrons + Positrons 500>E> E E E E E E E E E Power from Region 3 (vertex range 135<z_0<3400 cm) PREX-II PREX-II with Fringe with 30 cm Field extnd E. Range PREX-II (W/uA) (W/uA) (MeV) (W/uA) E< Photons 500>E> E<0.10 Neutrons 0.1<E<10 50>E>10 E<10 Electrons + Positrons 500>E> E E E E E E E E E

35 Hall Radiation e± Vertex Distributions Background e± vertex distributions for radiation that crossed the Hall Detector 35

36 Hall Radiation Background e± Distributions Background e± K.E. and vertex distributions for radiation that crossed the Hall Detector 36

37 Hall Radiation γ Vertex Distributions Background photon vertex distributions for radiation that crossed the Hall Detector 37

38 Hall Radiation γ Distributions Background photon K.E. and vertex distributions for radiation that crossed the Hall Detector 38

39 Hall Radiation n Vertex Distributions Background neutron vertex distributions for radiation that crossed the Hall Detector 39

40 Hall Radiation Neutron Distributions Background neutron K.E. and vertex distributions for radiation that crossed the Hall Detector 40

41 Current Status Collimator design We have a collimator design that can reach our goals PREX-I blocked only down to 1.27o and generated large background electron,photon, and neutron fluxes downstream (DS) of the collimator at septum and beam pipes PREX-II collimator+shielding reduced these fluxes up-to 90% by blocking electrons down to 0.78o Isolate neutron production to mostly within the collimator Best for shielding Pending heat calculation from engineering for practical considerations Neutron shielding Reduction of neutron flux (0.1<E<10 MeV) by order of magnitude Both Default or Proposed shielding designs work but prefer to use shielding in vacuum due to its advantages Out-gassing may be an issue for shielding placed in vacuum 41

42 Current Status Septum magnet fringe field Results from simulation show that extending magnetic shielding on either side of the septum pipe by about 30 cm remove the fringe field radiation issues This fix would require additional engineering time and cost but it is a very important fix that we need In any case, we can now proceed with our current collimator design and either of neutron shielding designs 42

43 PREX-II Do-To List Simulation based activation studies (for production running and decommissioning) Target chamber, beam line, and HRS' vacuum couplings Septum magnet implementation (require new coils) Polarimeter restorations (Moller and Compton) Resurrect the DAQ system Detector studies New PREX-II lead target construction Raster synchronization Source : 43

44 Supplementary 44

45 Specifications Comparison (Fluxes) Radiated out through the Collimator E Range PREX-II PREX-I (MeV) (10^12 /ua) (10^12 /ua) E< Photons E> Neutrons E< <E<10 E>10 Electrons + Positrons E<10 E>10 Total

46 Hall Background Radiation What is included in the hall background radiation simulation? Target, collimator, scattering chamber, vacuum box, septum magnet, septum pipe, beam pipe Supporting pedestal structure, hall wall and floor, dump 46

47 Fringe Field : Standard 47

48 Fringe Field : 10 cm Add. Shield 48

49 Fringe Field : 30 cm Add. Shield 49