Target

Target Working Group:• Greg Smith• Silviu Covrig• Mark Pitt• Konrad Aniol

Greg Smith (Jlab)MOLLER collaboration meetingSeptember 18, 2009

Summary of Target working group progress:We are busy building a ½ power prototype target…

(aka the Qweak target)

Outline:• Performance

scaling• Cryo capacity• Design concept

Target Specifications

• 150 cm LH2 (17.5% X0) at 20K, 35 psia• 5x5 mm2 raster area• 85 µA beam current• Total cooling power required 5 kW • 2 kHz helicity reversal frequency• Target noise contribution to asymmetry

width ΔA ~ 26 ppm < ~ 5% contribution to ΔA• Minimize window bkg • Safe & reliable ops

Design by CFD

GRS

Heater

Cell

Heat Exchanger

Raster

H2 Release/Safety

Window

Dummy

CFD calculations by S. Covrig (Jlab)

Design Considerations

Knobs to turn:• P & T• Vflow

• Araster

• nhelicity

• nraster

• Intrinsic φbeam

• Cell/Flow design• Window design

Constraints:• Ibeam & Ltgt

• Window bkg• Safety issues• Available Pcooling • Head• ΔAstat

• Time available• ASME

compliance6/24/2009GRS

LH2 Targets for Parity Violation

p / T / psia/K/kg/s

Lcm

P/I / EW / μA / GeV

Pv

W/cm3dbeam

mmΔρ/ρ

%δρ/ρppm

sample 25/20/0.6 40 700/40/0.2 396 2 1<1000

@60Hz

happex 26/19/0.1 20 500/35-55/3 765x56x3

?100

@30Hz

pv-a4 25/17/0.13 10 250/20/0.854 310 1.7 0.1392

@50Hz

e158 21/20/1.8 150 700/12/48 467 1 1.5<65

@120Hz

G0 25/19/0.3 20 500/40-60/3 346 2x2 <1.5<238

@30Hz

Qweak 35/20/1 35 2500/180/1.1 245 5x5<45

@250Hz

MOLLER 35/20/1 150 5000/85/11 120 5x5<26

@2000Hz

m

5

0%

50%

100%

150%

200%

250%

0 20 40 60

Incr

ease

in r

unni

ng t

ime

(%)

Target Asymmetry Width (ppm)

Target Boiling Penalty

2 kHz

500 Hz

30 Hz

Extrapolating Performance

Need similar performance to Qweak. Penalty rises rapidly with target noise & with flip rate:

FractionalTgt Single Full Extra Increase

boiling Raster Target Beam Helicity Mass OctantStatisticalBeamtime Abovewidth width length current Reversal Flow Rate width Required Counting(ppm) (mm) (cm) (uA) (Hz) (kg/s) (MHz) (ppm) (%) Statistics

G0: 238 2 20 40 30 0.29Qweak: 34 5 35 180 250 1.08 800 140 6% 1.03Moller: 30 5 150 85 2000 1.08 19125 81 14% 1.07

Power 2 -1 -1 0.4 1

Scaling the G0 Target Performance

This dependence determined empirically from a single test which mimicked nhelicity flipping using gate widths, and the Hall C standard pivot tgt. This is a bold extrapolation given how little we still understand it… Not reliable.However, part of the gain is purely statistical. That is reliable!

Would like more flexibility here!We know this knob works!

Option 7x7 mm2 ?

Note: G0 achieved σboil = 100 ppm with 3x3 mm2 raster. G0 achieved σboil = 68 ppm with 2* the pump head.

Extrapolating Performance

0.4

weak Hz2000

Hz30

l/s15

l/s4

μA40

μA85

cm20

cm150

5x5

2x2G0Q

Qweak = 238 ppm x 0.16 x 7.5 x 2.1 x 0.27 x 0.19 = 31 ppm

Raster Ltgt Ibeam Massflow nhelicity

Dependence on G0 target massflow was cubic! Here we take it to be linear (ultra-conservative).

Linear: 0.27 ( 31 ppm)Quadratic: 0.071 ( 8 ppm)Cubic: 0.020 ( 2 ppm!!!)

