Questions about configuring the thinkphp cache directory

Specific situation: Want to change the background add and delete, update the cache, the cache will be stored in the foreground temp directory. Based on thinkphp 3.23

Because of the use of 2 entry files, index.php admin.php for the foreground and background, the main is to separate the background to another domain name down the use. There are two application directory admin Home, want to store the data cache under the admin directly to Home/runtime/temp.
Tried to modify the

' Data_cache_path '       = ' __root__/home/runtime/temp ',

Invalid.
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