Mootools两种形式

My question is:

I have a table:

<table>
  <tr>
    <td>
      <form name="intervalForm">
          <input type="text" name="interval" value="5"></input>
          <input type="submit" value="OK"></input>
      </form>
    </td>
  </tr><tr>
    <td>
      <form name="intervalForm">
          <input type="text" name="interval" value="5"></input>
          <input type="submit" value="OK"></input>
      </form>
   </td>
  </tr>
  ...
</table>

My js(mootools) code:

$('intervalForm').addEvent('submit', function(e) {
        new Event(e).stop();
        var newRequest = new Request.JSON({
           url: 'ajax.php',
           onRequest: function() {},
           onSuccess: function(r){  
          if(r.status){
                 ...do action
              } else {
                 ...error here    
              }
           }
        }).send({data: this});
});

My js code is working for 1st row only. What should I do to make it working for other rows? Thanks.