Proposal for a programme of Neutrino Factory research and development

WP-3 The Target

The Neutrino Factory Target

Lead Author - J R J Bennett

CCLRC, RAL

Schematic diagram of the target and collector area

ParametersProton Beam pulsed 10-50 Hz pulse length 1-2 ms energy 2-30 GeV average power ~4 MW Target (not a stopping target)

mean power dissipation 1 MW energy dissipated/pulse 20 kJ (50 Hz) energy density 0.3 kJ/cm3 (50 Hz)

2 cm

20 cm

beam

Target Developments – so far

1. Mercury Jets

2. Contained Flowing Mercury

3. Granulated Targets

4. Solid targets

5. Solid Rotating Ring

Proton beam

Mercury jet Solenoid

Effective target length ~20 cm

Schematic diagram of the mercury jet target

To mercury pump & heat exchanger

Protons

Tube containing flowing mercury

20 T solenoid magnet

Schematic diagram of the contained flowing mercury target

Solid bar targetNeed to dissipate the heat:

a) water cooling difficult – “dilutes” target

b) radiation cooling not possible

c) need moving target – multiple targets

drive shaft

protons

spoke

solenoid coils

vacuum box

target

Rotating wheel target

1MW Target Dissipation (4 MW proton beam)

tantalum or carbon radiation cooled temperature rise 100 K speed 5.5 m/s (50 Hz) diameter 11 m

Plan View of Rotating Band Target (Bruce King et al)

shielding

rollersAccess

port

rollers

rollers

protonsto dump

cooling

coolingcooling

solenoid channel

1 m water pipes

x

z

The RAL scheme

Large rotating toroid cooled by

Thermal Radiation

This is very effective at high temperatures due to the T4 relationship (Stefans law).

40

41 TTAW

Schematic diagram of the radiation cooled rotating toroidal target

rotating toroid

proton beam

solenoid magnet

toroid at 2300 K radiates heat to water-cooled surroundings

toroid magnetically levitated and driven by linear motors

POWER DISSIPATION

0.01 0.1 1 10 100 1 103

0.01

0.1

1

10

100

1 103

power

MW10 m

10 m

v = 100 m/s

1 m

1 m

100 m

100 m

0.1 m

200 m

20 m10 m

2 m

0.1 m

1 m

2000 m

1000 m

radius/velocity

v = 20 m/s

v = 10 m/s

v = 1 m/s

v = 0.1 m/s

1000 m

10 m

100 m

10000 m

Thermal Shock

Simple explanation of shock waves

inertia prevents the target from expanding until:

the temperature rises by ΔT and the target expands by Δd (axially)

target

Short pulse of protons

Short pulse of protons

Time

t = 0

2d

t > 0

v is the velocity of sound in the target material; is the coefficient of linear expansion

End velocity

Δd

d v t

vTd

vd

t

dV

Shock, Pulse Length and Target Size

If a target is heated uniformly and slowly – there is no shock!

Or,

when the pulse length t is long compared to the time taken for the wave to travel across the target – no shock effect!

So,

if we make the target small compared to the pulse length there is no shock problem.

If No problem!

Assume t = 2 ms, V = 3.3x105 cm s-1 , then d = 0.7 cm

Also need sufficient pulsed energy input.

V

dt

Table comparing some high power pulsed proton targetsFacility Particle Rep. Power Energy Energy Life Number

Rate /pulse density of pulses/pulse

f P Q height width length volume thick material q N

Hz W J cm cm cm cm3 cm J cm-3 days

NuFact protons 50 1E+06 20000 2 2 20 63 20 Ta 318 279 1.E+09Number of pulses on any one section of the toroid 7.E+06

ISOLDE protons 1 3675 0.6 1.4 20 13 0.05 to Ta 279 21 2.E+060.0002

ISIS protons 50 180000 3600 7 7 30 1155 0.7 Ta 3 450 2.E+09

Pbar protons 0.3 1797 0.19 0.19 7 0.25 ~6 Ni 7112 186 5.E+06 Run I 3E12 ppp (Cu, SS, Inconel) Damage

Run II 5.E+12 Damage in one or a few pulses 13335

Future 1.E+13 0.15 0.15 30000

NuMI protons 0.53 0.1 0.1 95 2 C 600

120 GeV Radiation Damage - No visible damage at 2.3E20 p/cm2

4E13 ppp Shock - no problem up to 0.4 MW (4E13 at 1 Hz)8.6 ms Sublimation -OK

Reactor tests show disintegration of graphite at 2E22 n/cm2

NuMI will receive a max of 5E21 p/cm2/year

Beam and Target size

Facility Particle Rep. Power Energy Energy Life Number Rate /pulse density of pulses

/pulsef P Q height width length volume thick material q N

Hz W J cm cm cm cm3 cm J cm-3 days

NuFact protons 50 1E+06 20000 2 2 20 63 20 Ta 318 279 1.E+09Number of pulses on any one section of the toroid 7.E+06

SLC e 120 5.E+03 42 0.08 0.08 2 W/Re 591 1500 6.E+05SLAC 33 GeV Rotating disc, 6.35 cm diameter, 2cm thick 26% Re

Target designed to withstand shock

Radiation damage leading to loss of strength and failure when subjected to shock

FXR e Ta 160 100LLNL 17 MeV Ta 267 10

No damage

RAL/TWI e 100 4.E+04 0.2 25 mm Ta 500 up to 1E+06150 keV Thin foil 0.4 cm wide Range ~10 mm

Failures probably due to oxidation in poor vacuum

Beam and Target size

Table comparing some high power pulsed electron targets

Proposed R&D1.Calculate the energy deposition, radio-activity for

the target, solenoid magnet and beam dump. Calculate the pion production (using results from HARP experiment)

and calculate trajectories through the solenoid magnet.

2. Model the shock a) Measure properties of tantalum at 2300 K b) Model using hydrocodes developed for explosive applications at LANL, LLNL, AWE

etc. c) Model using dynamic codes developed by ANSYS

Proposed R&D, continued3. Radiation cooled rotating toroid

a) Calculate levitation drive and stabilisation system

b) Build a model of the levitation system

4. Individual bars a) Calculate mechanics of the system b) Model system

5. Continue electron beam tests on thin foils, improving the vacuum

6. In-beam test at ISOLDE - 106 pulses

7. In-beam tests at ISIS – 109 pulses

solenoid

collection and cooling reservoir

proton beam

Levitated target bars are projected through the solenoid and guided to and from the holding reservoir where they are allowed to cool.