Note: At 2 kHz flip rate, expect ΔA(stats) = 78 ppm.Need σboil ≤ 26 ppm to keep runtime penalty <

10%

Msrd 30 Hz Δρ/ρ in Hall AFrom Armstrong, Moffit & Suleiman (2004)Machined 15cm LH2 beer can cellsMeasured in Hall A with lumis

Confirms we win with Araster & νfan

G0 Raster & Pump ScalingS. Covrig et al., NIM A551, 218 (2005).

31 Hz pump

Measured width vs raster size(stats & tgt noise in quadrature)

42 Hz pump

6/24/2009GRS

10

The statistical width is given by:

1. We can reduce the relative contribution of the target boiling term by going to higher helicity reversal frequencies (increased counting).

2. Tests (VPI/Jlab/OU, June 2008) with a Hall C standard tgt indicate that the boiling term drops with frequency as:

Higher helicity reversal rates2target

2countingstat

4.0

Hz30targ f

Hz30

constant targ

80 μA60 μA40 μA20 μA

Measured

Cryo re-summary

• New 4 kW ESR-II– Available 2013 – 2014?– Nominally 4.5 K, 3 atm supply– Return at 2.5 atm (only ½ atm ΔP!)– Possibilities for 6 kW at 15 K ?

• Old 1.2 kW ESR will survive• Advised to plan for a hybrid HX ala

Qweak

• Excess CHL capacity a possibility (unofficially)

3 kW Hybrid Heat Exchanger

87.3 cm long, 27.3 cm diameter

• Cooling Power >3000 W!

• Combine capabilities of both 4K and 15K refrigerators hybrid HX

• 4 K: 2 layers, 2.4 kW @20 g/s

• 15 K: 1 layer, 900W @17g/s

• 24 liters of LH2.

• CFD: head & freezing.

• Head: 0.6 psi @ 1 kg/s

• Doesn’t freeze despite 4K coolant

• Basic design performance calculated analytically (counterflow HX):

Loads/Capacities: CHL 6GeV vs.12GeV

Unit Loads 6 GeV 12 GeV

North Linac South Linac

2 K (W)

50 K (W)

# 2 K (W)

50 K (W)

# 2 K (W)

50 K (W)

# 2 K (W)

50 K (W)

Static loads

Transfer Line 530 6360 1 530 7000 0.57 228 3990 0.43 302 3010

Original CM’s 16 110 42.25 676 4648 21.25 340 2448 20 320 2200

12 GeV CM’s 50 250 5 250 1250 5 250 1250

Dynamic loads

Original CM’s 72 42.25 3042 21.25 1530 20 1440

12 GeV CM 250 50 5 1250 250 5 1250 250

Totals 42.25 4248 11648 25.25 3598 7938 29.25 3562 6710

Capacities (W)

CHL#1 (W) 4600 12000 4600 12000

% of Full Load 92% 97% 78% 66% CHL#2(W) 4600 12000

% of Full Load 77% 56%

Color key6 GeV ops12 GeV opsBoth

From a talk by D. Arenius at ILC08, Univ. Illinois, Nov. ‘08

!vheatingviscousSo, 3

Viscous Heating

g

v

d

Lfh

g

vKh

g

vvh

L

LL

L

2

2

2

)(

2

22

221

(Abrupt Enlargement)

(Abrupt Contraction,Commercial Fittings)

(Circular Pipe)

Note: ΔP = hL ρ g, Re = v d ρ / μ, e ~ 0.0015 mm for Al pipes

A1, V1 A2, V2=V1*A2/A1

Flow

6.89efficiencypump

Head(psi)(l/s)Flow(W)HeatingViscous Ex: 15 l/s, 2 psi, 80% 250 W

30 l/s 2000 W!

Cooling Power Budget

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

0 1000 2000 3000 4000 5000

4.5K

15K

13K

Cooling Power Requirements

Pb(W) = Ib(μA) (g/cm3) t(cm) dE/dx(MeV/g/cm2) With: Ib=85 μA, ρ=0.072 g/cm3, t=150 cm, Pb=4.5

kW!

