# Fusion Instability Researcher Dr. Eliezer Hameiri Has Passed

Matt Moynihan - July 19, 2016

The Fusion Power Associates sent out a note that Dr. Eliezer Hameiri has passed.

**Who was Dr. Eliezer Hameiri?**

Dr. Hameiri spent his professional life at NYU’s Courant Institute. He was a professor of mathematics, who applied his talents to modeling plasma behavior. Plasma is a soup of (+) ions and (-) electrons. In some cases, it acts like a charged gas. In some cases, it acts like a fluid that conducts electricity. The math that predicts plasma behavior is a combination of the fluid equations and the electricity equations. Specifically it is the Navier Stokes and Maxwell equations. These combine to give us the magnetohydrodynamics model.

Dr. Hameiri probed these equations to help develop the theories behind the kink and ballooning instabilities. Today, these behaviors are taught in most plasma physics courses around the country.

**What are kink instabilities?**

Roughly speaking: when a current is moving through a plasma, it makes a magnetic field, which creates instabilities. Moving current always makes a magnetic field. The example most people are familiar with is the magnetic field around a wire when current is flowing through it. For that reason, it is nice to compare current in both wires and plasmas. This is shown below.

Dr. Hameiri started this work looking at current moving through straight plasmas. In straight plasmas, the magnetic field forms around the plasma, leading to an external magnetic field pressure. This pressure pushes against the plasma. This can be a desirable effect. For example, in plasma pinches - we want plasma to be compressed with this field. In 1958, pinches became the first man-made device to get controlled fusion. In pinches, this compression is welcomed; it causes the plasma to squash together and fuse. A step by step version of the pinch mechanism, is shown below.

But sometimes, this effect hurts us. For example - in tokamaks - this instability can lead to disaster. This disaster comes in the form of an external magnetic field, pressing against the plasma, leading to it fall apart. This magnetic pressure is always balanced by the internal plasma pressure. This situation is very common across all of the fusion field. In so many situations, we have a plasma and a magnetic field pressure interacting. It is so common that we have created a dimensionless number for it; the Beta number.

This is balance can fall apart, leading to both tight squeezing of the plasma and giant “ballooning” of the plasma. These are the kink and balloon instabilities, common in tokamaks.

Dr. Eliezer Hameiris’ theoretical work was critical to understanding how these behaviors start, function and end.