According to the “NASA Earth Science Instruments” section of noaa.gov's DSCOVR page,
DSCOVR will make unique space measurements from the first sun-Earth Lagrange point (L1). ... 1.5 million kilometers ... sunward from Earth ... The spacecraft will be orbiting this point in a six-month orbit with a spacecraft-Earth-sun angle varying between 4 and 15 degrees. [emphasis added]
It seems to me that if the orbit is perpendicular to the Earth-Sun line, the range of spacecraft-Earth-Sun angles would include negative angles, rather than ranging +4° to +15°. Or, it seems to me that if it is a long ellipse parallel to that line (which would allow a range of positive angles) it might not be a stable orbit (without using fuel). Are these ideas incorrect? More concretely, what plane will the six-month orbit be in, and what will its shape be?