Hybrid Illinois Device for Research and Applications (HIDRA)
The Hybrid Illinois Device for Research and Applications (HIDRA) is a medium-sized, toroidal, magnetic fusion device that has capability to operate both as a stellarator and a tokamak, hence the hybrid designation. HIDRA is the former WEGA (Wendelstein Experiment in Greifswald Ausbildung) stellarator which was the test bed for the W7-X device at the Max-Planck Institute for Plasma Physics. The reactor was moved from Germany to Illinois in the fall of 2014, being disassembled over an 8-week period from August to October and arrived in Urbana in early November. After 18 months of reassembly, the first plasma was on the 22nd of April 2016.
HIDRA is unique compared to most university-scale devices in that it has steady state operation. It can operate up to 10,000 seconds in “low field” mode. However, for most experiments the typical pulse length is between 600 to 1000 seconds.
The overall research aims for HIDRA is to concentrate on understanding the complex relationship between the plasma and materials inside the vacuum vessel of a fusion device and specifically concentrates on understanding the complex behavior that flowing liquid metal walls, and in particular liquid lithium, have as plasma-facing-materials (PFM) in such devices. This makes HIDRA one of a very few fusion devices willing to run liquid lithium as a PFM for plasma facing components (PFC).
HIDRA has a long, proud history in fusion and is probably one of the most well-travelled machines in the world. It has lived in three countries and four cities! The device started life off in Grenoble, France, as WEGA, in the mid-70’s with the first plasm being in 1975. Initially it operated as a tokamak doing RF and lower hybrid heating studies. In the late 70’s it was converted over to being a stellarator and continued to operate until 1982. It then moved to the University of Stuttgart where it stayed until 2000. Between 2000-2001 it moved to the Max-Planck Institute for Plasma Physics in Greifswald. This was part of the W7-X program where WEGA became a testbed for the superconducting modular stellarator Wendelstein 7-X (W7-X). Diagnostic, heating, and control system development was done on the machine from 2001-2013. Operations for W7-X became live at the end of 2013 and thus WEGA was “up for grabs”.
At the Symposium on Fusion Engineering (SOFE) in San Francisco in 2013, Professor Daniel Andruczyk found out about WEGA being available and was able to get an agreement from CPMI director Professor David Ruzic as well as then Department Head Professor Jim Stubbins and Dean of Engineering Andreas Cangellaris. Professor Ruzic took over raising money and negotiation for the next year and finally the device was zeroed out and gifted to the university. From late August to early October Professor Andruczyk, Professor Curreli, and several students travelled to Greifswald, Germany to disassemble WEGA and pack it up. In late October to early November, WEGA (now HIDRA) travelled across the sea and arrived in Illinois. Over the next 18 months the machine and infrastructure were upgraded and reassembled. As part of the department’s open house celebrations, HIDRA’s first plasma was achieved in front of over 100 guests at CPMI.
HIDRA plasma operations include: main working gases of hydrogen (H2) deuterium (D2); helium (He); argon (Ar); and other more specialty gases including neon (Ne), krypton (Kr), and xenon (Xe). Mixtures of these gases are possible as well with hydrogen and helium having been done in the past. Hydrogen/deuterium can also be performed for isotopic experiments as well as hydrogen, deuterium, and helium mixtures to mimic operating condition in reactors. Several diagnostics are available including spectroscopy and Langmuir probes in the plasma edge and on a fast-reciprocating arm, residual gas analyzers, pressure gauges, and microwave sniffer probes for doing power absorption studies. Three color cameras are also available for viewing into the plasma and an infrared-two wavelength pyrometer system is being developed to do material analysis teststand (HIDRA-MAT) surface temperature measurements. A block heater is also mounted on the north side of the HIDRA chamber for doing desorption measurements with lithium retention campaigns. An electron beam and fluorescent rod system can also be employed to do magnetic flux measurements to verify the shape of magnetic fields and compare them back to modeling. Currently, a Thompson scattering (TS) is being designed that will complement the Langmuir probe and allow continuous temperature and density monitoring as well as to measure plasma profiles. A flowing liquid metal divertor module and loop system have been designed and are being constructed. This will the first time a full flowing liquid lithium loop will be implemented into a proper toroidal geometry to test the many issues that such a system will face during operation in a toroidal environment. HIDRA has two ECRH magnetron systems for plasma heating at 2.45 GHz. One is a 6 kW system and a second is a 15 kW system. To overcome the density limit, OXB heating is used. On -axis magnetic fields up to B0 = 0.5 T have been achieved up to 60 seconds operation.
