Nuclear Fusion Energy- The role of the Plasma Focus S Lee & S H Saw Institute for Plasma Focus Studies INTI International University, Malaysia International Workshop on Plasma Science & Applications, 27 & 28 October, Tehran, Iran

Outline of Talk Energy crisis Fusion Energy The role of the Plasma Focus

Scenario: World Population stabilizes at 10 billion; consuming energy at 2/3 US 1985 per capita rate Consumption Shortfall Supply Fossil, Hydro, fission

Estimates of world energy production projected into the future in a scenario

Fusion Temperature attained Fusion confinement one step away Needs x10 to reach ITER Needs another 2x to reach Power Plant

Sizes of JET and ITER

Unlimited clean energy supply no need to restrict the growth of energy consumption, a better standard of living or the growth of population. Man can choose Figure 5: energy consumption into the 22nd century. Such unlimited growth (curve 4 of Figure 5) need not imply unbridled wasteful consumption. The best practice of environmental conservatism could be incorporated into growth, so that efficient and ‘green’ habits become part of the sustained culture of the human race.

Figure 5: Scenario Development of nuclear fusion energy is coming not a moment too soon. The critical point when total available energy starts to decline is seen to be reached just before the middle of this century; thereafter the consumption curve has to drop and Man will have to cope with a decreasing supply unless the increasing shortfall is made up by nuclear fusion energy

Large scale Fusion Experiments Tokamaks: Low density, long confinement plasmas Laser Implosions: Super-dense, sub-nanosecond plasmas Smaller scale Fusion Experiments Pinches: Dense, microsecond plasmas Plasma Focus (PF) An advanced pinch system

Superior method for dense pinches The Plasma Focus produces exceptional densities and temperatures. A simple capacitor discharge is sufficient to power the plasma focus.

Plasma focus (PF) Remarkably copious source of multiple radiations: x-rays, REBs, ions, plasma stream Hence many applications Fusion neutrons even in table top devices Same energy density over 7 orders of magnitude of energy storage 0.1J to 1 MJ Neutron Yield scaling established

THE PLASMA FOCUS (PF) The PF is divided into two sections. Pre-pinch (axial) section: Delays the pinch until the capacitor discharge current approaches peak value. The pinch starts & occurs at top of the current pulse.

Axial Accelaration Phase The Plasma Dynamics in Focus Radial Phase HV 30 mF, 15 kV Axial Accelaration Phase Inverse Pinch Phase

Radial Compression (Pinch) Phase of the Plasma Focus

Dynamic Shock Wave process heats efficiently However the dynamic process also has limitations; as we will see Ultimately limits existing plasma focus in causing a yield scaling deterioration; as we shall see

300J portable (25 kg); 106 neutrons per shot fusion device-at NTU-NIE

INTI UC Centre for Plasma Research -Plasma Focus & Pulse Power Laboratory 10 kV 2 Torr Neon Current: 120 kA Temperature: 2 million oC Soft x-ray burst: 100 Megawatt- 10 ns 23 June 2009 - First test shot of INTI-PF

1997 ICDMP (International Centre for Dense Magnetised Plasmas) Warsaw-now operates one of biggest plasma focus in the world, the PF1000

Scaling Properties 3 kJ machine Small Plasma Focus 1000 kJ machine Big Plasma Focus

Same Energy Density in small and big PF devices leads to: Scalability constant speed factor, [(I/a)/r1/2] for all machines, big or small lead to same plasma energy density from 0.1 to 1000 kJ of storage energy predictable yield of radiation Constant speed factor also leads to constant dynamic resistance, which causes present generation PF’s to suffer scaling deterioration, or neutron saturation- more about this later

One of most exciting properties of plasma focus is its neutron yield Yn Early experiments show: Yn~E02 Prospect was raised in those early research years that, breakeven could be attained at several tens of MJ . However quickly shown that as E0 approaches 1 MJ, a neutron saturation effect was observed; Yn does not increase as much as expected, as E0 was progressively raised towards 1 MJ. Question: Is there a fundamental reason for Yn saturation?

Chart from M Scholz (November 2007 ICDMP) purported to show neutron saturation

Global Scaling Law Scaling deterioration observed in numerical experiments (small black crosses) compared to measurements on various machines (larger coloured crosses) Neutron ‘saturation’ is more accurately portrayed as a scaling deterioration-Conclusion of IPFS-INTI UC research S Lee & S H Saw, J Fusion Energy, 27 292-295 (2008) S Lee, Plasma Phys. Control. Fusion, 50 (2008) 105005 S H Saw & S Lee. Scaling the plasma focus for fusion energy. Nuclear & Renewable Energy Sources Ankara, Turkey, 28 & 29 September 2009. S Lee Appl Phys Lett 95, 151503 (2009)

At IPFS, we have shown that: constancy of axial phase dynamic resitance leads to current ‘saturation’ as E0 is increased by increasing C0. Tendency to saturate occurs before 1 MJ From both numerical experiments as well as from accumulated laboratory data (D-D): Yn= 3x1011Ipinch4.5 Yn= 2x1010Ipeak3.8 Hence the ‘saturation’ of Ipeak leads to saturation of neutron yield Yn

Scaling for large Plasma Focus Targets: IFMIF (International fusion materials irradiation facility)-level fusion wall materials testing

Fusion Wall materials testing at the mid-level of IFMIF: 1015 D-T neutrons per shot, 1 Hz, 1 year for 0.1-1 dpa- Gribkov

