Nuclear Fusion Superconducting Magnets Can Be Used for Space Radiation Protection

The D’Onghia magnetic shielding crew hat, or CREW HaT, is a system that uses electromagnetic coils to deflect cosmic radiation from astronauts. The system consists of:

A ring of electrical coils positioned on arms roughly 5 meters from the spacecraft’s main body
A Halbach Torus, a circular array of magnets that creates a stronger field on one side while reducing the field on the other side
Superconducting tapes
When turned on, the system forms an extended magnetic field outside the spacecraft that deflects the cosmic radiation

The CREW HaT concept
The Cosmic Radiation Extended Warding (CREW) magnetic shield concept is based on a cylindrical Halbach array arrangement, or Halbach Torus (HaT). In the embodiment described here, the system consists of eight electromagnet racetrack coils disposed around the habitat region with rotating magnetic polarities. Such a configuration produces a magnetic field extending in the space around the CREW HaT while suppressing it in the habitat region at the center. Each coil is equipped with several rare-earth barium copper oxide (ReBCO) high-temperature superconducting tape wrappings to achieve the needed currents and generate a magnetic field in the surrounding space. The coils are equipped with dedicated cryocoolers, thus avoiding single-point failures. Solar panels may be considered to power the cryogenic pumps independently. Each coils’ containment structure is designed to support hoop stresses from self-induced magnetic forces. In addition, the coil support structure to the main body is designed to be deployable and withstand inter-coil magnetic forces.

The preliminary feasibility study, described in section III, shows that the optimized current is 4 million Amps, corresponding to a maximum magnetic field strength of about 10 T. This current can be achieved by wrapping the conductor N times so that a current Ic is effectively amplified to N× I1. To achieve such high currents, it is possible to use the recently developed high-temperature superconductors such as ReBCO. These wires’ high current carrying capabilities significantly reduce the magnets’ weight, while the strength of the fields can be about three times higher than of more conventional superconductors.

Commonwealth Fusion Systems (CFS) and MIT developed a 20 tesla superconducting magnet. The magnet was demonstrated in 2021. It’s the most powerful fusion magnet in the world. The CFS SPARC device, a collaboration between CFS and the Massachusetts Institute of Technology, will have 18 similar magnets. SPARC is currently under construction at a site outside Boston, with initial operations planned for 2025.

The CFS 20 Tesla magnets show that the 10 Tesla magnet designs for space radiation shielding are feasible. Even stronger 20-30 Tesla superconducting magnets for radiation shielding could be used if affordable mass production of superconducting magnets is standardized.

D’Onghia said their new configuration produces an enhanced external magnetic field that diverts cosmic radiation particles, complemented by a suppressed magnetic field in the astronaut’s habitat. The team believes their design can divert over 50% of the biology-damaging cosmic rays (protons below 1 GeV) and higher energy high-Z ions. This rate would be sufficient in reducing the radiation dose absorbed by astronauts to a level that is less than 5% of the lifetime excess risk of cancer mortality levels established by NASA.

Space radiation in cislunar and interplanetary space consists of solar particle events (SPE) and galactic cosmic rays (GCR). SPE particles, primarily electrons and light ions with energy up to about 100 MeV/nucleon, are originated from solar flares and coronal mass ejections. The burst events can last from hours to days with very intense particle flux. On the other hand, GCR particles consist of a steady and relatively low flux of particles, primarily protons and heavy ions with energy of 1 GeV/nucleon and above, and constitute a significant risk factor for long-duration missions such as those to Mars. Space radiation particles can penetrate habitats, spacecraft, equipment, and spacesuits and harm astronauts. Minimizing the physiological changes caused by space radiation exposure is one of the biggest challenges
in keeping astronauts fit and healthy as they travel through the solar system. Ionizing radiation is a serious problem that can cause damage to all parts of the body, including the central nervous system, skin, gastrointestinal tract, skeletal system, and blood-forming organs.

Astronauts on the International Space Station (ISS) receive radiation doses from space between 80 and 160 mSv per 6-month mission. In comparison, a standard medical chest X-ray delivers approximately 0.1 mSv. Although inconclusively, there is a 3% excess risk of death from cancer at a cumulative dose of 1000 mSv just below the 1200 mSv dose expected from a trip to Mars. Recently, NASA recommended that habitat systems have sufficient protection to reduce by 15% the exposure to the GCRs compared to free space. This achievement would keep the absorbed radiation dose from GCRs below 1.3 mSv per day for habitats in space. This risk factor sets the standard for setting radiation limits for men and women astronauts at different ages using estimates above the 95% confidence level (CL) for uncertainties in risk projection models.

Uncertainties occur related to predicting particle energy spectra, and the limited understanding of heavy-ion radiobiology leads to a level of uncertainty that requires extra margin when setting radiation limits.

There are two different approaches to protect spacecraft and astronauts from the harmful effects of space radiation: passive and active shielding. With passive shielding, space radiation is absorbed through a layer of material. It is the current solution adopted in space. Any material can stop ionizing particles up to a certain energy, above which they penetrate the shield.

For instance, an aluminum slab with 2, 4, 10 cm thickness (corresponding to a mass thickness of approximately 5, 11, 27 g/cm2
, respectively, which is the product of the density, 2.7 g/cm3, and thickness) can stop protons up to about 50, 70, 125 MeV.

Passive shielding may work for high-Z GCR particles at energies below 1 GeV/nucleon. However, while losing energy penetrating the habitat’s walls, GCR particles induce nuclear reactions, generating lower energy secondary particles, including gamma rays and neutrons.

Therefore, astronauts inside the habitat are exposed to the risk of this internal mixed radiation environment. Another problem is the excessive weight needed to achieve acceptable radiation mitigation. Polyethylene is a good shielding material because it has high
hydrogen content, and hydrogen atoms efficiently absorb radiation.

However, it may not be the best solution for a long-time space mission (e.g., Mars).

An example of passive shielding is the one suggested for the Artemis mission to ensure the safety of future space crews traveling to the Moon by producing well-fitted vests to wear in space.

While low-cost and lightweight, the vests are designed to protect vital human organs from radiation. Although this solution might work for the softer SPE particles, it has negligible protection from the more energetic GCR and secondary debris. As a result, it is inadequate to shield humans in long-haul travels to Mars.

The most promising approach to protect astronauts from cosmic radiation consists of generating a magnetic field that surrounds the spacecraft, similar to the Earth’s magnetosphere. In fact, on Earth, the geomagnetic field acts as an extended cocoon that shields life on the surface against the harmful space radiation. Feasibility studies showed that this strategy is superior to any passive shielding approach in terms of efficiency in reducing the impact of radiation on spacecraft. However, mass and power consumption are critical to the practical realization of such future devices.