Selecting range of records from each category

I’ve a table called dept with dept_id as foreign key in participants table. Training is to be in 4 batches (A, B, C and D) the participants of the training are coming from 5 departments.

I need all the departments to be represented in each of the batches. How do I select 20 participants from each dept per batch? So that for each batches I will have 100 participants.
NOTE: I am not looking at any specific order for the selection, I t can be random or not.

I’ve this query so far:

SELECT dept.dept_name,
       participants.full_name,
       participants.email,
       participants.phone_number
FROM   participants
       JOIN dept
         ON participants.dept_id = dept.dept_id
WHERE  dept_name IN ( "lifestock", "fishery", "media", "foodtech", "extension" )
ORDER  BY participants_id
LIMIT  20;