Some of the significant results with HIDRA operations have included that over 6000 plasma shots have been completed to date with a typical experimental shot length on the order of 600 – 1000 seconds (10 – 15 minutes) in length. This ability allows many different aspects of an experiment to be tested during one experiment and to have a benchmark and comparison all in one. The record operation for HIDRA has been 10,000 seconds which is just under 3 hours of continuous operations, and this was achieved while doing plasma chemistry studies. The most significant results have been to show that lithium will can achieve low recycling operation in a steady state device, where the recycling coefficient can be reduced by over 80%. This allows the plasma performance to increase significantly, in some cases by over 1000% in temperature!
| Parameter | No Li, high recycling | With Li, low recycling |
| Te (eV) | 15 – 25 | 50 – 150 |
| Ti (eV) | 1 – 2 | 5 – 10 |
| ne (m-3) | 3×1018 | 2×1018 |
The most surprising result of all of this is that lithium will not only pump and retain hydrogenic species, as one would expect with such a reactive element, but it also will pump and retain inert gases such as helium and argon which has been demonstrated on multiple occasions.
Lithium vapor shielding has also been observed in HIDRA, with an experimental campaign back in 2020, where the HIDRA-MAT probe with a W-Li sample was slowly moved towards the plasma to where the scrape-off-layer (SOL) region was interacting with it. A dramatic rise in the surface temperature was observed going from 250 C to 750 C in 10s of seconds. However, the temperature then leveled off at 750 C which is an indication of temperature locking, a feature of vapor shielding. This effect has been observed at MAGnetized plasma Generator and Numerical modeling for Plasma Material Interaction (MAGNUM-PSI) in the Netherlands at the Dutch Institute FOR Fundamental Energy Research (DIFFER) laboratory.
HIDRA continues to be a testbed for science and technology development with a new experiment into the survivability of additive manufactured materials and systems (3D-printing) in liquid lithium systems being undertaken. This involves a new HIDRA-MAT head being developed and built to accommodate a small internal flowing liquid lithium loop for samples to be tested in while being exposed to the HIDRA plasma.
HIDRA Campaign
| HIDRA Campaign | Dates | Notes |
| FP | 2016 – 2017 | First Plasmas: First plasmas performed and commissioning of HIDRA was completed. This included initially glow discharges and ECRH discharges. Long pulse achieved. |
| FLM | 2018 – 2020 | Flux Line Measurements: Magnetic flux lines were measured and ray-tracing codes verified. This used the e-beam and fluorescent rod technique. |
| HIDRA-MAT | 2019 | HIDRA Material Analysis Teststand: Development and commissioning of the mid-plane material teststand. Successful deployment and plasma exposure. |
| ZEUS | 2020 | Zinger of an Experiment Under Stellarator: This was the first lithium campaign where plasma performance increase was discovered in helium. |
| LEEX | 2021 | Lithium Exposure Experiment: First dedicated campaign to characterize the lithium-helium interactions and Langmuir probe plasma profile measurements. |
| VSE | 2022 | Vapor Shielding Experiments: First hydrogen experiments with very long pulse, 3600 s, to achieve vapor shielding conditions, was successful. |
| LIPS – 1 | 2023 | Long-pulsed Interactions with Plasma-chemistry and Surfaces: 10,000 s plasmas to characterize hydrogen plasma interactions with device surfaces. |
| HeRMES | 2023 | Helium Retention Mechanism Experiment in Stellarators: Surface heater experiments to identify the co-deposition mechanism for helium retention. |
| ArRMES | 2024 | Argon Retention Mechanism Experiment in Stellarators: Experiments with argon retention to confirm the co-deposition theorized and seen with helium. |
| HADES – 1 | 2025 | Hydrogen Absorption and Desorption Experiment in Stellarators: Hydrogen retention experiments with lithium, this is part of completing the overall operation of HIDRA. |
| MBFD – 1a | 2025 | Milestone Based Fusion Development program: Design of a flowing liquid lithium divertor for HIDRA with a loop. Magnetic field measurements, B = 0.5 T. |
| PPE – 1 | 2025 – 2026 | Plasma Profile Experiments: Fast reciprocating arm mounted Langmuir probe measurements of the plasma profile, these are high recycling experiments, no lithium. |
| HADES -2 | Current (2026) | Hydrogen Absorption and Desorption Experiment in Stellarators: Continuation of experiments in hydrogen and expansion into deuterium, neon, krypton and xenon. |
| Kenta | 2026 | Name name name name name name: Additively manufactured sample exposure to long pulsed HIDRA plasmas in hydrogen and helium. |
| LIPS – 2 | 2026 | Long-pulsed Interaction with Plasma-chemistry and Surfaces: Continuation of 10,000 s plasma pulses with hydrogen and helium and with lithium interactions to see the effect on plasma chemistry. |
| PPE – 2 | 2026 | Plasma Profile Experiments: Continuation of plasma profile with fast reciprocating arm mounted Langmuir probe and the changes seen with lithium operation. |
| HADES – 3 | 2026 | Hydrogenic Absorption & Desorption Experiment in Stellarators: Isotopic plasma experiments with Hydrogen/Deuterium and hydrogen/deuyterium/helium mixtures. |