# Presentation: 908580

## High-PowerTargets

- for Neutrino Beams and Muon Colliders

- K.T. McDonald
*Princeton U.*
- NFMCC Collaboration Meeting
- LBL, Jan 25-28, 2009

## Targets for 2-4 MW Proton Beams

*• *10-50 GeV beam energy appropriate for Superbeams, Neutrino Factories and Muon Colliders.
*	*⇒ 0.8-2.5  1015 *p*ps; 0.8-2.5  1022 protons per year of 107 s.
*• *Rep rate 15-50 Hz at Neutrino Factory/Muon Collider, as low as  2 Hz for Superbeam.
*	* Protons per pulse from 1.6  1013 to 1.25  1015.
*	* Energy per pulse from 80 kJ to 2 MJ.
*• *Small beam size preferred:
*	**  *0.1 cm2 for Neutrino Factory/Muon Collider, ** * *0.2 cm2 for Superbeam.
*• *Pulse width  1 s OK for Superbeam, but  1 ns desired for Neutrino Factory/Muon Collider.
*	*
-  Severe materials issues for target AND beam dump.
*	**• *Radiation Damage.
*	**• *Melting.
*	**• *Cracking (due to single-pulse “thermal shock”).
*• *MW energy dissipation requires liquid coolant somewhere in system!

-  No such thing as “solid target only option” at this power level.

## Radiation Damage

- The lifetime dose against radiation damage (embrittlement, cracking, ....) by protons
- for most solids is about 1022/cm2.
- * *Target lifetime of about 5-14 days at a 4-MW Neutrino Factory                                              (and 9-28 days at a 2-MW Superbeam).
- Mitigate by frequent target changes, moving target, liquid target, ...
- 	[Mitigated in some materials by annealing/operation at elevated temperature.]

## Remember the Beam Dump

- Target of 2 interaction lengths * *1/7 of beam is passed on to the beam dump.
- 	 Energy deposited in dump by primary protons is same as in target.
- Long distance from target to dump at a Superbeam,
- 	* *Beam is much less focused at the dump than at the target,
- 	* *Radiation damage to the dump not a critical issue (Superbeam).
- Short distance from target to dump at a Neutrino Factory/Muon Collider,
- 	* *Beam still tightly focused at the dump,
- 	 Frequent changes of the beam dump, or a moving dump, or a liquid dump.
- A liquid beam dump is the most plausible option for a Neutrino Factory, independent
- of the choice of target. (This is so even for a 1-MW Neutrino Factory.)
- The proton beam should be tilted with respect to the axis of the capture system at a
- Neutrino Factory, so that the beam dump does not absorb the captured ’s and ’s.

## Target Options

*• *Static Solid Targets
*	*- Graphite (or carbon composite) cooled by water/gas/radiation [CNGS, NuMI, T2K]
- 	- Tungsten or Tantalum (discs/rods/beads) cooled by water/gas [PSI, LANL]
*• *Moving Solid Targets
*	*- Rotating wheels/cylinders cooled (or heated!) off to side [SLD, FNAL   , Bennett]
*	**- *Continuous or discrete belts/chains [King]
- 	- Flowing powder [Densham]
*• *Flowing liquid in a vessel with beam windows [SNS, ESS]
*• *Free liquid jet [Neutrino Factory Study 2]
*	*

## Static Solid Targets

- Pros:
- 	- Tried and true – for low power beams.
- 	- Will likely survive “thermal shock” of long beam pulses at 2 MW (Superbeam).
- Cons:
- 	- Radiation damage will lead to reduced particle production/mechanical failure on the scale of a few weeks at 2 MW.
- 	- If liquid cooled, leakage of radioactive coolant anywhere in the system is potentially more troublesome than breakup of a radioactive solid.
- Must consider a “moving target” later if not sooner.
- R&D:  Test targets to failure in high-power beams to determine actual operational limits.

## Moving Solid Targets

- Pros:
- 	- Can avoid radiation damage limit of static solid targets.
- 	- Will likely survive “thermal shock” of long beam pulses at 2 MW (Superbeam).
- Cons:
- 	- Target geometry not very compatible with neutrino “horns” except when target is upstream of horn (high energy ’s: CNGS, NuMI).
- 	- If liquid cooled, leakage of radioactive coolant anywhere in the system is potentially more troublesome than breakup of a radioactive solid.
- R&D:
- 	- Engineering to clarify compatibility with a target station for Superbeams.
- 	- Lab studies of erosion of nozzle by powders.
- Personal view: this option is incompatible with Neutrino Factories.

