使用Laravel Storage Facade存储SQL查询

I've created a Controller that backups table data in the form of SQL queries. On the browser, there are three checkboxes which contain 3 tables: order,posts and products. Moreover, when I select these tables, I want them to be stored in the directory storage/app like backup_on[Date-Time].sql and automatically be downloaded right from the browser.. When I clicked backup, I've got this error

file_put_contents(/home/vagrant/code/laravelBackup/storage/app/backup_on[2018-07-04 08:39:15].sql): failed to open stream: Protocol error

Thanks beforehand. This is my code:

public function download($output)
{
    $time = Carbon::now()->toDateTimeString();
    $file_name = 'backup_on[' . $time . '].sql';
   // $file_name = 'database_backup_on_' . date('y-m-d') . '.sql';
   // $file_name = 'backup.sql';

    Storage::disk('local')->put($file_name, $output);

    // Storage::lastModified($file_name);

    $exists = Storage::disk('local')->exists($file_name);

    if ($exists) {
        // $name_of_file = 'backup';
        $headers = 
        [
        'Content-Description => File Transfer',
        'Content-Type => application/octet-stream',
        'Content-Disposition => attachment; filename=' . basename($file_name),
        'Content-Transfer-Encoding => binary',
        'Expires => 0',  
        ob_clean(),
        flush(),
        readfile($file_name),
        unlink($file_name)
        ];

    }

    return Storage::download($file_name, $file_name, $headers);
}