Switching a current source with a MOSFET
The circuit is fundamentally incorrect. The current produced by an (ideal) current source cannot be stopped by a series-connected switch; it must be diverted by a switch connected in parallel to the load (this is the so-called &quot;current steering&quot; technique). The reason for this is, as stated in the comments, that the current source will &quot;try&quot; with all its might to pass the current through the load. So, we can formulate another circuit &quot;golden rule&quot;:
The current can not be stopped; it can be only diverted.
A typical example of this technique is the so-called &quot;flyback diode&quot; connected in parallel to an inductor switched by a transistor. The transistor switch cannot (safely) stop the current produced by the inductor (acting as a very good current source) since it is connected in series. So, when it opens (cut off), the diode switch closes thus short connecting the inductor... and the current is diverted through the dioge.
Another solution can be to modify the OP's circuit so that the MOSFET acts as a controlled current source. For this purpose, just move the LED to the place of I1 and set the desired current by R1.