Minutes: E-linac Beam Dynamics meeting Nov. 18, 2008


Rick Baartman (chair, also note-taker)
Robert Laxdal
Sophia Yan
Shane Koscielniak
Yu-Chiu Chao
Marco Marchetto
Vaishali Naik

Dobrin Kaltchev

[Actions are in red]

Shane presented a list of beam dynamics activities including open questions to be answered.

The main jobs can be separated into 3 areas: Source, Buncher, Capture. Do we work on these areas in parallel (rather than serially)? Bob: Yes. We need a basic conceptual design of the injector by June 2009, as this is in our VECC collaboration agreement.

Source: Question was whether we wait for data from Friedhelm, or start simulations. It was decided to start simulations. Chao will do a literature search, check on getting a version of E-gun code, review advice given by Bill Diamond when he was here. Key questions are beam distribution in phase space including energy spread, cleanliness of gaps between bunches, transverse distribution variation between pulse middle and ends. It is to be remembered that a .5MW design means that the beam from the 100kV source will be 1kW; 10% loss is already 100W, so loss control is essential.

Additional info obtained after meeting: Friedhelm has started simulations using a code bought by Victor Verzilov, called Omnitrak. We can get E-gun as well, for reduced cost because we already have I-gun. But not clear that these can simulate the modulated grid of the triode. Chao and Friedhelm will share info.

Buncher: Since voltage is low, it is generally agreed that this is a warm device.

Shane is checking into the options in this region; key question is how long is the drift from buncher to capture. If too short, there is no room for diagnostics. This is a complicated optimization issue; we should even leave open the choice of source voltage. Shane needs help. Perhaps Chao or/and Marco.

Chao recommends using PARMELA in this region; Marco has recently received the license, but only one user at a time can use it. Another candidate is ASTRA (From DESY), which has the virtue that it is free.

(Calculations made after meeting indicate:) Space charge is not a small effect: at 100 keV, 4 mm dia. 15 pC (10 mA @ 0.65 GHz) spherical bunches double to 8 mm dia. in a drift of only 20 cm. This means focusing elements are a key component in this region, and the bunching system cannot be designed ignoring space charge. It may be better to push towards higher beam energy.

Capture: This section needs the most conceptual work, in the sense that there are many options still open: graded beta, 1.5 cells, etc. (See Shane's outline.) Shane recommends starting with a simple model instead of diving into complex simulations with ASTRA. Shane will continue his studies, and consult with Sophia, who is using TRACK (from ANL).

BBU: The main linac needs work on calculating BBU effects to specify HOM damping. This is somewhat longer term, but in the short term, need to make the same calculations for the CERN SPL. Baartman/Kaltchev are working on this.

It is emphasized that continued communication is essential. We should have another meeting within a couple of weeks.