Capsule Implosions

Platform Purpose

The implosion platforms used in the National Ignition Campaign (NIC) serve several purposes.

"Symmetry Capsules" or "SymCaps" (figure 2 below) are imploded inside laser-heated hohlraums. These are almost identical to ignition capsules except they do not contain a fuel layer but rather a hydrogen-helium gas mixture and serve as a surrogate to measure the shape of the implosion by imaging the X-ray flash emitted by the central hot spot plasma at stagnation. Because these are driven by a shaped laser pulse designed to keep the target on a low adiabat, they generate relatively cool, ~2–4 keV, relatively dense, ~20–40 g/cc, hot spot plasmas.
THD capsules are imploded inside laser-driven hohlraums and are designed to study and optimize the hydrodynamic assembly of the fuel without α-heating in a diagnostics-rich environment. They contain solid cryogenic fuel layers that are hydrodynamically equivalent to DT layers and have a composition of ~74% tritium (T), 24% hydrogen (H), and ~2% deuterium. The neutron yield is around 10¹⁴, which allows both neutron and X-ray diagnostics to work. The shaped laser pulse that keeps most of the fuel nearly Fermi degenerate results in very high densities in the main fuel, ~1000 g/cc, which surrounds a lower-density (~100 g/cc) hot spot with a temperature ~4 keV.
DT ignition capsules (figure 1 below) are imploded inside laser-driven hohlraums and are designed to ignite and burn producing ~10–20 MJ of energy. They contain solid cryogenic DT fuel layers. The laser pulse and target parameters must first be fine tuned precisely in a series of experiments before ignition can be expected. The neutron yield in these experiments can be expected to be in the range of ~10¹⁷– 10¹⁹ depending on the design. The burn is extremely rapid, lasting ~20 ps. Burn average temperatures and densities can be expected to be in the range of ~30 keV and ~1000 g/cc respectively.
Exploding pushers are directly driven targets that produce high-temperature, ~10 keV, relatively low-density (~5 g/cc) environments. The specific conditions depend on the design. Their main function in the NIC is to provide sources of 14-MeV neutrons for diagnostics commissioning. Targets typically consist of thin-walled glass spheres ~2 mm in diameter, filled with DT gas, although other gases can be readily added.

Figure 1: DT ignition implosion configuration.

Figure 2: Symmetry capsule target used for time integrated symmetry measurements. Target includes a low-yield (<10¹² neutrons) DD or DH gas filled capsule. Laser and Target Configuration

The laser and target configurations for this platform are summarized below:

Target	# beams	Laser energy/Pulse width
CH capsule with cryogenic THD layer	192	1–1.5 MJ ignition pulse
CH capsule with cryogenic DT layer	192	1.5 MJ ignition pulse
CH SymCap with H:He gas fill	192	0.3–1 MJ 2-ns Gaussian
Glass capsule with DT fill	192	0.3–1MJ 2-ns Gaussian

Diagnostic Configuration

There are a large number of diagnostics planned to measure neutron, X-ray, and γ-ray emission from these implosions.

Diagnostic Name	Acronym	Purpose
Neutron Time of Flight- 4.5m	NTOF(2)	Neutron time of flight measurement - 4.5 meter
Neutron Time of Flight- 20m	NTOF(20)	Neutron time of flight measurement - 20 meter (2 detectors)
Gamma Ray History- 1	GRH1	Time and spectrally resolved gamma emission
Radiation Chemistry	Rad Chem1	Neutron activation, gaseous collection
Radiation Chemistry	Rad Chem2	Charged particle activation, solid collection
Advanced Radiographic Capability	ARC	High energy, short pulse backlighter - 2 views (additional views planned to be available)
Magnetic Recoil Spectrometer	MRS	Neutron spectrum- neutrons converted to protons, energy analyzed by magnetic deflection
Hardened X-ray Streak Camera	hSXD	Hardened time streaked x-ray camera
High Energy X-ray Imager	HEXRI	High energy x-ray imaging system
Hardened High Energy X-ray Imager	HEXRI SE	Hardened version of HEXRI
Neutron Wedge Range Filter Spectrometer	WRF	Energy resolved particle emission- neutron yield and spectral shape, EMP insensitive
Neutron Imager	NI	Image primary and downscattered neutrons
Proton Emission	Protex	Analysis of emitted protons
Neutron Activation Detector	NAD	Absolute broadband neutron spectrometer by activation of witness foils

For further information on scientific opportunities at the NIF, please contact:
Dr. Christopher J. Keane, LLNL
PHONE: (925) 422-2179
E-MAIL: Contact us