laravel public variable for different controllers

I want to set a public variable so I can use it in different controllers. I tried this but it is not successful.

class HomeController extends Controller
{
 public $TravelId;
public function __construct()
{
 $this->TravelId=0;
}
}

then I used the same variable in another contorller

class HomeController extends Controller
{
public function index($cus_id)
{
    //unique key for each user
    $this->TravelId = $cus_id;
}
}
class Helper

{public static function Update($id){

$user_idd = auth()->user()->id;
 $user = User::find($user_idd);
 if ($user->isAdmin ==1){ 
  $user_id = $this->TravelId;
  self::$staticTravelId = $user_id;
 }
 else{
   $user_id = $user_idd;
 }

I want to use the user_id Inside the public variable here

via Chebli Mohamed