[Tpe] TPE - primary beam on target

[Larry Weinstein]

Dear Folks,

New data on Kapton irradiation from LHC (thanks Dave!) shows that 10^7 
Gray is a safe dose and that Kapton starts losing strength at 
several*10^7 Gy.

My previous calculation of the multiple scattering included just the 75 
um Al vacuum exit window at the converter.  This is 1e-3 RL of Al and 
gives 0.2 mr at 15 m upstream of the target (for a 2.2 GeV beam).  That 
results in a 3 mm (sigma) beam spot on target.

We also need to include the multiple scattering in the helium.  There is 
about 11 m of helium bag from 15 to 4 m upstream of the target.  This 
gives 0.2 g/cm^2 of Helium which is 2e-3 RL.  This will give 0.3 mr of 
multiple scattering centered about 10 m upstream of the target which 
gives another 3 mm (sigma) for a total width of about 5 mm on target.

That will reduce the radiation dose from 20 Gy/s to 10 Gy/s.  That means 
that we can run for 10^6 sec (300 hours) before accumulating a dose of 
10^7 Gy.

Since we plan to run for only one shift (8 hours), that gives us a 
safety factor (in terms of radiation dose ONLY) of more than a factor of 40.

- Larry

Larry Weinstein wrote:
> Dear TPEers,
>
> At some point, we want to run the primary electron beam thru the 
> chicane and onto the LH2 target.  There are two main concerns,
>  1) radiation in the hall due to the beam hitting vacuum and Helium 
> windows
>  2) radiation damage to the Kapton target windows
>
> There is a possibility that Hall C will be down tomorrow (Friday) 
> during the day shift.  If so, we could do the test then with minimal 
> impact on the other halls (since it will take time to tune the beam to 
> us).
>
> *Are we confident enough that the test is safe that we should proceed 
> for tomorrow or do we need to study this?*
>
> Here is my analysis of the energy deposited by radiation on the Kapton 
> windows at 1 nA:
> 6e9 e/s * 2 MeV/(e-g/cm^2) * 1 g/cm^3 * 1 cm = 12*10^15 eV/s = 2*10^-3 J/s
> (I used a 1 cm thick window, but this will divide out when we 
> calculate the energy deposited per mass.)
>
> Now we need the beam size on the windows.  The beam passes through a 
> 75 um Al window about 15 m upstream of the target.  t = 75 um * 2.7 
> g/cm^3 = 0.02 g/cm^2
> The radiation length of Al is 24 g/cm^2 so this is 10^-3 RL.
>
> The multiple scattering for a 2.2 GeV beam is
> sigma = (13.6 MeV/2200 MeV)*sqrt(1e-3) = 0.2 mrad
> Over a distance of 15 m, this is a spread of 3 mm.
>
> A block of Kapton that is (3 mm)^2(1 cm) has a mass of 0.1 g.  Thus, 
> the energy deposited amounts to a radiation dose of
> R = 2e-3 J/s / 0.1 g = 2e-3 J/s / 1e-4 kg = 20 J/kg-s = 20 Gray/s
>
> Kapton (according to the manufacturer's data) can withstand 10^6 Gy 
> with no change in mechanical properties.  At 10^7 Gy, it loses 25% of 
> its tensile strength and 50% of its elongation.
>
> 10^6 Gy corresponds to a time of 10^6 / 20 = 5*10^4 s = 14 hours.
>
> To reduce this we can a) run at lower energy (which will double the 
> beam spot size, reducing the radiation by a factor of 4) or b) run at 
> lower beam current (subject to the minimum current that the 
> accelerator can monitor).
>
> -- 
> 				Sincerely,
> 				Larry
>
> -----------------------------------------------------------
> Lawrence Weinstein
> University Professor
> Physics Department
> Old Dominion University
> Norfolk, VA 23529
> 757 683 5803
> 757 683 3038 (fax)
> weinstein at odu.edu  <mailto:weinstein at odu.edu>
> http://www.lions.odu.edu/~lweinste/  <http://www.lions.odu.edu/%7Elweinste/>
> ------------------------------------------------------------------------
>
> Spam 
> <https://www.spamtrap.odu.edu/b.php?i=433207705&m=5775e8bdb10c&t=20110113&c=s>
> Not spam 
> <https://www.spamtrap.odu.edu/b.php?i=433207705&m=5775e8bdb10c&t=20110113&c=n>
> Forget previous vote 
> <https://www.spamtrap.odu.edu/b.php?i=433207705&m=5775e8bdb10c&t=20110113&c=f>

-- 
				Sincerely,
				Larry

-----------------------------------------------------------
Lawrence Weinstein
University Professor
Physics Department
Old Dominion University
Norfolk, VA 23529
757 683 5803
757 683 3038 (fax)
weinstein at odu.edu
http://www.lions.odu.edu/~lweinste/

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