Cooling Power (W)

Mass F

low

(g

/s) Coolant Massflows for a 20K

tgt

4K

15K

Pump efficiency 60%Flow rate (liters/s) 15Pump Head (psi) 2Pump Power (hp) 0.5Beam Current (uA) 85Beam Power (W) 4562PID reserve (W) 150Pump heat (W) 75Viscouse heating (W) 345Conductive Losses (W) 50

Total Load (W) 5182

13K

5 kW He ΔP with existing Infrastructure

Supply: Annular space inside 2” od tube, .065” wall, A=0.6 in2

Return: 1 ¼” IPS pipe,Sch5 = 1.66” od, .065” wall, A=1.8 in2

LN2 Supply:Inner pipe 5” IPSOuter pipe 6” IPS Both Sch-10 A=7.4 in2

15 & 20 K: ¾” IPS pipe, Sch-100.884” id, A=0.6 in2

Effective Pipe mass volume ODH timePipe id Area rho(He) flow flow to 19.5% velocity

(in) (in^2) P(atm) T(K) kg/m^3=g/l g/s l/s (h) (m/s) L (ft) dP (psi) Pipe0.861 0.582 3 4.5 129.7 47 0.362 3.02 1.0 300 0.68 4K supply3.076 7.433 2.5 20 6.1 47 7.701 3.02 1.6 300 0.02 LN2 supply0.884 0.614 3 15 9.9 183 18.418 0.77 46.5 300 114.33 15/20 K0.884 0.614 2.5 20 6.1 183 29.987 0.77 75.7 300 186.46 15/20K1.756 2.421 3 15 9.9 183 18.418 0.77 11.8 300 3.25 4&5K supplies3.076 7.433 2.5 20 6.1 183 29.987 0.77 6.3 300 0.30 LN2 supply

Transfer Line Anatomy

ODH

• Last time relayed a potential ODH concern– Because of addt’l coolant flow

• However:– Hall engineer (Brindza) says Helium was

never an ODH concern no restrictive orifice• Cuz it rises, escapes hall thru dome vent

– ODH concern is on LN2 supply- it has a restrictive orifice• But we will not use the LN2 supply (as a LN2

supply)• No ODH issue here. But may be a flow

restriction.

Cryo Caveats:

• Both HRS’s (& septa) at 300K• No LN2 usage (supply line

hijacked)• SC Moller solenoid a special

problem– Was a challenge to solve for Qweak

• Minimal loads from the other halls– MOLLER will require ~all of the

coolant– This problem is scheme-dependent

• Some schemes impact other halls less

• No (low) losses in xfer lines• Stay flexible. Meet with cryo early

E158 Liquid Hydrogen Target

Refrigeration Capacity 1000WMax. Heat Load:

- Beam 500W- Heat Leaks 200W- Pumping 100W

Length 1.5 mRadiation Lengths 0.18Volume 47 litersFlow Rate 5 m/s

Disk 1 Disk 2 Disk 3 Disk 4

Wire mesh disks in target cell region to introduce turbulence at 2mm scale and a transverse velocity component.Total of 8 disks in target region.

Prototype for 11 GeV Møller Target Cell

Beam heating 4600 W @85 μANeed δρ/ρ < 26 ppm @ 2000 Hz

Predicted ΔP = 0.5 psid

Prototype: E158-type Target Cell150 cm long, 3” diameter

CFD byS. Covrig, JLab

150 cm

Beam

Shows obvious areas where improvements can be implemented. CFD: Disks do not seem to help!

• First CFD model has clear problems at flow inlet. Still:– ΔT(global) = 0.4 K– ΔT(beam volume) = 1.2 K

• Δρ/ρ = 2%• Clearly due to hot spot in the model

– ΔT = Q/(m CP) = 0.4 K (best you can do)

• Not an onerous situation

Bulk Heating

0

10

20

30

40

50

60

70

80

90

Critical G0 Qweak MOLLER

Hea

t Flu

x (W

/cm

2 )

Window Heat Flux

Film Boiling @ Windows

• MOLLER looks promising: careful design may eliminate film boiling @ windows!

Convective partPredicted by CFD

Total Heat Flux (dE/dx) / Araster

Threshold for film boiling

Two Phase CFD (window boiling)

6/24/2009

Rastered Beam profile on 0.005” Al cell entrance window

CFD simulation by S. Covrig

Entrance Window

Both Phases

Velocity Contours

Vapor Only(BLUE means no vapor there, ie just liquid).

LH2 Flow

Qweak Lessons

• ASME compliance has been a nightmare– Should be less onerous for Moller.

