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An international journal of news from the stellarator community
Editor: James A. Rome Issue 180 August 2022
E-Mail: James.Rome@stelnews.info Phone: +1 (865) 482-5643
On the Web at https://stelnews.info
Continuous cryogenic pellet
fueling system for the W7-X
stellarator
Toroidal magnetic fusion reactors such as ITER will be
fueled by cryogenic deuterium-tritium pellets accelerated
to high velocity (200–1000 m/s) into the hot plasma. Over
the last 40 years, Oak Ridge National Laboratory (ORNL)
and its partners have developed the physics and technology
of pellet fueling on toroidal plasma confinement
experiments around the world.
These experiments had plasmas lasting seconds, but fusion
reactors will require continuous fueling. The next stage of
pellet fueling experiments will be carried out using the
Wendelstein 7-X (W7-X) stellarator facility (major radius
= 5.5 m) at the Max Planck Institute for Plasma Physics in
Greifswald, Germany. W7-X has superconducting magnetic
coils and is designed to sustain plasmas for ~ 30 minutes.
Exploratory experiments on W7-X in 2018 [1, 2]
showed that injection of fifty, 2-mm H2 pellets at velocities
~ 200 m/s could sustain high-density (peak ~ 1020
m−3) plasmas heated with 5 MW of microwave power
with electron and ion temperatures ~ 3 keV for about a
second.
Over the last four years, a team of researchers from the
United States (ORNL, PPPL), Germany (IPP), and Japan
(NIFS) has developed a Continuous Pellet Fueling System
(CPFS) for W7-X (Fig. 1). The CFPS will inject 3-mm H2
or D2 pellets into W7-X at speeds of ≤1000 m/s with a repetition
rate of ≤10 Hz. The pellet size, speed, and repetition
rate can be controlled in real time to maintain
optimum plasma profiles. The major design challenge [3]
was extrusion under screw pressure of a ribbon of solid
hydrogen at a constant temperature of 15 K, maintained by
cryocoolers.
In testing at ORNL, the CFPS achieved pellet repetition
rates of up to 10 Hz for periods of 10 seconds (Fig. 2) and
4 Hz for periods of minutes (Fig. 3), which is sufficient to
begin the 2022 long-pulse campaign on W7-X. Progressive
improvements in repetition rate will be made onsite at
IPP by the US team as plasma pulse lengths increase.
The CFPS is now physically installed at W7-X by IPP and
ORNL staff. Integration into the W7-X operational control
system will continue in August–September 2022. Experimental
commissioning of the entire W7-X facility will
take place over the subsequent months, with the physics
research campaign beginning in November 2022.
The CPFS also serves as a prototype for ORNL development
of pellet fueling for ITER, which will required even
higher fueling rates.
In this issue . . .
Continuous cryogenic pellet fueling system for
the W7-X stellarator
Toroidal magnetic fusion reactors such as ITER will be
fueled by cryogenic deuterium-tritium pellets accelerated
to high velocity (200-1000 m/s) into the hot
plasma. Over the last 40 years, Oak Ridge National
Laboratory and its partners have developed the physics
and technology of pellet fueling on toroidal plasma
confinement experiments around the world. ........... 1
FY2022 LHD Research Forum
The FY2022 Large Helical Device (LHD) Research
Forum was held from 11–15 July 2022 via Zoom. The
LHD Research Forum was organized with the idea
that proponents and co-proponents can conduct
experiments at LHD more efficiently and effectively if
they know and understand all the submitted experiment
ideas. Thankfully, we have received experiment
proposals from Japan, Asia, Europe, and the United
States. .................................................................... 3