Our colleague Eugene Evans of PPPL has had his paper, “Particle-in-cell studies of fast-ion slowing-down rates in cool tenuous magnetized plasma,” accepted for publication in Physics of Plasmas. The article is tentatively scheduled for the April 2018 issue. A quote from the reviewer:
The paper … is an interesting, well-written paper that uses PIC to build upon earlier direct numerical simulation methods based on molecular dynamics. The authors present a clearly written discussion of the scaling properties of slowing down theory to support their numerical studies. The authors do a very good job describing the simulation approach they take… Of particular note in the paper is the good agreement between their numerical data and the sub-thermal model even when the effective computational log(lambda) was on the order of 1… the authors did not stop with their results but instead applied their conclusions to the FRC reactor, predicting that the neutron production rate is 100 times lower than a conventional DT Tokamak.
This paper is key to the low radiation levels claimed for our PFRC design, and hence the Direct Fusion Drive. The fast ion slowing-down is what causes the tritium and other fusion ash to exit the machine. You can view a preprint on arXiv.
We will post again once the paper is published and available from Physics of Plasmas.
Back in early September, PSS and PPPL were visited by a film crew from Australia. The project? Living Universe: An Interstellar Voyage, which will include a feature documentary, a 4 episode TV miniseries, and a podcast. The documentary touches all aspects of an interstellar mission, from exoplanets to astrobiology, including transportation – which is where our fusion engine work comes in. The film is in production now and the producers expect to launch in late 2018.
The PFRC experiment at PPPL is the only hardware the documentary team could find with a path to fusion propulsion! Dr. Cohen was able to run the machine for the film crew, and both Mike and Stephanie were interviewed extensively. We discussed the rocket equation and the fundamental speed of fusion products, and how DFD moderates that speed with additional propellant to produce higher thrust. For an interstellar voyage, DFD would have to be much, much lighter than we know how to make it today – but who knows what innovations in magnets are possible in the future!
How will you be able to watch the film and TV series? The film should do the rounds of museums and IMAX theaters. The TV series will be available for streaming from Curiosity Stream, a service which specializes in science, history, tech & nature documentaries. We will post an update when we have a firm release date!
We are pleased to report that an additional patent has been awarded for DFD! US Patent 9,822,769, “Method and Apparatus to Produce High Specific Impulse and Moderate Thrust from a Fusion-Powered Rocket Engine”, was published on Nov. 21, 2017. It’s now available from the US patent office website!
Here is a link to the patent from the Department of Energy’s Energy Innovation Portal! The inventor on the patent are Dr. Cohen, of PPPL, and three PSS engineers: Gary Pajer, Michael Paluszek, and Yosef Razin.
Fusion Rocket Engine
The first patent, “Method to Reduce Neutron Production in Small Clean Fusion Reactors,” was issued on September 9, 2017. The patent is available on Patentscope.
Sadly, the AIAA Space Forum in Orlando, FL was canceled due to hurricane Irma. So, we didn’t get to present our paper on our DFD mission to Pluto. AIAA has, however, published all the forum papers and is providing free access for a few months in lieu of the actual conference. This means anyone can download it!
Fusion-Enabled Pluto Orbiter and Lander paper:
Open access to the AIAA Space Forum technical program:
WHYY reporter Alan Yu has done a radio show featuring our work for The Pulse, which presents stories of health, science, and innovation. You can read the article and listen to a podcast of the show segment, which features Stephanie, Mike, Sam, and members of the NASA NIAC program including director Jason Derleth, external council member Ariel Waldman, and NIAC fellow Phil Lubin.
The headline for the show is, aptly, “Inside the NASA program that makes science fiction technology real.” Reporter Alan Yu visited the lab to see the PFRC in action during development of the show. The show played on the radio today, July 21, at 9 am and will repeat on Sunday at noon. Enjoy!
Dr. Sam Cohen and I had a good time at the Foundations of Interstellar Studies Workshop this week in NY! While we were only able to stay for the first day on “Energetic Reaction Engines”, there were many thoughtful discussions on applying fusion technology to interstellar travel. Here I am in the group photo from the welcome event Monday night, held at the Harvard Club with an interesting and wide-ranging display of interstellar art! (I’m in the first row on the far right).
Group photo from Foundations of Interstellar Studies workshop
The workshop was almost a mini-NIAC reunion, as NIAC fellows Phil Lubin and Ray Sedwick were there, and Heidi Fern was due to present her Mach Effect thruster on Thursday. Also NIAC External Council member Lou Friedman of the Planetary Society was in attendance (very back of the photo).
Our presentation for this conference focused on how the PFRC addresses the key parameters needed for a “net positive” fusion reactor: energy confinement, current drive, plasma heating, and plasma stability. We are often asked “why fusion will work this time”, and this paper does a good job of explaining why the PFRC is different enough from other approaches to work! The workshop is going to submit all of the papers to the Journal of the British Interplanetary Society, which is the oldest astronautical journal in the world (1934).
