What is the maximum flux of 1 GeV stably-trapped protons in Jupiter radiation belts? And in which L-shell?
This graph shows a flux of around 50 stably-trapped protons per m2 per sec on Earth, and I have read it's higher in Jupiter but I can't find the value.
A source would be appreciated.

 A: From this review of the radiation belts of Jupiter,

THE IN-SITU EXPLORATION OF
JUPITER’S RADIATION BELTS


A White Paper submitted in response
to ESA’s Voyage 2050 Call:

...

Jupiter’s radiation belts are contained within the planet’s magnetosphere, formed by a
magnetic field that is 20,000 times stronger than Earth’s. Jupiter’s fast rotation and material
from Io’s volcanoes that fills the system, aid the magnetic field to push against the solar wind
even further, giving to the magnetosphere enormous dimensions . Within this
giant system, the radiation belts grow into one of the most hazardous regions of our solar
system, trapping charged particles of extreme energies and fluxes.

...

Jupiter’s magnetic field is so strong that even ultrarelativistic, ~100 GeV protons can be
trapped near the planet, over 50 times higher in energy than at Earth . Most importantly, observations and theory dictate that processes which
may populate the radiation belts with ultrarelativistic particles do exist

...

Jupiter’s belts have a distinctively large variety of ions in comparable abundance to protons.
At other planets, ions at many MeV/n are typically
trace elements. Heavy energetic ions at Jupiter, such as oxygen and sulphur, originate
primarily from the moons through volcanism or particle sputtering. At lower abundances, ions
like helium, sodium, magnesium, carbon etc., have been measured. Furthermore, some of the
ions have a range of charge states
et al. 2017].

There is an extensive list of references.
The paper is about future measurements and their complexity, at the moment, as far as I understand, the value of 100 GeV protons trapped  is expected from the models, the existing measurements do not go above 100 MeV due to the detecting systems on spacecraft in the region, JUNO.
...
From paragraph 2.2

Jupiter’s innermost radiation belts (r<6 RJ), where very energetic
protons from CRAND may get more easily trapped, are being sampled extensively only by
Juno. Juno, however, cannot resolve the energies of protons above 100 MeV, even if the
instrument noise they create is recorded .

So as far as Jupiter is concerned one has to maybe wait for the new ESA project for 2050 for real data on fluxes.
A: The Jovian magnetic field is very large and as such, allows for a rather extreme set of radiation belts.
The following are taken from Roussos et al. [2021].  Note that it is a compilation of figures from Nénon [2018], Mauk [2014], Mauk and Fox [2010], Nénon et al. [2017], and Nénon et al. [2018].


This graph shows a flux of around 50 stably-trapped protons per m2 per sec on Earth, and I have read it's higher in Jupiter but I can't find the value. A source would be appreciated.

The units shown in your figure are commonly called number flux in space plasma physics.  Note that for unit conversion 1 MeV-1 = 103 GeV-1 and 1 m-2 = 10-4 cm-2.  So multiply the magnitudes in my figure by 10-1 for direct comparison with your figure from PAMELA and SAMPEX data (or just look at the black lines in the figures).
Side Note:  The L parameter refers to shells of constant magnetic field strength in an ideal dipole magnetic field.  Sometimes folks take care to tilt the dipole (relative to rotation axis and/or ecliptic plane) and add a stretched magnetotail.
