GEOGRAPHIC AND SEGMENT INFORMATION - Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Segment Reporting Information [Line Items]
Sales	$ 10,292	$ 11,224	$ 22,785	$ 19,862
Income (loss) from operations	(5,976)	(4,043)	(11,847)	(8,788)
Interest income	18	4	20	7
Interest expense	(3)	(2)	(11)	(6)
Other income (loss), net	607	97	586	4
Income tax (benefit) expense	96	107	166	173
Operating Segments | Advanced Energy
Segment Reporting Information [Line Items]
Sales	8,364	9,978	19,178	17,638
Income (loss) from operations	(1,252)	326	(2,591)	(276)
Interest income	0	0	0	0
Interest expense	0	0	0	0
Other income (loss), net	0	0	0	0
Income tax (benefit) expense	0	0	0	0
Operating Segments | OEM
Segment Reporting Information [Line Items]
Sales	1,928	1,246	3,607	2,224
Income (loss) from operations	469	263	786	260
Interest income	0	0	0	0
Interest expense	0	0	0	0
Other income (loss), net	0	0	0	0
Income tax (benefit) expense	0	0	0	0
Corporate & Other
Segment Reporting Information [Line Items]
Sales	0	0	0	0
Income (loss) from operations	(5,193)	(4,632)	(10,042)	(8,772)
Interest income	18	4	20	7
Interest expense	(3)	(2)	(11)	(6)
Other income (loss), net	607	97	586	4
Income tax (benefit) expense	$ 96	$ 107	$ 166	$ 173