set default value for form field

Hi,

This is the controller:     @thermo_detector = ThermoDetectorOrderLetter.find(@params[:id])

    @thermo_detector[:number_of_element] = '1 Element' # this is ok     @number_of_element_helper['1element'] = 'bla' # not ok

This is the view:    <%= radio_button(:thermo_detector, :number_of_element, '1 Element') %>1 Element <%= text_field('number_of_element_helper', '1element') %><br />    another radio button

This line is source of my problem:     @number_of_element_helper['1element'] = 'bla'

It made me got this error: You have a nil object when you didn't expect it! You might have expected an instance of Array. The error occured while evaluating nil.=

If I comment that, the code works: radio_button with value '1 Element' is checked, but the text field is empty. How do I send value from controller to this text field text_field('number_of_element_helper', '1element') where number_of_element_helper is not variable from model???

Thank you.