Does Reducing Synchrotron Radiation Enhance Particle Accelerator Beam Lifetime?

[gbz]

The main cause of decay of particle accelerator beams is the scattering due to residual gas particles in the vacuum rings. I read some research suggesting (in my understanding) that most of these free gas particles (CO2, CO etc) are the result of desorption from the surface of the vacuum tube (which carries the beam) due to synchrotron radiation from the beam. ie -- beam produces synchrotron radiation, which interacts with surface of the tube carrying the beam, resulting in desorption and release of residual gas particles which then collide with beam particles to cause scattering and beam decay. Is this correct? If we reduce beam velocity by a factor of 10, which would dramatically reduce synchrotron radiation (which in my understanding is proportional to 8th power of v), would that also proportionally increase beam lifetime? Any research on lower velocity beams out there?

 

[Vanadium 50]

First, you can't get high energy without high velocity, and second, it's not always gas interactions that limit the lifetime: at Fermilab's Tevatron its beam-beam tune shift.

 

[ZapperZ]

I read some research suggesting (in my understanding) that most of these free gas particles (CO2, CO etc) are the result of desorption from the surface of the vacuum tube (which carries the beam) due to synchrotron radiation from the beam. ie -- beam produces synchrotron radiation, which interacts with surface of the tube carrying the beam, resulting in desorption and release of residual gas particles which then collide with beam particles to cause scattering and beam decay.

You must always provide a reference. "I read some research" is very vague and tells us nothing on whether you read a valid source, or if you understood it correctly.

Zz.

 

[gbz]

Source: http://ieeexplore.ieee.org/Xplore/login.jsp?url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F4915548%2F4931945%2F04932295.pdf%3Farnumber%3D4932295&authDecision=-203>

@V50: How exactly does tune shift impact beam lifetime?

 

[gbz]

Link doesn't seem to work, source again:

Electron storage ring beam lifetime dependence on pressure and pumping speed
Halama, Henry J.
Brookhaven National Laboratory, Upton, New York 11973

This paper appears in: Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films
Issue Date: May 1985
Volume: 3 Issue: 3
On page(s): 1699 - 1702
ISSN: 0734-2101
Digital Object Identifier: 10.1116/1.573003
Date of Current Version: 18 June 2009

 

[ZapperZ]

If you read just the abstract, there are two issues that you should pay attention to:

The beam loss in electron storage rings depends to a large extent on the interaction of the beam with heavier residual gas molecules such as CO, CO2, and A due to bremsstrahlung and Coulomb scattering. The gas density inside the vacuum chamber is determined by the surface condition of the vacuum chamber, which is bombarded by photons (synchrotron radiation) generated by circulating electron beams, and by the installed pumping. During the initial commissioning severe limitations on the achievable beam current were observed due to large pressure rises. The x‐ray ring was shut down for several months and its vacuum system was updated and baked out. Residual gas spectra obtained after the shut down were typical of a well baked out system, i.e., hydrogen constituted ∼95% of the gas and the average pressure was in the 10-10 Torr range. During initial operation the composition of desorbed gases was 43% H2, 25% CO, and 16% CO2 and CH4. After 3 months of beam conditioning the desorption rate dropped by a factor of 5 and the CO, CO2, and CH4 peaks represented smaller percentage of total desorbed gas. Beam lifetime did not, however, show a corresponding increase.

First, he's talking about conditioning and initial operation. During this period, certainly there will be a lot of 'stuff' coming out. However, after a while, this is no longer a factor, so the beam lifetime does not have any relevance to such outgassing.

However, the 2nd point is a bit more puzzling. He is arguing that the beam lifetime depends on "... to a large extent on the interaction of the beam with heavier residual gas molecules...". Yet, in the very last sentence, he said that even when the concentration of CO, CO2, and CH4 dropped considerably after 3 months, no change to the beam lifetime could be observed! So how would one draw the conclusion that the interaction of the electron beam with these gas molecules is the dominant mechanism that affects the beam lifetime?

Zz.