Latest Results with the KWISP force Sensor at CAST

The KWISP opto-mechanical force sensor has started searching for solar chameleons through their direct coupling to matter. Its sensing element, a 100 nm thick Si$_3$N$_4$ membrane, was mounted in the focal plane of the CAST X-ray telescope and several solar trackings were completed using the unique capabilities of the CAST magnet. KWISP is designed to detect, with interferometric techniques, extremely tiny membrane displacements due to the force exerted by chameleons reflecting off it, while a specially devised chameleon beam chopper provides the reference frequency necessary for detection. We will present the initial KWISP setup, discussing its status and results.