We also discussed the parameters the propulsion system will need to achieve to reach Alpha Centauri in various time scales, as well as a more near-term mission deliver a gravitational lens telescope to 550 AU. Reaching Alpha Centauri in anything close to a human lifetime remains a significant challenge, but PFRC could be part of an architecture to reach the star in 300 to 500 years, and slow down enough to go into orbit around the potentially Earth-like planets there! The 550 AU telescope mission, however, could be achieved in as little as 12 years with just one small PFRC and is an exciting new mission possibility.
Our next interstellar appearance will be at the Tennessee Valley Interstellar Workshop in October in Huntsville, AL!
We have been selected for two NASA STTRs on their new topic, T2.01-9960, Advanced Nuclear Propulsion! Our research institution partner is Princeton Plasma Physics Laboratory. Our proposals were featured in NASA’s official press release! Here is a quote:
High temperature superconducting coils for a future fusion reaction space engine. These coils are needed for the magnetic field that allows the engine to operate safely. Nuclear fusion reactions are what power our sun and other stars, and an engine based on this technology would revolutionize space flight.
You can read our project abstracts as posted on NASA’s SBIR website:
These Phase I STTRs of $125,000 each will run for one year, at which point we have the opportunity to propose Phase II work up to $750,000. If successful, they will go a long way towards demonstrating critical subsystem technology needed for DFD and other high-tech space propulsion technologies!
A key feature of the NIAC program is making the project results available to the public. In that spirit, we are making our complete Phase I final report, “Fusion-Enabled Pluto Orbiter and Lander”, available on our website!
NIAC Phase I Final Report [PDF]
I’ve copied the executive summary below:
The Pluto orbiter mission proposed here is credible and exciting. The benefits to this and all outer-planet and interstellar-probe missions are difficult to overstate. The enabling technology, Direct Fusion Drive, is a unique fusion engine concept based on the Princeton Field-Reversed Configuration (PFRC) fusion reactor under development at the Princeton Plasma Physics Laboratory. The truly game-changing levels of thrust and power in a modestly sized package could integrate with our current launch infrastructure while radically expanding the science capability of these missions.
During this Phase I effort, we made great strides in modeling the engine efficiency, thrust, and specific impulse and analyzing feasible trajectories. Based on 2D fluid modeling of the fusion reactor’s outer stratum, its scrape-off-layer (SOL), we estimate achieving 2.5 to 5 N of thrust for each megawatt of fusion power, reaching a specific impulse, Isp, of about 10,000 s. Supporting this model are particle-in-cell calculations of energy transfer from the fusion products to the SOL electrons. Subsequently, this energy is transferred to the ions as they expand through the magnetic nozzle and beyond.
Our point solution for the Pluto mission now delivers 1000 kg of payload to Pluto orbit in 3.75 years using 7.5 N constant thrust. This could potentially be achieved with a single engine. The departure spiral from Earth orbit and insertion spiral to Pluto orbit require only a small portion of the total delta-V. Departing from low Earth orbit reduces mission cost while increasing available mission mass. The payload includes a lander, which utilizes a standard green propellant engine for the landing sequence. The lander has about 4 square meters of solar panels mounted on a gimbal that allows it to track the orbiter, which beams 30 to 50 kW of power using a 1080 nm laser. Optical communication provides dramatically high data rates back to Earth.
Our mass modeling investigations revealed that if current high-temperature superconductors are utilized at liquid nitrogen temperatures, they drive the mass of the engine, partly because of the shielding required to maintain their critical temperature. Second generation materials are thinner but the superconductor is a very thin layer deposited on a substrate with additional layers of metallic classing. Tremendous research is being performed on a variety of these superconducting materials, and new irradiation data is now available. This raises the possibility of operating near- future “high-temperature” superconductors at a moderately low temperature to dramatically reduce the amount of shielding required. At the same time, a first-generation space engine may require low-temperature superconductors, which are higher TRL and have been designed for space coils before (AMS-02 experiment for the ISS).
We performed detailed analysis of the startup system and thermal conversion system components. The ideal working fluid was determined to be a blend of Helium and Xenon. No significant problems were identified with these subsystems. For the RF system, we conceived of a new, more efficient design using state-of-the-art switch amplifiers, which have the potential for 100% efficiency.
This report presents details of our engine and trajectory analyses, mass modeling efforts, and updated vehicle designs.
Our paper “Direct Fusion Drive for Interstellar Exploration” has been accepted for the Workshop of Interstellar Flight that will be held at CUNY City Tech, 13-15 June 2017! The workshop is organized by the Institute for Interstellar Studies and City Tech’s Physics Department and Center for Theoretical Physics.
We will present the latest results from our NASA NIAC work on DFD design as well as applications to interstellar missions, including:
- A mission to 550 AU to perform gravitational lensing imaging of exoplanets;
- Flyby missions to the nearest star;
- A mission to go into orbit about a planet orbiting either Alpha-Centauri A or Alpha-Centauri B.
We received notice today, March 31, 2017, that our NASA NIAC Phase II proposal was selected for award! We will be able to continue working on the Direct Fusion Drive with PPPL for two more years. Hooray! Dr. Joseph Minervini of MIT will be joining our team to help advance our understanding of the trade space for the superconducting coils, using the very latest data from high-temp superconductor manufacturers. It’s going to be exciting research!
Here’s a link to NASA’s official project summary.