| Term | Definition |
|---|---|
| H-alpha studies | A diagnostic technique to study the plasma boundary by observing the alpha line (6563 A wavelength) of the hydrogen emission spectrum. |
| H-mode | High mode, a regime of operation attained during auxiliary heating of divertor tokamak plasmas when the injected power is sufficiently high. A sudden improvement in particle confinement time leads to increased density and temperature, distinguishing this mode from the normal L-mode, "low mode" . |
| halo currents | When the plasma column is displaced vertically a current is induced flowing from the plasma through the vacuum vessel (shortest way) and thence back into the plasma. It thus contributes to delaying the plasma vertical movement (Faraday’s law). |
| heat flux | The total flow of heat in heat exchange |
| heat sink | An element of a composite material or structure which acts as the main attractor of heat in the system. Thus in a cooled body the coolant is the ultimate heat sink, though often a solid material included for its good thermal conduction to the ultimate heat sink is often known as the heat sink and this is the role it plays among the solid elements. |
| heat sink lifetime | The time the underlying substrate (the “heat sink”) of a plasma-facing component can be reliably predicted to fulfil its functional purpose (and therefore not need replacement). |
| heavy-ion beam probe | A plasma diagnostic which probes the plasma with a beam of heavy ions. |
| helical twist | A spiral twist of constant form and usually of constant radius. Thus the magnetic field lines in the tokamak have helical twists around the plasma, forming magnetic surfaces on which the twist pitch is constant. |
| helicity injection current drive | A noninductive current drive technique. |
| helicity safety factor | Also known as the plasma safety factor, this is aproximately the ratio rBt/RBp (where r, R are minor , major radii of the torus, and Bp, Bt are poloidal and toroidal field strengths respectively). The safety factor is 2 x the number of times a field line circles the major axis of the plasma torus before going once round the minor axis of the plasma torus |
| high heat flux components | HHFCs, plasma-facing components on the ITER divertor, in particular the target plates. |
| high-heat flux | Power conducted or radiated from the plasma with loads exceeding 0.5 MW per square meter. |
| HIP | Hot isostatic pressing, a method of joining in which materials are assembled together in their rough final form and then heated in a chamber under high pressure for typically hours until good bonding between the different surfaces is achieved. Solid HIP involves the use of only solid materials, usually spot welded together beforehand, whereas powder HIP involves the use of metal powders in an effort to fill all gaps. Both processes have their advantages and disadvantages, and both are planned to be used on ITER. |
| host | The country that will provide a site for ITER. In the past, has referred to the countries that have provided sites for the JWSs of the ITER Design. |
| hot cell | A concrete-shielded chamber with a controlled atmosphere that can be used to work on radioactive materials and components witha view to repairing them and refurbishing them for future re-use, or dismantling them for disposal. The chamber is equipped with remote manipulators or robotic devices for this purpose. No human access is foreseen. |
| hot cell building | The building containing the hot cells and to which the components for refurbishing or disposal are brought from the tokamak. It usually also consists of thick concrete walls to provide radiation shielding. |
| Hot Isostatic Pressing | see HIP. |
| HT | (ITER) Home Team |
| HTL | (ITER) Home Team Leader |
| HTO | A chemical compound formed by one atom of hydrogen and one atom of tritium chemically bound to one atom of oxygen, with similar molecular characteristics as water. |
| HTRO | (ITER) Home Team Responsible Officer |
| HVAC | heating, ventilation and air conditioning |
| hybrid operation | Term used to signify an inductively driven plasma burn that has been extended by current drive systems but which is not fully steady state. |
| hybrid reactor | See "fusion - fission hybrid". |
To add a definition, correct an existing one or to request a definition.