Charged-particle spectroscopy for diagnosing shock ρR and strength in NIF implosions

Abstract

The compact Wedge Range Filter (WRF) proton spectrometer was developed for OMEGA and transferred to the National Ignition Facility (NIF) as a National Ignition Campaign diagnostic. The WRF measures the spectrum of protons from D-(3)He reactions in tuning-campaign implosions containing D and (3)He gas; in this work we report on the first proton spectroscopy measurement on the NIF using WRFs. The energy downshift of the 14.7-MeV proton is directly related to the total ρR through the plasma stopping power. Additionally, the shock proton yield is measured, which is a metric of the final merged shock strength.

Observation of strong electromagnetic fields around laser-entrance holes of ignition-scale hohlraums in inertial-confinement fusion experiments at the National Ignition Facility

“…As shown in figure 2, self-emitted 14.7 MeV D 3 He fusion protons were recorded by a number of wedge-range filter (WRF) proton spectrometers [23,24]. Two were placed on port DIM (0, 0) to probe protons emitted from the hohlraum LEH (pole direction), and another two were placed on DIM (90, 78) to probe protons emitted from the hohlraum equator, as shown in figure 1 and discussed in [21]. The active surface of each WRF is about 2.4 × 2.4 cm 2 , subtending an angle of ∼2.7 • at the capsule; thus it sampled a plasma area of ∼0.2 × 0.…”

“…In this paper, we discuss spatial and spectral measurements [21] of self-emitted charged particles (14.7 MeV D 3 He protons) from NIF indirect-drive ICF implosions, made simultaneously on particles leaving through laser entrance holes (LEHs) and particles leaving through the hohlraum equator. As we will see in section 2, data from recent NIC experiments have consistently demonstrated large nonuniformities in the fluence of self-emitted charged fusion products that leave capsules in ignition-scale hohlraums through the LEHs, providing compelling evidence of self-generated electromagnetic fields appearing around the LEHs.…”

Empirical assessment of the detection efficiency of CR-39 at high proton fluence and a compact, proton detector for high-fluence applications

“…CR-39 proton data obtained with wedge-range-filter (WRF) proton spectrometers 4,19,20 also display track overlap problems under certain conditions, which can impact measurements of yield, burn-averaged ion temperature, and areal density. NIF D 3 He exploding pusher shot N110722 produced a yield of 1.35 × 10 10 protons, and WRFs positioned 50 cm from the implosion were exposed to a fluence of 4.3 × 10 5 cm −2 protons.…”

Impact of x-ray dose on track formation and data analysis for CR-39-based proton diagnostics

“…4 Additionally, backlighting of HED plasmas with high-energy charged particles has recently provided new insights into magnetic and electric field generation and evolution in contexts relevant to ICF, basic plasma physics, and laboratory astrophysics. [5][6][7][8][9][10] The solid-state nuclear track detector CR-39 11 has provided the basis for many neutron and charged particle diagnostics 5,[12][13][14][15][16][17][18][19][20] for HED and ICF experiments at both the OMEGA laser facility 21 and the National Ignition Facility (NIF). 22 CR-39, a transparent plastic, detects charged particles with energy on the order of 1-10 MeV with 100% efficiency.…”

“…Similarly on the NIF, the measured x-ray irradiance from an indirectly driven ignition-scale implosion 35 is calculated to deposit ∼6 Gy in the most thinly filtered (100 µm Al) region of the CR-39 in the Wedge Range Filter (WRF) compact proton spectrometers. 18 The previous study with alpha particles suggests that for doses of this magnitude, the relationship between track diameter and particle energy may be modified, which in turn may impact data analysis.…”