Target Injection Update

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Target Injection Update Cryogenic sabot coil
resistance testing Injector cost savings from new
chamber design Reduced velocity target
injection Remy Gallix, Dan Goodin, Dean Morris,
and Robert Kratz Presented by Ron Petzoldt Naval
Research Laboratory HAPL Meeting March 3-4, 2005
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Non-contacting Electromagnetic Injector (400 m/s)

• An attractive force, self-centering,
  non-contacting accelerator has been proposed for
  IFE target injection (A. Robson)
• With an attractively accelerated sabot, sabot
  current would be imposed in a pre-injector
• A critical issue for this concept is the
  residence time of the sabot current (requires low
  resistivity)

Fr
Fz
High purity aluminum has low density and low
resistivity at cryogenic temperatures
Fr
Accelerating Coil
Sabot Coil
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Attractive Force EM Injector Requires a Long
Inductance/Resistance (L/R) Time Sabot Coil

• L/R must be much greater than acceleration time
  (L/Rgtgt 25 ms)
• where ao is the inner
  radius of a Brooks coil,
• b is the packing fraction, and h is the
  resistivity in W-cm.
• Lowest reported resistivity for ultra-pure Al h
  4x10-10 W-cm and h 2x10-9 W-cm at 15 K in 1
  Tesla field.
• 99.999 pure Al wire
• For ao 0.4 cm and b 0.75 this translates to
• L/R 800 ms (no field) and L/R 160 ms (1
  Tesla)
• In practice, metal impurity, wire winding (cold
  working), and joint resistance can decrease L/R

What L/R can we obtain in a prototypical sabot
coil?
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We Performed a Coil Current Decay Time
Measurement in High Magnetic Field Down to 4 K
The experiment includes three separate coils
Induction field coil
Pickup coil
Induction field circuit
G10 form containing all 3 coils
Sabot coil
We induce a current in the closed sabot coil by
rapidly stopping the induction coil field We
measure pickup coil voltage to determine the
sabot coil current decay time constant
Induction current
Sabot current
Pickup coil voltage
This would be easy except for the addition of
cryogenics and high magnetic field
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Cryogenic Measurements Were Made In up to 0.9
Tesla Magnetic Fields
Pressure relief
Vent
He Liquid
Magnet
Coils
Magnet
G10 box
He gas
Cryostat
Tests were run from 4 K up to room temperature
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Tests were conducted in collaboration with GAs
EM Systems
Magnet tooling
Test area
Some current EM systems projects
Urban Maglev
Superconducting Homopolar motor
EM aircraft Launcher
Leveraging experience in other GA divisions
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Magnetic Field Decreases L/R at Cryogenic
Temperatures
15 K pickup coil V vs t with 0.9 Tesla field
Natural log of 15 K data (B0.9T)
At 15 K (Soldered) L/R 53 ms (B0 T) L/R 32
ms (B0.9 T) 1s / 31.5
but we wanted gtgt25 ms
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Annealing and Welding Coil Substantially Improved
L/R
15 K

• At 15 K (Welded and Annealed), L/R 170 ms (B0
  T), L/R 72 ms (B0.9 T)
• Further improvements may be possible
• - Next step sabot-to-sabot consistency and
  refinement of techniques
• Larger coil size would increase time constant
  but increases mass and cost

This indicates that L/R will be sufficient
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The Magnetic Confinement Concept Substantially
Changes the Target Injection Requirements

• Target survival (gt 25 m/s injection velocity)
• Only one target in chamber at a time
• (gt 32 m/s at 5 Hz)
• At this point, we are evaluating 50 m/s
• 13 cm acceleration at 10,000 m/s2
• Opens door for other injection mechanisms
• (Mechanical, pneumatic, electric, etc.)
• Without gas in chamber, 1 mm placement accuracy
  has been discussed - a challenge to be
  demonstrated
• Without sabot separation and with in-chamber
  tracking, the target flight distance could be
  reduced from 17 m to 10 m

Magnetic confinement should make target
injection easier (i.e. slower)
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Calculations also indicate that plasma heating is
dramatically reduced with a lower gas density
Non-radiative target heating vs time
Plasma density and temperature vs time for DT gas
Non-radiative target heating
In-chamber interval
In-chamber interval
1-D results for 10 m radius chamber 1013/cm3
0.3 mT at 300 K
Prediction non-radiative heat load lt 0.1 W/cm2
at 100 ms after ignition acceptable heat load
Ref Simulation of afterglow plasma evolution in
an inertial fusion energy chamber B.K. Frolov,
A.Yu. Pigarov, S.I. Krasheninnikov, R.W.
Petzoldt, D.T. Goodin Journal of Nuclear
Materials 337339 (2005) 206210
Simplified injection concepts are being evaluated
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Low-speed Mechanical Injector Concepts
OBJECTIVE Inject bare DD targets into
vacuum at 5 Hz (160 million cycles
/year), with v 50 m/s upwards and
acceleration a 10,000 m/s2, without
introducing gas into chamber.
A SOLUTION Use reciprocating pusher to inject a
target every 0.2 s.
OPTIMUM For minimum stroke use maximum constant
acceleration e.g., 10,000 m/s2 for 5 ms
gives v 50 m/s in 125 mm.
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Conceptually- Targets could be Transferred from
Cryogenic Fluidized Bed to Mechanical Injector
Fluidized bed
Targets accelerated out of tray
Target injector

• Many linear actuator options
• Mechanical
• Pneumatic
• Coil gun

Rotary tray
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Injector Actuator Options
Simple spring - doesnt work
Geared Crank or Cam
Insufficient energy per mass
Sinusoidal motion Long stroke bellows Extra
revolutions between strokes
Coil gun
Pneumatic
No dynamic vacuum seal Cooling and electrical
feed-throughs into vacuum
Drive cylinder inside or outside vacuum
Coil or iron insert
Traditional accelerator options are also easier
at low speed - Electrostatic, induction
accelerator, rail gun, .
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A 50 m/s Mechanical Injector Should Significantly
Reduce IFE Target Injection Costs
Mechanical Injection
EM Injection
Target injection cost comparison for an nth of a
kind plant
Assumes 10,000 m/s2 acceleration
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Summary and Conclusions

• Measurement of EM injector sabot coil current
  decay down to 4 K and up to 0.9 Tesla show
  sufficient residence time is achievable
• Magnetic protected chamber substantially changes
  target injection requirements
• Velocities like 50 m/s allow much shorter
  acceleration length
• Alternate injection concepts are being considered
• nth-of-a-kind injection costs should be reduced
  for power plants
• Simplicity and reliability should be enhanced