def to_file_async(self, destination, format='csv', csv_delimiter=',', csv_header=True):
    """Start saving the results to a local file in CSV format and return a Job for completion.

    Args:
      destination: path on the local filesystem for the saved results.
      format: the format to use for the exported data; currently only 'csv' is supported.
      csv_delimiter: for CSV exports, the field delimiter to use. Defaults to ','
      csv_header: for CSV exports, whether to include an initial header line. Default true.
    Returns:
      A Job for the async save operation.
    Raises:
      An Exception if the operation failed.
    """
    self.to_file(destination, format=format, csv_delimiter=csv_delimiter, csv_header=csv_header)