solr search module

I have this params array:

$params = array(
'fl' => 'id,nid,title,body,format,comment_count,type,created,changed,score,url,uid,name,sis_project_release_usage,ds_project_latest_release,ds_project_latest_activity',
'rows' => variable_get('apachesolr_rows', 10),
'facet' => 'true',
'facet.mincount' => 1,
'facet.sort' => 'true',
'facet.field' => array(
'im_vid_'. _project_get_vid(),
'im_project_release_api_tids',
),
'facet.limit' => 200,
'sort' => $query->solrsort,
);