Lightroom, while merging pano, consumes my space on C drive

Hello. I have (on my laptop) small SSD "C" HD (125GB), free space around 25GB (but I moved catalog onto D 1TB drive).

When I start to merge pano in LR, this amount radically goes down towards to zero and when I merge 6 or more photos, within the process it reaches 0GB and LR annonces an error - not able to finish the work. To free the space on my C drive helps only to close LR or even to retstart laptop. What to do to avoid that, please? Thank you. 

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