Fast capacitor bank 10x PF1000-Fully modelled- 1 Fast capacitor bank 10x PF1000-Fully modelled- 1.5x1015 D-T neutrons per shot Operating Parameters: 35kV, 14 Torr D-T Bank Parameters: L0=33.5nH, C0=13320uF, r0=0.19mW E0=8.2 MJ Tube Parameters: b=35.1 cm, a=25.3 cm z0=220cm Ipeak=7.3 MA, Ipinch=3.0 MA Model parameters 0.13, 0.65, 0.35, 0.65

Ongoing IPFS numerical experiments of Multi-MJ Plasma Focus

50 kV modelled- 1.2x1015 D-T neutrons per shot Operating Parameters: 50kV, 40 Torr D-T Bank Parameters: L0=33.5nH, C0=2000uF, r0=0.45mW E0=2.5 MJ Tube Parameters: b=20.9 cm, a=15 cm z0=70cm Ipeak=6.7 MA, Ipinch=2.8 MA Model parameters 0.14, 0.7, 0.35, 0.7

IFMIF-scale device Numerical Experiments suggests the possibility of scaling the PF up to IFMIF mid-scale with a PF1000-like device at 50kV and 2.5 MJ at pinch current of 2.8MA

Scaling further- possibilities 1. Increase E0, however note: scaling deteriorated already below Yn~E0 2. Increase voltage, at 50 kV beam energy ~150kV already past fusion x-section peak; further increase in voltage, x-section decreases, so gain is marginal Need technological advancement to increase current per unit E0 and per unit V0. We next extrapolate from point of view of Ipinch

Scaling Plasma Focus from Ipinch using present predominantly beam-target in Lee Model code

1. Using above Fig compute Pout at 1 Hz assume efficiency 0. 3 2 1.Using above Fig compute Pout at 1 Hz assume efficiency 0.3 2. Then compute E0 budget to generate the required Ipinch at each point; so as to get Q=2

What we need for Focus fusion energy based on D-T (note: 1 D-T neutron has 14.1 MeV of KE) Choose 24 MA point from above graph: Ipinch : 24 MA D-T n from scaling: 3x1019 Kinetic energy: 64 MJ Rep rate: 1 shot per second Then Pfusion (0.3 efficiency): 20 MW If E0=10MJ; input power at 1 Hz 10 MW Net Power 10 MW Technical Requirement: Ipinch= 24MA using E0=10MJ; Rep rate required: 1 Hz

Thermonuclear Plasma Focus Reason why PF fusion is beam-target is PF temp not high enough. If use additional external heating from present 1 keV to 10 0r 20 keV, then Yth is dominant

Thermonuclear Plasma Focus

Thermonuclear fusion in PF with additional heating: Tech. Targets Select a point from Fig 3 for discussion 10MA point at 20keV gives 3x10^19 D-T n /shot This is equivalent to (Fig 1) b-t at 24 MA At 1 Hz eff 0.3 (Fig 2) gives 20 MW If require Q=2 (ie net power of 10 MW) TechnologicalTargets: 4 MJ to generate 10MA 6 MJ to provide additional heating to 20keV

Plasma Focus Reactors Beam-target regime improvement in technology is required: to generate 24 MA pinch current from 10MJ at 30kV Thermonuclear regime: plasma focus operation; with 10 MA from 3.5 MJ, no High voltage limit then use additional heating (6 MJ budget) to reach 20 keV Enhancement techniques: Radiative collapse induced by Kr or Xe doping Current injection using current-steps or beam injection

Radiative collapse increases number density Yield proportional to n2, volume and duration n2 ~ rmin-6 Volume x duration ~ rmin4 Thus yield ~ rmin-2; if compression increased 100 times, yield increases 10,000 times Present radiative collapse involves hot spots containing only small proportion of pinch particles Need gross (column) collapse

Thus radiative collapse is demonstrated in the numerical experiments Pease & Braginskii postulated that D pinch may undergo radiative collapse at 1.6 MA (so-called P-B current) Krypton PF undergoes collapse much more easily, even below 105K, due to increased 1.thermodynamic degrees of freedom and 2. radiative degrees of freedom Our model code includes thermodynamic effects and radiative effects coupled to the dynamics. Thus radiative collapse is demonstrated in the numerical experiments

Numerical Experiments on 3 kJ PF demonstrating pinch column undergoing radiative collapse at optimum presssures 0.1 Torr 0.5 Torr 0.9 Torr 1.1 Torr

Small (3kJ) PF Pinch undergoing column radiative collapse at pinch currents as low as 80 kA

Kr- doped deuterium PF shows order of magnitude neutron yield enhancement To learn to utilize this effect for large PF yield enhancment through radiative cooling and collapse

Conclusion: Tokamak programme is moving steadily towards harnessing nuclear fusion energy as a limitless clean energy source for the continuing progress of civilisation Alternative and smaller scale experiments will also play a role in this most challenging technological development – eg in neutron source at level of IFMIF Scaling towards fusion reactor regimes is discussed; dependent upon technological advancement in production of larger currents from a budget of stored energy Compression enhancement from radiative collapse of Kr-doped D-T PF also being experimented with numerically.

Nuclear Fusion Energy- The role of the Plasma Focus S Lee & S H Saw Institute for Plasma Focus Studies INTI International University, Malaysia International Workshop on Plasma Science & Applications, 27 & 28 October, Tehran, Iran