why is my code not working?

syms Tbrem(Tk)
n20av=1.1;
%time [s]
tauE=1.2;
%internal radius [m]
a=2.0;
% ellipticity
k=1.8;
%external radius [m]
R0=6.2;
%magnetic field [Tesla]
B0=5.3;
%inverse aspect rdius
epsy=a/R0;
% volume [m3]
Vp=2*pi*R0*pi*k*a^2;
sigmav =(10^(-6))*exp(-21.38/(Tk^(0.2935))-25.20-7.101*(10^(-2))*Tk+1.938*(10^(-4))*Tk^2+4.925*(10^(-6))*Tk^(3)-3.984*(10^(-8))*Tk^4);
sigmavn =sigmav/10^(-22);
Sa=(2.31*10^(5))*(n20av^(2))*sigmav;
Imax=7.5;
Sohm=(1/Vp)*(5.6*10^(-2)/(1-1.31*epsy^(1/2)+0.46*epsy))*(R0*Imax^(2))/(a^(2)*k*((Tk)^(3/2)));
Sb=6.14*(10^3)*(n20av^2)*Tk^(1/2);

%T bremsstrahlung
Tbrem(Tk) = Sa+Sohm-Sb==0;
sol = solve(Tbrem,Tk);

[Rik]

Judging by the warning message your code is working fine, but your system of equations might not be solvable in their current form.

[Franco Belletti]

thanks!