Target Target Working Group: Greg Smith Silviu Covrig Mark Pitt Konrad Aniol Greg Smith (Jlab) MOLLER collaboration meeting September 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% X 0 ) at 20K, 35 psia 5x5 mm 2 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 V flow A raster n helicity n raster Intrinsic φ beam Cell/Flow design Window design Constraints: I beam & L tgt Window bkg Safety issues Available P cooling Head ΔA stat Time available ASME compliance 6/24/2009 GRS

LH 2 Targets for Parity Violation 5

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

This dependence determined empirically from a single test which mimicked n helicity 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 mm 2 ? Note: G0 achieved σ boil = 100 ppm with 3x3 mm 2 raster. G0 achieved σ boil = 68 ppm with 2* the pump head. Extrapolating Performance Q weak = 238 ppm x 0.16 x 7.5 x 2.1 x 0.27 x 0.19 = 31 ppm Raster L tgt I beam Massflow n helicity Dependence on G0 target massflow was cubic! Here we take it to be linear (ultra-conservative). Linear: 0.27 (  31 ppm) Quadratic: (  8 ppm) Cubic: (  2 ppm!!!) Note: At 2 kHz flip rate, expect ΔA(stats) = 78 ppm. Need σ boil ≤ 26 ppm to keep runtime penalty < 10%

Msrd 30 Hz Δρ/ρ in Hall A From Armstrong, Moffit & Suleiman (2004) Machined 15cm LH2 beer can cells Measured in Hall A with lumis Confirms we win with A raster & ν fan

G0 Raster & Pump Scaling S. Covrig et al., NIM A551, 218 (2005). 31 Hz pump Measured width vs raster size (stats & tgt noise in quadrature) 42 Hz pump

6/24/2009 GRS 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 rates 80 μA 60 μA 40 μA 20 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 Q weak 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 g/s 15 K: 1 layer, 24 liters of LH 2. CFD: head & freezing. Head: kg/s Doesn’t freeze despite 4K coolant Basic design performance calculated analytically (counterflow HX):

Loads/Capacities: CHL 6GeV vs.12GeV Color key 6 GeV ops 12 GeV ops Both From a talk by D. Arenius at ILC08, Univ. Illinois, Nov. ‘08

Viscous Heating (Abrupt Enlargement) (Abrupt Contraction, Commercial Fittings) (Circular Pipe) Note: ΔP = h L ρ g, Re = v d ρ / μ, e ~ mm for Al pipes A1, V1 A2, V2=V1*A2/A1 Flow Ex: 15 l/s, 2 psi, 80%  250 W 30 l/s  2000 W!

Cooling Power Budget Cooling Power Requirements P b (W) = I b (μA)  (g/cm 3 ) t(cm) dE/dx(MeV/g/cm 2 ) With: I b =85 μA, ρ=0.072 g/cm 3, t=150 cm,  P b =4.5 kW! Cooling Power (W) Mass Flow (g/s) Coolant Massflows for a 20K tgt 4K 15K 13K

5 kW He ΔP with existing Infrastructure Supply: Annular space inside 2” od tube,.065” wall, A=0.6 in 2 Return: 1 ¼” IPS pipe, Sch5 = 1.66” od,.065” wall, A=1.8 in 2 LN2 Supply: Inner pipe 5” IPS Outer pipe 6” IPS Both Sch-10 A=7.4 in 2 15 & 20 K: ¾” IPS pipe, Sch ” id, A=0.6 in 2 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 LN 2 supply- it has a restrictive orifice But we will not use the LN 2 supply (as a LN 2 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 Q weak 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 Capacity1000W Max. Heat Load: - Beam 500W - Heat Leaks 200W - Pumping 100W Length1.5 m Radiation Lengths0.18 Volume47 liters Flow Rate5 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 μA Need δρ/ρ < Hz Predicted ΔP = 0.5 psid Prototype: E158-type Target Cell 150 cm long, 3” diameter CFD by S. 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 C P ) = 0.4 K (best you can do) Not an onerous situation Bulk Heating

Film Windows MOLLER looks promising: careful design may eliminate film windows! Convective part Predicted by CFD Total Heat Flux (dE/dx) / A raster 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: P b (W) = I b (μA)  (g/cm 3 ) t(cm) dE/dx(MeV/g/cm 2 ) –With: I b =85 μA, ρ=0.072 g/cm 3, t=150 cm,  P b = 4.5 kW! Viscous Heating: P v (W) = 6.89 Flow(l/s) Head(psi) / ε –With: Flow 15 l/s, Head 1.3 psi, ε=60%  P V = 225 W PID Loop (feedback): need heater power to control T –Reserve ~ 150 W Pump heat: P p (W) ~ 20% (Pump power (hp) * 745.7) –With: pump power = 0.5 hp, P pump ~ 75 W Conductive losses: –Guess, 50 W

2004 Cryo Agreement Confirmed during spring, ‘09 tests: See TN

Closest Comparison: Qweak Still virtual, but many lessons learned Novel, dual HX technique & design approved Use large A raster & v flow (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

P max Considerations Lower P: – Don’t go sub-atmospheric – Thinner windows = less bkg – Lower warm gas storage P – Less gas inventory Higher P: – More cavitation headroom = P op – P VP. Cavitation occurs at trailing edge of pump blades when P < P VP. For LH 2 P VP (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 GRS Settled 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/cm 2 –~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 Loop CFD calculation by S. Covrig, UNH