## Flowing Liquids in Vessels

- Pros:
- 	- The liquid flows through well-defined pipes.
- 	- Radiation damage to the liquid is not an issue.
- Cons:
- 	- The vessel must include static solid beam windows, whose lifetime will be very short in the small proton spot sizes needed at Superbeams and Neutrino Factories.
- 	- Cavitation in the liquid next to the beam windows is extremely destructive.
- 	- Leakage of radioactive liquid anywhere in the system is potentially more troublesome than breakup of a radioactive solid.
- R&D:  This option is not very plausible for Superbeams and Neutrino Factories, and no R&D is advocated.

## Free Liquid Jet Targets

- Pros:
- 	- No static solid window in the intense proton beam.
- 	- Radiation damage to the liquid is not an issue.
- Cons:
- 	- Never used before as a production target.
- 	- Leakage of radioactive liquid anywhere in the system is potentially more troublesome than breakup of a radioactive solid.
- R&D:  Proof of principle of a free liquid jet target has been established by the CERN MERIT Experiment.  R&D would be useful to improve the jet quality, and to advance our understanding of systems design issues.
- Personal view:  This option deserves its status as the baseline for Neutrino Factories and Muon Colliders.   For Superbeams that will be limited to less than 2 MW, static solid targets continue to be appealing.

## Palmer (1994) proposed a solenoidal capture system.
Low-energy 's collected from side of long, thin cylindrical target.
Collects both signs of 's and 's, 
 Shorter data runs (with magnetic detector).
Solenoid coils can be some distance from proton beam. 
 4-year life against radiation damage at 4 MW.
Liquid mercury jet target replaced every pulse.
Proton beam readily tilted with respect to magnetic axis.
 Beam dump (mercury pool) out of the way of secondary 's and 's.

- Low-energy 's collected from side of long, thin cylindrical target.
- Collects both signs of 's and 's,
-  Shorter data runs (with magnetic detector).
- Solenoid coils can be some distance from proton beam.
-  4-year life against radiation damage at 4 MW.
- Liquid mercury jet target replaced every pulse.
- Proton beam readily tilted with respect to magnetic axis.
-  Beam dump (mercury pool) out of the way of secondary 's and 's.

- Target and Capture Topologies: Solenoid

- Desire  1014 /s from  1015 p/s ( 4 MW proton beam).
- Highest rate + beam to date: PSI E4  with  109 /s from  1016 p/s at 600 MeV.
-  Some R&D needed!

- R. Palmer (BNL)
- Neutrino Factory Study 2

## Solenoid Capture System for a Superbeam

- 	momentum,                                                        on exiting the solenoid.
*• *If the pion has made exactly 1/2 turn on its helix when it reaches the end of the
- 	solenoid, then its initial *P**r** *has been rotated into a pure *P**φ*,   * P*r* = 0* on exiting
- 	the solenoid.
- * *Point-to-parallel focusing for
*	**	**P**π** *= *eBd / *(2*n *+ 1) *πc.*
- Narrowband (less background)
- 	neutrino beams of energies
- * *Can study several neutrino
- oscillation peaks at once,
- (Marciano, hep-ph/0108181)

- Study both ** and   * *at the same time.
- * *Detector must tell ** from    .
- Liquid argon TPC that can identify slow protons:
- 	 *** **n **** p e**-**X    vs.     p **** n e**+**X*

- (KTM, physics/0312022)

## Simulation of Solenoid Horn(H. Kirk and R. Palmer, NuFACT06)

- Simulation of Solenoid Horn(H. Kirk and R. Palmer, NuFACT06)

*B** vs. **z** *for 3 + 30 m solenoid:

- Results very encouraging, but comparison with toroid horn needs confirmation.

