You can not use the control field to set in the email text. To set the value you have to set the text in temparory field. You can set the label of control field to temparory field by $PROCESS$ PERFORM-ACTION-GET-FIELD-LABEL field id in the active link.
and then use the temparory field in notify action.
My control field is a button so it doesn't have any values so I'm not clear when you say "To set the value you have to set the text in temparory field".
I just want to use my button to open a Dialog form when it is clicked in the email that user receives some thing looks like below
You recently contacted US IT Service Desk with an IT issue INCXXX . We would greatly appreciate your participation in a brief online survey about your experience.
Please click here to take part in the survey."