Parameters of the NF Target

1
(No Transcript)
2
Parameters of the NF Target Proton 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)
3
Schematic diagram of the RAL radiation cooled
rotating toroidal tantalum target
4

• The New Programme
• Since NuFact04 the RD programme has altered
  significantly
• Simulate shock by passing a pulsed current
  through a wire.
• Measure the radial motion of the wire to
  evaluate the constitutive equations (with 3.).
• Use a commercial package, LS-DYNA to model the
  behaviour.
• Life time/fatigue test. 50 Hz for 12 months.
• Investigate the possibility of widely spaced
  micro- bunches of proton beam to reduce the shock
  impact.

5

• Proposed RD (2004)
• 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.
• 3. 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 - 105 pulses.
• 7. In-beam tests at ISIS 107 pulses.
• 8. Design target station.

6

• Shock, Pulse Length and Target Size
• When a solid experiences a temperature rise the
  material expands. Because of mass inertia there
  will always be a slight lag in the expansion.
  This causes pressure waves to ripple through the
  material. When the temperature rise is relatively
  large and fast, the material can become so highly
  stressed that there is permanent distortion or
  failure - shock.
• Short high intensity beam pulses will give rise
  to shock in a target.
• The shock wave travels through matter at the
  speed of sound,
• where E is Young's modulus of elasticity and ? is
  the density.

7
The time taken for the wave to travel from the
outer surface to the centre is given by If
the beam pulse (tp) is long compared to the
characteristic time ts, then little energy goes
into the target in this time and the shock wave
in the target is reduced. If the target is
small compared to the beam pulse length the shock
is reduced. If No
problem! Must have sufficient pulsed energy
input!
8
The Proton Pulse

• Proton beam macro-pulses and micro-pulses.
• Traditionally we have considered the micro-pulses
  as 1 ns wide and the macro-pulses as 1 ?s wide.
  The temperature rise per macro-pulse is ?T 100
  K.
• For the tantalum bar target, radius 1 cm and
  length 20 cm, then
• The time for the shock wave to travel a radius
  is 3 ms
• The time for the shock wave to travel a half the
  length is 30 ms
• However, in the RAL proton driver scheme with 10
  micro-pulses, it is likely that they could be
  spaced apart by 40 ?s, thus reducing the
  effective thermal shock to only ?T 10 K.

9
Goran Skoro, Sheffield University
10
Pulse Heating Pulsed ohmic-heating of wires can
replicate pulsed proton beam induced shock.
current pulse
tantalum wire
Energy density in the wire needs to be e0 300 J
cm-3 to correspond to 1 MW dissipated in a target
of 1 cm radius and 20 cm in length at 50 Hz.
11

• Transient Conditions
• Assume an electric field E is instantaneously
  applied across a conducting wire.
• Apply Maxwells equations.
• This produces a diffusion equation
• In cylindrical coordinates, where j is the
  current density.
• The solution is

? 1/?0?
12

• The Velocity of the Shock Wave
• Shock travels at the Speed of Sound.
• Can only use small diameter wires of up to 0.4
  mm to get current penetration into the wire.
• Choose a better material

13
Characteristic Times for the shock to travel
across the radius and for the current to
penetrate the wire (square pulse).
14
Doing the Test The ISIS Extraction Kicker Pulsed
Power Supply
Exponential with 20 ns rise time fitted to the
waveform
Voltage waveform
Time, 100 ns intervals
Rise time 100 ns Voltage peak 40
kV Repetition rate up to 50 Hz. Flat Top 300
ns Current Peak 8 kA There is a spare available
for use.
15
Solution for the case of an exponential rise in
current
16
1000 ns
100 ns
j/j0
30 ns
10 ns
1 ns
r/a
Current density versus radius at different times.
Wire radius, a 0.3 mm.
17
j/j0
0.1 mm
0.2 mm
0.3 mm
0.4 mm
0.6 mm
, s
Current density at r 0 versus time (t, s), for
different wire radii (a, mm).
18
The average current density over the wire cross
section versus time (t, s), for various wire
radii, (a, mm).
0.4
0.5
0.3
1 mm
0.2
0.1
19
Effect of different pulse lengths (shown by
arrows), for exponential current rise of 30
ns. Goran Skoro, Sheffield University.
20
Effect of different pulse lengths (shown by
arrows), for exponential current rise of 30
ns. Goran Skoro, Sheffield University.
21
Energy Density in the Wire
22
Pulse Current Requirements
The current, I0, required to dissipate 300 MJ m-3
at the centre of the wire within a time ts, for
different wire radii.
23
heater
insulators
to pulsed power supply
to pulsed power supply
test wire
water cooled vacuum chamber
to vacuum pump or helium gas cooling
Schematic diagram of the test chamber and heater
oven.