Design of an Inertial Fusion Energy Target Injection & Tracking System Ronald Petzoldt, Dan Goodin, Mike Hollins, Chuck Gibson, Neil Alexander, and Gottfried Besenbruch LASER IFE Program Workshop Naval Research Laboratory 6 February 2001

: Complete preliminary and final design of new injection and tracking system Overall purpose: Design and build high-accuracy, rep-rated injection and tracking system suitable for both direct & indirect drive targets Funding $700 K Schedule -Complete preliminary design* (Jul 01) -Complete final injection and tracking system design (Feb 02) * Coordinated with OFES task to initiate preliminary design

Recent work leading to this project : Computational and analytical thesis prepared at LLNL Target Injection, Tracking, and Beam Pointing for Inertial Fusion Energy : Experimental injection and tracking experiment carried out for room-temperature, indirect drive targets at LBNL -Position prediction accuracy of ± 100  m achieved at 3 m distance, 70 m/s, and low repetition rate - Current requirements: Direct drive- 400 m/s and ±14  m at 16 m; Indirect drive 180 m/s and ±100  m at 9 m and 6 Hz Present: Updated analytical and design work for more capable direct and indirect drive target injection in progress at General Atomics - Conceptual design completed September Ultimate goal is injection of cryogenic targets into (simulated) high temperature chamber

 Target injection critical issues 1) Withstand acceleration during injection 2) Survive thermal environment 3) Accuracy & repeatability 4) Ability to accurately track targets Experimental Plan for IFE Target Injection & Tracking, GA-C23241 (Oct, 1999) The target injection program is planned to address key issues

Several devices could propel targets into a reaction chamber Gas gun is recommended accelerator Magnetic accelerator option is backup with potential for non-contacting operation

Schematic diagram of planned experimental test facility

Early sabot testing is encouraging Sabot separation experiment Identified in CDR as area for more testing. Near term sabot testing Vacuum separation Post firing separation Sabot deflection

The sabot deflector is needed for direct drive targets

Tracking related requirements: Direct drive Target velocity: up to 400 m/s Target size: ≤8 mm diameter (nominal is 4 mm) Injector accuracy: ±0.3 mrad Tracking accuracy: ±14 µm in all directions at “chamber center” - Tracking detectors more than 9 m from “chamber center” Tracking detectors located ~>0.5 m off flight axis (for neutron shielding) Gas density of flight tube: Consistent to ± 4x10 –8 kg/m 3 for out of chamber tracking  ~3x10 –5 torr for air at 300K Target injection frequency 6 Hz

Basic target tracking layout Each detector is - A pair of orthogonal transverse position detectors - A timing photodiode (axial position) - Light sources Position at CC is triangulated from D1 and D2 Additional timing photodiodes precede detectors for exposure (“shutter”) control as needed 2.5 m 4.5 m9 m Detector: D1Detector: D2Detector: DCC Potential Flight Paths Gas Removal Sabot Removal Detector Light Source

Linear array photodiode — transverse position 8192 x 1 element array CCD camera available with 7µm x 7µm pixels, 57mm long -Offloads digitized pixels (8 bit) with 4 channels at 25 MHz each 12.2 mm FOV / 8192 implies 1.5 µm resolution or better can be achieved Detector: D1Detector: D2Detector: DCC Light source Si photodiode X2, orthogonal X

Gated area ICCD array— transverse position ~1024 x 1024 array gated intensified CCD camera Short gate (shutter) to freeze motion; 2 ns at 400 m/s is 0.8 µm Detector: D1Detector: D2Detector: DCC LASER X2, orthogonal z x Light source

Injection and tracking design summary Conceptual design review was completed with minor comments & preliminary design is underway A gas gun is used for target acceleration Sabot separation testing has begun Target transverse position is measured with linear photodiode arrays and performing high speed arithmetic on pixel outputs Transverse position is predicted by triangulating early measurements and compensating for gravity Axial position measurement is accomplished with timing photodiodes

: Develop concepts for electromagnetic injector as backup The gas gun is a simple, demonstrated technology. An electromagnetic launcher has the potential advantage of non-contact operation. Overall purpose: Develop design concepts and conduct feasibility testing for advanced electromagnetic injector as a backup for gas gun. Schedule: (Funding $200K) Develop design concepts and conduct preliminary feasibility testing. (Feb 02)

: Develop concepts for cryogenic transfers in injection system Thermal isolation of cryogenic components Cryogenic cooling Remote target loading Overall purpose: Develop high volume cryogenic target handling concepts; ensure feasibility of upgrading injector to cryogenic operations. Schedule: (Funding $100 K) Develop cryogenic target handling concepts for experimental injector (Feb 02)