- ⇒* **P**⊥** *minimized at selected *P*tot:

- 3-m solenoid gives 2 narrow peaks in * *spectrum:

- 3+30-m solenoid broadens the higher energy peak:

## 2nd Oxford-Princeton Workshop on High-Power Targets, Princeton, 6-7 Nov 2008

- Thursday AM
- 1. McDonald: Introduction
- 2. Graves: Hg Containment Concepts
- 3. Ding: Hg Jet Optimization
- 4. Park. MERIT Results
- 5. Kadi: Eurisol Liquid Target Studies
- Thursday PM
- 6. Rennich: SNS 3-MW Rotating Target
- 7. Fitton: T2K Target
- 8. Rooney: T2K Beam Window
- 9. Davenne:. Pelletized Target for ISIS
- 10. Hylen: DUSEL Target Options
- 11. Bennett: Solid Target Studies
- 12. Bennett: Absorption in Solid Targets
- 13. Skoro: Visar Studies for Solid Targets
- 14. Loveridge: Helmholz Coils for Wheel Target
- 15. Caretta: Tungsten Powder Jet Target
- 16. Brooks: Model for Production by Low-Density Targets
- 17. Brooks: Pion Production Update

- Friday AM
- 18. Bricault: e- Targets
- 19. Samulyak: Hg Jet Simulations
- 20. Davenne: Hg Jet/Pool Simulations
- 21. Skoro: Simulations of Thermal Shock in Solids
- 22. Simos: Material Irradiation Studies
- 23. Efthymiopoulos: CERN Target Test Facilities
- 24. Hurh: Fermilab AP-0 Target Test Facility
- Friday PM
- 25. Long: Discussion (IDS)

- _[http://www.hep.princeton.edu/~mcdonald/mumu/target/index.html#2nd_OP_workshop](http://www.hep.princeton.edu/~mcdonald/mumu/target/index.html#2nd_OP_workshop)_

## EUROnu WP2 Workshop, CERN, 15-17 Dec 2008

- http://indico.in2p3.fr/conferenceDisplay.py?confId=1586

## T2K Target (C. Densham, RAL)

** ****Graphite rod, 900 mm (2 int.lengths) long, 26 mm (c.2****σ****) diameter.**
** ****20 kW of 750 kW Beam Power dissipated in target as heat.**
** ****Helium cooled (i) to avoid shock waves from liquid coolant,s e.g., water and (ii) to allow higher operating temperature.**
** ****Target rod completely encased in titanium to prevent oxidation of the graphite.****   **
** ****Pressure drop ~ 0.8 bar available for flow rate of 32 g/s.**
** ****Target to be uniformly cooled at ~400°C to reduce radiation damage.**
** ****Can remotely change the target in the first horn.**
** ****Start-up date: 1****st**** April 2009.**

## Extrapolating NuMI 0.3 MW Targeting to a 2 MW beam (J. Hylen,FNAL)

-  **NuMi target: graphite fin core.**
** ****Water-cooling tube provides mechanical support.**
** ****Target is upstream of the horn.**

-  **Nova target for 0.7 MW.**
** ****Upstream of horn.**
** ****Graphite fins, 120 cm tota.l**
** ****Water-cooled Al can.**
** ****Proton beam ******** = 1.3 mm.**

-  **DUSEL target for 2 MW.**
** ****Embedded in horn.**
** ****Graphite fins in water-cooled can should be viable to 2 MW.**

## Target for the CERN SPL at 2.2 GeV and 4 MW (M. Dracos, Strasbourg)

** ****50-Hz beam ******** substantial electromechanical challenges for pulsed horn.**
** ****Target inside horn.**
** ****Hg jet target often considered, but would a solid (or powder target work? **

## U Target for 0.5-MW e Beam (Bricault, TRIUMF)

## SNS 3-MW Target Option (Rennich, ORNL)

- 30 rpm with 20-Hz pulse frequency and 1-s pulse length, 7-cm diameter.
- Water cooled by 10-gpm total flow.
- Design life: 3 years.

