The most formally correct way to write laughter in Esperanto is "ha ha ha". That is, the word "ha" repeating two or more times. This form is found in dictionaries. (e.g. here and here)
(There should formally be spaces between the syllables, because writing "hahaha" as one word technically implies stress on the second to last syllable: haháha. Although in informal contexts, which is most of the time in Esperantujo, it's acceptable to ignore this rule in my opinion. Especially in this case, because it's not really a word.)
However, "ha ha ha" is more than an expression in the dictionary. Most of all it's an imitation of the actual sound people make when laughing. And since people can laugh in different ways, laughter can also be written using different variations, imitating the actual sound. For example, "a ha ha", "he he he", "ho ho ho", "mŭa ha ha", "ni hi hi", and yes, also "ĥa ĥa ĥa".
You say this feels difficult to pronounce to you, but that is a matter of perspective. As someone who has both an h sound and a ĥ sound in their native language, "ĥa ĥa ĥa" feels to me like a totally natural variation of "ha ha ha". In fact, I regularly use a ĥ sound when I actually laugh. Most often at the start. ("ĥa ha ha") Or, when chuckling, it might even come out as "ĥ ĥ ĥ".