In July 2020 Physics Today published a letter from Wallace Manheimer (page 10) written in response to the article “The challenge and promise of studying burning plasmas” by Richard Hawryluk and Hartmut Zohm (December 2019, page 34). Manheimer criticizes the international fusion experiment known as ITER and the prospects for commercial fusion. I would like to point out an error in Manheimer’s calculation, which, as it turns out, further supports his criticism.
Manheimer asks what the results of ITER would mean for power production. He applies a conservative thermal-to-electric power conversion factor of one-third to the projected 500 MW thermal output of ITER, and from that he concludes that ITER would generate a gross output of approximately 170 MW of electricity (MWe). He then says that the 50 MW heating input would require 150 MW of electrical power, leaving “virtually nothing for the power grid.” Manheimer’s calculation would mean a net electrical output of about 20 MWe.
Manheimer, however, doesn’t account for the net plant power drain—known as the balance of plant—which is at least 150 MWe. That value includes such power drains as liquid-helium refrigerators, water pumps, and vacuum pumps. When one includes the injected heating power and the plant power drains, a reactor designed like ITER would result in a net loss of 80 MWe, at best.
ITER was never designed to provide net electricity or net thermal power across the entire reactor. Instead, it was designed only to generate net thermal power across the plasma. But in its public communications, the ITER organization until only recently did a poor job of communicating that distinction. That led to, as it did with Manheimer, the common misunderstanding about the expected power balance for ITER. That misconception does not account for at least half of the expected input power.
