def getTOFbeta(ins, dsp):
    """get TOF peak profile beta
    
    :param dict ins: instrument parameters with at least 'beat-0', 'beta-1' & 'beta-q'
      as values only
    :param float dsp: d-spacing of peak
    
    :returns: float getTOFbeta: peak beat
    
    """
    return ins['beta-0'] + ins['beta-1'] / dsp ** 4 + ins['beta-q'] / dsp ** 2
