After returning from the Mzulft ruins in the quest "Revealing the Unseen", you find Ancano has sealed himsef with the Eye of the Magnus. The Arch-Mage, Mirabelle, and you manage to break the ward, and as the Archmage approaches Ancano, there is a flash and you lose consiousness. When you wake up, Mirabelle is lying hurt on the ground, Ancano is behind a forcefield, and Savos Aren is nowhere to be seen.

Open your quest journal:

Ancano has done something to the Eye of Magnus, causing the orb to release incredible amounts of energy, and possibly putting the area in danger. I need to find the arch-mage and make sure he's safe

Find the Arch Mage

Exit the Hall of the Elements to the courtyard. You spot the Aren laying on the ground, not moving. Tolfdir approaches and asks you what happened in there. Tell him Ancano has done something with the eye. He will tell you Aren is dead, and that the eye is doing something to Winterhold. He wants you to head down to the Winterhold to make sure the people are safe. He will go find Mirabelle. You need to secure the town of Winterhold which could also be affected. Your objective now is to protect the town of Winterhold.

Go down to the town. On the way, update Faralda with the situation and ask if she can help. She and Arniel will join you in the efforts to protect the town.

When you reach the town, you find it is being attacked by floating spheres. Your goal is to Defeat the creatures infesting winterhold. You need to kill 10 of them to complete this quest. Defeat them, and loot the soul gems from them. Winterhold is now safe from the creatures attacking it. Mirabelle needs to be informed of what's going on. You need to report to Mirabelle Ervine.

Climb back up to the college and enter the Hall of Elements. Tell Mirabelle Winterhold is safe for now. She will tell you that the Eye of Magnus cannot be reached and continues to Jeopardize the college. Tolfdir and her will try and keep this contained, and that you need to get your hands on the Staff of Magnus. Tell her you are off to Labyrinthian. She will tell you that Savos gave her something before he died. Something related to Labyrinthian. She will give you the Torc of Labyrintihian, and Savos Aren's Amulet which increases your magicka by  50 points.

This completes the quest "Containment" and starts "The Staff of Magnus" which is the next quest in the College of Winterhold line.