• Biggest problem: lack of management support for early testing– This will not change. Priority goes to “next

experiment”, & polarized targets.– Only solution I see is to build offsite, then

test here (ala G0).• We can build on-site. But then forget early

testing.• ASME complicates this, but it’s still possible

• Hold initial design review early

The End

ASME

Qweak target design authority: D. Meekins

Target Cooling Power Loads

• Beam: Pb(W) = Ib(μA) (g/cm3) t(cm) dE/dx(MeV/g/cm2)

– With: Ib=85 μA, ρ=0.072 g/cm3, t=150 cm, Pb = 4.5 kW!

• Viscous Heating: Pv(W) = 6.89 Flow(l/s) Head(psi) / ε– With: Flow 15 l/s, Head 1.3 psi, ε=60% PV = 225 W

• PID Loop (feedback): need heater power to control T– Reserve ~ 150 W

• Pump heat: Pp (W) ~ 20% (Pump power (hp) * 745.7)– With: pump power = 0.5 hp, Ppump ~ 75 W

• Conductive losses: – Guess, 50 W

Cryo Systems Capacities and Loads in equivalent g/s Rao Nov-10-04

Assumptions:

1. No degradation in the CHL & ESR Cryo Capacities 2. No increase in cryomodule static (vacuum) and dynamic loads 3. No increase in Hall magnet and transfer line static (vacuum) loads

Loads Capacity Present Near term Option -1 Option -2 Option -3 Option - 4 Option - 5Cryo loads Expected FEL @ Present FEL_Off Hall-A_Off SBR_On 4_Kw_On

FEL @ Present

CEBAF Linac 5.5 GeV 188 188 188 188 190 188 188CEBAF Linac 5.8 GeV 196 196

FEL Linac 20 20 20 20 20 20 20 FEL FL03 full power 10 10 10 10 FEL new Injector 5 5 5 5

Halls Base loads on ESR Ref. 11 11 11 11 11 11 11 11Halls Base load on CHL 5 5 5 5 5 5 5 5 Hall-C Moller 2 2 2 2 2 2 2 Hall-A Septa 5

CTF load on CHL 5

Total Cryo loads 224 241 226 208 226 241 249

Cryo CapacitiesCHL Capacity 235 235 235 235 235 235 235 235ESR Capacity 11 11 11 11 11 11 11 11SBR (estimate) 20 204 KW_Capacity_if installed 40 40

Total Cryo Capacities 246 246 246 246 246 266 286

Shutoff Hall-A (Credit) 7Shutoff Hall-C magnets (Credit) 2 2 2 2 2Shutoff Hall-C Target (Credit) 2 2 2 2 2

Available for Targets 22 5 24 42 31 29 41

2004 Cryo Agreement

Confirmed during spring, ‘09 tests: See TN-09-041

Closest Comparison: Qweak

• Still virtual, but many lessons learned• Novel, dual HX technique & design

approved• Use large Araster & vflow (viscous heating

limit)• Cryo-agreement negotiated fall 2004

– thru JROC: all ADs, cryo, tgts, Qweak– Coolant supply methods identified

• High pressure loop higher T, more cooling power, more sub-cooling

• CFD calculations steering cell design• Fast (~300 Hz) helicity reversal

Pmax ConsiderationsLower P:– Don’t go sub-

atmospheric– Thinner windows = less

bkg– Lower warm gas storage

P– Less gas inventory

Higher P:– More cavitation

headroom = Pop – PVP . Cavitation occurs at trailing edge of pump blades when P < PVP . For LH2 PVP(19K) ~ 10 psia.

– Higher boiling temps• Run at higher T

more cooling power• Run at fixed T

more subcooling– Less film boiling

at windows? » No (App. 9.1)6/24/2009

GRSSettled on 35 psia & 20 K

Comparisons

• 2.4 times Qweak

• 17 times G0 forward

• 20 times E158

Moller

Energy Loss (11 GeV, 150 cm LH2)

• Ionization Energy Loss– 4.995 MeV/g/cm2

– ~10% Higher than at lower energies– 54 MeV total (what counts for heat

load)• Bremsstrahlung Energy Loss

– 1.74 GeV ! total– That’s 16%! Forget your focus!

The G0 Target LoopCFD calculation by S. Covrig, UNH