from the cryopanel 1 and reducing its surface temperature to 30 to 20 degrees kelvin argon is solidified on the surface of the cryopanel 1 and the work space pressure is reduced to 10 6 torr or lower a radially directed open flow channel 3 is positioned in front of and in juxtaposition to the cryopanel 1 inside the channel 3 is a radiant cartridge heater 4 mechanically supported by ceramic supports and powered by means of a variable speed motor 19 through electric leads from slip rings 11 on the drive shaft 9 a rheostat 20 varies the power input to the cartridge heater 4 the drive shaft 9 sealed by a rotary vacuum seal 10 is adapted to rotate the channel 3 sequentially to expose segments of the cryopanel 1 to radiant energy emanating from within the channel solidified argon is sublimed and moves through a fixed duct 8 toward a blower mechanical pump combination 17 a liquid nitrogen shield 7 well known in the prior art separates refrigerant tubes 2 and the cryopanel 1 from the interior of vacuum vessel 12 fig2 is a view looking at the rear of the cryopanel 1 a low temperature refrigerant flows through the refrigerant tubes 2 drawing heat from the cryopanel 1 fig3 is a view looking at the front of the cryopanel 1 as shown in fig3 the channel 3 is mounted rotatably on the surface of the cryopanel 1 applying heat to the surface as it moves means such as a variable speed motor not shown is provided to vary the rate of rotation of the channel 3 honeycomb structure 13 having a multitude of individual cells separated by their walls or partitions extending generally normal to and forming the plane of the.