- Concentric Shaft
- Channels

- Gun Drilled Hub

- Tantalum Clad
- Tungsten Blocks

- Circumferential Manifolds

- Shroud Cooling
- Channels

- Proton
- beam

## Material Irradiation Studies (Simos, BNL)

- BNL BLP Studies:
- Tantalum (0.25 dpa):

- Water-cooled/Edge-cooled TRIUMF target (1022 *p*/cm2):

- BNL BLP Studies:
- Carbon (0.25 dpa):

## Pelletized Target Option for ISIS (T. Davenne, RAL)

- Target being in pellet form allows high temp operation without high stresses
- No cooling water to moderate neutron flux
- Scope for more than 160kW?
- Ref: Sievers (2003)

- 800MeV, 160kW, 50Hz
- 90kW heat removed in water

- Section view of target concept:

## Fluidized Powder Targets (O, Caretta, RAL)

-  **Powders propelled (fluidized) by a carrier gas flow somewhat like liquids.**
** ****Powder grains largely unaffected by magnetic fields (eddy currents).**
** ****Flowing powder density ~ 30% of solid.**

**Carrier = air at 3 bar**

**Carrier = helium at 3.5 bar**

**Carrier = helium at 2.5 bar**

**Carrier = helium at 1.5 bar**

-  **Mechanics of a quasicontinuous flow system are intricate, but good industry support.**
** ****Erosion a critical issue: ceramic inserts?**

## Solid and  Powder Target Studies (R. Bennett, RAL)

** ****Studies with fine tungsten wires pulsed by high currents indicate that such wires could survive the “shock” from 4 MW proton pulses if the target is operated at high temperature ******** continual annealing.**
** ****A Static tungsten target would melt in a 4 MW beam, so need moving target (wheel?).**

-  **A low-density powder target can be advantageous for a high-Z material with large pion absorption.**
** ****Model: if p = pion production in nominal density target, and a = fraction of pions absorbed in this target, then the yield is**
**Y(f) = f p (1 – f a)     where f = fraction of nominal density.**
**Y is maximal for f = 1 / 2 a,    so if a > 1⁄2, better to use f < 1.**

## CERN MERIT Experiment (Park, BNL)

- Proof-of-principle demonstration of a mercury jet target in a strong magnetic field, with proton bunches of intensity equivalent to a 4 MW beam.
- Jet disruption suppressed (but not eliminated by high magnetic field.
- Particle production remains nominal for several hundred s after first proton bunch of a train.

## Hg Cavitation Simulations (Samulyak, BNL)

- 15 s                30 s              45 s

- “Transparent mercury”:

- Exterior view:

## Damage by Mercury Droplets (Davenne, RAL)

- A 3-mm-diameter mercury droplet impacting a stainless steel plate at 75 m/s is predicted to cause significant damage.
- Ti-6Al-4V is predicted to be more resistant to damage due to higher ultimate strength and shear strength.

- Model: A drop of radius *r* and density ** vith velocity *v* causes pressure                    *P = F / A ~  (****p / ****t) / **** r**2** ~ [2 m v / (r/v)]  / **** r**2** ~ 8 **** r**3** **** v**2** / 3 **** r**3**,      **                        ** **P ~ 8 **** v**2** / 3  *independent of the radius!
- Example: **mercury *= 13.6e3, v = 100 *m/s  *P ~ 325 *MPa ~ tensile strength of steel.
- The velocity of an atom of mercury vapor at room temperature is *200* m/s.

## Mercury Target Facility Issues (V. Graves, ORNL)

**ORNL can extend the studies of a mercury target facility, begun in Neutrino Factory Study 2, in the context of the International Design Study for a Neutrino Factory. **
**A small effort in underway to design a mercury collection pool (beam dump)**

## Mercury Beam Dump Simulations (T. Davenne, RAL)

**A 20-m/s mercury jet causes significant agitation as it enters the mercury collection pool.**
**Mitigation of this agitation by baffles or a pebble bed (Study 2) should be (re)considered.**

## Future Target Test Facilities at CERN (I. Efthymiopoulos, CERN)

**Options include:**
**Old WANF tunnel:**
**A new area associated with the PS2 (2016):**

## AP-O Target Test Facility (Hurh, FNAL)

## Option for Follow-On Studies (without Beam) at ORNL (V. Graves, ORNL)

- A new fusion test facility in bldgs 7625, 7627 will be completed in late 2008.
- Several 10-MW power supplies available.
- LN2 dewar 20-t overhead crane, equipment pit.
- Could begin with zero field studies (nozzle optimatization, Hg splash in pool,....)
- Eventual option to use MERIT magnet at 15 (or 20!) T.

- Bldg 7625

- Bldg 7627

- Vertical field power supplies (capability of each)
- 650V peak
- 15,000 A pulsed > 5 sec
- Voltage and/or current can be controlled by SCR gate waveform control