the practice being studied here, where tibetan monks raise their body temperature, is called tumo. here you can see it illustrated in a mural that is in a temple behind the dalai lamas palace. i was told the man is visualizing a letter A moving through his central energy channel:
https://hell.twtr.plus/media/eec0f8e52a1e15c8efb0b066310238d6ec9be89f9e039dff611dd9e43c56c76b.file
https://hell.twtr.plus/media/1f6ff15b05cba2a46a8e40b164ec6673648622705a3f85d4e1ed544a4ab1d352.file